The Knowledge - Velocette Owners Club

The Knowledge
Being a compendium of eGroup discussions compiled from
http://autos.groups.yahoo.com/group/velocette/
January 2002 - December 2004
Complied and Edited by:
2002 Les Carman
24 January, 2003
2003-2004 David S. Liebl
March/May 2005
Provided courtesy of the VOC and VOCNA

Table of Contents
A. Diagnosing Troubles
1) Hard Starting, Poor Running ................................................ 1
2) Poor Gearchange ....................................................... 13
3) Faulty Electrics ......................................................... 16
B. The Engine
1) Bottom End & Crankcase ................................................. 19
2) Cylinder & Piston ........................................................ 36
3) Cylinder Head & Valves ................................................... 44
4) Timing Gear & Pushrods .................................................. 64
5) Oiling System .......................................................... 74
6) Crankcase Breathing ..................................................... 92
7) Racing & High Performance .............................................. 100
C. The Electrics
1) Ignition & Timing ....................................................... 107
2) Sparking Plug ......................................................... 115
3) Battery, Dynamo & Magneto .............................................. 118
4) Lights & Horn.......................................................... 126
5) Electric Conversions .................................................... 129
D. The Carburetor and Fuels
1) Carburetor ............................................................ 141
2) Fuels ................................................................ 154
E. The Drive Train
1) Primary Drive, Chainwheel and Clutch ...................................... 158
2) Gearbox.............................................................. 170
3) Final Drive, Chains & Cases .............................................. 181
F. Running Gear
1) Steering Head, Forks & Shocks ............................................ 194
2) Brakes, Wheels and Tires ................................................ 206
G. The Frame and Ancillaries
1) Cables & Controls & Instruments........................................... 215
2) Bodywork, Paint & Polish ................................................ 232
H. Manuals & Spares ........................................................... 234
I. Miscellaneous ............................................................... 239
[Editors Note: These contributions to http://autos.groups.yahoo.com/group/velocette/ have been
organized according to the general subject under discussion. The apparent beginning of discussion of
a new topic is indicated by:
L While the eGroup message # has been retained, the messages are no longer strictly
consecutive. The full text of the messages, in chronological order, can be found in the eGroup
archives. Terminology and spelling is multinational, reflecting the membership.]
Disclaimer: The opinions expressed herein are those of the correspondents. No claim is made regarding the
validity of their assertions. Please enjoy and benefit from them nonetheless.
i

A Diagnosing Troubles
A.1 Hard Starting and Poor Running -
L #223 At last year's Stanford Hall Rally my Venom did not want to start. After I had exhausted
myself a volunteer from the inevitable crowd that were watching finally managed to get it going. On
kicking it over, it had now developed a habit of spitting back enough neat petrol for it to be seen
running down the oil tank. It got me home OK and ran well at higher revs. After repeating this
performance a couple of times I tackled all the obvious things, plug, BTH manual magneto points,
pickup etc. with no joy. I then changed the carburettor, from monoblock to concentric. This was
easier to start but ran lumpily at low revs and this time spat a small quantity of neat petrol back
through the carburettor on each firing stroke; again it seemed to be OK at higher revs. Getting more
desperate I have removed the cylinder head to find no problem with the inlet valve or seat. I have
taken off the timing cover and found the cams, followers and gears all to be in apparently excellent
condition. What next?
#225 I had the same problem on my 58 Venom, after fitting a new Monobloc. Spitting back at low
revs indicates richness, which is controlled for the first quarter of throttle movement by the Pilot Air
Screw. Try screwing it out a little at a time (to weaken the mixture) until the spitting stops. You may
have to adjust the throttle stop afterwards to obtain a satisfactory tickover.
#228 One of the major reasons for a Venom spitting back is due to the large amount of valve overlap
that a M17/8 cam gives. If you check out most Venoms after a run, you will find petrol and oil debris
on the oil tank that has been jettisoned from the carbs. A MSS with a softer M17/7 doesn’t suffer from
this. Check your valve timing, remembering to use the increase valve clearances. You will find that the
timings will not be spot on mine were 65–39–50–55 rather than the 65-35-45-55 as specified. If yours
are out you can spread the error by moving the cam a tooth either way to see if it helps.
L #431 Since the main bearings failed in my `54 MAC after getting back from Bavaria last year I
haven't been able to get the bike to run properly. I've had a number of problems including nipping up a
piston since, possibly unrelated. I have discovered, in the course of investigation, that the bike has an
M17/7 cam and followers as fitted to MSS and early Viper. Has anyone else got an MAC with this
cam? If so is the cam set up according to the marks on the wheels? I've checked the cam timing with
the valve clearances set to 30 thou inlet, 35 thou exhaust (as specified for the MAC). The results are
as follows (M17/7 spec in brackets) [Inlet opens 25deg BTDC (19deg) - opens early Inlet closes 50deg
ABDC (49deg) - closes late Exh Opens 50deg BBDC (49deg)] opens early Exh Closes 16deg ATDC
(19deg) - closes early I've tried taking cam lobe centre readings but as I haven't got a dial gauge it
proved to be difficult to be accurate enough to perform the check. Can anyone comment on whether I
have the valve timing right or not? Should I get a dial gauge and do the cam lobe centers? This is
driving me mad. My MAC used to be an easy starting good performer. Now it doesn't start well and
coughs back through the carbs.
#431b Just a further thought - the MSS with a M17/7 cam has ignition timing 36deg BTDC fully
advanced. Does the ignition timing follow the type of cam i.e. if I'm using an M17/7 cam (MSS type) in
my MAC in place of the M17/5 (MAC type), should I change the ignition timing from 38degrees to 36
degrees? I have a sneaking suspicion that I should. This is most perplexing. Before the recent
problems the bike ignition timing was set by the roadside, after yet another ATD spat its fibre teeth,
using a piece of stick found at the roadside with a rough estimate of about 11mm for the piston crown
distance BTDC. The bike has been running fine ever since:-)) I've never used a degree wheel until
recently. Precision measurements ain't what they are cracked up to be. Going to get a dial gauge and
check the cam lobe centers.
#434 You might check your ATD to make sure that the springs are still okay, I had one break once,
the ATD went into full advance. Velos are very sensitive to ignition timing, less so to cam timing. But
the timing at full advance won't affect starting much. If you want to check the cam timing on a /7 with
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VM/MSS followers you should use 50 thou clearance as specified for the cam. This should yield
numbers closer to the spec. Also, it is not well documented but there is more lift on the 86mm cams, a
/8 has 20% more at the lobe than a /4. I don't have the others handy to measure, but I'll bet the /5 and
/7 also have different lifts.
#435 Thanks for the note. I had already tried checking the cam timing with the 50thou gap and ended
up with crazy readings. Last night I read the MSS Maintenance Manual I have and it said check with
30thou gaps (the MSS used the M17/7 cam). I tried this and the cam timing came out to within one
degree of spec as I have it set up. I also got hold of a dial test indicator and checked the dwell and
calculated the cam centre point. That came out to within half a degree. I doubt that it could be
adjusted closer than that. At least that’s one thing sorted out. The bike won't start at the moment. It
has good compression (for a re-ringed motor) and a fat spark at the plug. I am beginning to suspect
that the fuel has gone off. Its possible that it could have been there the best part of a year. When the
bike started on Tuesday it was coughing/spitting back through the carbs a lot, particularly on small
throttle openings (i.e. while trying to start) indicating, I think, that the mixture is weak. I blew out the
idle drillings yesterday but now it won't fire up at all. If the fuel has separated and/or the volatiles have
evaporated then surely that would make the fuel calorific value lower hence the mixture would be
weak (higher air to fuel energy ratio)? Does that make sense? Maybe the small amount of fuel in the
float bowl was still good and once that had been used up the remainder was bad? Anyway, tonight’s
job is to get some fresh fuel, drain the tank and carbs and try again. I hope that’s what is causing the
problem but I've never experienced petrol going off (although I've heard others talk about it). The ATD
springs are OK. The ATD was overhauled a few years ago with a new fibre wheel and springs. I have
set the mag timing to 38deg BTDC fully advanced. The MSS manual says 36degrees BTDC. I
wouldn't have thought that this would make too much difference to whether the bike would start or not.
#436 I have had similar problems with my Venom recently ( see earlier posting on 'spitting' ). After
repeated checking of valve and ignition timing, cleaning out of carbs jets etc. without benefit, I
changed the carburettor to an old spare. Hey presto the damn thing ran as well as ever. I suspect that
the float height was wrong.
#442 Well, I found the reason the MAC wouldn't start - the ATD had come loose. Idiot!! I had checked
that there was a spark at the plug and it seemed fine. Anyway, now the bike is running again there
seems to be a lot of noise from the timing chest of the engine. My Haynes says that if the intermediate
timing gear is only in shallow mesh then the symptom is a mechanical clacking noise. If I turn the
engine over by hand this is what I hear. Has anyone else experienced this? I plan to check the mesh
tomorrow evening and if necessary adjust the intermediate timing pinion..
L #501 anyway I cleaned up the points and gapped them and checked out tappet clearances
and generally checked the bike over, primary adjustment, etc etc. I cracked the bike up and went for
a run. it was quite tall geared with a close box and a 19 tooth gearbox sprocket. it went like the wind
and pulled 105 on a chrono clock absolutely no problem. I thought wow this is some motorcycle. I
went out and about on it for about a week and I was batting down a dual carrigeway doing about 80
when a fiesta xr2 passed me, I thought not having that and changed down and followed, they hit just
over the ton and slowed and I thought lets get passed. I was just about to pass them when BANG a
noise like a shotgun then nothing, the motor just died. I costed to a halt. I kicked the bike over and
plenty of compression, I then checked the spark, seemed ok, no noise when I kicked it over, I thought
weird. a couple of friends pulled up and asked what was wrong, I told them what had happened and
they offered me a push. the bike would fire but not start. investigation showed that it had blown a
condenser, I had the mag rebuilt and the bike ran fine. next job I did was to take off the oil tank and
wash it out. it was sparkling, very clean. I put new oil in and went for a run, it ran great. a week later I
was out on the bike and it tried to seize up, I came home on tick over and stopped the bike and put it
on its side stand and oil poured out of the chaincase. I thought what’s going on. I looked into the oil
tank and there was no oil. I scratched my head. investigation revealed that the tube in the oil filter
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was blocked with debris. something at the time that I was unaware of. apparently if the bike has had
a automatic mag fitted at sometime in its life and stripped the teeth, the remains go down into the
motor and the oil pump will pass it and it will lodge in the cross drilled hole. this is what I had
happened to mine and it cost me a set of main bearings because after the event they whined like hell
and they had to be changed. I got the work done at Criterion and they advised to leave out the tube
which I duly did, and no problem.
L #515 I have a 1961 Velocette Venom Clubman 500. It starts fine when cold but if it stalls it will
not start up again when hot. I have recently had my magneto (Lucas KF1) overhauled (about 2
months ago,) but it still will not start when hot.
#516 Same thing happened to me who ever did your magneto didn't do it properly, I would ditch the
whole thing and go electronic,
#517 I have a Thruxton which also will not start when hot. The magneto was done by Dave Linslay
and I am totally confident he did a great job because it flies when I get it started, regardless of how
hard I ride it and how hot it gets. Before the mag. was reconditioned the motor was inclined to
missfire under load and was down on power. When we had leaded fuel (oh no, not the unleaded fuel
saga again!!) available in Australia, I never had this problem of hot starting. The odd thing now is that
when the motor has been running and then stopped, there is a white vapour which 'curls' out of the
Concentric MKII and if I open the throttle and get the inlet valve open (it's easy to look down the
carbs throat on a Thruxton) until the white vapour clears, it fires up readily - the same thing happens if
I remove the spark plug and kick it over a few times - it starts easily. It is definitely not flooded and
the NGK B8ES is dark brown to black and not wet or fouled. This may sound like I have been out in
the sun too much but I can assure everyone that this is always the case when the motor is hot.
#526 Try fitting a quarter or three eights inch heat insulating spacer between the carbs and head.
Although I agree that just because a mag has been rebuilt does not mean that it is working. This
happened a few months ago to someone in our VOC center, replacing the mag with a good old one
cured the problem. Additionally if you are running a NGK B8ES or equivalent spark plug with a
compression ratio of about 8 :1, try going down a grade to B7ES, this helped in three cases I know of.
L #883 I was out on the MAC (1951) the other day when the engine unusually stopped when I
closed the throttle at a junction. It started again first kick and I carried on. It did the same thing again a
minute or so later. Again, it started OK but this time I noticed it wasn't pulling so well. After a short time
the engine started to run very rough and then just stopped. I pushed home - not very far, fortunately.
Now, the engine is firing early, during the compression stroke I think, and pushing the kickstart back
up against my foot. I also get an oily-smelling blowback through the carbs. I know it's a timing
problem, but haven't had to deal with this before so I was wondering if anyone could advise me on
what probably went wrong so I know where to start.
#884 It sounds like you have stripped the fibre gear wheel on the magneto. when you take off the
timing cover, and if this is the case, remember to flush out the lower end of the motor to get rid of all
the bits of fibre teeth. I believe there is a firm that now make replacement auto advance units in alloy.
#892 I had the same problem once, & suggest you check your mag timing gear which is probably fibre
& may have stripped a tooth.
#888 Another word of advice - DO NOT use an alloy replacement for the fibre gear. These will wear
quite badly and deposit alloy shards in the sump, which will do rather more damage in the long term
than the bits of fibre. If you are going to replace with anything then use a steel gear.
#889 I'm a fan of the John Hales modified ATD's, superb, and in my MSS. BUT Those nice people at
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Criterion have been supplying very good adjustable ALLOY pinions for years ( NOT for ATD's ) and
I've never had any problem with shards filling up the engine.
#890 I used an alloy replacement pinion on my ATD after the fibre one did the disintegrating thing
many years ago, and when I stripped the machine quite a few years but not so many miles later the
pinion was showing signs of quite severe wear and there was a fair amount of alloy around, mostly
little bits but all about the length equivalent to the width of the timing gear - it didn't take much
deduction to see where it had all come from! I replaced the pinion again about two years ago with one
of John Hales' steel gears and so far so good, no sign of wear at the last inspection when I had the oil
pump overhauled earlier this year.
L #977 My 1959 Venom exhibits poor hot starting. I'm fairly new at Velocette set up (I had my
last one about a third of a century ago). Cold it starts almost first kick. When hot it is very unreliable. I
am using a Champion N8 plug. Is it set up or starting technique? When I remove the plug after a non
starting episode it can be wet, sooty and hot. There is a good bluish spark. Ideas anyone?
#983 In almost all cases of this sort, the magneto capacitor and/or coil is responsible. They degrade
with heat. What model magneto do you have? The Lucas are more susceptible to this malady than
BTH.
#985 My '57 Venom had exactly the same problem with a reluctance to start hot. Try a Champion N4C
spark plug. Get the points in the magneto exactly right. I replaced mine. Don't flood it, not much
throttle either. If you think it is flooded. Hold the valve de compressor in and swing the starting lever
about 12 times. Try starting again without flooding.
#987 Just a few points which may help with poor hot starting - excuse any that you find pb obvious:
For a magneto to work decently it of course has to be in fair nick. The points gap is 12 thou. Plugs
should have a gap of 18 thou (not 25 - that’s for electronic ignition) The usual plug cap is a resistor
type and that is not what you want with a mag. Don't use a resistor type lead either - solid copper is
the only one to use and forget resistor type plugs. In case you are worried about interference, my Mk !
has no suppressors of any kind fitted and it causes no interference (as far as I know!) although I
know it should. In the past I have had trouble with Champion plugs playing up when hot, they always
seem OK cold. I have used NGK for some years and they seem to cope well with hot or cold starting.
#994 If there is a good spark when hot, you are flooding the engine on hot start. Just grab a fistful of
throttle (open it about ½ to 3/4 or so) and kick. The greater throttle opening will reduce venturi effect
in the carbs and pull less fuel and more air on the start, evaporating excess fuel accumulated in the
carbs and getting the mixture correct. A hot motor will also cause a slight expansion of the fuel in the
fuel bowl, possibly pooling fuel in the carbs (this varies by carbs type), causing flooding at hot start.
Comments about the magneto are applicable if the spark is weak when hot. Magnetos are velocitychallenged
at kickstart speeds, generation of the correct primary current requiring everything to be in
good order for a hot spark. Resistance in the secondary will limit their performance at start. Get rid of
resistance plugs, caps and wires.
#1035 when I purchased my MAC. it was a poor hot starter until I found it had the wrong projection
type plug BP6ES instead of the standard B6ES .I know the MAC has a lower compression ratio etc
than the viper & venoms and that the magneto resistance should be reduced to a minimum. But the
reduction of the gap to 18 thou instead of the Velocette’s recommended 23 thou, would in the 50s &
60s be asking for whiskered up plugs. but that said we did have Cleveland Driscoll 101 octane petrol
in the UK that any old biker, will tell you made your bike go like a rocket. Are you saying that the
demise of lead in the petrol fouling, the plug is not a problem now?
L #1201 I recently overhauled my Venoms top end with Omega piston and Total Seal piston ring
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set (gapless second and 3 piece oil ring) and head is overhauled too. Now it`s real pig to start, The
new rings are very tight and it`s hard to get good enough kick to get motor spinning, it will bang once
to three times then spits back and dies. The ring gaps are ok so is the ignition. I got three different
carbs Amal Mk1,5 Amal MkII and Mikuni round slide 32. Which is best one in your honest opinion to
get good gold start. And do anyone have general settings for these carburettors? My garage is quite
cold, under 10celsius and only oil I could get my hands to is Silkolene 50 which is too thick in these
conditions. Two days ago it fired in first kick but wouldn’t idle but spits to carburettor, yesterday it did`t
start at all...oh what a cursing...and my friends got a good laughter and advice to look some 350 or
250 for the next bike!
#1203 I'd rank order the ease of starting and idling as MKII, MKI. I've little experience with Mikunis on
English bikes. I can share with you that I recently bought a 75 Bultaco Alpina 370cc fitted with a MKII.
The previous owner had great difficulty starting the bike. He told me the carbs had been cleaned
several times and that the 370 cc was notoriously hard to start. It would take 40 or 50 kicks some
times. A brief study of the idling circuit disclosed the float bowl was dirty and the small drilling at the
bottom of the bowl was plugged. After cleaning the bowl and the idle jet, the bike now starts 1st or
2nd kick in all weather. It idles and performs wonderfully. Part of the starting problem I had on the
Alpina was my wanting to open the throttle while kicking. Once I had the carbs clean, leaving the
throttle closed results in a reliable start every time. My '60 Gold Star has a 1036 AMAL MKI which has
a removable idle jet. "IF" tickled just right, kicked thru 2 or 3 times with the compression release pulled
in, the bike starts in 1 - 3 kicks every time. Again, like the Alpina, the carbs must remain closed till the
bike fires. This bike likes a 25 pilot quite well, but loads up quickly with a 30 pilot. In conclusion, I
believe the idle circuit on the MKII, with its enrichner circuit, makes it superior technically to the MKI or
Monobloc. It seem each bike has its own combination. I'd suggest you look carefully at the idle circuits
and starting "drill".
#1207 Could be that you have some oil in the crankcase, this will slow the flywheels enough to stop it
starting up. Drain the cases and try again. You are making life hard enough with straight 50 if its cold!
#1211 I drained the crankcase first thing but there wasn’t much oil. I must clean the carburetor, it has
been standing for few months. The cold certainly makes things difficult, oil is so thick it hardly drains
from crankcase, ah it`s so nice to live here in cold Finland... And kicked enough the oil starts to leak
from primary chaincase under the crankshaft, is that normal? I believe that it is...
#1212 If the ambient temperature is well down (as I believe Finland is at this time of year) straight 50
grade oil will cause a huge amount of drag - the stuff is like glue at low temps. Try changing for a
multigrade 20W50 such as GTX for the winter and revert to 50W if you feel the need in the warmth of
summer.
L #1637 A wet morning to be sat at this gizmo & ponder a little. As a first time Velo owner, and
unfortunately bus pass owner, with only a certain allocation of kicks left in me, I was looking at
message #1588-'normal starting drill'. I can start this machine (a std. MAC),but I'm aware that it's
usually more by luck than judgement. I'd appreciate a proper table of events to obtain the easiest
possible start. Spark, Timing & petrol supply are all good.
#1638 To start my MAC I turn on the petrol, close the air slide, find compression, lift the piston over
TDC, release the valve lifter, long swinging kick with no throttle. Usually starts OK hot but can be
reluctant when cold. Tickling the carbs just wets the plug. The secret is the lifting the piston just over
TDC and the long swinging kick.
#1639 This works for me: turn on the petrol. Wait a few seconds. Pull in the valve lifter and turn the
engine over a couple of times to draw in some mixture. Release the valve lifter. press down on the
kickstart until you feel compression, hold your foot there while you pull in the valve lifter and turn the
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engine a little further, beyond compression. Release the valve-lifter, let the kickstart return to the top
and give it a long kick all the way down. From cold, my MAC usually starts first or second kick this
way. Mine doesn't like any throttle while starting and you find out by trial and error how much choke (if
any) it likes. The Velo instruction book suggests flooding the carbs a little, but mine doesn't like that
and will invariably flood big-time so I leave the carbs alone. Hope this helps.
#1648 The only thing I would add is to grip the brake lever when you have the throttle at the
appropriate setting (for me about one sixteenth open). This stops you inadvertently opening the
throttle when you swing your boot (and the rest of your body) downwards. My Venom was always a
first time starter, until during an enforced lay of I completely forgot to hold the brake lever, it became a
pain to start. When I remembered to hold the brake lever again it started first kick. Finally flooding, a
lot of individuals drown the carbs rather than flood it. Try lifting your finger off the tickler immediately
you see first signs of petrol emerging
#1645 I too am a first time Velo owner (though unable to claim a bus pass for many years yet!). I have
a 1953 Alloy engined rigid MAC. The best way I have found to start it is to 1. Turn the fuel on. 2. Flood
the carbs. 3. Close the air leaver fully 4. Gently turn the engine over with the Kickstart until it comes
onto compression, 5. Allow the kickstart to return to the top of its stroke 6. Pull the decompressor. 7.
Gently kick the kickstarter until it is at the bottom of its stroke. 8. Let the kickstart return to it upright
position. 9. Kick as hard as you can blipping the throttle as you do it. It usually needs between 1 and 3
kicks to start. For some reason contrary to the other reports I have read here I have never got it to
start without flooding the carbs.
L #1742 After much searching have just acquired 1968 Thruxton with one previous owner from
new, alas now deceased. Only 36K certified miles from new and meticulous documentation. It starts
ok but will not run cleanly without cutting, coughing and refusing to rev properly most of the time.
Vibration also seems excessive. Mag/points are fine, timing is correct and plug (NGK) is new. GP
carbs is on recommended settings for needle/slide although slide does look a little worn. Surely a
carbs overhaul is not warranted at this mileage?. Compression is good and records show recent
Seymour bottom end rebuild. I am using an octane booster. Clearly, consultation with previous owner
is not possible, but I doubt he would have accepted such poor running. I would appreciate guidance
on how to proceed logically, apart from selling it quickly for a profit!
#1743 Obvious things first (as I found with mine when I bought it after it had stood unused for a few
years).
Take the carbs apart and make sure all the jets are clear of evaporated residue. New petrol.
Put on a new HT lead (but not a resistor cap). You say it doesn't run properly "most of the time". If it
runs well sometimes I would think around bad electrical connections. I had a badly crimped LT feed at
the coil which wasn't obvious because it was under an insulated crimp. Misfires/cutting out until I
found it. If it starts well but misfires when hot, what about insulation between the cylinder and the
carbs? or faulty coil? Sorry if these are too obvious and you've tried them, but if it's starting well I
wouldn't have thought it was too serious a problem. The only concern I'd have would be why it had
needed a bottom end rebuild after only 36k miles.
#1752 Resleeve the carbs. GP slides wear at an alarming rate. Mine was consuming a new slide per
year until I took the most recently worn out slide and the carbs to a carbs resleever near Sydney
Australia in 1982 and it came back with what appears to be a SS sleeve on the slide and a good fit in
the body. I then set it up as per the book (except some versions of the book say No3 slide and it
definitely has to be No4 to run crisp and clean on the midrange) and didn't have to touch it until last
year when I couldn't get a sensible static float level after an engine overhaul. That problem is being
addressed using a Keihin float needle and seat conversion screwed into the original matchbox float
chamber seat (as written up by VOCNA Pres Cory Padula in a recent FTW article). One other problem
I now have, which doesn't appear to be implicated with your VMT, is excessive wear of the cam ring
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housing of the K1FC mag. There is so much slop after many years trouble free running, that poor Ol'
Faithful ended the Cape to Cape Grape Rally here in Western Australia with the cam ring supported
between a couple of beer can shims to provide some semblance of a consistent points gap and hence
a steady advance setting. Tried another cam ring but it was just as sloppy so the wear is definitely in
the housing, as you would expect. Took some tracking down but eventually got to the crux of the
problem. However two months later, the beer can remedy lives on. So, don't give up in despair, don't
sell it for a profit, just keep tinkering and using the beast until you develop a deep and meaningful
understanding and you should find it becomes the easiest starting of Velos which defies the Classic
motorcycle press generated image of being only suitable for hairy chested musclemen. If it won't fire
by the second kick after a generous tickle (very hard to get at unless you can lift the rear of the tank
enough to slide the left hand in above the battery box) then something else is amiss. And don't forget
to use two fingers on the front brake when you crack the throttle a whisker to be sure it fires and runs,
so that the vigorous body action of the long swinging kick doesn't end up translating to vigorous but
unintentional rotation of the twistgrip.
L #1845 Some time ago, when rebuilding the engine of my Venom Clubman (now 1200 miles), I
got a new concentric, the old one being worn out. It was fitted with 30 pilot jet and 270 main, as
specified, but valve cutaway is 3 instead of 4. Being supplied by Nick Payton, I suppose it is not too
wrong, and it works well at mid throttle. Problems occurred at tickover and full throttle. First, I used to
have a very irregular tickover, very weak mixture, even with air screw fully in. It then needed flooding
and closed choke even for starting when stinking hot. I checked everything (level, channels...), to find
the base of the body, supporting on the bowl, where is the paper gasket, was not flat, and the pilot
system was sucking air instead of fuel. So I turned it flat on the lathe, getting about .2 mm off. Then it
worked very much better. It is even better now without pilot jet.
An other problem remains : full throttle, even on 2nd or 3rd gear, it hardly goes over 5000 rpm. Just
releasing the throttle gets 200 extra rpm. That's not enough, and indicates it is still weak. Will I fit a
larger jet, larger than the specified 270, or look for another cause in the carbs, or elsewhere, or throw
the whole stuff away, and get a Monobloc ?
#1847 I've got exactly the same full throttle problem with my Clubman fitted with a new concentric.
I've tried main jet sizes 270 -300 and settled in the end for...270. Then I began experimenting with
needle position. In position 2 the bike runs well except at full throttle and doesn't rev over 5000. In
position 3 acceleration is improved but doesn't go above 5000 and at constant rpm the bike has a
tendency the run irregular. Also pick up is worse as you snap open the throttle I'm also considering
going back to a monobloc! Hope someone knows more about concentrics than we do.
#1848 I wonder if the float needle is passing enough fuel at WFO and 5000 rpm? Sounds like they
are running out of fuel. Did they run ok at WFO and 5000+ rpm with the monobloc? If so, higher float
level or larger bore float needle and seat may be needed.
#1849 Can’t add much to this except maybe a few more things to try/consider - systematically:
I) exhaust system is strangling performance a bit - is it original silencer ?
ii) check fuel taps are passing sufficient fuel etc.
iii) performance will drop off if cyl head is getting sooty
iv) obviously - carefully check ignition timing
v) check for other air leaks (e.g. exhaust system / carbs to head etc.)
vi) try changing sparking plug
#1851: 1. it is the original silencer. 2. fuel lines are ok. 3. the bike did have a decoke 500 miles ago. 4.
and I did check ignition. it is spot on. 5. I don't think there are air leaks, but will check again. 6. I tried
champion n4, ngk B8ES, ngk B8EGV. No difference in full throttle running. Although the last seems
the best!
The bike is a 99% standard Venom Clubman mk2, except for carbs and alternator (alton).
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#1858 Regarding the slide needle, it doesn't matter at full throttle. But I will check the level needle
flow, even though you can hardly modify it.
#1865 I think you will find that the float seat will need adjustment. I do know that most of the new
carbs have the float seat set too high. a friend of mine who runs a bike shop always has to adjust the
float seat. he uses a brass drift to lower the seat. I seem to remember 80 thou being used
somewhere. also on the triumph/bsa three cylinders, the racers had their float bowls modified to give
extra fuel. I have details how to do it. it involves a small milling job. if you want the info, give me a
shout. cheers.
#1863 If the float level is set too low the float needle may not open enough to allow the fuel to reach
its proper level in the float chamber causing a lean condition at WFO regardless of the main jet size.
In this case the restriction of the inlet needle is acting as the main jet, that is, it is limiting the amount
of fuel going in to the carburetor air stream. And yes, weak 50 year old valve springs can cause valve
bounce. But 50 year old strong ones will not.
L #2002 If I leave my bike running on tickover ,it has periods of about five seconds (a long time
when you're wondering whether it's going to stall) of running at varying speeds. Adjusting the air
screw seems to have minimal effect. I'd guess that it's something to do with carburettion but exactly
what I'm not sure. Plug looks OK so don't think it's that. It's got to be something to do with the pilot
feed because at full whack it makes me feel like I was seventeen again (Ariel, I have to admit -But
Hartley tuned)
#2004 Could be a worn slide taking a little time to settle into place and leaking a bit of air until it has.
#2075 Have you checked the face of the carburettor where it bolts to the manifold ? It is quite
common for this to bow (warp) if over tightened. If so either reface using a piece of glass and fine
grinding paste or fit a soft cork or similar gasket with a smear of silicon sealer to see if that effects a
cure.
L #2047 I have spent an inordinate amount of time trying to prevent my newly rebuilt Viper
basket case from pinking once the engine was hot and under load at low revs (even when gently
feathering the throttle). Eventually after lots of experimenting with timing without real success( it is coil
ignition so the base plate of the contact breaker can be moved to advance or retard the ignition
easily), a friend suggested the mixture may be too weak ( needle position 2nd groove from top). I
raised the needle to the bottom groove to establish if any change and the problem was instantly
cured. I have since fixed the needle in one groove down from middle and the engine will only pink if
severely provoked now. I have never known an engine to be so sensitive to mixture strength under
load before to result in the degree of pinking I was experiencing.
L #2285 HI everybody on the list, Pete here, have recently joined the forum and have read
eagerly the discussions about all things velo. I myself have a Venom veeline clubman and have
recently ripped off the electronic system in order to go back to the original mag. However, even with
the assistance of friends, one of whom has had velos for many years, the correct timing is eluding us.
I understand the timing should be 38 degrees before top dead centre, although that is certainly how
we are setting the timing up, every time we go and start the bike the timing seems to be out, this has
varied from being 34 degrees before to being so far out the bike is just kicking back. So what is
happening, it could possibly be that the bike is on the wrong stroke. What I am not sure of is what
happens if the bike is on the wrong stroke, what are the symptoms? Although nothing seems to be
moving with respect to putting and tightening on the auto-advance retard unit, the timing remains out. I
am now wondering whether there is something so obvious that I can't see it. Have checked to make
sure the timing disc is not moving, the points are not moving during the instalment of the
auto-advance retard unit, etc. Any suggestions would be greatly appreciated, the bike is my main form
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of transport for work and therefore I am keen to get it back on the road asap. In advance of any
suggestions thanks, Living in the Essex area if there is anybody nearby who might be able to help.
#2286 If the bike will start, you are obviously on the right stroke of the cycle, or the bike would not run,
nor would even fire. You do not state which magneto you are using, but do mention auto advance. I'm
sure you realize the timing spec, 38 degrees is full advanced, which requires the auto advance
mechanism's bob weights to be "locked" in the out or advanced state, when setting the timing. Rubber
blocks or small wood wedges work well for this.
L #2565 How slow a tickover can you achieve on a Clubman ? And do you tune it fully
advanced, or fully retarded, or in between ? My engine is in very good general condition, fitted with a
newly rebuild BTH mag (really excellent job done by Dave Lindsley) and a concentric (pilot jet 30). The
best even tickover I can achieve is in slowing down the carbs at full advance to about 1200 rpm, and
then retard ignition to slow to 1000rpm, about half way. Under 1000 it will run quietly for a while, and
then stall, usually as the traffic lights turn green, with 50 cars waiting in the lane behind, as you know.
Do you think I could expect better? I remember a mate MSS idling at some 500 rpm or so.
#2567 If you want a really slow tick over on a VM fit multi rate coil springs. The difference is amazing.
The valve is pulled straight back onto the seat hence sealing is better and the lower seat pressure
means less internal resistance throughout the motor. Having said that with a M17/8 cam you'll be
lucky to get slower than about 900rpm . The MSS has softer cams and heavier flywheels (well some
do) and that really makes the difference.
L #3054 I've completed the winter rebuild which included new mains, big and little ends, piston,
valve guides (used old valves as they were OK). When I started it up today there was lots of smoke,
which I expected from the oil I'd used during the reassembly. I went for a ride of about 15 miles and
was really pleased with the way the bike felt. BUT, when I got back home and left it ticking over while I
had a listen to the engine, the exhaust smoke reappeared. I'm not talking about the odd wisp of
smoke here, it's really smoking badly (enough for me to think the neighbours might not be happy) and
seems to get worse the longer it ticks over until the engine finally misfires and stops. The plug is oily. I
can't believe this is still "assembly" oil. My logic is that if it's not "assembly" oil, it can only be getting
into the combustion chamber down the guides or up past the piston, all of which are new. My options
now are to try another ride to see if it will clear, or to take off the head and cylinder again to see if I
can see a problem. Any suggestions would be welcome. I feel as though I might be missing something
obvious but can't think what it is. The only thing I've done any differently building this engine is that I
got a local machine shop to ream the new guides to suit the valves and it came back with the valves
fitted and lubricated with "assembly fluid". I felt the valves for fit (they were fine) and then assembled
springs etc. I've never used "assembly fluid", just an oilcan, could this be the cause? I'll speak to the
machine shop on Monday. I really would welcome any advice or suggestions, the bike was running so
well I really don't want to start to take it apart again, but if I have to, so be it.
#3055 Was the bike on the side stand when it was ticking over? If so the top of the guides will be
submerged in oil, with the throttle closed the guide acts like a drinking straw.
#3056 Either your oil pump is not returning the oil to the tank and you are wet sumped (do a careful
monitor of the oil level in the tank), or you oiled the rings and piston during assembly. Modern oils are
so good that the rings will refuse to seat if not assembled dry. The good news is that if you clean all
the oil off of the rings and piston and reassemble, they should seat just fine. If you used the one piece
cast iron oil ring, your engine will use more oil than if you used a modern three piece ring. I get all my
rings by size from Hastings (800) 776-1012
#3057 If it's any help, I was riding my venom between Portsmouth and Derby about a million years
ago when all of a sudden it started to spew smoke out of the silencer. Investigating the problem
9

showed that the rocker box was full of oil. It turned out that a small piece of gasket material had found
it's way into the rocker box drain pipe, blocking the return. Once it was winkled out and the top end
reassembled all was fine then and for years after that. I guess that I may have had some wear in my
valves/guides but it won't have been terribly bad.
#3058 The one mistake that a lot of people make after a rebuild is that they put quality oil into the
motor. have you used running in oil. very preferable after a rebuild. needs to be in about 500 miles
and then dropped and then a good quality oil added. millers do a running in oil to break in new or
rebuilt motors. if you put in quality oil at the start you can glaze the bore, as the oil is so good, it wont
let the rings bed in. this could be an answer as to why the motor is smoking. also check the cross
drilled hole in the return in the oil tank, the one that the tube goes over in the filter chamber. make
sure that there is no debris in there, as this can restrict return flow and up the level in the motor. this
can also contribute to the motor smoking, as the oil level gets higher, the flywheels will fling it up the
bore. hope this info might be of some help.
#3059 Thanks for all the replies. Here are answers to the questions you posed and where we're up to:
The bike was on the centre stand not the side stand when ticking over and making smoke. There was
a good oil return flow to the tank. Compression feels fine. I had oiled the barrel and piston/rings using
Silkolene 40. I'm using the same oil in the tank. I understand what's been said about rings not bedding
in but I'm sure the amount of smoke it's producing is more than would be caused by this alone. If it
were a 2-stroke the amount of smoke would indicate a problem. About 24 hours after being used and
making smoke I drained the crankcase and got around 100cc of oil. Thinking about drain down from
inside the engine over 24 hours I don't think this is excessive. This and the good return flow is inclining
me away from wet sumping as being the cause. This pointed me more at the top end and the
suggestion of blocked oil drain from the rocker box. I removed the oil drain pipe (head to pushrod
tube) and this was clear. I was half hoping for a gush of oil from the rocker box but there was only a
drip. Poked into the drain holes with a cable tie and I'm certain they are clear. So where now? I won't
be able to do any more until next weekend so please keep thinking. What about the fact that it seems
to get worse the longer it ticks over and is more pronounced on the overrun? My current plan is to go
for another run in the probably vain hope it sorts itself out, then, if it doesn't, start by removing rocker
box then head then barrel and checking as I go. I have a nagging feeling that the cause might be
really simple and might just be very embarrassing - in a way I hope it is!
#3060 When you take the head off - and it's looking like you are going in that direction - unseated
rings will give you a fairly even deposit of soot on the outside margin of the piston crown. You'll have
oil on the stem and tulip of the intake valve if that guide is at fault and lots of soot in the exhaust port if
that guide and valve are letting oil by. I've tried knurled guides a few times and sometimes it worked,
sometimes it didn't. I'd suggest valve guide seals with knurled guides, but that may not be an option
here. Hope you don't have to dig this deep.
#3062 I have had a think about this, and it might be a guide going up and down with the valve. I have
seen it happen before. velocette idea of putting guides in without a landing is not a good idea in my
book. hope you sort it out. cheers.
#3061 My experience is that a lot of oil getting by the rings will keep the top of the piston clean at it's
circumference with the carbon growing like a weed just 1/4" away from the bore
#3063 The oil surely comes from the head. The smoke development will get worse during a long tick
over period because the head gets hotter and hotter and this might increase the gap between guide
and head. When checking for loose valve guides, make sure to do it when the head is hot because it
might be that they are a tight fit when cold. If the guides are really loose, you probably have to bore
out the guide holes because of the action of the rocker they will not be round anymore but somehow
elliptic. Then you need to buy/make oversize valve guides and re-cut your seats afterwards.
10

sorry mate, hope this is not the case.
#3064 I had an appalling amount of smoke from my MkI a while ago. It was expensive to buy all that
R! The cause was a cracked oil ring which had fallen into four pieces. New ring = no more smoke; no
re-bore etc.
#3116 Sorted the smoking out and, as I feared, it was something I'd done and am duly embarrassed
about. So here it is, just to complete the story and prevent anyone else doing the same. The ideas
about oil covering the guides as a cause pointed me in the right direction. I took off the rocker cover
and poured oil into the recesses on the top of the head to see how much needed to be in there to
cover the guides. The drain rate was slower than I'd expected but the exhaust side was significantly
slower than the inlet. When I had fitted the rocker cover I had used what I thought was a very small
amount of silicone sealant on the gasket. The fixing screw just in front of the pushrod tube had taken
some silicone down in front of it and squeezed this into the exhaust side rocker drain drilling, partially
blocking it. I hadn't realized that the two rocker drain drillings are just broken into by the fixing screw
holes. The drain was reduced to maybe two thirds of its full diameter. Anyway, cleaned it all out,
refitted the rocker cover with no sealant, started it up and it still smoked but by no means as badly.
Went for a ride, maybe 10 miles, no sign of smoking afterwards so think that what there was just
burning off from inside the exhaust. There we are then, Ian with red face but relieved.
L #3777 My 1938 MSS has an old AMAL 276, with the remote float. It has been running a bit off
for the last 500 miles or so. The bike will run fine when opening the throttle from idle through wide
open. But if I hold the bike at 3/4 throttle, it will cough every 2-3 seconds. If I open the throttle a bit
more, the bike runs great. On my last two rides, I've just kept the throttle opened a bit more, or a bit
less, than the trouble spot, and everything has been fine. I'm guessing that the slide is slowly wearing
out, but shouldn't that affect the carburation at lower rpm levels? Maybe the needle jet is wearing
out... I guess I'll pull it apart and look inside.
#3779 It's quite possible the slide is worn after many years - you can bore out the body and re-bush,
but it's a fiddly business. Before that I'd take it apart and clean out thoroughly - try the easy things
first. Is there a leak on the carbs flange joint -? this would affect slow running worst. Needle worn -
probably the jet it runs in is more likely . The fact that it's only happened in the last 500 miles suggests
a blockage etc rather than wear which would take many 1000's of miles to show up, and happen so
slowly you'd hardly notice.
L #4281 Hello all, this past weekend was the first shakedown run for the new MAC on our fall
club ride. Things didn't go too well. After getting about 10 miles from home, at an intersection, it quit
and refused to start again. After waiting for about 20 minutes it did start, and I continued, but it wasn't
running very well. The further up the canyon I went the worse it ran. It seems to run really well as long
as the road is flat and I don't push it too hard. Does this sound like a magneto problem? Does anyone
know about Kirby Rowbotham engineering in England that offers an electronic ignition conversion
inside the existing magneto? Coming down the canyon it was backfiring and spluttering all the way. I
think it felt like ignition trouble. Anyone on this list have any thoughts?
#4286 Does it still have the fibre mag wheel? If so check the teeth for wear. I had a problem years
ago where the timing kept altering by itself. I fitted a steel wheel and ran with ignition fully advanced,
no problem with a MAC.
#4282 Poor hot starting is classic magneto trouble. While you could go electronic I'd suggest that you
just get the magneto rewound by a reputable company and it should be fine. I had the same problem
with my 1954 MAC when I first got it and the rewound mag transformed starting and has been good
for 8 years now.
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#4283 Most likely the magneto, but first make sure the petrol can get into the carbs quickly. I changed
the mag ( which meant lifting the barrel to remove it, and just how are you meant to get to those 3
nuts?) only to find that the tap filters only passed a dribble that run the bike fine until you tried to go
faster!
#4284 Do you have the proper heat proof gasket on the carbs / cylinder head joint? (K180/3). I had
similar problem with poor hot running /starting performance. When I replaced the paper gasket with
the proper one the problem went.
L #4689 I have just purchased a restored 1956 Venom and can't get it to run other than with the
choke open (air slide closed). As this is my first ever Brit Bike ( or indeed any bike that did not run as a
starting point!) I am at a bit of a loss where to start with changing the settings. The previous owner
indicated that the jetting is standard so I am guessing I need to play initially with the pilot air adjusting
screw. Is there such a thing as a standard setting from which I can then twiddle ( similar to the
procedure on my Airhead BMW's Bing Carburettors) ?
#4690 Look at: www.croesus-consultants.co.uk/v-tec (the Group owner’s) and a treasure trove of Velo
info (including carbs settings). For guidance on checking the settings try:
www.hitchcocksmotorcycles.com which has the AMAL hints and tips for setting up your carbs.
#4699 Assuming an Amal Monobloc is fitted. I'm not sure what you mean by choke open/air slide
closed. Choke open usually means the air slide is not obstructing the choke of the carbs (the air slide
is in the up position in the body of the carbs). However if the choke has to be used (closed/down) to
make to make the engine run once warm it is obvious the mixture strength is far too weak. Firstly
check all the jets and slide are as per the manual and that there are no blockages obvious in any of
the jets. Check that the needle valve is clipped in the middle position or one groove up or down from
this. The pilot valve should be one and a half turns out from fully screwed in as a starting point.
(Screwing out weakens the mixture and enrichens it)
#4702 sounds like the pilot jet is blocked.
12

A.2. Poor Gear Change -
L #3 I have a 1969 Thruxton which is very difficult to change from 1st to 2nd gear.
#4 Having just stripped and reassembled my gearbox ten times to try to eliminate a non-returning
gear leaver I have become very familiar with the selector mechanism. Firstly I would suggest you try to
isolate where the problem lies i.e with the selector mechanism or with the sliding gears and dogs.
Firstly reassemble the gearbox with the selector mechanism only i.e. camplate, forks, rods, etc leaving
out the gears. Use a new gasket but no jointing compound and just three bolts. Try the mechanism to
see if the fault is with the selector mechanism. If all is OK, just add the layshaft and associated gears
and try this. Then try it with just the mainshaft and associated gears. Hopefully by now you may have
isolated the area in which the problem lies. A few tips on the selector mechanism, I compared three
different camplates and the notches were a different form on each. On two of them they looked as if
they had just been quickly ground out on a hand grinder. With an oilstone make these notches a nice
smooth transition, I found you could safely “round” the edge of the notch to half depth. While the cam
plate is out just polish the circumference with the oilstone. Saying all that I don’t think the camplate is
your problem, as you have tried two different ones. Next look at the striking pawl GC23/2. Two
possible problems here. This may make contact with the cam plate pivot on full travel, stopping the
cam plate from fully engaging. The solution is to grind a small amount from the hole, making it slightly
larger at the contact point. Next culprit could be the centralizing lever BK99/2. The solution is to grind
a little from either side of the crescent shaped cut out i.e. having done that you may need to grind the
back of the crescent to maintain clearance.
L #786 Rebuilding a '69 Velo Clubman I've had an early introduction to the wondrous clutch.
Took it apart, fitted new inserts, and put it back together again. Great, except that tightening
everything up now leaves the clutch springs almost fully compressed with no movement to allow the
clutch to disengage. I've read all the technical notes on the web, pulled it apart ten times, but still no
joy. As best I can see, relining the plates should make no difference. The sandwich of plates is no
doubt thicker, but the spring holder is independently adjustable to accommodate this. What happens
when I try to screw the sleeve nut on is that the springs compress until they are virtually bound (i.e.
about 20 mm) before the sleeve nut can tighten against the boss in the back plate to secure the clutch
assembly. Winding the spring holder further in simple presses it against the thrust pins and starts to
disengage the clutch. Incidentally, in case it might be relevant, the chain wheel is well out of alignment
with the engine sprocket. The wheel would need to be 4-5 mm closer to the gearbox for alignment,
although the tooth wear suggests it's been running out of plumb for a good while. All very odd. The
clutch was together and operating properly before disassembly and only the spherical thrust washed
has been renewed, because of pitting.
#787 Sounds like you have fitted the chainwheel, back to front?
#800 Many thanks for your reply. It would certainly put the chainwheel in alignment, but unless I've
misread every reference I can find, there are four plates between the back plate and chainwheel, and
only two plates between chainwheel and front plate (which is why the chainwheel has a shallower rim
on this side). In other words it's not possible to fit the chainwheel back to front.
#803 I think you've misread the references. There should be two plates between the backplate and
chainwheel, and four between the chainwheel and front plate. The later clutch was (as is normal with
Velos) a development of the earlier clutch whose basic design was the same, but which had two
fewer plates. These were added on the outer side of the assembly to cope with the extra output of the
later engines, but without having to change any more components than necessary, so the inner side
of the clutch remained the same with only two plates and the original chain line was kept. The
shallower rim therefore fits to the inside (towards the backplate). Contrary to what you say, it IS
possible to fit it the wrong way round, but you would also have to stack the plates wrongly too. One
other thing to watch for is that the bend on the tabs of the plates is in the right direction. From the top
13

of my head and without reference to the books, the bend is away from the chainwheel on either side.
Should be obvious with the bits in your hands - things will touch if you get it wrong!
#805 Who has misread the references? With backplate fitted to a disused sleeve gear held in the
vice. And quoting directly from the red book: "Fit the first clutch plate in position followed by a spacing
plate, second clutch plate and second spacing plate. Note that the external tongues on the clutch
plates and internal tongues on the spacing plates must all point away from the chainwheel, i.e.
downwards." It goes on to say centralize all the plates then fit the chainwheel with the deeper slotted
rim underneath. It continues "With the chainwheel fitted put on the third spacing plate and clutch plate
in that order and with their tongues pointing upwards." It says centralize the plates and fit the front
plate. Personally I agree with Chris Wood and message 787.
#816 Sorry everyone, I stand corrected. Just checked the books and Tony is of course correct. That'll
teach me to jump in feet first without checking my facts! Can't see how the chainwheel can be fitted
back to front with all the plates in the correct order though. The only other thing I can think of is that
the plates have become displaced during fitting to the sleeve gear splines.
#827 Are you sure you haven't fitted the thicker 7 plate inserts in error?
#829 Many thanks for your suggestion. The inserts I've used came with the bike, amongst a batch of
25 year-old spares. I soaked them in oil to soften them and fit them more easily. Maybe they've
swollen? They are about 9/64ths thick, say 3.5 m.m. Forgive my ignorance of the 7 plate clutch. Do
my inserts sound like the wrong ones?
#833 New VM style inserts are 1/8" thick. The earlier type are close to 3/16". Is it possible that when
you put the clutch back onto the sleeve gear you forgot to fit the loose sleeve on the sleeve gear first?
Maybe also, even though you used the old one, is it the correct nut? They came in two lengths, the
longer one being used for the 9-plate clutch. Are you using the correct length pins for the release
mechanism? Or did you use 'new' big-end roller without shortening them?
L #4006 Why does my venom jump out of first gear just after setting off ?
#4007 I would guess that the engagement dogs have rounded off somewhat after countless clonks
into first. The same happened on my thruxton after 27000 miles. The cog material proved too hard to
re-dress with tools available to me at the time and was regretfully remedied by a new pair of cogs.
#4008 It is also possible that the dogs are not fully engaging. This situation would also, over time,
promote rounding off of the dogs as previously described. A lack of full engagement can arise from
several factors [or a combination of these factors]. Having now rectified a similar situation, I
encountered the following: 1) worn shifter fork faces; ii) the figure-8 shaped hole in the actuating lever
internal to the transmission needing to be ground slightly at its extrema, thus allowing the cam plate to
fully rotate to the required index detent; iii) the camplate indexing pawl having it's point worn off so as
to not accurately engage the detent with the necessary force and/or precision; and iv) excessive wear
in any part of the camplate ratcheting pawl, the pin that drives it, or the indexing hub itself. Polishing
the edge of the camplate results in smoother and more precise shifting.
#4009 Another possibility, on older boxes the 1st gear cog could get knocked along the bronze bush
after years of clunking into bottom, thus reducing the depth of engagement of the dogs. Later boxes
overcame this by having a 2 piece bush, pressed in from either side.
#4010 Your first gear is located by it's bushing too close to the right side of the box, allowing only
partial engagement of the sliding dogs moved by the shift fork. The fix is to make up a new pair of
flanged bushings for the gear with a thicker flange on the right side (or a one piece bush that is a
14

press fit in the gear with that thick flange on the right ) such that the gear will allow full engagement
with the dogs. This flaw was widely discussed in the English Fishtail some years ago and I remember
the recommendation being made that the gear should be moved left by .055". Sounds arbitrary to me.
Every gearbox that I use gets shimmed as tightly as I can do it such that the outer gears on both sides
of the sliders get the most engagement possible and so that the sliding rings or gears engage equally
in both directions. British boxes were all designed with 'assembly tolerances' which can be usefully
closed up for more precise engagement, and the VM/MSS box seems to have had the first gear flaw
designed in.
#4011 I hope you did not scrap those gears. After a similar experience with my Venom: jumping out of
gear on drive then eventually jumping out on coast, I had to stop holding the gearchange pedal with
my toe and do something about it before my selector fork was worn away. Not only were my 1st gear
dogs rounded off; some amateur mechanic had tried to hand grind them straight again - bad news. I
was guided to an engineering firm that could cut the dogs back until the rounded part was removed
then re-harden the faces; ditto the sliding gear that the first gear mates with. They used a spark
erosion technique and they ensured that each drive dog was cut back to the same angle. Otherwise,
the drive load would have been unevenly spread between the dogs, with the prospect of consequent
failure. The 'one off' charge for this work was prohibitive but, between us, a friend and I managed to
find four sets of gears which required salvation. This brought the cost down to £60 per pair of gears.
At first, I thought that the thinned down dogs might shear but after comparison with the simple round
pegs/holes on the first gear of an AMC box, one of the toughest in the business, I had no worries.
Increased backlash was indistinguishable, no doubt because it was insignificant compared with that
already in the gearbox, primary and final drive chains. Between us, we have ridden 5,000 miles on
these refurbished gears with no problems.
#4013 Had this problem years ago on my thruxton. The dogs were rounded as expected. Careful
undercutting with an angle grinder did the trick - never jumped again.
15

A.3. Faulty Electrics -
L #1 I have a Viper which has no battery connected - it has 6V electrics and a Lucas E3L
Dynamo. It has a LUCAS regulator - on the mudguard - although not taken this apart to see if std or
something like JG conversion underneath/ How do I know whether to use positive or negative earth -
some manuals say negative some positive - any tests before connection? If I get it wrong and run the
bike - what damage if wrong polarity - could I be looking at? If the battery is connected and the lights
turned on - I assume ammeter would show '-' when lights on if right way round - if connected wrongly
'+'? is this feasible? Anyone know a source ok KIF magdrives - are these fibre or steel?.
#2 You've worked out the best quick test - checking which way the ammeter swings. However, if you
have an electronic regulator then it can indeed be damaged if you connect up the battery the wrong
way round. So either look into the "Lucas" regulator can or simply disconnect it for the test. Another
way, if the ammeter had been disconnected, is to see which direction the dynamo motors in; but that
takes longer and isn't 100% reliable. Or the colour coding of the wires will indicate what it was
originally.....but an owner may have reversed everything. It depends if you have an autoadvance unit
or manual. If manual, it is a simple steel wheel. The Owners Club can supply top-quality drilled and
lightened versions of these. If autoadvance it originally was fibre, that could strip, so steel
conversions are available. I believe Dave Lindsley has everything for K1F magnetos, he's at 0706
365838 196 Pilsworth Road, Heywood, Lancs OLI0 3DY
#724 If you have ignition trouble, make a two foot stick with a small damp sponge attached to the end
and also a wire between the damp sponge and the other end of the wire (grounded) with a 12 volt
neon lamp somewhere in series. Start the bike and slowly wipe the HT lead from pickup to spark plug
cover. Any flashing of the neon lamp indicates a crack or leak and the whole assembly should be
replaced and reevaluated.
L #3305 Hi I need help please how do I check to see which part of the charging system is faulty,I
have a 1955 MAC with a Miller dynamo 36w and a K- tec regulator, the label on it states that it is a
(K-tec dynamo reg +ve earth 199931006p) the battery is a positive earth and all the lights work when
battery has been charged.When the the lights are on the ammeter shows an approx 5amp discharge.
With the lights off and the engine running the ammeter does not move, with the lights on and the
engine running the same 5 amp discharge, all relative connections have been checked.
#3349 This may get long-winded but I will do my best! The first thing is that the K-Tec is designed for
a lucas dynamo, but don't despair, the miller dynamo is fine but needs to be modified. The cut-out
under the cover needs to be removed, and the resistance windings are not required. One end of the
field coil connects to the brush that is earthed to the body, the other end becomes the 'F' terminal. The
other brush becomes the 'D' terminal. Assuming this has been done, remove the drive belt, and the
wiring from 'D' & 'F' to K-Tec. With another length of wire, join 'D' & 'F' on dynamo together, and touch
it briefly onto the -ve battery terminal. The dynamo should motor in the direction that it will turn on the
bike, ie anticlock looking at the pulley. If it does not motor there is a problem with the dynamo,
possibly you have connected the resistance coil, not the field coil. If it turns in the wrong direction,
simply swap the two ends of the field coil. Motoring the dynamo like this will ensure that the residual
magnetism is North/South the correct way round, (possibly all that is wrong with your setup). The
dynamo is self exciting, that is that a small voltage is generated by the residual magnetism in the
dynamo body, this voltage is fed back into the field coil which makes the body more magnetic, which
generates more voltage which makes the body more magnetic etc etc ... the regulator simply cuts
supply to the field coil when the output reaches the required level. If so far all seems OK replace the
belt, connect the wire still on 'D' and 'F' to a sacrificial bulb (the good 1/2 of and old back light bulb)
the other side of the bulb to earth, and start the bike and rev it quite hard, when the now unregulated
magnetic runaway starts, the bulb will light, and almost certainly blow the other half of the bulb. This
will prove conclusively that the dynamo is ok and that the fault is elsewhere. Check all connections,
and that the K-Tec itself is earthed.
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#3358 Have done as you suggested and dynamo motors in an anti clock wise direction. I have also
had an output from it and a system output but the charging is intermittent.....I have a field resistance
of 4.6 ohm's I have hard wired the k-tec to earth on the battery which is +ve earth. I've come to the
conclusion that the k-tec is shot.....will try to get another one. Do you know who makes them, also is
they a way of testing the k-tec to prove it functionality.......
#3361 Sounds like your reg may be shot. I don’t know where you would get another K-Tec. A few
people I have spoken to don't rate them too highly, but I have no personal experience of them. I have
got V-Reg units on 2 of my bikes and (touch wood) have had no problems. They are available pos or
neg earth, and can be made 6 or 12 volts. I got mine from AO Services. 01953 884681.
L #3872 I switched the sidelight on and smoke appeared from headlight shell. The brown/white
wire cover from the light switch appears to have melted slightly. I do not know where to start looking
for the fault. Brake light and horn work. Any advice greatly appreciated.
#3873 Tracing an electrical fault in a vintage motorcycle or car is a comparatively easy task, -
especially if there has been smoke & a melted wire ! treat the problem as if the electricity is water
running through a pipe, (the wires) - smoke /melted wire equals a leak somewhere to the
frame/tinware of the machine, - that is where the water is running out on to the 'ground' Work away
from the ammeter power source, in this case it has come as far as the main switch without problems, -
but somewhere from there on, & PAST the melted wire, there is a 'leak' to ground, (earth) most
probably a wire rubbed bare or even a wire broken & fallen off a connection & sitting on the
surrounding metal work. In your problem it has to be somewhere along the 'side light' (?)/ taillamp
wiring, but there is also the possibility that an instrument panel illuminating globe, (speedo, ammeter
illumination etc.) has a wire touching metal . If you have been 'servicing' your machine in a major way
immediately before the 'fire' occurred, go straight to where you have been working, it quite often
happens that a wire gets 'pinched' under a bolt head, or between 2 adjoining pieces of metal work, -
this happens all the time ! Circuits (waterpiping) vary, & in quite a lot of cases have been modified
over the years to the owner's choice & extra fuses installed, but certainly not in your case, as a blown
fuse would have been the result instead of the outpouring of smoke. One would have to conclude that
you are not proficient in the use of an electrical 'multi meter' tester, but certainly in your case, a pair of
good eyes should solve the problem ! let us know the result
#3896 Thanks for the advice. The problem was on the tail lamp wiring, under the tank, not in the
headlight where the smoke was coming from and where I was looking. I insulated the bare bits of wire
in headlight and still had a problem. I had forgotten about the tail light being on the same circuit. I
insulated a wire under the tank and the system seems ok now.
L #3904 My dynamo won't charge, it was o.k. till couple weeks ago and just suddenly stopped
charging, I sprayed the rotor with WD40 and it started charging again for 2-3 miles then stopped again
sprayed WD40 again and it charged again did this several times then stopped charging completely, I
fitted new brushes and it worked ok for a few minutes then stopped charging again, any ideas what it
could be? I have recently had a transistorized regulator fitted as it was over charging I have checked
all of the connections and they are sound.
#3906 Dave, make sure that the commutator is clean (rub with fine emery cloth and rinse w/contact
cleaner) and that the brush holders are smooth and clean inside. If playing with the brushes helped,
that's probably it. They are probably just sticking. I wouldn't blame the regulator. My 60W Lucas has
done the same thing. Stuck brushes.
#3907 It's better to use sandpaper because emery is metallic! Well, that's what I learnt when I was an
apprentice motor-fitter.
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#3912 I concur with Tom. If I don't use the Venom for more than a couple of days I always have to
take off the dynamo end cover and "waggle" the brushes, WD40 helps. When I use the bike every
day I never have the problem.
#3909 First thing to check is whether the dynamo motors when connected across a battery? If it
does, then the problem is almost certainly not with the dynamo. What sort of electronic regulator have
you fitted? That would be my first suspect! Is it a Miller or Lucas dynamo? I don't think WD40 would
be good for the armature.
L #4813 I Have put new bearings in and new brushes and eureka the dynamo's charging again
10 miles later it's stopped charging. Running it with out the end cover there is no arcing around the
brushes(it is going round) no movement of the ammeter.It has a good battery fully charged am only
measuring 0.52v+ at the field and output terminals with the engine above tick over ...as this is a bike
that is in daily use any suggestions on the best way to go for the least amount of pounds would be
greatly appreciated.........
#4815 In order of probablity.. are the brushes free or have they jammed? Is the wiring in good order?
is the regulator OK? Try 'motoring' the dynamo - if it goes OK then its almost certainly OK. 0.52 volts
seems a bit low - if you've got an electronic regulator this may not be enough to fire it up - transistors
need at least 0.7 volts. Give the engine a really good blip ( 4000+rpm) and see if things burst into life.
A bit of detective work required!
#4816 Dirt on the commutator? Are the brushes contacting? I would see if the dynamo motors and/or
disconnect the dynamo from the regulator and see what voltage you get to earth. If the battery is fully
charged then you shouldn't see any current at the ammeter unless you turn on the lights or depress
the rear brake pedal.
#4817 Hi, If it passes the motoring test, I would also try leaving F and D connected together (as for
motoring test) and ,without the regulator connected, run the engine and measure the output wrt to
ground. There should be a sudden increase from near zero to 6volts or more as revs go up to say
1500-2000. Dont exceed this rpm or do it for longer than it takes to get a measurement or you could
'fry' the dynamo. Also I find that an 'old-fashioned' moving-coil (needle) type meter is best as the
electronic/lcd meters often respond to all the interference from the ignition and commutator sparking
and you cant get a meaningful reading from them.
18

B. The Engine
B.1. Bottom End and Crankcase -
L #198 Tony described the correct way to fit an oil seal to stop oil exiting the main bearing –
now I will describe a “bodge”, that a fellow club member used to fix the same problem. Clean the
inside of the sprocket with alcohol or some other solvent, place a circular bead of silicone around the
part of the sprocket that abuts the main bearing boss. Smear light oil on the main bearing boss, slide
the sprocket on and rotate at least one revolution. Lightly screw on the shock absorber, spring and
nut. Leave it for 24 hours, before reassembly.
L #264 What methods have members of this group used to overcome slack oil pumps in
crankcases? I have just come across this with an engine I am building out of autojumble parts and I
am thinking of having the main oil pump body hard bearing chromed, anyone any comments .
#281 The only method I have come across but never used, is to sleeve the crankcase – a skilled
engineering job.
#364 You can use grinding compound on a plate glass plate to remove the wear on the oil pump
base, but I would expect a surface grinder to do a more efficient job. The only other problem I could
think of, was if the pump was slack in its bore then when the crankcase warmed up the differential
rates of expansion may allow air to be sucked into the pump. However I feel this would be unlikely.
L #369 Anybody know how to get the flywheel off a two stroke? The engine freed off in my U
last night, but that now means I can't lean on the stuck piston to undo the flywheel nut. My reading of
the engine section drawing on www.Velocetteowners.com is that the nut acts as an integral puller -
or am I way off the mark? Also discovered that the Mag appears to have automatic advance - hence
no cable for it. Despite standing for 50 years it still gives a (feeble) spark.
#370 I am not familiar with the model U but I did own a GTP. I believe the nut is separate from the
pulley/flywheel/sprocket assembly. If the engine is in the frame and the transmission is still intact, try
putting it in gear and applying the back brake while trying to remove the nut. It may work but no
guarantees.
#380 Thanks for the reply. I discovered that the pulley was just bolted onto the flywheel - a home
mod I think! The nut does however act as a puller for the flywheel, and I was able to both undo the
nut and break the taper fairly easily by jamming the crankshaft against the conrod with a block of
wood. Unfortunately I think I moved the flywheel round, so now have no idea where the Mag was
timed at, but I am sure there must be a fairly easy way to re-time it when it comes to rebuilding the
engine.
#375 I'm rebuilding a 1957 MAC and have a couple of problems that I would appreciate some advice
on. It has suffered a fair amount of neglect, and the oil pump (which I have removed)feels a little
'rough' turning it by hand. Is it a very specialized job to rebuild these or would a secondhand one be
more advisable? If the latter is the case, anyone out there got one for sale? The other problem is that,
at some time in the engine's life, the main bearings have been turning in their housings, causing
some slight damage to the faces. The current bearings are in good condition, and the outer races
feel tight in their housings. I have heard that one can use Loctite in cases like this, or have the
housings machined and fitted with inserts.
#377 The pumps themselves aren't that difficult to overhaul. The trick is getting the components lined
up so that the pump turns freely and then goes back into the case without wrecking the bore. If
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you're unsure, take it to someone who is. I think I would take the pump apart before I bought a new
one and assess the damage. You may find that it's only minor damage. As far as the cases go,
again take your cases to someone with experience in that area. I'm sure the problem isn't that bad,
but you don't want to put the engine back together until you've verified it. I am not a big fan of Loctite
on main bearings. There's too many things that can affect adhesion. The better way would be to bore
and sleeve the mains back to standard.
#378 Please read the manual. There is a special "clamp" tool to line up the oil pump casings. The
removal and replacement of the pump assembly required the heating (carefully) of the crank case to
allow the differential expansion of the two dissimilar metals to release the pump. Always bolt the two
halves of the crank cases together to prevent distortion. Brute force and ignorance will result in
damage to the oil pump drive spindle and the crank case housing bore.
#512 Here's my nightmare, from yesterday, which began when I followed the 'red book' instructions for
fitting the oil pump back into the crankcase. "Heat up the case around the oil pump housing using a
blow torch." Heat up? How hot? The BMS manual talks about "considerable heat". How considerable?
I broke a corner off the oil pump's cast iron base plate, by hitting it off axis with a hardwood drift while
trying to drive it back into the housing. A Good Samaritan, an old-time Velo expert, took pity on me,
heated the case, withdrew the pump, cleaned up the abuse, replaced the base plate and refitted the
whole thing. Now I know, having watched him, what considerable heat means. Blowtorch? Propane
gas flame? Forget it. He used a 'cool' oxy flame. Here's the drill as I'd now write it. Heat the crankcase
until it will easily char-grill a thick fillet of steak in thirty seconds. Continue heating until it is barely
possible to remain in the same room as the crankcase. When the sound of racing fire engines can be
heard, and the jaws on the vice are starting to melt, drive the oil pump into the housing. If it doesn't
drop in with one gentle tap, you need more heat. Okay - wild exaggeration - but if the manuals had
hinted at the very considerable temperature needed, and given the hint that very little force is needed
to insert the pump when the temp. is correct, I might have saved myself a lot of grief and my mate a
lot of time.
#523 I can't remember where I learnt it from, but the answer to "How much do you heat the
crankcases to remove the oil pump or main bearing races" is an easy one. You can use any
reasonable heat source from plumber's blowlamp through to an oxy-acetylene torch - nowadays I've
found that a good electric hot air gun works well with a little patience. Heat the case until spit sizzles
off as soon as it touches the metal and the pump or race will drop out or in perfectly. I've used this
method as a guide for many years and it's never failed yet. If you don't get the cases up to this
temperature you will really struggle to move either component.
L #513 Throwing my Venom engine together at the last minute before the rally, I finally got in a
test ride the day before the start and half way to Washington. Got it hot and realized I didn't get the
preload right on the mains and could wiggle the crank when hot. Damn! The bike was noticeably
smooth though, smoother than I'd ever recalled it being. Just rumbled a bit at idle. I had all but given
up on using it for the rally then suddenly came up with a bodge extra ordinaire. With it still hot I pulled
the primary and drilled 3 holes in the case around the periphery of the outer race and tapped it in
with a punch. I was then able to slide a .002 feeler gauge between the race and the case, so it
moved in about that far. I squirted some green loctite in the gap, tapped the holes for 8-32 set screws
to butt up against the race, went to bed and prayed. The bodge worked great but I noticed right away
the engine felt rougher. Paul D'O told me years ago that his tapered main Velos always felt rougher
when cold then smoothed out when the cases heated up. I wonder how much the .004 spec pinch on
the crank affects smoothness. I suspect I may have preloaded my mains even more with the bodge.
Also was told by longtime Velo guy Dee that the tapered mains are very forgiving and I probably
could have just left it alone for the rally.
#518 I have to say it's brilliant clever, but I would have done it with the engine cold if I had the nerve
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to do it at all, then you have a better idea of what the preload is relative to the standard. How did you
get a feeler gauge in there? But on the subject of preload on taper roller mains, I think they are
indeed very forgiving. If you read the Bible of Bodges, i.e. the compendium of tech articles, there are
stories of everything from zero to 12 thou preload on the taper rollers. The fellow using 12 thou
reckoned his engine was extremely smooth! Go figure. All I know is that when I set up my VMT mains
13 years or so ago, I went according to the book with no problems to report so far. And re cush drive
taking out the drive side mainshaft, it's too bad the factory didn't use the KTT style cush drive which
sits on a taper and doesn't pull on the shaft at all. All those years of hammering/pulling away on the
shaft can do it no good. And re torque and oil on the threads; how on earth do they stay together at
all, knowing all the ways in which it's possible to get it wrong. Perhaps ignorance is bliss after all..
#522 I've had both of the problems mentioned here at different times in my Venom's life. The drive
side mainshaft pulled out of the flywheel not long after I'd had the big end replaced by an engineering
firm who I suspect didn't really know what they were doing. This can be rectified permanently by
pressing the shaft back into position, making sure that the breather holes line up and are clear, and
fixing the shaft in position by a spot of weld or by pegging the joint. So far mine has lasted over 20
years and is still going strong! The broken drive side crankcase was a much more recent problem,
occurring only a couple of years ago. This time I sent the case to Seymour's who machined out the
damage and manufactured a new top hat bearing support in Dural which was then screwed and
Loctited into the case. This is apparently an old method of strengthening the cases used by racers in
the past, which is totally invisible until you remove the engine sprocket or split the cases, and is very
neat. One of the great beauties of this method is that you continue to fit bearings in exactly the same
way as before, since the expansion rate of the repair and the original material are to all intents and
purposes identical. I've done quite a few miles on the machine since and can honestly say that it's
never run smoother!
#525 Regarding heating crankcases, I wait for my wife to go out for the day and use the kitchen oven
when rebuilding an engine. The RHP catalogue says, “Do not exceed 120 degrees C or the bearing
hardness will be effected.” I have found elsewhere that the maximum temperature is 160 degrees C.
At this temperature the bearings knock out when brought down sharply on a piece of MDF and the
pump slides out of the bore with a very gentle tap. Ralph Seymour used soap turning brown when
rubbed on an ali head to indicate the right temperature for fitting valve guides.
L #514 however they do have problems and the one that is number one in my book is the crank
axle pulling through the flywheel on the drive side. they have a taper but its not enough. I mention this
to other owners and I usually get the answer its years old and if it was going to do it, it would have by
now. my answer for what its worth is never assume anything. my mate had his vm rebuilt and I timed
it up for him and it ran great, and sounded really sweet, 600 miles later he was out on a run and it
developed a bottom end rumble, he asked what I thought, I had a quick listen and said that is mains,
he said it cant be its only just been done. I said I reckon the crank axle has started to pull through,
take off the primary and have a look. he did and the end of the case had come off and there was all
the shims as well. you couldn’t have cut it off neater in a lathe. the problem is that having a spring
under constant tension acts as a puller and sooner or later it will come out. I had my motor down and
sure enough it was on the move. I had mine welded up but I have since learned that this is not really
the way to go. the trouble is that when you weld it, it tends to distort. the best way is to go to Nick
Payton in London my mate did and he machined the flywheel and put in a flanged shaft and pinned
it. game over as regards problems in that area. I intend to have mine done that way as well. he also
made and machined a crankcase half and paired up the cases for what I considered a very
reasonable price.
L #708 A friend who wants to build up a 1959 MSS from a pile of parts has two pairs of
flywheels. The dia/thickness of one pair is 209mm/20mm and the other is 196mm/18mm. Is the
smaller pair from a Viper maybe? Is the larger pair correct for an MSS?
21

#714 Technically they are both for the MSS (or Viper for that matter). Velocette changed the
dimensions of the flywheels to reduce oil drag as the larger set are a very tight fit in the crank cases.
This took place in approximately 1958. Additionally the smaller flywheels give the main bearing
housing an easier time, particularly if your MSS has the small bearing housing. The MSS with the
heavy crank is supposed to be a super bike to ride due to the heavier flywheels and softer cam, so the
choice is up to you,(although Veloce must have had a good reason for reducing the flywheel size).
Just one check, I am assuming you are talking about a spring frame MSS engine number 10001
onwards, as the iron MSS also has the larger flywheels with a 96mm crank and bolt up big end. I am
about to build a spare engine for my 1937 MSS sprinter, and cannot make up my mind whether or not
to turn down the flywheels to the smaller size or leave them as is to benefit from the greater flywheel
effect off the line. Is there anyone who has any experience of this?
#720 Flywheels size: I had the large MSS wheels in my 86mm stroke Venom for years and finally put
the smaller wheels back in this year. About the only advantage I could notice was it's a bit easier
getting the clutch out leaving a stop sign with the larger wheels. Once under way, first gear
acceleration is better with the light wheels. My other swingarm Velo has 96mm stroke. I had occasion
to do the big end a couple years ago and while I had the wheels split I carved them down to the
smaller size as well, removing four pounds of metal in the process. Same result as the Venom,
quicker in first gear. I don't believe the large flywheels aid vibration much. Given the same balance
factor, the only benefit the larger wheels have is smoothing out the power pulses, and in the case of
a Velo the size of flywheel compared to the power pulse is enormous.
L #862 Can someone tell me the length of the Venom conrod please?
#864 According to the technical site, the rod length is 6.875" centre to centre.
L #952 Are Mk 1 KTT flywheels common to any other model (i.e. Mac)?
#955 Mk I flywheels. These are basically the same items used on Mk I K models from about 1931 up
to the Mk VIII. The size of the crankpin changes in this period and earlier versions can be modified.
The main thing is that the wheels are steel in place of cast iron as used on the earlier K type motor.
The mainshafts are the same of course on all the above motors with the tapered drive side shaft. The
MAC wheels are similar but different. You may be better off starting from scratch and machining up
new wheels and shafts, the drawings are available.
L #1042 Was hoping someone could recommend Engine Balance percentages for an Iron MSS
(1946) and an Alloy MAC (1960). Both bikes are used as regular rides, not racing if that makes any
difference.
#1044 The only information I can find for the MSS comes from P88 of Burris's latest book. "The
balance factor was altered from 70% (iron MSS) to 55% (alloy MSS / VM/VR heavy flywheel)
influenced by changes in mounting methods. The bad vibration in the long stroke engine was
reduced. Later 65% was adopted as the balance factor for the lighter flywheels" Unfortunately I
cannot discover the source of this information to validate it. Based on my experience of the long
stroke MSS, it doesn't vibrate badly.
#1047 Stick to 70 percent. I once rode a friend's Clubmanized Venom, set up to 55%, and it was the
hardest shaking single I've ever ridden - worse than a KTM Duke! My Venom was in bits at the time,
and I remember thinking, "If this is as good as it gets, my Venom is staying in the boxes." But once
he rebalanced it to 70, it was fine. Don't know where Mr. Burris got his info, but it sounds like
bullpucky to me. Another Veloist, one with more mechanical ability than most, told me that he has
measured several 86mm engines and has found that Veloce used 70 percent on all. My experience
with overweight pattern pistons (which reduce the factor) indicates that you don't have to stray very
22

far from original to ruin high rpm smoothness. Finally, I have a 1953 Cycle magazine with a 1000 mile
test of the swingarm MAC that quotes a 70 percent factor.
#1052 I have just heard (second hand from Dad) that Phil Irving in 'Tuning for speed' suggests 66%.
It may be tin tacks in the end, but is it possible to get a British single running smooth across most of
the rev range with only primary balance to play with?
#1054 regarding engine balance there is a firm in holland called Dymo Track. they are second to
none as regards balancing. they are the only firm I have ever met who can balance a triumph and
you end up with no vibration. they have very sophisticated machinery to do the job, plus they
understand motorcycles as martin the owner has a Norton commando which he balanced and he
uses regularly. I don’t know if they have ever balanced a velo but I do know that they have done
goldstars. triumph cranks can be up to 100 grams out of balance plus the wrong balance factor. he
told me that sixties triumphs used 85% balance factor on the 650's and he told me that it is wrong
and the balance factor should be 74% add that to up to 100 grams out on the crank and you get a
vibro massager.....as they do. there is also the way in which the engine is installed into the frame....i.e.
in a different frame. twin downtube like featherbed or hung in the frame...i.e. Seely. the engine
balance has to be altered to suit the frame..i.e. the harmonics. check out Dymo Track
www.dymotrack.nl/ you might be glad you did. plus they also heat treat conrods as they work harden
and become brittle. he told me that the ceiling for rods was 100,000kms about 60,000 miles, after
that you are in the red zone. after heat treatment you are back to as a new rod and you can start
again. cheers.
L #1056 I have good condition MOV flywheel ,big end ,etc. but the main shaft is rusty. I would
like to change the shafts from MAC flywheel I have, which main shaft is good condition but mess in
the big end. Question is how it could be done , and what I have to be careful to do this?
#1059
If you look at the inside of the flywheel you will see what looks like a pin between the main shaft and
the flywheel. It is in fact a threaded stud. Drill it and try to extract it with a broken stud extractor. If it's
tight drill it out. Press the shaft out using a hydraulic press from the drive shaft side, take care not to
damage the thread on the end of the main shaft. Try to line up the two halves of the stud holes and
press the pin through from inside the flywheel. Press the pin in until it is flush with the flywheel. Odds
on you will have to re drill and re tap the stud hole a larger size as the hole / threads will not line up.
#1345
I confirm about pushing out the main shaft from flywheel again. It is linguistic problem, I think. "a
hydraulic press from the drive shaft side" Means both flywheel main shaft pushed from drive side?(
timing-side one from pushed from flywheel side and drive-side from end of shaft?) Or both shafts
pushed from end of shafts into flywheel ?
#1358
The drive shaft has a taper on it, so having removed the threaded peg press the shaft from the
outside of the flywheel towards the inside.
L #1043 I was hoping someone could recommend Engine Balance percentages for an Iron MSS
(1946) and an Alloy MAC (1960). Both bikes are used as regular rides, not racing if that makes any
difference.
#1044 I am just about to balance the crank on a iron MSS sprint engine I am building. The only
information I can find for the MSS comes from P88 of Burris's latest book. "The balance factor was
altered from 70% (iron MSS) to 55% (alloy MSS / VM/VR heavy flywheel) influenced by changes in
mounting methods. The bad vibration in the long stroke engine was reduced. Later 65% was adopted
23

as the balance factor for the lighter flywheels" Unfortunately I cannot discover the source of this
information to validate it. Based on my experience of the long stroke MSS, it doesn't vibrate badly.
#1052 I have just heard (second hand) that Phil Irving in 'Tuning for speed' suggests 66%. It may be
tin tacks in the end, but is it possible to get a British single running smooth across most of the rev
range with only primary balance to play with? Anyone truly happy with their mounts?
#1047 Stick to 70 percent. I once rode a friend's Clubmanized Venom, set up to 55%, and it was the
hardest shaking single I've ever ridden - worse than a KTM Duke! My Venom was in bits at the time,
and I remember thinking, "If this is as good as it gets, my Venom is staying in the boxes." But once he
re-balanced it to 70, it was fine. Don't know where Mr. Burris got his info, but it sounds like bullpucky
to me. Another Veloist, one with more mechanical ability than most, told me that he has measured
several 86mm engines and has found that Veloce used 70 percent on all. My experience with
overweight pattern pistons (which reduce the factor) indicates that you don't have to stray very far
from original to ruin high rpm smoothness. Finally, I have a 1953 Cycle magazine with a 1000 mile test
of the swingarm MAC that quotes a 70 percent factor. For what it's worth...
#1048 Remember the MSS in question is an Iron MSS, different frame, stroke etc. all affecting the
balance factor, so 55% may be OK.
L #1213 Does anyone have any useful advice on crankshaft balancing?
#1214 Having some practical experience in static balancing in twins and singles, I can provide some
small details if desired. It is well established that single cylinder engines can not be balanced to
completely eliminate vibrations. The annoying vibrations a rider may feel are generally caused by a
harmonic resonance caused by the reaction of a given engine in a given frame at a given RPM. The
annoyance can not be eliminated, but the period of greatest vibration can be moved to a RPM that is
less annoying to the rider and depends on the intended use of the machine. Thru much testing,
manufacturers have found that a specific imbalance can be applied to a given crankshaft to move the
vibrations to an RPM that best suits most riders for the intended use of the bike. In simple terms this
imbalance can be specified as a balance factor, a percentage of the actual reciprocating weight. The
balance factor, I.E. the percentage value differs for each engine, but for singles, generally lies
between 50% and 68%, with numerous exceptions. In most cases, the factory got the "compromise"
right and unless you are making drastic changes in reciprocating weight, you can either ignore
attempting to rebalance the crank, or alter the new reciprocating parts to have the same weight as the
original parts.
#1217 I have found that reciprocating weight is far more important than actual balance factor (within
reason). Velo's have very heavy rods, pistons and pins. A standard Venom reciprocating mass is
about 800g. In my Thruxton with Carillo rod, lightweight pin and hand carved piston it's about 600g
(and that's with 97mm bore vs 86m). I also have ten ½" grub screws installed radially in my crank shaft
with access holes at the front of the engine. I can add or remove enough weight to change the
balance factor from 65% to 75% in about 5 minutes. The difference in minimal. It is a very smooth
machine, much smoother than my bone stock Venom. I won't do another crank with a stock Venom
rod as the reciprocating end of a Carrilo is over 100g lighter. Try grinding that off a piston.
L #1326 I am looking for MOV big end pin or assembly. VOC spare lists the M192 nold stock
pattern component without nuts-one piece component So what is the difference between pattern and
genuine? How quality different? What I am looking for is good quality (cost as well) Do you know any
recommended place I could ask for the part? genuine pin is still obtainable? Or may be pattern one is
higher quality? What does one piece component means? ( My old one looks one piece )
#1335 Two piece big end pins have a pressed on hardened sleeve over a pin that has a parallel
24

centre. It is most likely that the pin that the VOC made came from Alpha Bearings, so is probably OK.
The only way to tell would be to have it tested. At GBP20, my counsel would be to buy it, as I am sure
Bob Higgs would not have stocked it if over the many years the VOC has sold them, there have been
any complaints regarding the pin quality.
L #1939 I have just heard the distinctive nock of the big end from my 58 Viper. I hope it's the
small end but won't know until I remove the barrel. I've ordered a new big end bearing and small end
bush and gudgeon pin plus circlips in anticipation. May be able to pass on some dimension if it is the
big end. However I may as well check the main bearings at the same time. Does any one know what
the designation number is on the main bearings in order to confirm the correct ones are fitted? Also,
how does one lap in the big end?
#1950 You can find the designation on the main bearings under "bearings" on
www.croesus-consultants.co.uk/v-tec/ If anyone need dimensions of main bearings I have access to
some of the original works drawings including big end and outer race. As per 's post I suggest you
read "Tuning for Speed" on how to lap big ends.
L #2027 I've managed to find a pair of flywheel webs machined for the mainshafts but not for the
crankpin (venom). Could someone give me a measurement for the gap between flywheel halves
(conrod + .008" ?), and measure the distance from the flywheel boss to the end of each mainshaft
(i.e. how far does each mainshaft protrude from the crank web)
#2040 If it helps the shoulder to shoulder measurement of the pin is 0.8125 + 0.002. All flywheels I
have seen have the mainshafts flush with the inside of the flywheels.
L #2154 Anyone know what the crankshaft side float should be for an all ally engined MAC? Got
a feeling that I read `less that 1 thou' somewhere. This seems pretty tight to me.
#2157 According to the BMS generic Velo workshop manual, side (end) float is 0.0015" for all engines
except for the MSS which has tapered bearings. e
#2162 Thanks for the reply. 1.5 thou seems pretty tight to me. Isn't the MAC the only Velo single that
doesn't have taper roller mains?
#2163 The Velo singles that had taper roller mains were VM, VR, Alloy MSS, Late iron MSS. All the
others have ball or roller mains. If you set up the mains with 1.5 thou., i.e. nothing, there will be much
more at running temps. With the design of the timing gears etc this is the only correct clearance. It is
normal to set up the OHC Velo engines with no clearance at running temperature. This gives a slight
nip when cold which disappears when near running temp. After some running there is then a free but
not loose bottom end. The same applies to all 'non-taper roller' Velo bottom ends.
#2184 I've done it this way on a number of bikes with success (end play adjusted for the current victim
of course) so I am going to once again quote the BMS Velo manual:
"With main bearing outer rings correctly shimmed and in the crankcase, the timing side half can be
threaded over the shaft. Set the connecting rod in the cylinder opening and turn the half assembled
job over to fit the drive side crankcase. Check all crankcase oilways and freely lubricate all bearings.
Fit the bolts and tighten up the nuts gradually all the while checking the flywheel assembly for freedom
of rotation. At the first sign of tightness, stop work and measure the gap between faces with a feeler
gauge. If it is less in some places than others than the bolts have not been tightened evenly. Correct
and check again. MSS engines with taper-roller bearings must be shimmed so that all side play is
removed with the faces apart 0.005" and no more. The shimming is then correct and the drive side
case can now be again removed, and the face lightly smeared with "gasket goo" and reassembled. If
the crankcases meet, or in the case of the MSS engine, the faces come closer than 0.005" before the
25

earings are nipped, extra shimming may be required. All engines except the taper rollered MSS
should have the flywheels perfectly free to revolve when the engine is cold with side float of not more
than 0.0015.
L #2385 I had a fairly dramatic failure (in terms of disconcerting noises) at about 80 mph last
week and, after stripping the engine, the drive side main bearing has broken through the end of the
bearing housing, the result being a thin disc of aluminium + shim that use to be attached to the
crankcase. Although relatively new to Velos, I understand why it has happened (I didn't build this
engine, so I don't know how well or badly the crank axial float was set up, nor whether the bearing
housing was damaged at some previous time in it's 40 year life). Anyway, the obvious option is to find
another crankcase half or pair and rebuild. However, I've spent the afternoon taking measurements of
the whole bearing housing and crankcase around that area and it seems to me that a repair in the
form of an aluminium "top hat" could be turned and tig welded to the crankcase. The crankcase walls
are around 0.4 in. thick in this region ...not exactly over generous, but sufficient to attach aluminium of
~ 1/4 - 5/16 in. thickness. The primary chain back piece of tinware will need a few mods, but that's
trivial. Has anyone ever heard of such a repair being undertaken?
#2391 Nick Payton - 0208 540 2118 - can solve your problem as he gets reinforced drive side
crankcases made and machined to match your surviving timing side case. Seymour's at Thame -
01844 212277 - did, and I believe still do a top hat conversion. This involves fitting a steel insert -
similar to a smaller version of the type fitted to a Matchless G.50. Criterion Engineering - 01793
790219 also manufacture a strengthened drive side case.
#2392 Send it to Seymours - they did this conversion (which I understand to have been a "racer mod"
in the past and stronger than original) for me recently and a beautiful piece of work it is - invisible after
the engine is rebuilt and treated exactly the same way as a standard case when it comes to fitting new
bearings etc. No need, and probably unadvisable due to the distortion that could take place, to weld in
position. The conversion is simply sealed with an appropriate grade of Loctite and held in place with
screws.
#2393 Just to offer a small correction Tony, the Seymour conversion uses a Dural Top hat, not a steel
one. Steel would be unsuitable since the different expansion rates would give problems in
fitting/removal of the bearings - i.e. the bearing and ring would have similar expansion rates making it
necessary to use a press to remove the outer ring - impossible due to the semi blind nature of the
hole.
#2394 I had a set done in the early seventies and was advised to drill three small holes to "drift" out
the outer race if necessary. I still have the cases with the steel top hat. I can understand that they
have obviously changed the material over the years. I am intending to use my steel hatted cases
for a road Venom I'm building out of all the spares I have acquired since I took my original Venom
onto the race track and 'tile o'man. Incidentally did you know that Veloce were obviously aware of the
weakness? Some of their engines for the Island were fitted with a split steel top hat around the
bearing outer, but they appeared to be retained by interference fit as the "brim" of the hat wasn't very
wide. I won't name names, but there is a member of the club who has the afore mentioned engines
and I've seen them. I used to have my reinforced crankcases (both sides) made locally, that source
has now ceased, but they may become available in the future. I will advise anybody who is interested
in due course as they become closer to a reality. No it's not me making them. A final comment, I used
some larger parallel roller bearings in my latest engine which survived this years Manx. When they
have been stripped and examined, if all is well I will be altering my other "Manx" engines accordingly.
#2397 I'd like to ask about using roller bearings: What about crankshaft end thrust? Is it so small it can
be ignored?
26

#2400 Plan B may not be such a good idea - if the MSS cases are numbered 12078 or earlier they will
have the small driveside main bearing boss. Based on your experience you can work out why Veloce
beefed this area up. Also will need new chaincases, to accommodate the smaller boss.
#2402 Not quite sure what you mean by a "split steel top hat" and can't understand how such a
conversion can be held in position by interference. A solid item, yes, but a split sleeve will change
dimensionally quite dramatically due to the pressure of interference. If I were to use a steel top hat
conversion I would make a solid sleeve a good tight interference fit in the bored out case and make
the bearing outer race a push fit in the fitted sleeve. I'd like some additional security for the sleeve -
either a screw or two or at very least an appropriate engineering adhesive. Honda (and others) have
used steel sleeves on the main bearings on a number of their single cylinder machines for many years
but the sleeve is cast into position so is unlikely to move. Personally I prefer the Dural method since
expansion rates between case and sleeve are very similar, and you have the advantage of improved
material properties in the critical area. My original cases lasted through almost 40 years of use and
abuse - not raced but seen a lot of very hard road use - before the drive side did the usual trick and
had to be sleeved. Ask me in another 40 years whether the sleeve lasted the pace!
#2408 I have read with some interest about the crankcase failure and the suggested remedies. no
one has mentioned the probable cause and the solution. for my money, I would say that the crank
axle is pulling out of the flywheel and I would fix that before I did anything else. by putting in a top hat
and strengthening up the crankcase is not solving the problem of the crank axle. if the crankcase has
popped the end of the case off, you have to ask why. if the crank axle is coming out it will take the
main bearing with it which will push on the end of the case and pop off the end of the case off. I would
have the flywheel split and have the flywheel modified and a flanged main shaft fitted and pinned
before I did anything else. Regarding a top hat fitted into the old case, I myself am not keen on having
three screws in there that could back out and go into the motor. in my opinion that is poor engineering.
a new crankcase half that is thicker and paired up to an existing half must be the better and more
logical solution. the design of the original cases is ok provided that the pre load is right and the
flywheel axle is modified. I have heard people say to me that if the axle hasn’t moved in years, then
why should it in the future. well I would say that with a spring wound up on it for years on end and
acting like a hammer drill and an inadequate taper on the crank axle, sooner or later it will fail. modify
and forget, that’s my way of thinking. its like running a three cylinder triumph/bsa with alloy rods, you
know that someday they will fail. I hope you can use this info. cheers.
#2418 Another way of removing the outer race is to put the crankcase half in the oven and then crank
it up to full power. it’s a good way of uniformly heating the case and all you have to do is wait for a
clunk as the outer race drops out. it will usually do this as the oven approaches full heat. I regularly
used to do this with bsa victor cases and it works every time. just for a bit of history, neil kellys bike
which won the tt in 1967

#2420 The end pops off the drive side crank case, haven't you been reading the e.mails, try and
keep up! Seriously you are quite right, that is why Veloce recommended heating to about 100C or
immersing the case in boiling water! Tried that one and they never budged. I rang the heat treating
company I've used for various jobs and they stated that under the circumstances I quoted they would
not heat the cases to more than 150C and certainly nowhere near 295C. Apparently they heat to
250C for stress relieving and 350C for annealing. Incidentally he reckoned that the age of the material
wouldn't matter greatly. Billy, the guy also reckons that unless you are standing and waiting for the
bearing to drop out as the oven and the cases warm up and then switching off immediately. Thus
keeping the temperature as low as necessary for the bearing outer to drop out, you could be
subjecting the cases to excessive heat and inadvertently softening them.
#2406 I was recently responsible for stripping and re-building the engine from the Niel Kelly
production race machine that won the 1967 TT. The drive side crankcase was bored out to 2.375" to a
depth of 2.027" from the mating face. The "top hat" was machined to allow the normal interference fit
between the bearing and the crankcase, so that as the case expanded and contracted the bearing
would be held under the same interference fit as if no "top hat" was fitted. The purpose of the "top hat"
was to spread the end load on the bearing to the brim of the "Top hat" as well as the bottom of the
bearing retaining hole.
#2416 I think I can now visualize the construction and your explanation of the purpose of the split
helps my understanding. However, I think that the reason for the split is in fact to compensate for the
difference in expansion rates between the two materials. The split, as you say, allows the case to hold
the bearing under the same pressure as if it were set in the aluminum case. The alternative
conversion which utilizes a dural top hat does not of course require a split since the expansion rates
of dural and the original alloy case are very similar. I much prefer this method since this also means
that there will be very little differential movement between top hat and case in service as well as
permitting the "normal" method of bearing fitting and that Dural has superior properties to the original
alloy casting. To me the use of steel in this application presents more problems than it cures. Which
brings me on to Tony Ainley's suggestion that the use of a puller is a preferable method of extracting
the bearings to heating the case and dropping on a block of wood. The cold extraction of an
interference fitted bearing in an alloy case will result in some galling of the hole walls, eventually
leading to a poorly fitting bearing. If the case is heated to a similar temperature to that required to
remove the oil pump, the outer race will all but drop out of its own accord with no risk of galling.
Dropping on a block of wood is only really required if the race is gummed up with old oil, and little
more than a light knock should be enough to shift the race. I suppose that on really stubborn
examples a combination of heat and bearing puller might be the way to go!
#2421 I have always favoured the 'spit test' when heating alloy bits such as crankcases. Heat them up
and spit at the heated surface. When the spit forms a ball which hops around on the surface that's it -
no more. This is around 120C I would reckon. I cannot claim originality for this. It came from Stan
Johnson, who new a thing or two about building motors from many years ago!
#2425 Shimming the mains out is a piece of cake. use an old outer with the outer ground so that it a
push fit in the case and then shimming is easy. I am shocked that you wouldn’t reuse the bearing after
welding it to get it out. a bit of wet and dry and a scraper and its as good as new, takes about half an
hour. if you are heating a crankcase in an oven, always be near it so you can hear the bearing drop
out. as soon as it does I remove the case and leave it on a concrete floor to draw the heat out of it. I
wouldn’t have thought that heating a crankcase up would affect it in any way. dymo track in holland
heat up alloy rods until the molecule structure is altered to stress relive them and they must get very
hot. you are better heating up something uniformly rather than in one area because the cool alloy on
the rest of the part will draw heat away from were you need it. boiling water isn’t enough in the heat
stakes, the oven is the answer, or acetylene works well. we all have our different ways of approaching
things, just a few of my ideas. My comments are based on the heat applied. An oven can and does go
28

way over the heat required which is safe for the heat treatment applied to the cases (or head etc)
Exceed that and you spoil the material. The same goes for using acetylene to heat castings - its too
much heat. Overheat the cases and they will fail in the future is my guess. Also bearings are a pair -
the inner and outer races are not interchangeable. Hence you cannot shim mains up unless you use
the bearing inner and outer that are going to run together, the difference may be small but so is the
clearance you are setting. This applies to taper or parallel roller types. The 4 thou preload is a figure
given in a manual. Its not the absolute right figure as you say; its not what the works used on their
motors either!
#2433 It wasn’t my idea to shim bearings up using a slave outer but dodkins, because that’s how they
used to do it. when a machine is turning out bearings by the thousand my guess is that they are the
same. I have bought timkims that had the outer made in one country and the inner made in another
country, so they have to be the same. as for excess heat ruining a crankcase, I just don’t buy it. when
dymo track stress relive alloy con rods they heat them up to a very high degree and the forces on
them are enormous, and they don’t fail. alloy is a malleable metal that work hardens with use and
heating it up wont do it any harm at all. but I will check it out, here where I live we have a shipyard and
I will see if I can talk to a metallurgist about this. if I am wrong you can have my profound apologies.
#2442 What preload do you recommend, and what did the works use? Also, I wonder what SKF and
Timken say the tolerance on bearing pair width is? It would make sense that the tolerance should be
insignificant, but wonder what the manufacturer(s) says
#2445 The way to set the shimming for the lower end, is to shim the crank to nil clearance with the
cases heated to normal running temperature. I believe that the 4 thou pre load was ok on a new
motor, but as they work harden with use it is preferable to set the crank at zero with a warm motor.
That’s what I was told by a very good authority. Regarding the timkin bearings, when the timkin
bearing company learned that velocette were preloading their motors, the refused to give any sort of
warranty on them and if they did fail under warranty, it was down to velocette to stand and failure on
the bearings. I believe that they never had a claim regarding timkins under the bikes guarantee. if you
are shimming out, I would go with the slave bearing outer race idea. it will save you no end of time.
#2430 Holes in the cases to remove bearings come in very handy, especially if you have to remove
those Japanese (Club supplied) taper bearings. Even the grand master Geoff Dodkin always had two
holes in his "split" steel top hat bushes to aid removal of the outer race. In service those holes are
easily covered up by gasket goo. I like them. I combine heat and slight taps through the holes to free
the races. I guess I know why my parallel main rollers failed : they were definitely not of the C3 variety
which means increased clearance. I am happy if I can get here Imperial bearings at all, beware to ask
for C3 ! And in all roller bearing cranks the mains are C3 type. Thus combined with a much smaller
bearing area, plus a crank which flexes probably a lot when thrown around at 6000 revs all contributed
to their failure after 2000 kms. Although I had two drive side cases separated from the bearing boss, I
never had the tragedy of a moving mainshaft. God thanks. One reason for the cracked boss I know
today : I adjusted the primary chain, and did not tighten up the gearbox bolts enough. When I tried to
escape a thunderstorm on the motorway I trashed the engine very hard. The rear chain pulled the
gearbox backwards tightened the primary chain and too much stress was put on the (small diameter)
main bearing boss. End of game : rumble, rumble......Why my Thruxton with flanged shaft and heat
treated cases had the boss popping off, I do not know.
#2434 If a bearing is coming out and staying out then the welding method is the easy way to remove
it. to shim out the motor a slave timkin outer ground so it is a push fit in the crankcase makes
shimming easy. I read about doing it this way from an article that geoff dodkin wrote years ago. it
makes sense to me. you say that your motor blew the end off the case with a flanged shaft and
thruxton cases. its possible that it might have been wrongly preloaded in the past which might have
weakened it.
29

#2403 It seems some people are interested in end float of parallel roller bearings and therefore intend
to use them. here are my experiences with parallel roller bearings, maybe well known facts for the
enthusiasts in this group but not for me when I rebuilt the engine... To prevent a pushed out left main
bearing seat I used one side lipped parallel roller bearings intended for a 500cc Ariel single (w = 5/8")
with the end float set to 0,01mm when cold. When warm this increased to 0,1mm. After 2000km noise
developed from the region of the drive side main bearing. The engine was dismantled, the bearing
showed severe pitting on the inner race. As the pitting was spread over the whole area of the race I
don't think the end float has been critical. It also turned out that the outer races on both sides turned
inside the (unmachined, no top hat bush etc.) housing. The reason for this is that the timken taper
roller bearings have a slightly larger outer diameter than standard parallel roller bearings (+ 0,01 -
0,02mm). This, taken together with the fact that the housings are at least 30+ years old and worn
accordingly, gave this rather unhappily result.
I don't know whether this problem has been caused by a manufacturing failure or if the load applied to
this kind of bearing by the engine is generally to high. Maybe a wider bearing will eliminate this
problem but then there is still the risk of the turning outer race. I will now revert to taper parallel
bearings in conjunction with strengthened drive side housing from Nick Payton.
#2411 After a collapsed drive side main bearing boss in my Venom, I thought to bring this problem to
an end with parallel rollers. I guess I used RHP bearings- very expensive ! End float was set to
0,02mm which increased to 0,08mm when hot. A dural top hat bush was used, but its inner diameter
was machined to accommodate that minimal smaller outside race of the lipped parallel roller bearing.
Everything was fine, when after 2000 km the evident roughness of the engine was felt. Upon
inspection, a worn outside race was identified which has turned in the top hat bush as well. I did not
inspect the inner race which was probably worn as well. My conclusion why Veloce fitted taper
bearings is that the bearing area of the taper version is appr. 25% greater than of the parallel roller
bearing, which is quite substantial. Although I play round with VM and VMT engines for a long time, I
really never had failed taper main bearings, "just" broken drive side casting bosses. In reference to the
top hat bushes I want to mention that I have an unslotted steel top hat bush in my VMT secured with 3
M5 counter sunk allen screws. No problems since 20.000km. The story of the slotted steel top hat
bushes I can confirm, having in my stock two of them, and both are originating from Geoff Dodkin.
This grand master of Velos obviously had some thought behing this slotted version. However the
technical reason for the slotting I have not found yet. When buying taper rollers be careful before
fitting and measure the outside diameter and the inner one of course. Some (Club supplied) are
Japanese made, with fractional larger outside diameter. No problem to fit them in hot cases, but a pig
(or near impossible) to remove them again !
#2414 Hello Johann, so it seems that the parallel roller bearings are generally overloaded. I also
noticed the noise from the bottom end after a 80+ mph blast. Nevertheless I would like to know the
exact specifications of the bearing you used. Width, type of cage, number and diameter of the rollers,
play etc. to compare this with mine. I used bearings of 5/8" width, steel cage and on the outer race is
written "c2". When I ordered the bearings I clearly stated to get them with increased play. I know that
in the metric system a "c3" means increased play but I am not sure what c2 means and if this
annotation is the same for the imperial system. Maybe anybody from the island can help me with this?
#2417 Regarding removing an outer race from a blind hole or crankcase or steering head etc, the last
thing I would ever do is drill holes to try and drive it out. an easy way to remove the outer race without
heating the case is to go round the inside of the outer race with an electric stick welder. run a weld
around it and then let it go cold and then it will fall out, easy peasy lemon squessey. when the weld
run cools, it contracts taking the outer race with it and it will fall out, or at the very most a light tap on
wood and out it comes. but hey, you knew that. tar ra a bit.
#2422 Great idea - so long as you don't want to use the bearing again! No good if you are going
through the procedure of shimming up a set of bearings which involves fitting, measuring, removing,
30

shimming and finally refitting the outer race! I'm with you on the oven idea though, so long as her
indoors doesn't object to the Sunday roast being tainted with oil fumes! Personally I find the use of a
hot air gun played over the case works very well - just don't keep it directed continually at the one
spot. A gas torch should be used in the same way to ensure as near even heating of the case as
possible.
#2437 I used the following parallel roller bearings : RHP LRJA1J (RR), steel cage, 11 rollers, lipped on
the outer race. Because they are slimmer than the taper rollers, a distance shim of 4mm thickness
was used between flywheels and inner race. Although I got 53% discount, those two bloody bearings
still cost me 54 Pounds. Expensive experiment. For the bearing abbreviations : C2 means tighter
clearance then standard, in our case between 0,001mm and 0,011mm. Standard clearance, which I
used is between 0,006 and 0,020mm, C3 means clearance between 0,015 and 0,033mm, C4
between 0,028 and 0,046mm, C5 between 0,030 and 0,053mm. If you used C2 type (nearly a
precision bearing for armatures etc.) and I standard ones, and both failed, and even precise Japanese
single cylinder engines use C3 and C4 bearings, we should go at least to C3 or C4 or even, if
available at all, to C5. Would be interesting to know what type of bearings Ralph Seymour used in his
conversions.
#2453 I fully agree with you regarding the costly experiment.... If you are right, there is no need to
waste anymore thoughts about why the bearings failed. What puzzles me is the fact that the bearings
I used were intended for an Ariel 500cc engine and I don't think that the crank assembly of those
engines is stiffer than that of the Velo. Are you sure that in the imperial system c2 means the same
than in the metric system? Nevertheless, to be on the safe side I will use the taper roller bearings.
They are also much cheaper... keep it between the hedges, taper roller.
#2455 I just looked up an English bearing catalog as well and they have the same explanation for C2
like the FAG one. C2 has smaller clearance than standard. Maybe you got yours by error. C3 should
be the right ones. But again with parallel rollers you loose a lot of bearing area, and therefore they will
not last as long as tapers. I also went back to tapers with all the preload labor, and knock on wood, no
rumbling noises till today.
#2480 Phil Irving in various books confirms, C2 is designed for tight outer race, push fit inner race. C3
is for tight inner and outer race.
#2440 Well, I set up the mains on my Thruxton about 12 years ago according to 'the book', using a
propane torch to gently heat the cases (until my spit danced on the surface) and slamming them on a
big flat block of wood to remove the races, then shimming to 4 thou as measured at the crankcase
gap before bolting it all together. It has survived many, many hours of flat out running in these years.
Is it me, or are there too many ways to skin a cat? Peter, what was the pre-load the works used with a
taper roller main setup?
#2446 I hinted at the way Veloce assembled flywheels into the cases previously. This is how they did
it for special cases: 'shim the outer bearings to a point at which the flywheels will just stop in any
position yet spin freely when the crankcase reaches working temperature. This can be checked by
carefully warming on a gas ring' (Advice from Jack Passant) The same method is the one I use for
setting up K type bottom ends too. The pre-load is there to ensure that the flywheels cannot hop
about when the cases expand. That degree of expansion will differ from case to case to some extent.
Hence the 4 thou as a production standard which is still a good guide. Hands up who wants burnt
fingers?
#2447 Finally a definitive concise 'how to do it' on setting up c/cases ! While I cannot claim to have
worked on any post WW 2 Velos, apart from a 46 & 48 KSS, I did set up & assemble a few early KSS
engines, & I found out from good advice of that time what really worked ! Yes, we did carefully drill the
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2 small holes & a small pin punch was always at the ready in case the races didn't come out at the
first bang on 'the big block of wood' usually a solid timber bench that most of us possessed back in
those days, but there were times when the races just fell out as the cases were heated, - & yes we
also watched the spit bubbles do their dance ! Also when the arc welder came into use, we soon
'invented' the ring of weld in outers method, although for my part, I used it in my daily workplace on
bearings the diameter of which, rivalled the outer diameter of Velocette c/cases! I have to mention that
we never aspired to reuse 'outers' after, 'careful use of scrapers & wet & dry' ! Yeah, I know ! The
flywheels just sticking at rest at working temperatures was aimed at, but not always religiously
accepted, you sort of knew your engine, & what you intended to do with it, & trusted the new, (&
sometimes inspected & found to be worn bearings) & then you went out & rode & raced your
Velocette as the maker intended. I can only talk of the Mk1 KSS really, & never considered that the
motor was being 'thrashed', but I sure as hell rode mine hard, & over long distances interstate at high
speed, certainly 80 MPH & faster if possible at times. One thing I can truthfully claim, & that is that I
never had a bottom end failure of any kind back in those years, & only in recent times did I experience
a broken big end with the Mk.2, & that was explained by a batch of badly manufactured replacements,
with an inbuilt stress spot. It's a well known experience thing that 'M' series derivatives suffer when
used hard, as did the very first MOV's & MAC's but failure has virtually always been the result of
racing, (road or track !) & is one of the facts of life for a Velocette racing enthusiast, & most of the
modifications & 'cures' have their merits, but the facts are, that the designs are quite old now, & it is of
great credit to Veloce that these machines continue to be successfully raced by enthusiasts. Good
luck to you all, but bottom ends will continue to fail, possibly more frequently as time goes by ! I am off
for 3 weeks of doing nothing in Queensland, but progress has been made on the 'G' restoration, & the
frame diamond with the replaced bottom frame tubes & the welds cleaned up, is sitting up on a
purpose built stand with the cleaned up motor in place, (not yet fully dismantled) all ready for the early
GTP gearbox which I am collecting while away, to be blocked up into position, & then the measuring &
double checking, to be done before the rear section of the frame is manufactured from a collection of
early two stroke frame remains, & of course some new lengths of tubing where necessary .
#2449 Since some people are drilling three 120 degree spaced holes behind the mains outer to aid its
removal, would it not be possible to tap these and fit set screws? It would then be possible to set up
the crank end float on a fully assembled engine at normal running temperature. The drive side case
seems to fail on those engines assembled with too much pre-load, rather than because of the shuttle
loading of the crank, so the screws should be able to withstand axial loading.
#2456 In the last year I've renewed mains in 2 different machines and found in both examples that the
original shimming gave the correct nip when cold (4 thou as near as I could gauge it, which wasn't all
that near. You know the routine - 6 thou here 3 thou there add them all up and make the average
answer equal 4, even if it ain't quite.). This lends support to Billy B's assertion that the bearing cups
are close enough in thickness to use a slave to get the setup right if you are starting from scratch - it
would certainly save a lot of time otherwise spent heating and banging. As a precaution the final setup
could be checked for freedom without radial play at operating temperature, whatever that is! Maybe in
the oven, or in my case the hooded gas barbecue (a less controversial place to hide an assembled
bottom end) at 80 to 100 deg C?? When VMT457 was first stripped down in the late 70's I found it
had been converted to parallel roller mains for racing purposes - standard practice for serious racers
of the post war M series here in Oz. I have heard the tapered mains referred to disparagingly as trailer
wheel bearings by old time racers. However since racing wasn't on the agenda for me and VMT457
and the tapered mains were readily available and affordable, I converted back to tapered rollers and
my fledgling attempt at Velocette engineering led to over 20 years of trouble-free performance - I only
renewed them last year because I had it apart for other reasons and didn't fancy having to get back in
there within the next 10 years or so for mains maintenance. Speaking of VMT's, if I remember rightly
their cases are heat treated to deal with the greater power output and likelihood of sustained high
speed work. Does this then theoretically make them more susceptible to weakening by the inexpert
application of heat? As far as optimum nip goes, Paul Z has posted stories of trials with 10 thou nip,
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and reported that it gave a smoother engine. So just how much latitude is there in the recommended
nip? It seems to me a fair bit, since the normal operating temperature must vary considerably. Just
say you ride south from Alaska and then travel through the Arizona desert, as some of our North
American Velo owners have done. More nip in summer, less in winter? In practice I think not, but if the
theory requires a precise level of nip, shouldn't we be doing this? Finally, if Paul D'O's infamous
Courgette still has no top hat in the drive side crankcase after all these years, then I rest my case.
With a crank set up so it is properly supported (whether by parallel or tapered rollers) the majority of
Velos will stand up to sustained hard road use over long periods of time.
#2457 Just to add another tip which might be useful to all who might want to take on the job of
shimming main bearings, I too have found that the method of measuring the gap between cases with
feelers to be rather hit and miss, even though it is the technique recommended in the red book.
Having pondered on the problem I came up with this method which I'm sure others have also used
judging by some of the other posts on the matter. First, remove the outer races and shims from both
cases and refit the races. Ensure that the mating faces are thoroughly clean and free of any residue
of gasket compound, then assemble the crank into the cases and bolt them together all round. Then,
either fit the timing gear steady plate, clamp your magnetic stand to it and mount your dial gauge so
that the probe is pressed against and in line with the end of the crank, or fit your timing cover with dial
gauge adapter fitted in the oil jet hole as per Tony Ainley's photo. Rest the assembly on the bench on
the drive side crank end so that the mainshaft is vertical and take a reading from the dial gauge. Raise
the assembly off the bench and take a second reading. The difference between the readings is the
end float, which should now have 0.004" added to it, the result halved and shims equaling this final
amount should be fitted behind each outer race before final assembly. I found that this method took a
lot of guess work out of the process and has given me a sweet running bottom end.
#2466 I am interested to hear the suggestion that the red book preload value is an approximation, I
think it was suggested, and that a better way is to shim to zero play at operating temperature. Would
someone who has done this explain how they accomplished it? It would seem to me that determining
operating temperature, getting all the bottom end parts to that approximate temperature and
assembling would be near impossible. Also, perhaps it is just me, but I always assumed the reason
that the drive side broke out of some velo engines was due to the loads applied by the tapered roller
design. These bearings resolve the loading applied by the combustion and compression pressures
into a radial and axial component, the axial is a result of the tapered design, and this put an outward
force into the assembly which, in some cases found the weakest point at the drive side bearing
housing perimeter. I'd really like to hear more discussion on this subject if everyone can stand more.
#2468 Putting top hats into crankcases is a bit like having a thorn in your hand and taking aspirin for
the pain. do you continue to take aspirin for the pain or do you pull it out and effect a cure. i.e. most
crankcases fail because the crank axle is pulling out. modify the flywheel and have a flanged axle
fitted and pinned and the preload set up correctly, i.e. zero clearance at working temperature. the use
of a slave outer bearing is invaluable for doing this, as you don’t have to keep trying to get the outer
bearing out as a normal interference fit. dodkins used this method, and if you think it through, it is the
most sensible and logical approach. if I bought another velocette the first thing I would do is to have
this mod done. if I bought a thruxton and because of their very high prices, I would fit a modified
crankcase half supplied by nick payton and use the bike with that fitted. the price is so cheap, its
almost a joke. tremendous value for money. the original half could always be put back on the motor, if
ever there was a time to sell it. going back to the taper bearing set up, one outer race is the same as
another. a machine does not spit them out at different sizes, cnc programmed machines just don’t
that.
L #2654 What's best to use for sealing the crankcase halves? Don't want any crazy colours!
Unfortunately the motor wasn't sealed properly and it's leaking from the inside into one of the back
mounting lug holes and coming out at either end, took me ages to trace it!
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#2656 Two products are in my quiver. If the mating surfaces are in excellent condition and I have no
reason to suspect a problem, I use Hylomar Aero Grade. If the surfaces are otherwise, I use Three
Bond 1014. Depending on your location in the world, Honda Bond or Yama Bond may be more readily
available and are comparable in quality and characteristics.
L #2661 I have fitted new bushes top and bottom to my 1961 venom and reading the technical
info came across this which refers to the top bush:- "Original bushes were slightly shorter with a
machined grove to allow the oil to seep back to the fork leg. Only suitable for the 1.250 dia.
stanchions." My bushes do not have this return groove will this be a problem?
#2685 Don't worry, most of us are using non grooved bushes
L #2862 When I dismantled my engine for a re-build on the main shaft up against the main
bearing and behind the front sprocket somebody had put an eighth washer. This you could see had
been done to stop the primary chain from rubbing the case behind you could see where it had taken
chunks out before. with regard to this mod the engine worked fine and the clutch worked fine. with the
washer in place the two sprockets were in line but remove the washer and the primary chain starts
taking chunks out of the crank cases and primary chain case
#2865 Veloce seemed to have various offsets for the front sprocket, on a selection I have they vary by
anything up to .060". Dependant upon which front sprocket I have on my Venom racer, I also use a
washer .100" thick to provide correct chain alignment and also ensure that the inner face of the
sprocket clears the main bearing boss. Obviously the thickness of washer (if necessary) can vary
according to the shimming behind the main bearing outer race and the relative position of the crank
within the cases. As you say, the washer helps to line them up correctly in your engine and it works
satisfactorily. I only replied to make you feel better and to let you know that you are not alone!
#2870 After running my VM for over 10, 000 miles with obviously misaligned sprockets ( you should
see the scuffing on the outboard side of my clutch chainwheel!), I eventually got them to line up by
making a spacer out of an old main bearing inner race ground to about 0.10" thick. Before you shoot:
yes, I've got the chainwheel in the right way round and there are no weird spacers behind the
engine/gearbox mounting plates. The gearbox final drive ball race is fully home in its housing (except
it's not truly the final drive bearing on a Velo, of course) and the gearbox is a standard Prefix 12.
Everything works fine but my primary chaincase "pants" or, if you prefer, "oilcans" when I pull in the
clutch and this would explain why my downshifts are a bit rough. So what is causing the complete
clutch assembly to be offset towards the primary chaincase outer cover by what appears to be one
tenth of an inch? I do not accept that this could be the result of cumulative wear on the original Veloce
jigs.
#2871 Seems to me that you would cure both the misalignment and the flexing of the case by
reducing the length of the spacer behind the backplate of the clutch, no?
L #3709 I am in the process of rebuilding my 53 MAC engine. However I am finding it very
difficult to set up the end float. The book says there should be no more than 0.0015in of movement.
However the best I have managed is 0.002 at BDC and very slightly tight at TDC. Is this likely to cause
a problem? I cant understand why the end float should vary with crankshaft position?
#3711 Difficult to diagnose at a distance, but I think I'd strip the engine and check the complete
flywheel assembly for truth.
L #4164 Does any one have the specifications for ramp height for the engine shock absorber
and sprocket? If assembled without the spring should there be room for the two ramps to turn over the
peaks? mine can and has about 25 thou clearance as well. I believe this unit to be the cause of my
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"clutch slip". Everything seems to be in order with other used items I and my friend have to hand. Can
any one shed some light on this assembly? Has anyone had their unit fail. I’ve heard about broken
springs but mine is intact though again I don’t know what the free length should be. I stripped the
clutch down and found the outer friction plate tangs were fouling the clutch cover plate, (new bonded
plates used)I straightened the tangs and reassembled with confidence. Ran the bike without the outer
chaincase and found that it seems to be the shock absorber is spinning at mid revs on full throttle. At
this engine speed you don’t get the machine gun noise which is why the clutch became prime suspect
in the first place. Your experiences will be appreciated.
#4166 I don't believe that the ramps should be able to clear each other. Sounds like your drive side
shaft is pulling out of the flywheel, a common failure corrected by installation of a 'nail head' shaft.
#4167 I'm not sure, but I don't think it matters... if the spring breaks it will still be too wide for the ramps
to pass each other. I had the spring break once on my Thruxton.. at low throttle openings it made an
awful racket and vibrated a lot, but once opened up things smoothed out. Fortunately only 15 miles
from home and I had a spare spring. Had the 'nail head' mod done by Dodkins when my big end went
some years ago as a precaution. Apparently the old shaft had pulled out some 20 thou or so.
#4172 The factory drawing show the ramp height to be 0.250" +/- .010" above the face, or 0.406"
trough to peak. I am referring to the shock absorber - the sprocket from peak to face is 0.375". From
peak to trough on the sprocket is 0.406". The factory drawing show the ramp height to be 0.250" +/-
.010" above the face, or 0.406" trough to peak.
#4168 Can't be that the shaft is pulling out, I had the flanged mainshaft fitted. Checked the free length
against one of the original shafts and it appears about the same, well within a few thou. So does if it
rides over the peaks like mine., is it worn? or has the spring suddenly lost it's temper?
#4179 I have experienced shock absorber clutch slip, the symptoms of which where not so much
machine gun as gear teeth stripping noise. my problem was caused by drive side main shaft slowly
eating its way though n/side flywheel causing extra clearance in shock absorber assy. The engine ran
well still!! the way to check is looking down onto big end, both end of main shafts should be flush with
inside faces of flywheels, my drive side one was 3 to 4mm below.
L #4479 Hello group, is there anybody who has used a carillo rod in a venom/viper engine? I'm
just in the process of lifting a venom engine to it's next tuning level and as the con rod seems to be
damaged after 90k miles of (hard?) service it might be worth a try. However, there is no Velo rod in
the Carillo catalogue but I remember somebody mentioned to use one in his (racing?) engine. Any
information appreciated.
#4480 Still got one in my racing Venom, contact Nick Payton and he can identify/ supply it.
L #4723 Does anyone known what the right size crankshaft oil jet is for a Venom with the early
type crankshaft fitted? There seem to be 2 different bore dia. in my collection of parts. One is bored
approx. 2.3 mm and the other about 3.3 mm. Which one to use?
#4743 0.078" with a tolerance of +0.003
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B.2. Cylinder and Piston
L #101 My white Venom Veeline - is running great. It has an Aussie piston now, after problems
with Omega ones, and the Total Seal rings (first time I ever saw a 2 piece second ring!) give it the
best compression I can remember. The only time it has stranded me in 13 years and 30000 miles
(since its long sleep and reassembly) was when the infamous fiber gear stripped. It now has a steel
geared ATD like yours
#116 I'd love to know more details about the Aussie Venom piston and ring set you mention. Can you
forward me details re-manufacturer etc.
#119 Aussie pistons because of problems with Omega ones ? Sounds interesting. I dislike too a
great extent those primitive Omega cast iron piston rings. Easily identified by its charcoal black color.
Just changing the oil ring to a modern 3 piece design cut oil consumption to zero on my VMT. Modern
chrome compression rings create then the required healthy compression. But in recent times it proved
impossible to convince the local automotive parts dealer to sell ring sets for just one piston. So where
can I buy modern rings for Velo pistons, and if a complete piston is needed, where can I buy them
already fitted with rings of 2000 technology, not 1930ies ?
#120 A couple of you have asked, so here is everything I know about Velo pistons and rings. I include
the history so that you don't repeat my mistakes. A.k.a. one rider's experience Based on advice and
experience from other local owners, when I reassembled the Venom back in '88 I decided to scrap the
original one-piece oil ring and use a 3-piece one. This seems to be a requirement when using modern
oils. I found a Toyota pickup motor (22R?) with the "same" ring dimensions and bought a set. When I
tried to fit them (not an easy task, the oil ring's expander is very stiff) I soon discovered that the third
ring land (groove) was too narrow by a few thousandths. That's how I met Mike Parti, an incredible
restorer and collector (his favorites are pre-war - as in WW1) who turned the land wider for me. This
set worked fine until the top ring broke at the "top" punch mark and destroyed the original piston. This
happened 50 feet from the end of a 1000 mile VOCNA ride, I coasted in so it doesn't count as a
breakdown! After that I went through 2 Omegas in the original cylinder, each set to 6 thou or more,
and both seized repeatedly. I used the supplied top and second rings and the Toyota 3-piece oil ring.
With the cylinder now beyond last overbore, I had another sleeved (the original was not cosmetically
perfect, remember this was a Veeline) and installed a used standard piston (Wellworthy), same rings
again. This lasted a couple more years until I got tired of the poor performance caused by leakage
behind the pushrod tube. Apparently the sleeved cylinder would not stay round when hot. Honing,
new rings, changing oil grades, nothing helped. On conversation with Ed Gilkison I found that the
VOCA (down under) had arranged for some pistons to be produced. Unfortunately, gentle readers,
the one I was supplied (.060" oversize, for a mighty 517 cc) turned out to be the very last, and I have
heard that no more will be produced. Dunno about MAC ones. There is an alternative, however, so
read on. The advantage of the Aussie item is that it is made from a very low-expansion alloy. It came
with instructions to set up at 5 thou at the top of the skirt! This gave a clearance of only 3 thou at the
bottom, the normal measurement location. It nipped up slightly when I gave it a bit too much stick
during break-in, but a quick pass on the Sunnen and at about 4 thou at the bottom of the skirt it is
fine. I didn't even change the rings, just filed the high spots on the piston. 90 mph sitting up is no
problem, and blow-by is minimal. Ah, the rings. They are made by Total Seal, and the part number
(remember, these are 87.5 mm) is #C 3445 047 059 157 (TS1). My set was made under license in
Oz, but I suspect that a good racing equipment shop (check out Streetfighters!) can supply them.
They came with a hard chrome top, 2-piece 2nd, and 3-piece 3rd . Compression is amazing, cold or
hot. You DU types (Mr. Tesser) should contact your Tech Secretary if you need more info. I turns out
that many SoCal Veloista have ordered pistons from a local firm called Venolia. They make pistons to
order, and have copied the Venom design (I think they have drawings for a MAC one, too). This is
also done in low-expansion alloy, and can be furnished with whatever style rings you desire. Cost is
not prohibitive. Their website is at www.venolia.com. Again, I have not had personal experience here,
but they come well recommended. And they have not caused their riders any Summer Ride mishaps,
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to my memory. This is the current crucible of Velo reliability, and quite amusing to watch when it's not
your bike!
L #458 I've just got a +60 piston for my MAC from Founders Day today. I measured the skirt and
compared it to 68mm +60thou which gives approx 5 thou skirt clearance (or about 2 thou per inch).
Does this sound OK? Too big? Its an all alloy engined 1954 MAC. I was wondering if it is possible to
use an iron cylinder in an alloy motor.
#459 I have a MAC from 1952, rigid, AL-engine, but with an iron barrel. The engine sounds very
good. I didn't know if this was original or something put together later. Then I found in Fishtail 264,
page 30-32, "Useful information for rigid MOV & MAC", where it was said under "Engine, no. 6: Alloy
engine with either iron or alloy cylinder introduced 1951 (from MAC 15982). This engine had split
skirt piston." So that's the point, either iron or alloy cylinder. It works. When Velo introduced the ALengine
they obviously worked up all the stocks of iron barrels.
#460 Give Tony a call at Hartlen engineering, he should help you. Tony has been reboring motorbikes
for many years including doing a lot of work for Geoff Dodkin. I took my MSS barrel and piston to him,
and before I even spoke he correctly identified what it was. He also does cylinder sleeving at what I
think are reasonable prices. His number is +44 (0) 1483 202540.
L #701 Has anyone got a Venom with Venom(Omega)piston and Viper-head?. I have a -56
Venom endurance with .040 Omega Thruxton piston and head from Viper. I have opened up the
combustion chamber to make room for piston and calculated the CR to be 8.9. I`m going to fit one
more decompression plate which should lower the compression to 8,4. Criterion said that I should
use the MSS-flat crown piston with machined Viper head but then the compression have to be too
low I think... What's the point with Mss-piston? I don't think that the 8.4 is too much or is it (we have
98-octane fuel here in Finland).
#707 You may want to look at articles on squishing in Fishtails 294 and 304. In the UK using 4* LRP
with compression ratios above 8.0 will cause pinking. The only other issue I can think of regarding the
MSS piston is being flatter is there will be less of an obstruction to flame travel (improved flame travel
is the main benefit of squishing). There is always a compromise to be made between increasing the
CR and obtaining the best combustion chamber shape.
#720 For the fellow who mentioned using a Thruxton piston with a Viper head, this would be a
mistake. The reason Viper heads are used on 500s was to take advantage of the smaller chamber
size, use a flatter piston dome (MSS) to aid flame travel and incorporate some squish area as well.
Opening the Viper head out to take the high dome Thruxton (same as Venom) piston would negate
these advantages. My squish head bike runs 10.5:1 compression on 92 octane unleaded with only
28 degrees total advance.
#726 Bloody hell, so I ruined the Viper head because I made the combustion chamber to full
hemispherical shape... So is it now same side as Venoms combustion chamber or is the Venoms
chamber more deeper than Vipers? So you use unmodified Viper head and MSS-piston or what?
Because Criterion-people said that you must machine the edges of combustion chamber to match
cylinder bore edges, but then it is the same shape as Venoms I believe or is it? If I now put MSSpiston
I don`t have compression at all..
#732 I'm afraid by cutting the Viper chamber out to fit the Venom piston all you have now is a Venom
head with smaller valves and ports (which some would argue is not all bad). The chambers are the
same depth. I believe the general way it's done is to machine the Viper chamber just enough for the
MSS piston to clear around the circumference by whatever you desire for squish band, in my case
.035. I am not one who believes a 500 can run up top with the small Viper intake port and valve, so I
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have a Venom head with the sides welded in for a 'bathtub' chamber.
#734 So, I ruined a perfectly good Viper head, great job. I just understood wrong the method to
convert the head. In my case the bike came with just bored cylinder and new Omega Venom piston
but without original head. With the bike came a Viper head which naturally don`t fit with Venom piston
so I went on and opened up the chamber so I can use the new Omega piston. The head has bored
out (to 30mm) intake port but smaller valve. I have also a new Venom intake valve. So if I change the
seat and valve do I then have basically a standard Venom head? And is this job to be trusted to
normal automotive workshop or is there danger that the seat can drop when engine heats up? I
heard that the head must be heated up before installing a new seat. Otherwise the head is in very
good condition...The bathtub-welding sounds interesting, I saw the same in Commando-head with Dshaped
exhausts ports and that was very effective indeed. Is your welder interested doing any more
these heads to some foreigner abroad perhaps...:-) P.S. How can you use such a high compression
ratio (over 10) because in previous messages some said that over 8 cr causes pinging at least with
English petrol? Is that squish band so effective that you can use higher compression ratio?
#735 At this point in your shoes since you have a new piston, matching fresh bore and a new valve I
would put in the Venom intake valve, shim the cylinder for whatever compression ratio guys who burn
your petrol get away with and call it a day. Nothing wrong with a good running Venom spec engine. I
probably have twice the horsepower of PdO's Velos and he still passes me. I think he leaves his
brake levers at home. If you are interested in high speed hunting down of Norton Commandos or
modern machinery (one of my favorite pastimes) you can get more umph but you'll need to work up to
a Thruxton size carbs and intake. I have a Venom head ported out to 34mm with no welding (go up
with the port, don't lower the floor) and it works well with 36mm carbs. I think the factory claimed 5hp
increase with the few Thruxton squish head engines they built, sounds a bit much to me. The squish
is good for about 1 point increase in compression ratio in my experience. You could run twin plug (I
do in both my squish and non-squish Velos) and get some of the benefit of squish that way but don't
expect more than a hp or two. I run 35 degree advance instead of 38 in the non-squish motor with
twin plug. Can't do it with a mag though. If you do twin plug, put a 10mm plug in vertically, you can
get it out on the same side of the bike and without taking the tank off. More details on how to if
needed. Valve timing, particularly the point at which the intake valve closes during the compression
stroke, has everything to do with effective compression ratio. Just last week I changed cams in the
Turd ('59 Venom). With the /8 cam I had in it, the intake valve was closing late (I couldn't use factory
timing, valve hitting piston), the engine was sluggish in the mid range but not a hint of detonation. I
replaced with a /5 cam (I have high ratio rocker arms for .5 inch lift so don't really need all the
duration of /8 cam in a 500cc) to close the intake valve about 10 degrees earlier on the compression
stroke. Mid range power went way up, no loss on top however a bit of pinking now due to the
increase in effective compression ratio. When degreeing in your Velo cam, the spec you are most
interested in is the closing of the intake valve, it is by far the most important of the four valve events. I
have trusted automotive machine shops that have experience with VW or other air cooled engines
with Velo seats, so far no failures.
L #745 On another VMT I blew a hole in the piston I did read about another soul who had the
same problem ...Should I strip the engine to find the bits in the oilways etc.....what is the main cause
of this in velos....is there a filter of any kind that can prevent the oil pump from getting ruined.....it
seems that it was an Italian piston is this a possible
#746 A friend of mine blew the piston in his venom earlier this year. Although he had only owned the
bike for a short period it had been running fine prior to the problem. He checked the ignition timing
and that was ok. The only thing he could attribute the problem to was that he had replaced his petrol
tap and when he examined it he found that the flow of petrol through the tap was restricted. This may
have caused a weakened mixture leading to overheating. He took the safe option and completely
stripped the engine to remove the bits of his piston - it would be a pity to rebuild the top end only to
38

have engine failure due to restricted oilways or a pump problem. There is a suction filter plug in the
bottom of the crankcase that stops debris from reaching the pump, but I'm not sure how effective this
would be in stopping fine bits of alloy, from the holed piston, reaching the pump? The Velo owners
club do quite a nice conversion kit that replaces the fabric oil return filter in the oil tank with a more
efficient cartridge type filter. The kit also allows return oil to bypass the filter if it becomes clogged.
However, this is on the return side the oil having already returned through the scavenge side of the
pump which would not help in this case. I would also be interested in any body else’s comments
regarding holes in pistons.
#747 If you've melted metal in your engine, doesn't it sound like a good idea to clean it thoroughly
before you run it again? I know someone who's on this list who didn't strip after a piston became a
breather pump, and he sheared his oil pump shortly after rebuild, seizing piston #2! As aluminum isn't
magnetic, it's really hard to drag the little bits out. At the very least, take the engine out and flush
everything very thoroughly, and blow it out with compressed air. You just might get away without
taking the cases apart... Petrol vapor/spitback is a function of valve timing, and is normal at low rpm's
with an M17/8 cam and Thruxton followers. It's part of the compromise for high rpm performance.
#748 While I haven't holed a piston, I did buy an engine with a holed piston. On striping the engine I
found "blobs" of ali in the crankcase, which had wedged between the crank and cases. Aluminum was
crushed in the main bearings. It also lodged Aluminum in the pump which seized the pump, striping
the oil pump drive worm and cracking the pump housing. The oil pump requited stripping to clean out
all the contamination.
#753 I have never holed a piston or got anywhere close, and I'm not known for treating the machine
gently. The main reasons for holed pistons are weak mixture, over advanced ignition timing or low
grade fuel, all of which I would expect to produce an horrendous amount of audible detonation
(pinking) long before any damage occurred. However, if an engine is run at certain speed/load
conditions where it is close to the pre-ignition limit, coupled with any or all of these factors, failure will
be extremely rapid. One other possible cause could be the use of a spark plug of the wrong grade
(too hot or soft), creating a hot spot in the combustion chamber. Couple this again with any of the
factors above and the same disastrous consequences will result.
L #964 I have freshly bored Venom with Omega piston. Piston rings are those "black" ones. Is it
better to change these to chrome rings and three piece oil ring? And can you get those rings
anywhere to suit Omega?
#965 Standard Velo-sized rings should fit the Omega piston. Modern oils prefer a three-piece oil
control ring. IMHO, the best rings are made by Total Seal, they include a chromed top ring, two-piece
"gapless" second ring, and three-piece oil ring. Your "black" rings are plain cast iron. Total Seal has a
website (www.totalseal.com) and dealers in many countries. Their HQ and manufacturing facilities
are in Arizona, the phone number is 800 874 2753. They should be able to give you appropriate part
numbers, or even sell directly.
L #1093 My venom has never behaved like what it oughta, and I have spent many long hours
trying to find out why. The bike looks cobbled together from other models, but all the bits are right
according to the parts catalogue, for a standard venom. I've stripped and rebuilt, but still not good
performance and too much vibration. Current theory is that the piston is too tight in the bore. Existing
piston is stamped VM STD, and is solid skirt (no split). So does anyone know correct gap between
piston and bore for this type of piston in iron cylinder. Currently it is about 2.5 thou if memory serves
me right It's a bit odd that a bike of this age is going around on original bore and piston without any
apparent wear, so presumably the previous owner (or builder) never solved the bike's mystery.
#1094 Is that `per inch of bore' or the clearance between skirt and cylinder? If it’s the former then its
39

OK, if it’s the latter then its way too tight.
#1095 The conventional wisdom is for new Omega pistons to have .006" clearance in iron bores and
.004" in alloy bores, as measured 90 degrees to the crank centerline. It sounds as if a curmudgeon
was in your bore, doing as PO's all over the world are wont to do. A piston this tight will be busy
turning friction to heat and wasting your power, trying its darndest to seize.
#1114 I have some original fitting instructions as supplied with the piston for Hepolite pistons. The
information is as follows: Air-cooled (doesn’t state whether iron or alloy barrel) - solid skirt, .0015 inch
per inch of bore at the bottom of the skirt, .0025 per inch of bore at top of skirt.
#1118 As I am currently building an iron MSS engine using a JAP speedway piston which requires the
barrel to be shortened and sleeved, therefore I have been investigating piston clearances. I spoke to
Tony at Hartlen engineering who did all the boring and sleeving work for Dodkin, Roy Smith and
currently Nick Payton. His knowledge of Velo pistons, barrels, clearances etc is exceptional. He
confirmed roughly the figures in Fishtail of between 4 to 6.5 thou, however he did say it is not so strait
forward as it sounds. He also stated that Veloce did more experimental work on pistons and barrels
than the other manufacturers.
#1419 This may be a daft question, but I have a new Hepolite piston for my '35 MAC any it doesn’t
have an orientation arrow on it. One of the valve flats is larger than the other, which I take to be the
inlet side even though the valves (iron head) are identical sizes - can anyone confirm this please?
#1420 Good question, I've been trying to find that out for the MSS. I believe inlet and exhaust valve lift
is the same on the MAC cam, and as the exhaust valve is heavier it tends to float first. Therefore this
is how I set it up in my MSS. The other thing to consider is using plastercine or Blue Tac work out
which valve is closer to the piston
#1421 So you have the larger flat towards the exhaust then? As the valves are identical sizes, how
does the exhaust valve float first? I was tending towards having the larger flat by the inlet to give
greater clearance around the new inlet charge when the piston is close.
#1422 As the exhaust valve is significantly heavier than the inlet on the MSS due to the difference in
the 5/16 to 3/8 stems it tends to float first. If you use a cam where the inlet lifts more than the exhaust
it is a balancing act. As long as you have 0.080" clearance on the inlet and 0.115" on the exhaust you
should be OK as these are the recommended racing clearances.
#1423 I have been occasionally proved wrong in the past, but EVERY engine I have ever put together
(and I've done quite a few in my time) has ALWAYS had the larger cutout towards the inlet valve. On
most machines the inlet valve is larger than the exhaust, or in some instances there are more inlet
valves than exhausts - viz 5-valve Yamahas or 3-valve Hondas. The piston may be the same spec
used in a number of different models, some using differing valve sizes, some not. I would still fit the
piston as above as a matter of course unless otherwise dictated by the manufacturer.
#1424 Logically I would agree. The MAC and MSS have the same valve sizes, so I'm just going on
experience and what my selection of scrap pistons tell me. Also the proximity of valve to piston is
influenced by cam timing, so you work it out for your own particular situation.
#1426 On the MAC the larger valve pocket goes to the exhaust side. Don't know why though!
#1427 Just a point in your reply re the MAC piston. I always build engines using .25" valve drop at
TDC. This was Veloce practice and Ralph Seymour was insistent too. Besides which it works!
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#1429 Thanks - my information came from David Holmes, Brian Giles et al. with the plasticine method
the valve is closest to the piston prior to TDC. I bet that if you calculate both methods they would
probably work out similar.
L #2596 Im rebuilding my '58 Venom and have a few questions. Is the oil groove in the small end
bushing essential? As my more modern bike don’t seem to have this anymore.
#2597 Regarding the small end bush oil grove, I would stick with it. if you are having problems turning
the spiral oil groove, cut a straight grove through the oil hole.
L #2632 Could anybody please confirm the standard bore size of a 53 alloy MAC? The figure I
have is 2.677 inches. However this does not seem to add up with what I have measured on my bike:
The bore measures 2.821 inches with the piston 2.803 inches (has + 30 stamped on it). This seems to
be nearer +126 thou from standard? It just does not seem to make sense.
#2633 68mm is the standard bore size with plus .020 ro.040 oversizes.
#2634 Maybe you've got a Triumph piston in there. I've heard that this is a common substitute for a
MAC piston. Can't remember exactly what the bore for a 500 Triumph is but 71mm would match what
you have. Anyone know the answer? More importantly from my point of view as the owner of a 1954
alloy MAC, have you used the bike with this bore size? If so it gives me a lot more scope as I'm still on
a rather rattly +40 at the moment and was wondering how big I could go.
#2639 Grove lists mac pistons up to +60, give them a try.
#2641 I am running a 71 mm piston intended for a unit 650 Triumph twin (std bore) in our '56 MAC. I
wrote an article about this for FTW. I know you Brits like your homegrown parts but the cheap
Taiwanese piston has half the thermal expansion and is lighter than the Hepolite. I am running it at 3.5
thou clearance, try that with a Hepolite or Omega! An original MAC std bore piston (Wellworthy), with
rings and pin, weighs 316 g; the import 71mm assembly is within a gram. The Hepolite weighs 327 g.
My experience with O/S Hepolite and Omega pistons is that they weigh considerably more than std;
this produces more vibration at higher rpm unless you are willing to rebalance the flywheels. Our '51
iron MAC has a +40 O/S piston from Oz and shakes mercilessly above 55 mph, it will be next. By
using pistons from the Triumph twin range one can accommodate bore sizes from 68 to 73 mm (the
limit for the thickness of the liner). The bad news is that the pin is larger, requiring boring and/or
replacement of the small end bush. I was not successful in getting perfect alignment when I replaced
this "in situ", it really needs the cases and flywheels split and the job done on the bare rod. With an
increase in compression ratio and a slightly bigger carbs this offers a considerable increase in
performance. 71 x 96 = 380cc.
#2635 A 500 Unit Triumph has a 69mm bore, but I heard a piston of a 750 would match...
#2636 Yeah, 69mm was ringing a bell but I can't help thinking that some of the 500's had a 71mm
bore (maybe the pre-unit 500's?). 650's are much bigger. I'd need to consult a Hepolite catalogue or
one of Bacons Triumph books. Is your piston a Hepolite? If so, what’s the number?
#2637 The pre unit 500s have a longer stroke than the unit twins (I think 81mm respectively 65,5mm).
The 650 unit construction uses the same bore than 500 but has a longer stroke. This may explain why
they are not considerably faster... I don't know the dimensions of the pre unit 650 twins. they had
nearly the same stroke than the pre unit 500s so the bore should be considerably bigger.
#2640 I had exactly the same problem on my MAC no 2 and with a bit of help from Nick Payton found
out I had a Triumph Daytona piston the little end is sleeved as the triumph has a smaller gudgeon pin
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and she is using BSA rings this apparently was a fairly common substitution for a +60 piston, the only
real problem is the increased compression ratio (roughly 10.5) and valve clearances have to be
watched, but she runs very well and has a nice kick back every now and then just to remind me who is
the.
L #4152 I had a big-end failure recently that resulted in a bit of swarf scoring the bore and piston
on my Venom. The piston is serviceable but the cylinder bore is a bit too badly scored to reuse. The
obvious solution is a +.060" piston (Mike at Grove has these in stock) and a rebore. I'm already at
+.040". However, I'm wondering if anyone has tried Nikasil plating the bore and if so what their
experience is. I think there is enough material to skim about .005" to .010" off the bore to remove the
scoring and this would be the depth of the plating. Would you run the same clearance as cast iron?
Will the standard rings be OK ?(I know you can't run chrome-chrome , but Nikasil?). The cost of new
piston/rebore vs Nikasil seems to work out about the same.
#4153 A friend of mine had his iron VMT barrel nikasil plated from worn .040 back to standard! He
went through Dave Smith. It seemed to work fine.
L #4177 Dose anyone know what the inlet bore for a 49 mac ( iron ) should be? I have a head
that I think is for a mac but the carbs inlet seems small by comparison to the head I have on my mac
now, although it may be nothing because the head that is currently on my mac has been changed a
lot. Someone put in bigger valves ( from god knows what ), and has ported it nicely but it is not
preforming well and I suspect that it was set up for the kind of driving that I do not do. looking thru the
parts book many items are shared between the mac and mov and I want to make sure that I do have
a mac head and not a mov head so any help on what the differences between the two would be
helpful. just trying to save myself a lot work if the spare head is not for this bike.
#4204 Mov 7/8", MAC 15/16"
L #4375 I recently bought a 1936 rigid mac which had not been standing for too long after
getting it running and 200m of trouble free riding it seized up while riding up the wendover bypass I
left it a while to cool down and it freed itself, got it home and took the head and barrel off it had only
minor scores on the skirt of the piston , I thought I had found the cause of the problem when I noticed
one of the holes on the skirt of the barrel was blocked after unblocking and reassembling and a new
concentric carbs I took it for a spin yesterday and after 10 miles it did it again! it seems like a heat
seizure but I don’t know why any ideas?
#4376 The simple answer is that the piston got too big for the bore. The real question is, Why? The
variables are cold piston clearance established by whomever bored the cylinder, and the amount of
heat buildup in the piston during use as the piston will expand in tandem with it's temperature. The
place to start is to measure the piston clearance and compare to specification (which I do not know). If
within spec, you are simply running too hot and the piston is expanding with the heat until seizure.
Excess piston heat is generated most often by lean carburetor settings, although incorrect spark
timing or high compression ratio can be the culprit. Unfortunately, the maker's recommendation for
carburetor settings cannot be relied on today due to changes in fuel chemistry, so you are looking at a
sometimes long and agonizing education as you learn how to work with the beast. A useful and easy
assist is a cylinder head temperature gauge, using a sender that is a ring held under the spark plug.
These can be bought from www.westach.com and many other suppliers.
#4382 Hello all, I would be very much interested to hear what other listeners have to say about this
new engine seizure problem. Over the past 5 years I have been working restoring a 1956 Ariel VH
Red Hunter- 500 single. This bike has an aluminum head, aluminum piston, and cast iron cylinder.
The first engine rebuild I used a 7.5-1 compression ratio piston, per the piston manufacturers
suggestion I bored it to 4 thousands clearance. During the shakedown ride, about 20 miles from
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home, going about 45 mph the thing seized, locking up the rear wheel. Ill tell you, a full power slide at
45 mph, in traffic, on a bike that you have spent two years, and many thousands of dollars restoring,
is not something I would recommend to anyone faint of heart! After getting to the side of the road, and
waiting to stop shaking, amazingly it started again and seemed to be running fine. Off down the road I
went again, about a mile or two and it seized again! Two full speed power slides in one afternoon was
enough for me. The bike seemed to run fine after that. After putting about 100 miles on it, I crashed it
head on with a car in an intersection. It was the classic car making a left hander in front of me as I
entered an intersection. Of course the whole front end was mangled. Not to mention my own person.
The bike sat for nearly a year. When I started to fix it again, I decided to have a look at the cylinder to
see what had become of the seizing issue. The engine thankfully was not damaged in the crash. The
piston and cylinder wall had light score marks just as Dave described. I made the decision to fit a new
9.0-1 piston this time; I thought it could use a little more power. This was a different manufacturer of
piston than the first rebuild I did, but the recommendation was still 4 thousands clearance. After a very
long rebuild period, and much searching for parts, painting, etc., etc., the bike was finally finished. I
was very careful with the break in period; never more than half throttle, never more than 50 mph, etc.
After about 500 miles of this kid glove treatment, I took the bike on its first real club ride. Riding up
Wolf Creek Pass here near my home, I started to push it a little hard, and I'll be damned if it didn't
seize again! No wheel lock up this time. As it started to loose power I immediately pulled in the clutch
and it promptly quit. I waited for about 20 minutes and tried to continue up the hill, I got about 200
yards, and it started to seize again. It was as if the old Ariel was saying how tired she was and refused
to climb the canyon road anymore. I rode it all the way home, mostly downhill and flat, about 125
miles, with no problems. I did receive the Bent Valve award for this club outing, the equivalent of a
DNF. From that time I have ridden it only sparingly, 10-20 miles at a time, and really taking it easy.
Once again the fall Oil Bath club ride was scheduled for September 25th. I again decided to take the
Ariel. I mixed in about 12 oz. of Slick 50 with the oil. The climb up Wolf Creek Pass went fine, no
problems. It seems to be running great, good compression, good power for an old 500. I am not
advocating exclusive use of Slick 50, but it sure seemed to help.
#4377 What clearance do you have between the piston and the barrel?
#4383 got the barrel off and I can just squeeze a 4thou feeler gauge between the piston and the bore
the piston says 1.d:10 and +20
#4386 For my money that sounds too tight. I'd be erring towards a piston skirt to barrel clearance of
6thou rather than 4. It might rattle a bit but it won't nip up on you.
#4388 The problem with lots of clearance is that while the piston is rattling, it's also tipping. When
tipping, it's wearing the corners off of the rings and rounding off the rings on the surfaces contacting
the bore. When the rings don't seal well, hot compression gasses heat the skirts, thereby expanding
them, sometimes into seizure. Far better IMHO to set the pistons to specified clearance and keep
them cool with mixture and timing. An EGT and a CHT gauge will allow you to monitor temperatures
as you make the tuning adjustments. You'll spend about $150 US, about the price of one piston, to
say nothing of the several that you might ruin while tuning in the olde fashioned manner.
#4389 True enough. The maximum wear recommended by Velo was 0.008" so 6thou clearance
(which would include the design clearance) would be well within that. I guess that the real answer
should be to bore the cylinder exactly to size so that you get the correct manufacturers clearances as
the piston will have them built in. Sometimes it doesn't seem that simple though.
#4381 Regarding seizures: I had a similar problem with an iron MSS recently. After a rebore to the
'correct' clearance for the piston supplied (thanks VOC Australia!), it seized up lightly several times,
with gentle riding, on the way to a rally. As I had further to go still, it seemed the best solution would
be to raise the carbs needle a notch; result, no more of that sudden slowing down!
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B.3. Cylinder Head and Valves
L #6 Recently we have had two different makes giving problems with seizure of inlet valves. The
Velo, a late Venom, fairly new to us, is almost certainly because the machined boss on which the
M38/4 valve spring bottom holder sits was badly cast, and is off centre. Late heads are called
"diecast" but in fact, the ends are formed possibly by a die, but the central part is a core as in
sandcasting. The boss is off centre laterally, and does not support the M38/4 properly on one side.
We welded and remachined, and hopefully this will cure the problem. The spring tended to tilt the
valve laterally when pressure was applied. Hairpin valve springs are probably prone to the problem of
different pressures between the two individual springs. One answer might, at the top of the valve
stem, to make two demi-spherical parts to allow the springs to tilt a little without transmitting lateral
thrust to the valve. Or fit coil springs, but make sure the seating for the spring, and the top collar, as
well as the spring, have perfectly parallel faces.
L #201 I have a 1955 MAC which I am building at present and as some bits were missing: rims,
mudguards, seat etc, I am doing it as a street scrambler with 21" front wheel and 18" rear, stainless
guards and Thruxton seat. Looking at the inlet valve guide yesterday and being slightly bemused by
the fact they are straight sided. Obviously another Velo idiosyncracy. I started to think about valve
guide seals. I also happen to own a Armstrong MT500 with the Rotax 500 engine. Believe it or not
the Rotax valve guide seal fits the MAC inlet guide. Anyone got any reason that this might not be a
good idea.
#202 I have never had a problem with burning excess oil via the guides on a pushrod velo.
Restricting oil to the guides (particularly the exhaust) may cause the valve to seize.
#203 I had an intake valve seize some years ago, it was a Manley SS intake in a silicon-bronze guide.
The clearance was per the Red Book, and no seal was fitted. It just picked up some guide material on
the stem, which was removed with emery cloth and the Venom took us home the next day. Methinks
there is precious little oil in a pushrod Velo rocker box to begin with...and it has a hot, brutal life.
#205 Contact The Cylinder Head Shop. They have a technique of swaging a centre into the guide.
The guide has lateral corrugation which hold the oil and allow finer valve stem/guide clearances to be
used.
L #233 Do I win a prize for spotting that the desmo setup on the front cover of Fishtail 323
shows that the exhaust cam follower appears to have a roller on the rear follower instead of the usual
"slipper" I have an article from Motorcycle Mechanics 1962 which shows ALL to be slipper type. Does
anybody have any knowledge about this apparent variation. Does anybody have the fitting
instructions or a copy as supplied by BMG. Is there anybody out there still alive from the BMG days
who could give some advice/clarification? Lets hope so on all counts!! There was a firm in California
called "BHB Cyclery" Do they still exist? They used to advertise BMG desmo stuff and were
advertising as recently as August 2001, but alas not desmo gear, but a Thruxton so equipped. Do
any of our American friends know the answer
#234 I have seen two sets of BMG kits here in the USA outside of a bike, and know of one VMT with
a kit installed. The two I've seen had the skids not rollers, and I'm not sure rollers would work due to
space considerations. Remember, they follow the cam on both top and bottom, in a 'c' shape. One of
the uninstalled desmo kits was very interesting, as it had broken a pull-rod and wreaked havoc; the
diameter of the rods was quite small, only slightly bigger than a GTP oil pump rod (there's your Velo
memory test). From what I've heard, there was essentially no difference in performance between the
BMG kit and standard. BUT the Thruxton locally with the kit installed held a speed record at
Bonneville, and I think I recall seeing a period road test showing a BMG-kit Thruxton lofting its front
wheel(!). Ed Gilkison has a kit which he's studying for possible reproduction; bug him about it if you
want one!
44

L #489 has anyone had any problems with venom/viper thru studs, that hold the head and
barrel down. I just bought a venom off a guy and when he fired it up it started to blow slightly at the
head. this confused me a bit as velos don’t do that. the holding down method is excellent and I have
never known it happen. I got to thinking about it and I asked the guy if he had used stainless instead
of the originals, he replied yes he had. I have seen this before with guys with triumphs and BSA's the
stainless application doesn’t seem to be up to the job. I would guess that the original material would
be a good grade tool steel and the stainless would be an unknown quantity. could anyone please
give me any feedback about this. I took out one of the studs to examine it and I noted that the nut
was direct on the head. Should
#492 Stainless engine studs are known to work loose. There should be a washer under the Nylock
nuts, and normally (but not always) there should be an “O” ring underneath.
#493 Would you recommend using the original studs instead of the stainless items, ?. I have zinc
plated the originals and was considering putting them in. what do you think.? does the stainless studs
require a bit more tightening ? I believe that they were pulled down to 24lbs originally.
#494 The original studs and one hopes the Velo replacements would have been calculated to "do the
job". Stainless steel used id free machining, normally A2 and one would suspect the UTS (Ultimate
Tensile Strength) would be up to 50% less than the original steel studs. People automatically think
stainless steel is stronger. Change them.
#496 I wouldn't recommend exceeding the factory torque specs for stainless or other studs, the
consequences are a lot more vexing than re-torquing the head or replacing the studs themselves.
I've found that a Velo, or any other bike, left sitting long enough in conditions where there is a cycle of
heat/cooling, like normal daytime/nighttime cycles, will loosen its nuts up. This is most dramatic in hot
climates, obviously not as much of a problem in England! It sounds like the bike in question with
stainless studs is more in need of the proper nuts and washers than new studs.
#497 There is very little difference in elasticity and thermal expansion between various grades of steel
(including most "stainless"), so torque specs should not vary either. A higher tensile strength only
allows more torque, not needed here. The failure mode would be a broken or stretched stud, which
I've never heard of in a Velo. Stripped, yes. Make sure you oil the threads. The key is using the
correct washers, they are thicker and hardened. The O-rings help against leaks, as do Nylock-type
nuts. If you kept the C.R. down maybe your nuts would stay tighter,
#498 316 by which Ron probably means 316 S16 is a very superior stainless to the commercial A2
which is more a kin to 304 S31. 316 S16 has good strength and creep factors. It is also the material
used extensively by us in ships. So if you drive your Velo into the sea the bolting will be OK.
#499 Agreed, The thread in the Aluminum is the weakest part of the equation. A clean lubricated
thread will produce up to 25% more squeeze for the given torque. Lubricate the threads with oil.
Grease is used to prevent rusting.
#500 I have read all the comments and take on board what was said. I think that putting oil on the
threads is a no no as it tends to send the torque settings haywire. as regards the stud pulling out of
the crankcase, this is possible and the cure is 4 helicoils which are two and a half times stronger than
a thread tapped into alloy. the o rings are another must, and the later breathing setup is another
must if the engine is to become more oil tight. also a one piece pushrod tunnel is a very good mod,
one that I would recommend. does anyone know the thickness and od of the washer on the holding
down stud, these were omitted when someone built the motor. I thank everyone for the response. I
was told by Mr Dodkin to pull the head down to 24lbs, is this right ?
45

#503 The literature says 20lb./ft, remember Aluminum expands more than steel. I set mine to this and
have no problems.
#509 I cant agree about oiling the threads, in a manual it says torque settings and in brackets if
it was to be lightly oiled it would say lightly oiled, not dry. my mate went to an engineering seminar
and they got talking about torque settings, and something that always sticks in my mind was that the
guy doing the talk said, if you tighten a bolt to 40lbs dry and then add oil to get to the 40lb dry torque
with oil would be 5lbs. that has always stayed with me. when torqueing a bolt or nut I always check
that the thread has no tight spots. dirt or uncleanliness is not an option. the problem that I have
found is that adding oil makes the bolt skid and it cant click off until a much higher poundage is
added. I once tightened the rocker oil feed domed nuts on my rocket three and forgot to clean out the
threads with brake cleaner, what happened was the torque wrench wouldn’t click off at 22lbs and it
pulled out the threads in the domed nut. and that was due to oil. I am not Mr perfect when building
motors but sometimes things are logical.
L #665 I have a venom with alfin barrel. I have adjusted the tappet clearance to .006 and .008
iaw the owners manual. On other classic bikes I have with aluminum barrel and iron liner the
clearance is adjusted to 0. You only verify that the pushrods can easily be rotated by hand when
engine is cold. On my bike there is clatter from the tappets when the engine gets warm. I am
considering to adjust the tappets as described above. Will I have a problem
#667 You will probably burn out the exhaust valve and seat. You say there is clatter from the tappets
when the engine gets warm, usually tappet noise reduces when the engine gets warm.
#668 Well it's easy enough to check your tappet clearance hot. On my alloy barrel Velo the clearance
typically increases .002" or so when hot (check your own as I'm using aftermarket cylinder and studs).
By the time I get the tank off the cylinder head temp has dropped to 200F or so (400F during full flog)
so it's probably even a bit looser at times. BTW, I quit using feeler gauges to check clearances along
time ago (especially with one piece pushrods). Since one turn of the adjuster is .038", it's an easy
matter to turn the screw to zero lash (pushrod won't spin), then back off 1/6 or 1/4 turn to get .006 or
.008. Not perfect but works for me.
L #756 Just finished a rebuild on VMT457 and discovered a trap with recycling head gaskets. It
can be done - just anneal the old one and put it back in. Up to the point where it has become too thin,
that is. After tracing a misleadingly metallic chirping noise to puffing around the head joint, we lifted
the head and measured the thickness of the old gasket 0.025". We then rifled through the parts bin
and found a motley collection of new and used gaskets, some a good fit in the head, others loose and
thus prone to sit off centre and protrude into the combustion space (and in one case I heard of,
protruded so far as to actually catch on the edge of the inlet valve!). Chose a reasonable one and
measured it 0.045". Annealed it, bolted the plot back together and problem solved.
L #771 What is the size of the standard Viper inlet valve head diameter?
#772 My information says, Inlet 1.69 inches, exhaust 1.56 inches - but I haven't checked Viper valves
physically
#775 So the exhaust valve is the same in all venoms and vipers but the vipers inlet valve is smaller
(and of course thruxton has 2" inlet valve I believe...). Is there a significant loss of power if I use a
Viper head with 30mm intake port and small intake valve in Venom (combustion chamber is shaped
to match Venom)?
#776 Now - Viper exhaust is smaller. check in the engine section here
www.croesus-consultants.co.uk/v-tec/ I have an engine simulation program, which I have just
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checked for a Venom with Viper valves. While I cannot claim it's accuracy (vendors claim less than
5%) it shows approximately a one BHP reduction in peak output, and a similar amount of torque
reduction (ft - lb).
L #976 I have a Viper head in my venom and I'm thinking of changing the valves to the bigger
ones of venom. Now I`m wondering if there is enough room for the bigger valves to operate. The
combustion chamber is machined to same size as venom`s. So is there a danger of valves to clash
or is the valve geometry and location same in Viper and Venom?
#988 Yes, the Venom, Viper and MSS shares the same valve angles ( and bare casting) which I
understand to be 35 degrees. The Thruxton valve angles are 33 degrees. You will of course require
new valve seats.
L #1174 Dave Smith, a Velo agent here in the US, offers a squish head conversion with several
stages of tune. I chose a 'fast street' rather than full race job, and here's what was done: The intake
and exhaust ports were reshaped, resulting in a 1 1/4" choke. New valve seat angles, new lighter
valves, coil springs w/ alloy retainers. The combustion chamber was shaped for a squish effect,
coupled with the new piston which looks like a Manx or G50 item; i.e. flat on the top, deep valve
cutaways, with the piston protruding about ½" over the top of the barrel at TDC. The combustion
chamber sides were milled flat to match the piston. After measuring the height of my connecting rod
over the crankcase, the barrel was shortened slightly for correct clearances, the piston being a little
shorter than standard. The oil return line from the valve spring cavities had to be bent a little to fit, and
Thruxton type pushrods of the correct length are used. As the pushrod tube is the sliding type, it is
unaltered. I haven't tried the engine yet, as I'm waiting for my TT magneto to be rebuilt. I'm taking the
time now to polish and lighten the valve train, again to 'fast street' and not too radically lightened. As
the intake is now ported to 1 1/4", and the bike is a '61 Clubman, I would like to use a TT carbs, as
this is original for the machine. The bike in general is completely correct in appearance and really
beautiful; Dunlop alloy rims, early reverse-lever rearsets, Tickle 2ls brake, chrono tach, braided zinc
fuel lines, etc. I have the original head and barrel sitting in a box.
L #1220 I'm intending to fit a thruxton type inlet manifold to my squish head venom. Does
anybody know (or is able to determine) the length of the inlet port, let's say from the valve to the
middle of the mixing chamber?
#1222 The required length for the inlet depends on the power characteristics of the engine. Say for a
VM with max. power at 5900 the length from valve seat to inlet is around 15.25" with max power at
6200 rpm (clearly non standard) the length would be nearer 14.5". If you have a GP carbs with a
longish tapering inlet bell mouth this will affect these lengths to some extent. I don't know how the
VMT manifold fits with the above figures but there is likely to be compromise due to the available room
to fit it all in. In practical use any extension can be beneficial and the calculated lengths apply only to
that rev range.
#1259 There are many formulas to work out ideal induction lengths. Gordon Blair from Queens
University Belfast, who has more expertise than most in this area gives the following empirical
formulas for induction lengths (see: “Design and Simulation of Four-stroke Engines”). He maintains
that it is accurate to about 3%. The induction wave is reflected up to five times, and the equation for
the length is: L = aC -- N Where L = Induction length from valve head to end of bellmouth in mm. a =
reference speed of sound at 340 at 15 degrees C, 346 at 25 degrees C C = Dimensionless intake
ramming factor for first ramming peak = 8900, second = 6600, third = 5150, fourth = 4150. If your
playing around with lengths I suggest you tune the length so you get the best peak at 6000 RPM,
which automatically determines the next ramming peak. This I work out to be secondary ramming
peak with a length of 377mm, at 20 degrees C. This gives the third peak at 4685 RPM The theory is
that then you get the exhaust to resonate between these two peaks.
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#1261 Does the shape of the inlet port affect the "intake ramming factor" and did Blair also determine
the corresponding outlet factor? If he did it would interesting to know the temperature of the exhaust
gas, as this seems to affect the sonic speed and is therefore important for the calculations.
#1264 The answer is yes and yes, to get an exact answer you need to create a computer simulation -
he tells you how to do it in his book. It really is a very complex subject, that's why I gave his empirical
equations! In particular the bell mouth taper has a major effect on the resonant frequency. Exhausts
are even more difficult due to the "wave interference during superposition" (his words not mine) the
empirical exhaust formulas are not as universal as the intake empirical formulas. Next to Phil Irving's
"Tuning for Speed" this is the best book I have come across, but a word of warning. It's expensive, I
did thermodynamics at University, but a lot of the derivations of equations I found challenging (i.e.
beyond me). If you can get it on inter library loan it's worth a read, you will learn more about how a
four stroke engine works than you could ever imagine - but it also frightens you with what you don't
know.
#1265 The Thruxton head to carbs manifold is (total length) 3 and 7/16 inches, note of course that the
carbs slips over this manifold by approx 3/4 inch. From valve stem (where it leaves the guide) to
manifold = 3 inches. From manifold to carbs bellmouth (measured using rubber mounted 38mm
Concentric Mk2 - (which is too big but gives a good guide)) = 7+3/4 inches, gives a total of 10.75
inches.
L #1269 I am considering to install coil springs on a Venom engine that is going to be used for
classic racing. Does anyone know if there is some kind of mathematical formula to be used to
determine what kind of spring to use with regards to weight of valve mechanism and desired rev limit.
#1272 I suggest you call Nick Peyton, who supplies racing coils springs and alloy retainers, cost about
GBP38. Nick's number is +44 (0)208 540 2118. Also Seymour's sell similar items. You will need to
machine a grove in your head to accept their length. I will mail you a picture of the springs and caps.
#1278 Is the modification worth doing. What I understand there is a certain risk on a nonThruxton
head that valves meet if revved over 6200. If this is correct will coil springs cure the problem.
#1304 Thomas
Most of the serious racers in the UK fit them so I expect there is a good reason for doing it. Slightly
different bike, but I am about to fit them on my pre war MSS, for one thing the alloy caps are less than
half the weight of the original MSS ones. Obviously only fit them if you are going to seriously rev the
engine. If you are going to do that you should also lighten the cam followers, pushrods, rockers,
adjuster (drill and / or use a Triumph adjuster) and use a ally lock nut. If you are going to do this you
will need a bench grinder, Black & Decker Powerfile and polishing mops.
L #1339 I have a 49 mac 350 that is oil fouling the plugs, probably due to oil seeping past the
rings etc, it is slow to foul but it dose make it hard starting when it happens. have any of you had a
good experience with oil additives like slick 50 to tighten things up a bit? or should I just bite the bullet
and start saving / searching for rings etc.
#1343 If your oiling problem occurs after you have left the bike standing for a couple of days. Odds on
it's not getting past the rings, it's seeping past the valve stems and guides. If you think about it oil is
pumped to the rockers where it then flows into the valve spring cups. They then fill with oil, until it
reaches the level of the hollow rocker spindle, then it can flow back to the timing chest for
recirculation. So the valve cup acts as an oil reservoir. You may be able to fit valve stem seals as per
MKII KSS, or you can fit drains to the valves spring cups. I will include details of how to do this when I
post the valve lightening mods.
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L #1356 Can anyone advise me? I have a Venom Clubman that I have done about 200 mile
since a complete rebuild, which someone else did. Yesterday when pulling away (quite gently) it
suddenly stopped and ground to a halt. When I tried to start it had no compression and was blowing
back through the carbs. I have removed the head to find that the valves have "kissed" each other with
the result that there is a small mark on the inlet valve and its slightly off its seat. I cant remove it yet as
I need to get a spring compressor. Anyone any ideas what caused this and what to check?
#1357 I have had this happen years ago after a rather heavy use of throttle which led to highish revs;
the valves touched! There is little clearance between the valves at certain times and valve float can
lead to an argument between them. Check also for foreign bodies keeping the valves off their seats,
incorrect tappet clearances or other 'sticking'.
#1362 I had a new inlet valve stick in my Venom's guide after about 500 miles. It was a SS valve,
allegedly set at 2.5 thou, but still picked up the bronze in the guide. It ran fine the day before, but on
(push) starting after a cold night, it rattled. Had to pull down the head and sand the bronze off while
my fellow VOCNAers partied and made sympathetic noises. We made it home 400 miles the next day,
though. The slightly bent valve seemed to seal well enough. I replaced the valve, reamed the guide
out just a bit, and it ran fine for several thousand miles after that.
#1365 I have removed the head and inspected the valves. The exhaust seems to be OK but the inlet
valve has picked up badly in the guide and has some streaks of bronze guide material in several
areas. I have measured the valve in several places including the unworn sections and it seems to be
two and a half thou under 5/16 of an inch. However, when I checked the guide I am unable to get a
5/16 piece of silver steel through it. I guess this means that the valve is running without the correct
clearance. I will be fitting a new inlet valve tomorrow and reaming the guide to 5/16 in an effort to
achieve a few thou clearance.
L #1396 If there are those of you who like me have been looking for OHC gland nut tool (part
KA55 ) here's a tip . At your local Halfords store you can get Draper tool stock number 59277 in the
cycling section , 'Locking ring adjuster ' for £5.99 ( $10 ) it needs a little grinding off so that it will go
behind the drive tube , but seems to do the job.
#1397 Another useful tool for removing cams from a cammy, is a ball joint extractor. It works as if it
was specifically designed for the job. You can buy them for about £6 /$10 from many car accessory
shops.
L #1755 Here's a question for the cammy gurus out there, or those hot on performance cams .
I've spent the day checking and re-checking valve timing on the Mk IV KTT racer that I bought recently
. (fitted with a KSS Mk II head ) I'm sure I have it right with rocker adjusters set so that the rockers are
centralized on their eccentrics ( clockwise to decrease setting of exhaust and increase setting of inlet )
and 25 thou gaps as per KSS II checks. What I am getting is ; Inlet opens 70 deg BTDC Inlet closes
60 deg ABDC Ex opens 75 deg BBDC Ex closes 30 deg ATDC . I've compared this to the profiles on
the database , KSS 1,11, KTT IV and V settings and the M17/8 (KTT VIII )settings and see nothing
like it . In my case the inlet seems to open up to 20 deg earlier and close up to 10 deg later than most
of the Velo 'performance' cams , exhaust also opens earlier . Does anyone recognized these settings
or have any comment on them or experience with anything similar ? The bike hasn't run for years and
that's why I'm stripping it for a check . The cams and rockers show no wear . It has a 1 1/8 10TT9
carbs set up to the same as Viper Clubman spec. and was pulling 20,44.22.55 teeth on the sprockets
( higher than a Viper ) , it has TT ratio's in the box , so it was obviously going well . Combustion
volume is about 42-43cc which makes it about 9.3 CR same as the Viper C/M My 39 KSS racer I used
some years ago had K17/8's in and went well .
#1757 Before considering the valve timing, have you set the rockers correctly? In the end of the
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ocker there is a V. This points 'inwards' towards the plug on inlet and exhaust. Check the end pad is
central on the valve stem too. Next have you checked the degrees with the correct checking
clearance? It seems so but try 12 thou or 20 thou which is right for the K17/5. You may have a K17/8
which needs 20 thou checking clearance and your figures could be close for one of those.
#1758 That's one big lumpy cam, maybe e a custom grind. You might try retarding it some to bring the
lobe centers closer to Velo spec. I think you are at about 85/115 now. The intake valve must get close
to the piston on opening unless you have a big valve relief. Also with all that overlap the valves must
be getting close to each other. 60 degrees seems a bit early to close the intake with so much duration.
Have you run it this way?
#1761 I have checked the timing again with various gaps from 12 up to 30 thou and at 30 thou gap I
get 69,57,73,27 . I am measuring from an accurate TDC and with an accurate gauge with the vales
set correctly judging the closure when it nips the smallest feeler I have ( 2 thou ). Things do indeed
open up early . I have not had the cam box stripped to see if there is any number on the cam as I was
wanting to measure everything up before I pull the motor down for an inspection and clean ( Ignition
timing , valve timing , the clearances etc ) . How would I go about 'retarding ' the valve timing Paul , is
it a simple matter of putting the top drive one tooth out of current alignment ? It could be possible that
the timing is out as there is no scribe mark on the top bevel to align with that on the cam drive gear
,alignment is marked with paint dots . Having said that what marks there are and scribe lines are all in
the correct position at TDC. When I had my KSS racer I simply stripped it put it back as the Velo KSS
tuning sheets , put a new K17/8 cam on and ran it ( untouched and without fault ) till I sold it . So
playing about with the valve timing is something I am not familiar with . Maybe I will have to wait and
measure the valve to piston gaps then if it looks OK, wait again and see how it runs ? I'd like to find
out who built it and may be able to get some info via 'Fishtail', It does look to my eye as though the
bike was built by someone who knew what he was doing .
L #2164 I am fitting a thicker spacer / insulator between the head and the carbs on my Venom. I
will need to replace the studs with longer studs or bolts. Question: What size and pitch thread is in the
head ?
#2176 5/16 BSF, 22tpi.
L #2298 I have a 1951 rigid MAC and as there was a slight oil-leak from the head gasket I
changed it, but there's still a slight leak. I find oil between the cylinder fins and on the magneto just
behind the cylinder. The gasket was a copper ring. Should I have heated it up or anything before
fitting it?
#2299 Is it an iron head? If so there shouldn't be a gasket. If it's an alloy head then you should have
annealed the gasket by heating it to cherry red and then quenching it in cold water to make it soft
before fitting it.
#2300 There are no oilways running through the head gasket face on a Velo so the oil leak cannot be
attributable to a leaky gasket. More likely that you have the usual leak down the cylinder studs. To
cure this, countersink the stud holes in the top face of the head and fit a suitable "O" ring under the
washer. For additional oiltightness use a new Nyloc nut on each head stud.
#2301 I have a '35 MAC which has a copper gasket too - to anneal a copper gasket, heat it red hot
and then quench it in cold water. This should enable it to be reused nicely.
#2302 thanks for your advice too. There is oil running down the cylinder bolts, as you say. I noticed
when I last had the head off that one of these bolts is not quite straight, not by much, but it's almost
certainly making a difference.
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#2305 I have been annealing copper all my working life by heating to 'cherry red' & quenching, & of
course it works if the heating is done correctly. But a few years ago, I was informed by an 'expert' that
it is only the careful heating that is necessary , the only thing that the quenching does, is remove all
the oxides etc. & make it nice & clean ! I have tried this, & it certainly appears to be true, - but I still
quench anyway as I can't resist that cleaning action.
L #2544 My MAC is running like a top at the moment and running in is going really well, I only
have one problem(for the time being) and I don’t know whether it is typically MAC or not. There is a
fairly light tapping noise on startup from the top end which seems to go after a run but it is either
always there and I sometimes don’t notice it (tappets are spot on and running a 17/7 cam and
followers), a regular Velo rider informs me this is because its an all alloy motor, any ideas?
#2545 What condition are the rocker bushes in? On an alloy MAC these are split alloy housing with an
oil feed. Hence they may well quiet down when oil is pumped to the head. The tappet clearances can
still be set even in this state. Its common and a sod to mend as one half of the bearing is in the head.
#2546 I’ve seen better but I’ve also seen worse there was some minor scoring on the outer edge of
the uppermost part of the bearing surfaces which polished off easily I’ve had them apart since (200
miles) and there is no repeat of the scoring which I put down to an old injury, my other macs bearings
are u/s and I have an engineer friend who has offered to syph bronze some sleeves with new oil
ways, I don’t know if this has been tried before but should be an alternative to the criterion conversion,
anyway I am still left with this noise. I seem to remember reading an article that suggested that a mac
should sound something like a bean escaping from a tin .but as this reads it doesn’t help at all
#2562 I had an MAC once that made similar noises though it had thick rubber grommets stuffed
between the alloy cylinder fins. Eventually, it was discovered that the oil pump's performance had
been seriously impaired by an air leak on the pipework 'twixt pump and tank and more bubbles than
oil were reaching the rockers. Without wishing to cause too much concern: I am slowly rebuilding the
"Viper in Clubmans trim" that was sold by the VOC when they were raising funds to buy The Chapel at
Huncote. Each element of this project was donated by a club member and so it was no surprise to find
that some components required attention. The valve gear had obviously been run for too long with
zero oil pressure and the alloy bearings were badly scored to the extent that aluminum had become
"plated" onto the rocker shafts. New rockers would not have retrieved the situation so I elected to
have the old ones metal-sprayed oversize. This is labor intensive as the shafts have to be ground
concentric, metal-sprayed, hardened and then ground to the required oversize. It cost me £90 and
that was three years ago but any engineering firm that met-sprays crankshafts could do this work. The
tricky bit is getting the rocker housings and caps bored oversize (+0.020" in my case) as a fair degree
of precision is required and. of course, the oil feed groove must be maintained.
L #3250 My MAC has an annoying loud clacking coming from the top somewhere. I thought it
might be a noisy tappet, but now I'm not so sure. When I had the rocker cover off I was turning the
engine over with the plug out and noticed that the exhaust valve closed with a definite "click." Please
help a beginner - should the valve be making this noise? And does the whole description sound
familiar at all? Any ideas on how to stop the noise - it's interfering with the delicious
thump-thump-thump from the other end.
#3255 Make sure the valve lifter isn’t touching the bottom of the cam follower.
#3260 I had a similar problem with my MAC I tried the valve lifter and all seemed well, the rocker
carriage had picked up some swarf and was causing a tight spot on the rocker arm I took the whole
thing to bits polished the alloy surfaces and put it back together, be careful with reassembly making
sure the surfaces are well oiled I even prime the top of the carriage where the indentations are for the
feed, funnily enough both of my MACs have the same noise on start up a bit tinny but as soon as the
51

oil circulates they quiet down, that’s why I think its important to run them for a few minutes every week
if not in use to keep oil circulated
#3284 The rocker carriage is held down onto the head by 3 bolts. Make sure that none are stripped,
as if one of the end ones in particular is stripped the carriage will flex up under the load of opening the
valve, and 'clack' back onto the head when the load is released.
L #3430 I had resigned myself to the fact that I would have to take off the head and stripdown
the head and fit new valve guides to stop my 1957 Venom from smoking during running. This would
mean missing some outings in the spring sunshine. Following advice from a friend I checked the drain
tubes linking the rocker box to the push rod tube. First I found the exhaust rocker box full of oil and
then I found some very small pieces of debris (possible gasket sealer) in the pipe work. Five minutes
later the pipes were certified clean and after re-assembly - no smoke at all from the exhaust.
#3435 I found a similar problem with my 55 MAC it had oil residue around the barrel in the head
gasket vicinity I had noticed this when I bought it and thought it to be a possible leaky head gasket,I
decided when buying it a good check over off all adjustments would be a good idea my friend lent me
a manual and some advice ,we noticed that when we were checking the tappets the rocker block had
no gaskets and the wells underneath were full of oil I got gaskets from Nick Payton and since they
have been fitted and the engine cleaned to oil deposit around the cylinder head has not returned.
L #3535 Hi, Which sealant is best with the VSL rocker box gasket ? Light compound I use so far
is efficient, but this greyish stuff of the gasket takes hours to be rubbed off from the box and head. I
wonder if polymer compounds like loctite or 3 bonds used for timing chest are suitable.
#3536 Try a tube of Yamabond. It's made for just this sort of application.
#3538 I use the sticky grey stuff (Permatex Ultra Grey in the US) on the bottom side of the gasket and
peelable silicone seal Permatex High Temperature orange stuff) on the top. This allows me to reuse
the gasket since it stays stuck to the head while the rocker box will easily lift off. Clean it off with
acetone or methyl ethyl ketone (MEK), reapply the silicone seal, let it set overnight, and Bob's your
uncle. I easily clean off the sticky grey stuff with the acetone or MEK.
#3541 I have raced an MOV (alloy MAC head) for 7 years and KTT Mkviii for 4 and used no paper
gaskets anywhere. I used mainly Permatex Ultra blue 77B . Tappet covers were regularly removed
and replaced with no subsequent leakage. Good idea to smear on one side only, remove after 24
hours and carefully remove any inside overflow. Threebond 1211 is a good Japanese product too but
2 ½ times the price of the "blue". (retired from racing in 2002 but restoring Mk1 KTT NO 96). noted
previous discussions re oil, Castrol R SYNTHETIC was best, stopped cam and follower trouble on
high revving MOV. Plus advantage of several meetings use against regular disposal of "R"
(vegetable.)
#3546 I use a smear of copperease high temp grease on both sides of the re-inforced rocker gasket
on my Viper. It doesn't leak despite being removed 4 or 5 times recently (thats another story)
#3553 Dodkin and Seymour recommended Green Hermatite on the rocker box - horrible stuff, but it
works. By the way research and personal experience leads me to recommend Blue Hylomar on ali to
ali surfaces, Welseal on most gasketed surfaces. Grease on the gearbox chain case gasket, Silicone
ONLY on exhaust flange to pipe and with care on rigid pushrod cups rocker box joints.
#3557 The service manual says, for the rocker box gasket, "Fit a new gasket; sticking this to the
rocket box with a light smear of grease, or Gasket Goo jointing compound."
52

L #3663Does anyone have dimensions of original MK1 valves. In particular the stem length. My
Mk1 valve seats have been cut down so low into the head over the years that we are uncertain how to
set the inserts close to original. If the present valves were fitted with new inserts we would have no
hope of achieving correct tappet clearance even with valve stem caps fitted. The head is in Melbourne
and I have not had a report yet if there is enough "meat" left to retain inserts. The seats may have to
be restored by welding which I believe is a very tricky technical job. There is an old timer in Melbourne
who no longer works. He used to build a coke fire and set the cast iron heads in the fire , heat the
head, and then gas weld the seats while still sitting in the coke fire. Unfortunately these old craftsmen
are a dying race. ( I refer to Melbourne as I live in Shepparton 112 miles North of Melbourne). Any
advice of previous experience with this problem would be appreciated..
#3666 I have just had a rummage in the attic and found 3 old valves, 1 inlet and 2 exhaust. They all
measure around 3.64 inches (3 41/64") I hope this helps.
L #3672 There is a 1 1/2" long steel exhaust pipe pressed into the head. Mine does not quite
bottom against the head, it leaves about a 3/32" gap with almost an inch protruding. I heated the head
up in the oven at 300F for an hour and whacked the pipe but it didn't budge. Should I do something
about it or let it be? The head is stripped except for valve guides, seats, and carburetor studs. I don't
know if the pipe has moved during use.
#3674 My Venom exhaust stub is similar to yours Mark, except the gap is more than 1/8". When fitting
new guides I thought to use the oven opportunity to shift the stub further in - no chance! I reckon that
it's been like that for most of its life and it hasn't moved in the 12,000 miles I have ridden so I just
forgot about it (until I read your e-mail). A regular Velo jumbler, don't know his name, once told me
that running a bead of MIG weld around the outside of the stub heats the alloy around it sufficiently for
the stub to almost "drop out". Only worth a try if your stub is so corroded that you really have to fit a
new one.
#3675 And when you fit your new one, do the "Thruxton mod" of drilling and tapping a hole up through
the bottom of the head and Loctiting a cap head screw in place to ensure it doesn't loosen again, as
sure as eggs is eggs, it will!
#3677 I appreciate the responses. The stub is in good condition so seems like I should put a holding
screw in now.
#3680 I recently replaced the exhaust outlet stub on a Viper head, because it had corroded to the
point where it was impossible to tighten the pipe onto it. It had moved out about 1/8" when I first
noticed it about 30 years ago, and had moved no further in probably 100,000 miles of severe
thrashing. I had one hell of a job removing it, and ended up cutting 2 grooves about 1/8" apart almost
through to the ally, chiseled this strip out the squeezed the remainder to remove it. If you are not
going to replace it, I would not bother with the locating screw, as it won't move on its own. I am certain
any movement only occurs when the metal is new, bright and shiny!
#3681 I removed a stub a while back by arc welding a spiral on the inside. I intended welding a thick
washer inside to get something to hit but this was not necessary as it "let go" while cooling. The
principal is that while the weld cools, the outside diameter of the stub shrinks. The same principal
works for bearing outer tracks. Remember the words of wisdom from Jean-Michel:- "You know it is
going to finish with the hammer, so hit it before you lose your temper."
#3682 I replaced mine for the very same reason, and using the same method. Mine too had moved
out by about 3/16", but was as solid as a rock. The replacement however continually came loose until
I coated it with a liberal amount of Loctite and fitted the retaining screw. It has never come loose
since! It does make me wonder though, If so many stubs are in the same position, with a gap behind
53

ut solid in the head, if this was in fact how they left the factory?
L #3683 I recently tried to have an exhaust guide replaced. The machinist told me the new
replacement guide would be too loose in the head. It was decided to replace the guide with a steel
one made with a bronze sleeve put in by the machinist (machining a guide from another application
was abandoned after the parts supplier could not provide a similar guide to machine). Is this fix
acceptable. Should this have been tackled in another way. Would the steel pressed into the head
rather than bronze be a problem?
#3684 Your local friendly Velo parts dealer should have guides in oversizes.
#3685 You may have a problem with different rates of expansion, as the alloy head will open up the
hole at about twice the rate that the steel will expand, while bronze guides have about the same rate
of expansion as the head. Increasing the problem, the Velo head is not very thick at that point,
resulting in poorer support for the guide than some others. The Norton Commando 750 used cast iron
guides in some engines and they were well known for not staying tight. Norton solved that problem in
the 850 by increasing the OD of the guide quite substantially. If it were mine, I would see if a good
Velo shop like Dave Smith (in the USA), or Grove Classics (in the UK) could supply an oversized
guide, and if not, I would have one made up in bronze. A relatively new hard bronze material known
as ColSiBro is reputed to last well in that use. Those heads are too expensive to fool around with.
L #3759 I have decided that after some 20 years of neglect to attend to the total lack of
compression and performance of my Venom. Rebore now done, but valves, seats and guides in bad
way. The seats I can get recut, and I have got new valves (bought new over 20 years ago) that are
marked V111 (inlet) and V112 (exhaust). Obviously lead-free was not an issue then, can anyone tell
me if these are OK to use or should I bite the bullet and buy some more? If so which? Also the VOC
have various guides on offer. Should I go for the Colsibro ones? The old exhaust valve is marked
N80, but by the look of it is where most of the compression was lost.
#3760 The inlet valve will probably be ok. the exhaust valve- N80 - was a nimonic one, Velo original
spec. Modern valve will be 21/4NS, maybe two part. The valve guides in Colisbro are excellent.
L #3782 I rebuilt my Venom engine in 1995 last time, and only had small jobs done since. It
works fine. So I decided to lift the head for a check and decoke, what I did last night. At first sight,
everything was nice. But when I cleaned the valves, the inlet one showed heavy hammering on the
circumference, on about 300/. The impacts seems to be radial on the valve head. The piston cleaning
is not completed yet, but it doesn't show any particular marks so far. There are three possibilities I can
consider: The valve was hit by the piston, a foreign matter, or the exhaust valve. The head shows
some pits under the plughole (not close to the valve) which where there for years if I remember well.
Assuming the piston will not show heavy marks when bright clean, I do not think the valve hit the
piston nor a foreign matter, which would have damaged the much softer alloy. So could it be a valve
interference ? Camshaft is a M17/8. Could weak valve springs have caused valve bounce (they are
original '57)? I usually drive to 5000-5500 rpm, and rarely to 6000+, but it sometimes go. May be last
time was too much.
#3783 I've seen valves that were hit by the piston or by the other valve, and the cause was obvious in
each case, the piston showing clear markings or the other valve showing markings or bent stems. In
either case, the inlet valve would not show markings around it's circumference as it does not rotate.
Foreign matter damage would show up across the combustion chamber, not just the valve edges. The
thing that makes the most sense to me is leakage around the valve, so I would turn the head over and
fill the chamber with petrol to check for leakage. Hairpin valve springs do not have a long life and
cannot be successfully adjusted for their weakening condition. They are difficult to test for strength
and will allow valve bounce when weak. The clearance measurement recommended in the manual is
54

for new springs and entirely avoids any consideration of weakness. I ALWAYS convert to coil springs
which can be easily assessed for strength or weakness. Do NOT use aluminium collars, as the
standard collets will pull through. I use collars machined from titanium bar or steel. I've usually used
springs for the BSA B50 (same as late Gold Star) which will give a seat pressure of about 100# and a
fully open pressure of about 220-230# when correctly shimmed. These numbers seem to work well
with a M17/8 cam. The last coil spring conversion that I made used a set of springs made by
Kibblewhite www.blackdiamondvalves.com/ to fit Triumph T140 which allowed slightly higher seat
pressure, but I really didn't see any advantage over the B50 springs. When packing up the springs
you'll want to leave .060"-.100" clearance to coilbind in order to prevent rapid spring weakening in use.
Check the new springs for pressure using a pillar drill (drill press) and a bathroom scale in order to find
out the pressures at various compression measurements up to coilbind. After checking new springs to
coilbind, they will take an initial set slightly shorter and weaker than initially and will remain in that
condition until abused by heat or over revving. If using the B50 springs (BSA P/N 65-2494 & 65-2495),
you can avoid a lot of work by simply packing them up to the above recommended clearance to
coilbind, tested by levering the springs to coilbind, using the rockers as levers after a trial assembly of
the engine. Be sure to include a heat insulating washer under the exhaust spring seat to prevent early
weakening of the spring
#3785 The valve timing is correct, although not perfectly on the spot, few degrees out. I really think
there were some impacts, as ridges can be seen on the valve edge. But no marks on the ex valve or
elsewhere. Still puzzled ! Suspecting weak springs, I will consider renewing them. As they are a nice
original Velo feature, I would prefer to stick to hairpin ones (they usually work, don't they ?), but will
consider coil ones if there is a real benefit.
#3786 I have 'dinged' an inlet valve like this in a VM. It leaves no mark on the exhaust valve.
#3793 Closer exam (with a magnifying glass) shows tiny but undoubtful marking on the ex valve.
What surprises me is how small it is, versus inlet valve badly damaged. Inlet is marked M2/7, ex.
M2/17N80. Could Nimonic valve be so much harder than inlet material? So, or the springs are too
weak, or the chronometric tacho pessimistic and I over revved, or both.
#3801 All you ever want to know about valves can be found here
www.gsvalves.co.uk/technical_information.htm (download the pdf). G&S have manufactured valves
since the 40's, they manufacture valves for the VOC, Grove et al. The guys there are really helpful,
and rather than telling me to "go away" when I stretched and tuliped a valve that may not even be of
their manufacture, they were really interested and wanted to help. Regarding Aluminium valve caps,
most of the UK Velo racers use Nick Payton valve caps and springs and as yet I know of no one who
has had a failure. PS Nick springs are of Porsche origin. You need to set the installed lengths to 1.310
exhaust, 1.340 inlet. On a Venom or Viper this will probably require machining a counter bore in the
head and lining it with a shim to set the length and avoid hammering the Ali.
#3784 Just a small point re rotating valves. Veloce designed the collar arrangement to allow the
valves to rotate and thus even out wear etc. It is possible that the inlet valve can be struck by the
exhaust valve with some enthusiastic over-revving. If the springs are tired this happens more easily.
Also, is the valve timing correct?
#3787 Well, Velocette may have said that the design would allow the valves to rotate, but that doesn't
mean that the valves actually did. A careful examination of the striking points on the ends of my
extensive collection of used valves shows line contact from the rocker on most of them. And the ones
that do show wear all around on the striking point would do so after removal (to reseat) and
reinstallation. While it's true that the valve and collar assembly is not prevented from rotating, the only
way that they could rotate is if the spring pressure was released during operation, like during valve
float, eh? Even then, they would have to have something to cause them to start twirling in the guide,
55

wouldn't they? And what would that be? No, it looks like a propitious sales gimmick to me. " By golly,
the way those collars are designed would allow rotation, no? Well let's advertise it as a benefit, then"
#3794 Do you have / can you share any more details on HOW to make a coil spring conversion or
point me / us towards a source.
#3795 The easiest way is to contact Nick Payton on 0208 540 2118 and ask him.
#3884 I copied a Webco (US) alu alloy coil spring conversion in titanium, using B50 BSA (Goldstar)
springs. The Webco conversion of top and bottom spring seats retained by the Velo split collets were
known to fail due to the shallow wedge angle of the Velo collets pulling through the soft alloy collars.
Absent a Webco kit to copy in titanium, you'll have to get a set of the springs that you want to use and
define the configuration of the necessary collars, turn them up and install. Or buy a set that I'm told
that Nick Payton offers in England. The critical points are that the springs are compressed to within
.060"-.100" of coilbind at full lift (max. Tighter will lead to failure) and the seat pressure should be in
the area of 80-100#, with 220-240# at full lift. You can check these numbers on a bathroom scale
under a pillar drill. After making the titanium spring seats (collars), shim under the bottom one to get
the installed height correct and use a phenolic insulating washer under the exhaust spring seat in
order to prevent heat damage to the spring.
L #3897 Members may know from previous requests for help that I am putting a MKII KSS
engine in a Viper spring frame. I have to make a new head steady for the KSS in the spring frame as
the frame lug is further back. The old steady of tube with flattened ends has one hole elongated. Was
that to allow for variability in manufacture or for the engine to move?
#3899 Make your head steady to fit with round holes. The idea is to hold the top end still, not let it
shake about. I have a KSS / RS hybrid and I love it.
L #3922 I have recently purchased my first Cammy(1938 KSS) and everything seems ok except
the bevels are whining. Any helpful hints on how to or where to get advise or technical information on
setting them up correctly? Any help much appreciated!!
#3933 One can pretty much assume that the bevels have done a lot of hours in their life, possibly,
(probably ?) in a state of incorrect mesh adjustment, so the whining may be no more that the
anguished cry of badly worn or incorrectly meshed bevels, or possibly they are in fact meshed too
tightly. Back in the old days when everything was new it was possible to reduce the noise, (by correct
adjustment) to an almost unnoticeable 'purr', but as the years rolled on, - a bit of 'whine' became the
norm, despite care taken in setting everything up correctly. Basic set up is still just that ! the bevels
should mesh completely with each other, that is, the outside & inside ends of the teeth should be flush
with each other when fully assembled. This normally accomplished by shimming the main bearing
bodies correctly, & at the same time ensuring that the bevels have only the minimum amount of
clearance, & are certainly not 'binding' Fanatical attention to the meshing, (too close) can result in
damage to the bevels, but over the years it is more likely that the teeth have suffered from being just
plain out of adjustment, & the resultant incorrect wearing pattern on the teeth ensuring that even
though correctly set up, there will still be noise. However, I have found that with care in setting up, the
noise (whine ?) can be kept at quite acceptable levels. The fact is that your noise could easily be from
worn bevels, but first, mesh & backlash can be checked by a visual inspection, - removing the plug
(early cammies), or cover from the top bevel case, & also remove the magneto drive. With the motor
on TDC firing stroke & no pressure on the cam train a rough idea of the meshing can be seen or felt
with a bit of fiddling, it will certainly be pretty obvious if the meshing is too wide, & with a bit of close
observation, possibly see if the teeth of the bevels are out of whack with each other. Apart from this,
only correct adjustment can be carried out, & hope that the bevels are not too badly worn from long
term mal-adjustment. I have to say, that unless you are completely conversant with the requirements
56

of meshing bevels correctly, you will have to turn to someone who IS !. You have to also consider that
the motor may have been assembled with the crankshaft incorrectly positioned endwise, or maybe the
cam shaft has the same problem. The vertical shaft 'end' float has to be checked, there is always the
chance that fiddling with compression plates etc. has caused pressure to be placed on the bevels -
really - everything has to be fully checked to ensure that all is as it should be ! At this point I have to
point out that long ago I did away with gaskets, (paper & otherwise) for the bevel housings. Oil
tightness is taken care of by 'O' rings placed in the 'corner' of the joint, & the adjustment is done
simply by using appropriate metal shimming, without the problem of sealing the housing joints, the
faces of which in a lot of cases has been butchered & scarred over the years by ham fisted
mechanics. If this damage is bad, I machine the contact faces by a small amount just to give a true
surface, & also the thrust face of the vertical bushes, to bring the vertical dimensions back to
standard. This may seem rough justice, but carried out properly, is a simple cure for years of bad
maintenance. Surprisingly, the original methods of manufacturing the bevels must have been of the
highest standards, & most bevels despite rough handed maintenance are usually still performing well.
- I for one have never had a bevel disaster, but there have been times when I assembled a motor &
took it out for a test ride, & returned home & decided that I had set the bevels just that tiny bit too
tight, & so dismantled & re-adjusted, it's all part of the OHC mystique ! A simple test to decide where
the noise is actually coming from, is to run the motor just above idling, & with a screwdriver handle
pressed into your ear, place the business end of the screwdriver on the bevel housings in turn. You
will probably be horrified at what you hear, but it can give you some idea of what is going on. This is of
course an old engineer's trick used on all sorts of engine noises.
#3935 I've recently meshed the bottom bevels on my 39 KSS project. Goodness knows when this
motor last ran but it must have been some "tens" of years ago and was inherited in an incomplete
state. Anyway, on meshing the gears I have made sure that the tops and bottoms of the teeth are in
line using a combination of shims at both crankshaft and bevel housing. I have found that there's a
"slack" point in the gears as I rotate the assembly despite the majority being seemingly nicely meshed
and no backlash. Checking the throw on the crankshaft end whilst assembled in the casings tells me
that it is a quarter thou out from perfect which should be fine. The problem seems to come from the
crankshaft bevel possibly worn and is reasonably slight. I've decided to continue, assemble and try the
motor as It is but it crossed my mind to make up a simple rig to "run in" worn bevels using an mildly
abrasive substance. I know that it goes totally against engineering ethics to carry out such a practice
and has the possibility of wrecking the tooth form but has anyone tried such a thing to "reclaim" worn
bevels?
L #4336 Hello folks. Kim's new 1930 KSS ran well on it's first outing this week, until things
started to break. After 140 miles, the exhaust rocker sheared off at the valve adjuster. Opening up
the cam box lid, I saw the ex. and intake cam followers had worn about .125" Removing the rockers, I
checked the camshaft, and each lobe had worn about .125" also. For those of you using metric
measurements, this translates to "way too much!" I haven't had time yet to tear apart the motor to
clean out the metal slivers, or to properly diagnose the problem. My guess so far is that the valve
springs may be too stiff. Possibly there wasn't enough oil to the cam, but it was wet with oil when the
cam box was opened up, and the parts had not turned blue due to overheating. I'm checking with the
previous owner/rebuilder to see if he has any thoughts on this. But I wanted to check with all of you
too. So I'm searching for the following: 1. data on valve springs - spring force at installed height, etc.
2. a replacement camshaft (possibly the KTT version) 3. a replacement exhaust rocker 4. exactly how
much oil should flow to the cam?
#4337 I too suffered from bad cam and follower wear on my KTP. I am no expert, but offer my four
pennorth for what it is worth. Any expert is welcome to correct me if I am wrong. With worn followers
the adjusters would be screwed through much further than normal, the valve moving in a straight line,
and the end of the adjuster moving in a curve, means that there is a skidding movement at the point
of contact, which is the force (with added leverage) that broke off the end of the rocker. Also I have
57

seen rockers that have been badly ground away to lighten them, In 1930 the camshaft was of a larger
base circle diameter than later models. This was reduced to reduce the surface speed of the cam past
the follower, and to reduce the wear you are now suffering. The cam follower skid inserts were
correspondingly longer. The oil gets into the cambox, via a groove cut ½ way through the bronze
bush, which lines up once a turn with a groove cut in the shaft to a point half way into the bush from
the other end. Disconnecting the drain pipe from the crankcase and running the engine will show the
rate of oilflow through the cambox. My KTP was producing about 1 drop a minute, despite winding the
oil pressure up to 16 PSI. ( recommended is 8 - 12 PSI ) My other Velos are not this oiltight anywhere!
I don't know what flow is recommended, but it must be a lot more than this. My Mk 2 KSS squirted oil
on the garage wall when I removed the drains from the head to check! I arranged 2 jets to feed oil
under pressure to the point where the cams and followers meet. I rode it to Stanford Hall, a round trip
of close to 300 miles, and for the first time, the valve clearance was unaltered when I got back. The oil
now leaking over the cylinder head is another matter, but I would rather that!
#4340 When replacing the bits in your cambox check: 1) There should be a groove in the large
bronze bush with a gap in it, this gap is opened by the flat on the camshaft once every revolution. I
add another half groove to admit a little more oil. 2) Check valve spring length & poundage. The MkI
springs are a little savage, I use a MkI outer and MkII inner to give everything an easier time. 3) Use
castor oil. Any mineral oil will result in knackered cams/skids. 4) Use a sensible cam a K17/5 will give
performance as good as any MkI type KTT. 5) If there is oil inside the cambox it will also show
outside! Hence no oil leaks = no oil. Pressure should be 10-12psi but this is at over 3000rpm and with
clean warm oil. If all is well inside pressure as low as 4psi can be OK. 6) Follow the above and you
should be able to ignore tappet clearances, my MkI goes for hundreds of miles without adjustment or
wear. 7) Another thought, carefully stone the skids to the cams to ensure full width bearing, use
marking blue to show the high spots; these will cause early wear.
#4338 I rode & raced only early cammy's for many years, & as I recall, even the heaps of wreckage
that I bought cheap because of oil starvation to the cam box never matched what you have described
? .125 inch is as you mentioned quite excessive. One thing that you don't mention, & that is that Kim's
jeans had not received a generous quantity of oil spots in 140 miles of riding ?, & this indicates that
maybe despite what you wrote, that there was little oil getting to the cam box internals ? My
experience with these machines is that if you have set the oil pressure to what the book says, & you
have actually checked with the engine running, that the top cam drive housing is in fact filled with oil
under pressure, there is a good chance that when you take your first ride, oil will in fact escape past
the oil sealing arrangements around the rocker pivot openings. & from here on it is a fine balancing
act to make sure that there is plenty of oil arriving at the cam/ follower sliding area, and the first line of
defense oil troughs inboard of the rocker pivots have a free flow path all the way down through the
drain tubes, - even then under normal running conditions, you could expect oil to get out of the cam
box, especially under extreme riding conditions, ( this assuming that the pressure was set as per the
book) . There is one point to make here, & that is that ' IF' the R/H side 'big bronze bush' has in fact
been replaced during the engine rebuild, & has been machined correctly, (?) is it in fact letting oil pass
through into the cam box ? . I have seen cases where a new bush has been fitted & holds the oil
pressure in the bevel chamber beautifully , but doesn't allow a metering of oil into the works
department, due in fact to some unthinking alterations in clearances (?) This situation is a virtual
impossibility as I remember, as the camshaft ( certainly on some models) has 2 precision ground
diameters the outer one being the greater, & this has to pass through the bush, for the bush to arrive
at it's correct position with the predetermined camshaft/bush clearance. Veloce played about with this
system a bit, with odd oilway metering tricks in the bush, but seizures at this spot were not unknown if
the owner/rider/ home mechanic, had reduced the oil pressure by fiddling with the regulating screw at
the rear of the bottom bevel housing, to the point where he no longer had the problem of oil leakage
from around the cam box, ( the worst case scenario starving the big end of oil also !). The point that I
am making is that such wear over such a short mileage would have to indicate oil starvation on a
grand scale at the cam followers. This despite the lack of blueing of the worn surfaces, - which had
58

already gone to the place in the sky anyway ! ? It doesn't take much oil to leave a 'film' over the
working parts. There is also the fact that the rocker arm lost it's business end, - I have heard of this
happening but never experienced it. I bought one 'bargain' with a split cam box housing due to
complete seizure of the camshaft to the bushing due to a complete lack of oil. It would seem that the
rocker arm failure may have been the result of a long fractured part, rather than too high valve spring
pressures. One would have expected this to happen shortly after start up, certainly not after the valve
clearances had opened up due to the wear. ( .125 plus .125 equals .250 that is a quarter of an inch
!!!!) That would have reduced spring & valve movement to Zero ! Sure check up on your valve spring
pressure, but have along searching look at quite a few other things. If of course the rocker had failed
at start up, take note that there is a slim chance that the valve springs may be so far from the correct
spec. that something 'bottomed out' at start up, & bent the rocker, & started the fracture. One thing
puzzles me, If the rocker sheared at the adjuster, why didn't it just fly off into the bushes, it would
appear that the breakage must have been further in, & even then I still cannot figure out how the
cambox cover plate would have been destroyed ? One last thought, - have the cams been replaced
with something with 'higher lift' without checking for possible complications ? I would certainly check
everything closely, I cannot logically explain the rocker failure at 140 miles but lack of oil has to be the
reason for the rapid wear.
L #4378 I was hoping someone out there had an excellent solution for sealing the bottom of inlet
and exhaust Valve cups on iron pushrod Velo Engines. Specifically my problem is a '38 MSS but
they're the same for all. Got to stem the flow for the Velo Rally at end of month. Any tips, materials,
recommended goo's appreciated.
#4379 I noticed in the "little red book of Velocette repair" (I apologize for not remembering the author's
name off the top) specific mention of this point. He offers several comments in this regard. I don't
have it by my side at this instant, but if memory serves, he states the following: 1) the cups
themselves can become distorted, and I believe his recommendation is to replace them. 2) he also
addresses the washers that are located between the cups and the valve guides that effectively pin
them in place. It is noted that these washers were redesigned at some stage, in such a fashion that
they establish a more effective seal. Again, he recommends replacing them when refurbishing the
cylinder head assembly.
#4397 As Burgess's book explains the valve spring cup was modified to improve sealing. One type
has an indent the shape of the gasket washer, the other type has a simple chamfer, unfortunately I do
not know which one of the two is the improved type. To seal the cup I use the standard fibre
washer/gasket smeared with silicone - similar with the joint on the top where the two halves of the
rocker box grip the valve spring cup, but only use silicone on the part of the joint that grips the cup (
the actual rocker box cover to rocker box joint I use hylomar) This seams to work quite well.
#4380 On my mac I get almost no leakage ( or it burns off before I notice ). I use the two fiber washers
listed ( m224/2 4 of them ) and blue hollimer ( sp ). seems to do the trick.
L #4572 I have a problem(again!)with my 36 rigid mac, this time it’s the head gasket I cannot
seem to get a good seal between head and barrel, when I first got it leaked and it had no gasket at all,
according to the spare parts list this particular replacement barrel should have one so I fitted one, still
leaked! tightened the head bolts up a bit more very gradually and you can guess the rest snap!
managed to break a bolt, the questions I am asking are can I get the barrel and head reground
flat?,could the problem be that it’s a replacement barrel but not head? are the any torque settings for
the head bolts? or have 68year old bolts just weakened with age and should I replace them all?
#4573 You don’t mention annealing the new ( or old ) head gaskets. Have you done that ? Makes a
big difference to sealing the joint.
59

#4574 Iid heat up the gasket before refitting it, not sure how hot I should have got it though.
#4575 I am a bit worried where you mention regrinding head and barrel flat. The head at least would
need to be turned, if anything. The barrel spigots into the head by approx 3/16", and the head gasket
is a copper ring about 3/16 wide that fits snugly into the head, on top of the barrel spigot. There
should be a small gap between the bottom face of the head and the top of the barrel, round the
spigot. If not you will need to turn back the top of the barrel a little to make the spigot longer. This will
raise the compression ratio a little, but will not be a problem as the MAC was made to run on 68
octane and can be raised quite a bit with advantage ( I took 1/4" off the barrel (at the bottom) and it
goes like heck!). I am not certain what torque to tighten bolts to, I would guess around 20 ft/lb. If you
sheared a bolt that was too tight and you were lucky not to have pulled a base stud from the
crankcase. Good luck. I think the MAC one of the most under-estimated Velos. By the way, anneal
copper by quenching in water when red hot. This is opposite to what happens with steel!
#4576 f you are concerned about having a pit or something that is causing a compression leak or if
the two faces do not mate correctly ( even with the gasket ) you can lap the two together with valve
grinding paste, my old ariel has a head that is spec to run with no gasket and that is how they tell you
to do it in the service sheet, it sealed very well but next time I had it ( the barrel) in for some work I had
the machinist let in a copper o ring into the top of the barrel, that did the trick but you still have to
make sure that the surfaces are pretty close. BTW it is also will raise the compression a little which is
good, unless you already have heat problems.... then it is bad, if you are worried you can fit a shim at
the bottom of the barrel.
#4618 On further investigation of the head joint leak on my mac I found that the sealing surfaces that
the head gasket seals against do not meet so by tightening down the head the outer flanges between
barrel and head meet first so there is no proper seal for the combustion chamber ( hope this makes
sense!) can I try a thicker gasket or two thin ones?
#4620 I would probably try two head gaskets for a fix until I had the cylinder off for some work, then I
would turn it down for clearance. If someone asked my advice on the matter I would tell them to see
someone about turning the cylinder to insure clearance. If your bike would be happy with two head
gaskets and you get no leak then bobs your uncle ( at least until you can make a proper fix).
#4582 Hi all, well known to some Velo owners, but not common knowledge, the fact that the early
cammies had a foolproof arrangement similar to Ariel system mentioned. The early cammies have 2
joint faces, the actual head to barrel mechanical surface, (outer & lower) & the separate inner sealing
surface. The procedure is to lap the mechanical surface with coarse grinding paste, then the upper
sealing surface with very fine paste. You check your progress until you have a perfect sealing surface,
checked with bearing 'blue' or fine chalk marks, then once again a final grind on the mechanical
surface with the coarse paste. (thoroughly clean then of course !) This system was pure Veloce
design, & properly carried out was perfect, having a full mechanical surface, & when this was pulled
down hard, you had the minute difference between the 2 different grinding pastes giving a perfect
pressure on the seal area with the head pulled hard down. Never ever had a problem if it was done
properly, but usually the first job that you had to do when you bought a second hand bike ! The
crankshaft drive was also by a lapped taper, & worked well, but there were cases when a backfire
may just 'crack' the joint. ( or it wasn't fully tightened) & that old shock absorber would wind off in a
flash, & apparently go through the early cast ally cases, later it could sometimes damage the sheet
steel primary case. I never had this happen, but I did have the taper just let go a couple of times when
I first bought a KSS (second or third ? hand ). Lapping with very fine abrasive powder & oil, &
checking with 'blue', & it never happened again. I am not sure about this, but I think Veloce may have
modified the taper angle a little to stop this occurring, possibly before full production began, but it
could still let go, usually at the worst possible time!
60

#4594 That other old Oz chap used the same head grinding system on his Vincent design. It does do
a good job but it does mean the barrel has to be off the bike and you have to be fastidious in
removing the grinding paste as it gets everywhere.
L #4676 I am a new member, returning to the fold after a break of 15 years, having bought a '60
Venom back in March which is in very nice condition.(I previously had a viper clubman which I used
day-in day- out for nearly 15 years and rebuilt twice having covered in excess of 100,000 miles.) After
7 months of relatively problem free, enjoyable riding and winter being upon us, I have decided to sort
out a few niggles, mainly oil leakage. The oil loss must be about 1 pint per 200 miles which mostly
ends up on the rear tyre. There is no evidence of loss from one particular gasket or seal the oil
appears to be seeping from various places mainly from the timing case cover (seepage all around the
gasket.) and running down the barrel/head retaining studs. Also the oil in the tank became black very
quickly after topping up the level. The seepage also was more evident when running the bike at high
speeds for long periods, therefore I assumed that the timing chest and rocker box was getting
over-pressurized and thought about fitting a crankcase breather. I have now stripped the top end and
have found that the exhaust valve guide is badly worn and I suspect the wear is due to the valve
guide not being fitted correctly i.e. the guide not being concentric with the valve seat, as the wear is
only on one side. Obviously the guide needs replacing and possibly the seat cut to suit. As I have not
done this before could anybody tell me if it is an easy operation? and are any special tools required?
(The Red Book simply says "Heat the head to 100 DegC and press the guide out"!) and if not, can
anybody recommend a specialist, preferably in the north west (UK) who could do this.
#4677 I use Martin Adams who is located in Brighouse between Wakefield and Halifax just off the
M62 Get the parts from the club take them to Martin who will do an excellent job. He always has for
me. If it needs seats which after considerable mileage it most likely will he will fit these as well. His
phone is 01484 715288
#4685 Try Nick Payton, one of the best Velo men around and fair prices too. I would be worried going
to an unknown cylinder head shop, first would they be able to source the valve guides and second
they have to be installed to a set length, I'd be happier with a Velo man set up and used to working on
our precious metal.
#4686 The Cylinder Head Shop NE Lincolnshire is probably the best known and most famous one in
the world. Heads are sent to him from all over the world and it is surprising how many Veloettes he
does particularly for the USA. He will also do your Tiger Moth engine or your racing engine. We paid
about £140.00 some four years ago for: - Inlet valve re-cut. New exhaust valve. Seats re-cut with
multi-angles. Valve guides resleeved with a corrugated liner (to retain the oil) allowing the inlet valve
to run at 0.001” and the exhaust at 0.0015” The man is a genius in his field.
#4698 I have recently replaced valve guides on a venom and viper head. It was a straightforward job
and successful. Follow the instructions in the book and you won't go far wrong. However before you
start have made up a pair of mild steel drifts for the purpose. The drifts need to be about 12 inches
long with an outside diameter of one sixtenth of an inch less than the outside diameter of the guide
and turned down at one end for a length of about one inch to the inside diameter of the guide less
about 10 thou of inch for a light easy sliding fit. I placed the head in the kitchen oven at 150 degrees
for half an hour ( make sure it is absolutely clean with no oily traces - wash with Gunk or similar and
rinse with lots of fresh water or your significant other will never forgive you). Take immediately to the
bench and have a pal hold the head steady and you'll find a few sharp blows on the drifts with a good
size hammer will take the guides out easily (don't pussy foot around at this stage as the head will be
rapidly cooling). To fit guides follow same procedure but also place guides in freezer first for an hour
and I also rubbed a smear of light oil on them. As to how far to have the guides protruding into the
rocker cover area, I have had conflicting advice as to what is advised in the workshop manual.
However both heads had the old valve guides protruding about three eights of an inch into this area
61

and I set the new ones to the same height as there seemed to be plenty protruding into the
combustion chamber for support at this setting.
#4703 There has been some good advice posted concerning guide replacement, but I did want to
address your question of doing it yourself. The procedure itself is not terribly difficult. To me the issue
is that when the guide is badly worn, then the valve and seat mating surfaces will be in need of work
as well. The old workbooks recommended lapping the valve with a light grinding paste after guide
replacement, which might be ok if the guide was not badly worn...., but. With modern(ish) tools, this is
best accomplished by recutting the seat and valve using the new valve guide, using tools not usually
available in a home shop. The issue is getting a good mating surface to form both a good seal and
also allow transfer of heat away from the valve head to the valve seat. So while the guide replacement
is something you could do, recutting the seat and grinding the valve face to correct angles is not. That
is the reason I think most Veloists have the valve, seat and guide repaired by a machine shop.
#4693 I have changed valve guides in my 54 MAC with no problems. I have a shouldered punch
which knocked them out with no trouble. Valve seats I haven't recut before as I don't have the tools. If
you need new seats then you might as well have the whole job done in one go.
#4694 Replacing a valve guide is easy-peasy! You will need a suitable drift and also a gauge to know
when the new guide is in far enough. Heat the head - to 'spitting' heat i.e. when a ball of water will
bounce around on the head and no hotter. With the head on a solid location - I use a wooden board
on concrete floor - drift the guide down into the port (not the other way round as there will be some
carbon etc that will not be removed.) The new guide goes into the freezer for a while. The drift to fit
the replacement needs to go over the outside of the guide and preferably have a spigot inside to
locate nicely. Heat the head and again fit the guide from above- i.e. from the valve spring side. Tap it
in to the correct point 0.343" above the lower face. After this the valve seat needs to be re-cut using
the new guide as a reference. It's not too difficult and was a task that just about every owner would
have done up to a few years ago. Read the workshop manual first. And get a decent sized lump
hammer - makes the 'drifting' in & out so much easier!
#4720 Valve guide removal should always be done from the combustion chamber side. Ed G. has an
assortment of Venom cylinder heads that have been broken by attempting to drive a guide out
downward. The top of the guide is often deformed during installation and may not go through the bore
easily. I prefer to tap the top and install an old bolt; then after heating the head a long punch can be
used to push the guide out. This avoids damaging the guide bore in the head. Installation is helped if
you have the correct stepped drift, this is easily turned from a piece of brass. Drive the new guide in
from the top. The head must be hot (275 - 300 F.), the guide cold. MAC guides and VM/VR intakes
can be turned from Harley ones, they are readily available in many ODs, in .001" steps. I've used
bronze Ampco 45 guides for '84 - '99 Evo twins with success. They only need to be shortened a bit.
Having the correct OD can be important, a mate's Clubman once had its exhaust guide exit via the
fishtail - in pieces and in public.
#4704 The 'accepted' way to do the job these days is to have the seat re-cut. This can be done at
home. Use the right tooling & its easy. However, before we were all educated, the way it was done is
to fit the new guide & grind the valve in as normal. If the valve & seat make good contact you need go
no further. As the Velo guides are a simple and normally accurate concentric turning there is a very
good chance that the lapping in will be sufficient. That's the way it always has been done and I've
never had a bad experience. Why make work & expense?
#4708 Can any member recommend a source of 45deg Valve Seat Refacing Cutters (preferably
carbide tipped)? I have that many seats to cut (not all of them Velo) it would be worth the investment. I
can make my own mandrels and am willing to part with good money for the right tool but the
Sykes-Pickavant prices are simply frightening. It's especially galling to find out that S-P do not make
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the kit but import it from the USA - marked up by about 100%.
.
#4709 Buy a set of Neway cutters. They are well made, using indexable carbide cutters and make
sets and individual cutters for almost every possible situation. They are really nice to deal with. A set
for your head will include at least a 30 degree, 60 degree and a 45 degree cutter. The 30 and 60
degree cutters are required to get the seat width correct and in the correct location for your valve.
Cost is approx. $400.00 USD.
#4710 Replacing valve guides is straightforward - providing you feel confident! If you are a little timid,
you won't hit the drift hard enough and it will heat up and bind in the head - I know from experience. If
you have access to Fishtail 113, I would recommend you make yourself special drifts that
automatically set the correct length from the head. Seymour's used to put the head in the oven until
the temperature reached the point when you smeared hand soap on it went black (the soap that is).
Does anyone know what temperature that occurs at?
#4722 I tried it once on a Venom and the valves picked up in the new guides so I sent the head to
Geoff Dodkin. Worth checking diameters if you also are fitting new valves. re reseating Many years
ago I saw a rig consisting of a drill with a grinding wheel with pilot The wheel was dressed with a
diamond on the same rig to the correct angel before each head.
#4761 As far as I remember, temp of soap blackening is about 400/C, which is about the annealing
temp of usual aluminum-copper based alloys. It seems quite hot for guides replacement.
#4714 A more scientific approach to determine the temperature of the aluminum would be to use a
product called "Tempilac" which is a crayon that is rubbed onto the surface and which melts at a very
precise temperature, and is readily visible through a glass oven door without having to keep opening
the door to spit on the head. The product is available in a variety of temperature ranges so the melting
point can be precisely tailored to the application.
#4737 Thanks for the information about Tempilaq. For people in the UK I've found this site, but
haven't contacted them yet. www.waltersandwalters.co.uk/index.html
L #4730 could any one tell me how far it is possible to bore out a 350 mac 1960 approx. i.e. cc
and what they use piston and so on.
#4742 I wrote a detailed article for FTWest about our "BigMAC" conversion. We fitted a Triumph 650
piston, 71 mm gives 380 cc. 72 mm (391 cc) leaves 2mm at the (thinner) barrel skirt, but this is close
to the point where cracks can occur at the rod notches. Your later MAC barrel will have round notches
which resist cracking, but clean them up with a Dremel. If you are willing to resleeve, 73mm might be
safe. You'll have to make a special small end bush, as the pin is a bit bigger than the Velo one. And,
depending on the piston top shape, the barrel may be shortened to raise the compression ratio. I also
have a MAC barrel with a BSA B series piston fitted, but have no further information. This came from
the collection of Ed Arnold, once a well-known racer here in California. This is a well-traveled road,
and can make a MAC quite a bit quicker. How are your main bearings?
L #4828 Hello, A quick one - which way round should a split skirt piston be fitted? Split to rear or
front of cylinder? I think that the split should be to the non-thrust side of the cylinder i.e. The front. Am
I correct?
#4829 Correct, split to the front
63

B.4. Timing Gear and Pushrods -
L #79 One way is to run the engine at tick over, and slowly screw out the adjuster until you just
feel the cam follower and valve lift lever (on the engine) make contact. Keep your hand on the lever,
you will feel when it makes contact. Back it off two to two and a half turns and tighten the lock nut.
That should give you 80 to 100 thou clearance. Check that the valve lifter works OK
L #81 My 1960 Velocette Venom is fitted with both the 0.010" and the 0.031" compression
plates on the cylinder base. Prior to my recent engine overhaul the tappet adjustment has always
been at the end of the useful travel with the adjusters screwed right through the rockers so that there
is only just enough tappet left for the nut to be tightened on. I have just renewed the valves, guides
and springs and had the seats recut. Very little recutting was required and the seats are in good
condition, i.e. not recessed into the head. When I torque the barrel and head using the info on Dai's
database I now find there is no adjustment left on the rockers at all. Did Velocette just have one size
of pushrod for engines fitted with or without compression plates or was this considered unnecessary.
I could not find any data on the length of the pushrods to allow me to check that mine are standard. Is
this data available or does anyone have a solution. The rocker arms are not significantly worn. I can
always get longer pushrods made up but I would prefer to understand first of all why the problem
exists.
#82 I had a similar problem on the exhaust side of my Venom. On investigation I discovered that the
replacement Nimonic 80 valve was shorter than the original. This reduction in length was from the
collet groove the top of the valve. Apparently these were manufactured in this way to improve the
valve striking angle. The effect of recutting the valve seats, and settlement of the compression plates
will be positive regarding your adjustment problem. Remanufacturing push rods is not difficult. Use
0.325 inch 16 s.w.g. tube (I have the spec somewhere if you need it)for the pushrods, you may need
to ream the bore 0.250 to get the spigots to fit in the bore. I used high strength retainer as well as a
precaution. By the way there is a simple lever tool you can make to help you lift out and in pushrods
without removing the rocker box. Get a steel bar about 18 inches long and on one end drill to fix a bolt
about 3 to 4 inches long that will fit into the hollow rocker spindle. Then drill the bar and fix a shorter
bolt that will go under the rocker. You can then lever the rocker up and lift the pushrod up to get the
lower end out of the cam follower cup, so that you can slide it out of the push rod tube
#96 I actually managed to track some pushrods down that were 3mm longer than mine that were just
the right size. I am now able to adjust the tappets easily, with plenty of adjustment to spare.
Incidentally I tried two different Velocette parts suppliers and their push rods varied by 2mm
L #272 Help/advice required from any LE cognizants I have twice had teeth broken from the
camshaft gear of my 1956 Mk 2 LE. I could find no reason for the first breakage, except that the gear
appeared to have had a broken tooth repaired on some previous occasion and perhaps the repaired
tooth let go and the bits took out a few of its neighbours. I then replaced the gear with another which
appeared in very good condition, but which had come from an LE which had burnt. Within 50 miles,
two more teeth broke on this gear, one of which was in the same relative location as one of the first.
There is no evidence of any seizure of the camshaft or tappets or valves, the pinion looked in worn
but reasonable condition, valve springs not spring-bound, valve heads did not hit the heads. In the
second case, the two broken teeth were on opposite sides, i.e., 180/ apart, leading to my thinking
that the first broken tooth had jammed in the pinion and done one rev to hit the opposite tooth, just a
surmise. The teeth are broken at the point of the camshaft rotation where the exhaust valve is in the
fully open position. I am looking for a replacement set.
L #687 Has anybody gained experience aftermarket or self made camshafts for the ohv velos? I
know that the original cams were quite good (50 years ago) but I think knowledge has improved a lot
since then and I wonder if can increase the performance of my venom with a cam of a more "modern"
shape.
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#688 Wholeheartedly Agree. Dave Lindsley converted mine thus and, I think, even used the original
cam ring with a bit of deft grinding. Never gave a moments trouble since. I used to find that the fibre
gear would strip if you cogged down for a steep hill or to overtake. Sadly the bike is no longer in one
piece. Starting was vastly improved too.
#689 There is a gent in the midlands who will take your ATD unit, remove the fibre pinion and cast it
into the bin for you, then replace said item with a beautifully machined and lightened steel pinion
which will solve all the tooth shedding problems and still retain the advantages of an automatic timing
device. Drop me a mail and I'll put you on to him.
#692 That man is John Hales, who can be contacted on +44 (1509) 813507. His price now is around
£60.
L #1213 has anyone done any work on valve timing on a venom? If the cams won't match the
book timings, how far out can one be before the performance is impaired? Is it best for the inlet to be
correct and the exhaust out or vice-versa, or somewhere in between?
#1215 Regarding Velocette cam timings as the inlet and exhaust cam are one "blob" you can only
really set one cam event. Even then this is not strictly true as the cam is pressed into the camwheel,
each tooth representing 7.5 degrees of crankshaft movement you can get it to within 3 or 4 degrees.
The most important valve event is inlet valve closing (IVC), followed by EVO. So I suggest you set the
cam as close as possible to the book IVC mark. You can also of course advance or retard the cam 7.5
degrees. Advancing the cam you should get slightly better acceleration, by retarding the cam you
should get slightly better top speed. However as I am playing around with cams and cam followers on
my sprint bike, I have mapped ex-factory M17/2, M17/7 and two M17/8 cams, lining the cams up using
the etched timing marks. Guess what, they are all over the place! I will load up the excel spreadsheet
a little later.
#1217 Basically the intake valve closing event far surpasses any of the other three events. It
determines at what point in the cylinder compression begins. Early intake valve closing creates higher
compression at lower engine speed and increases mid range power. Later closing allows more air in
at high revs and increases top end, provided the rest of your engine is up to it. Intake valve closing
comes in second in importance. Exhaust events are a tradeoff between extra time to push on the
piston or increased scavenging, but again with one two lobe cam the intake closing is the one you
want right. So what is right? On my Venom engines with /8 cam I run the timing as advanced as
possible (more than stock). It can only be advances so far as the intake valve will hit the piston on
overlap. Gives great mid-range with no noticeable loss on top but a bit of pinking at low revs if
compression is too high or timing too advanced. On well breathing motors such as Thruxton I run the
cam about standard spec (get the intake closing at spec and forget the rest). Also and engine that
continues to pink at low and mid range regardless of timing, fuel , etc., can be compensated by
retarding the cam. With the Velo's fine pitched teeth the cam can generally be advanced or retarded
one tooth (8 degrees) without interference but ALWAYS check piston to valve clearance. This can
easily be done by screwing in the rocker adjusters until the valve hits the piston and calculating how
many turns from zero lash (one turn equals .040) . Don't run with less than .060.
L #1400 With the Velo starting technique the valve lifter enables the exhaust valve to be opened
to get the engine turned over its compression stroke ready for the big swing (also good for stopping
the engine and other maintenance tasks). As I remember there is a flat at the end of the lifter that sits
just below the valve lifter thingy (exhaust bottom rocker). When you pull the decompression lever, the
flat rotates to come into contact with the rocker and lifts the valve. On my machine the valve lifter has
to travel a little before it comes into contact with the lifter thingy so I would imagine that it wouldn't take
much wear before it has difficulty in lifting the exhaust rocker. I perhaps wouldn't look too much further
and I'm sure that you've tried adjusting the cable.
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#1401 On my 1960 Venom the cable did not lift the cam follower and hence exhaust valve enough;
not sufficient adjustment on the cable. I fitted an adjuster, from a bicycle I think Halfords, and that
enabled me to adjust so that it lifted the valve. The adjuster has a slot to pass over the cable so I put a
turn of fine wire round it. Make the adjustment with the timing cover off to see the effect. The
alternative is to move the nipple on the cable by using a soldering iron to melt the solder and pull the
cable further through the nipple. Mike
#1405 The valve lifter is supposed to just lift the valve off its seat enough to let the compressed air out
of the cylinder and allow you to set up a good swing during the start ritual. If you set it up to lift the
valve too much it could interfere with the valve getting back onto the seat during normal running. That
would make noise before you smelled it.
#1406 The valve lifter is also used to stop the engine.
L #1619 I'd like to add a few words regarding the replacement of the timing gear with a steel
item. Yes John Hales is the man to deal with but has been noted he does it in his spare time so hence
the delay. Also he has the means to replace Vincent, BSA etc with a steel item as I believe Velocette
were not the only other manufacturer to use Tufnol items. However John has never seen any other
than Velocette stripped of teeth perhaps due to the fineness of the teeth. Also the weight of the steel
can be made the same as the Tufnol item. Could the use of Tufnol perhaps have been used for
conductivity reasons?
#2628 First is it normal to be able to hand pull all the timing gears out of the case without any pullers
including the cam gear except of course for the mag gear? Is it possible to do valve timing any other
way than it says in the manual?
#2630 Yes the timing gears (except for the pinion on the crankpin!) are retained only by the steady
plate. And I will repeat the cam timing tip I got from an old Fishtail, thank you "Rastus":
At TDC on the "off" (non-compression) stroke the valves will have equal lift. Worked for Rastus,
worked for me. This seems obvious when you think about it. A /8 may have asymmetrical opening and
closing but the valves still must not hit the piston at TDC. Remember that each tooth on the camgear
equals 8 degrees of crankshaft rotation. Cam timing is not an exact science. Ignition timing is!
L #1631 One of my 'foot' of followers have a 1 1/8 inch radius another 1 inch but I suspect
someone grind one in order to copy thruxton? Because there are no mark of intake or exhaust( quite
looks professionally done) but surely someone used before ( I can see the mark where they rubbed on
cam) so may be I will wait and see how timing and lift change when I put the crank in. but it was taken
from engine means it dose more harm than benefit? By the way , does large radius mean less lift?
#1635 More radius gives exactly the same amount of lift. While the valve timing remains the same,
the amount of valve opening is increased and acceleration loads on the valve gear are reduced. The
best way to see this is by looking at the valve lift diagrams I posted in the files section of the site a few
months ago.
#1641 Thank you for cam data sheet very nice stuff. while I was watching the graph, I felt bit scared.
because if cam follower have more the radius, just before closing exhaust valve and opening inlet
valve have more the chance of hit together , piston might be there as well! valve angle change of
Thruxton should be come from this? Or because of it 2" inlet valve? some one experienced the
Thruxton followers in standard venom head with high compression? I would not think that changing
valve angle of my alloy head MAC is non starter as well as changing the kissing valve each time I did
over rev. If I made the lift and timing graph, do you think there are any way to assess the chance of
kissing valve or piston on the paper? not in reality. If I have time I could make the animation of what
happing in cylinder head. but I do not think it is less important as I can not consider the floating valve
66

y higher rev, etc.
#1649 Don't worry changing followers in itself will not make your valves tangle. Regarding, hitting the
piston if you use a HC piston always check clearance with Bluetac. Dave Child's who successfully hill
climbs and sprints a Viper, has been experimenting with Thruxton followers. On the track he can't see
or feel any difference, it may of course show up on the dyno. If you fit a M17/8 into a iron Velo, make
sure that the top rocker does not make contact with the rocker box, this can happen on both sides of
the rocker. You will need to carve some ally off the drive side to gain clearance and make up
pushrods of a calculated length to avoid contacting the timing side.
L #1656 After reassembling my venom engine, the exhaust valve tappet adjustment, at correct
clearance, is screwed to the absolute limit of its travel, leaving barely enough thread for the locknut.
It's as if the valve stem has been shortened, causing the rocker to lift away from the pushrod in the
valve closed position. I suspect this extreme adjustment may compromise the valve opening. I don't
remember it being like this when stripping it down. I've thought through some possible causes, like a
thicker rocker box gasket, but none seems to make the kind of difference I'm seeing. Any suggestions
- glaring mistakes are not unknown in my workshop.
#1658 Just a few thoughts/things to try/check: Did you renew anything other than gaskets ? Did you
forget top of pushrod ? - too obvious ? Did you use new pushrods ? new valves ? if so - check lengths
etc. Is ex valve seating properly ? - i.e. is valve really closed ? Is pushrod properly seating on cam
follower ? Is inlet ok ? Is r/box tightened down ok and evenly ? ditto head. Did you pick up the wrong
tappet from another engine !?! (I did this once........) have you got a washer stuck under the r/box
between it and the head so its not tightened down properly (I did this once too.....a long time ago I
must add ! ) Does engine turn over ok by hand ? - take the t/cover off and watch what happens if you
have not already done so. If nothing seems amiss I'd be inclined to take the r/box and head off and
check carefully again. Make sure valves/springs/collets/shims etc all correctly installed esp that valve
is seating correctly. If re-using pushrods - did you maybe swap pushrods so in is now ex and vice
versa ? Did you dismantle the r/box at all or install new or 2nd hand r/arms ? Hope this helps a little -
there isn’t that much to go wrong in this respect so you should find it quickly enough with systematic
checking.
#1662 I had a similar problem when I rebuilt my engine last year (see group message 96). In the end I
just got slightly bigger pushrods (try Nick Paynton or Grove).
#1666 Andrews just about covered all the variables, I've had a similar problem caused by an exhaust
valve where the distance above the grove was shorter than on a standard valve. A slightly longer
pushrod cured the problem. The only thing I would add is there is no need to strip the rocker box off to
get the pushrods out ( it takes ages to clean the Green Hermatite of the head and rocker box). Just
make up a F shaped lever out of 18 inches or so of flat bar with the top of the F a bolt about 4 inches
long that fits into the hollow of the rocker, and another shorter bolt that will just go under the tapered
end of the rocker. You can then lever the rocker up through the inspection cover and slip the pushrods
out of the cups. However taking the rocker box off may be easier!
#1667 Alternatively - to remove pushrods without removing rocker box - take t/cover off, then steady
plate, then loosen off tappets and fiddle the pushrods out at the bottom - bit of a nuisance if you have
to remove exhaust first though if you have the swept back type. Also a tiny bit more fiddly with one
piece Thruxton pushrods this way. Where do you get the green stuff? - I cant find a supply up here in
the frozen North (where everything is blue)
#1678 You can also get Green Hermatite by mail order direct from Hammerite
www.hammerite-automotive.com in the frozen North!
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L #1669 Anyone care to guess torque setting for installation of a fiber ATD?
#1674 Snug, yes - about 10 - 12ftlb should be enough, but please, no Loctite. Make sure the tapers
are in good condition and clean before you assemble the plot and it should stay tight until the next
time you need to do a rebuild. Loctite can find its way into all sort of places you don't want it, and if
you don't use the correct grade you may never get it apart again!
L #2050 I have approximately .008" end float on the idler pinion in the timing case of my Viper.
This should be .001". Has anyone had experience of shimming out this end float? If so which end of
the bush is the shim placed ?
#2053 Shimming is not the answer. The official Velocette line was to replace the PB bush and line
bore it, as a eight thou shim will probably wear and break up. Also due to the helical cut gears, the
thrust face on the idler wheel is on the inside. The thrust face on the cam is on the outside plate; his is
why the crank case aluminum does not wear, and when you time the cams with the steady plate off
the cam constantly tries to jump out of mesh. If you do shim it I would periodically keep an eye on the
state of the shim.
L #2399 There are a couple of ways to deal with the end thrust created by the angled teeth of
the timing gears. Either use a lipped roller arranged so that the end load comes up against the lip, or a
ball bearing on one side with the same arrangement. The pre '53 long stoke engines did not use
tapered bearings.
#2401 As Frank suggests, I have used lipped roller bearings and they are set up with .005 end float
which increases to .010 when running. Side thrust caused by the helical gears appears to cancel itself
out especially with using the lipped rollers.
L #2491 I would be grateful for some help too. My 1967 Venom just stripped its second fiber
gear this year. I had the magneto rebuilt by Warren Wheeler last fall and it appears to be working well.
The fiber gear drives the magneto and has a centrifugal advance mechanism integral with is (i.e..
riveted on the outside). At the end of a 1000 mile tour in June, the very fine teeth on the fiber gear
stripped, leaving me stranded. I obtained a reconditioned unit (the advance mechanism on a used
gear) from Dave Smith in July and bike ran fine until a couple of weeks ago when I was stranded
again. Some folks advise replacing the fiber gear with a metal one and some folks advise converting
to a manual advance as well. I would be grateful for some advice.
#2493 I had similar woes when I bought my Velo MAC a good few years ago. I went through a few
fibre wheels as you describe. In the end I had a new fibre wheel fitted by Roy Price (he advertises in
Old Bike Mart) and have had no problems since. I do, however, always carry a spare. Others have
had a metal wheel fitted in place of the fibre wheel. As a long term solution, this has to be the best
(other than going to manual ignition ). Can't remember who does this conversion off hand but
someone on the list will remember.
#2495 The guy's name is John Hales +44 (0)1509 813507
#2498 But be warned that John Hales can take a long time to get the job done. 6 to 8 weeks was the
quoted time for me, but it was over 6 months before I got the ATD back.
#2500 Dave Lindsley does magneto work and has 30 years experience. 4401706365838. He did an
auto to manual conversion for me in the 70s and a complete overhaul last year. I had the hot mag
problem but now a good spark and starting. He advertises in Old Bike Mart. Another name I have
been given is Ross Davies in Wellingboro 4401933279134. Mike Daly may do Al gears 44
01785822568. He makes a range of new parts, some in stainless, for Velos.
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L #2524 I replaced the fibre wheel this year on my Viper after it stripped and have done 3 or 4
hundred miles since. The wheel was supplied by Mike at Grove Classics but the steel rivets supplied
were too short to peen over, I used brass rod of the same diameter instead. Over the years I have had
2 or 3 fibre wheels strip on other bikes and I would like to understand the real purpose of these, and if
replacement with a steel/aluminum version would be harmful. Also why are non fibre wheels fitted to
manual advance magnetos?
#2525 the only reason I have come across is steel wheels tend to be for manual advance retard
therefore need to be stronger as mistakes are more likely but easier rectified whereas fibre wheels are
reliant on automation and less able to make quick adjustments in the event of advance retard failure
which would result in major serious engine damage, by the way how much did it cost I need anew
/spare as well ,I usually depend on auto jumbles but!!!
#2526 The cost was approximately £27 for the fibre wheel including rivets (but check these are long
enough). replacement wasn't difficult.
#2527 The right way to do a mag is for it to be manual advance/retard. However in the interests of
making machines easier to handle, auto advance was provided. However, the timing wheels are then
changed to a fibre (and there are differing types) to reduce noise. Fibre being what it is any play or
out-of-true shafts will begin to break it up and the rest you know! Personally I would not use a fibre
gear and hence every one of my Velos has had manual ignition. The debris spread around in the
motor, oil tank & oil pipes when one lets go is a blasted nuisance (I know from a mates machine which
firmly made my mind up many decades ago)
#2528 Fitting a steel wheel increase the weight of an ATD from 500gm to 680gm. As ATDs have a
habit of slipping / unscrewing themselves under severe engine braking / kickback (particularly on high
comp engines), the extra inertia may increase this tendency.
#2529 An advantage of the automatic advance not mentioned so far is a better spark for starting. The
manual advance retards and advances the contact breaker relative to the armature. The magnetic flux
when the points open and the resulting spark are strongest at full advance. At full retard, which is
otherwise a good idea for starting, the spark is weaker. The automatic advance retards and advances
the contact breaker AND the armature relative to the crankshaft. Magnetic flux and spark are always
at maximum and starting is easier.
L #2537 Is it actually OK to use (or is it possible to fit) a steel wheel on a Velo auto advance
mechanism and use as per normal. I agree with what has been said that any BSAs' I owned in the
past did not strip the teeth but were known to occasionally slip. Has anyone a sure fire method of
ensuring the ATD does not slip in service ?
#2538 Make sure the tapers are clean, dry and undamaged and tighten the centre bolt properly - mine
has NEVER come loose or slipped and I have ALWAYS been able to remove it when required. I use a
John Hales steel wheel on my ATD and don't believe there is any significant difference in weight
between this and a fibre wheel although I will admit to not having weighed it!
L #2596 Im rebuilding my '58 Venom and have a few questions. Is the cam spindle hardened?
Or is it just some piece of nickel or silver steel. The cam spindle is worn oval and I wondering if I can
put it on a lathe, take 0.1 mm of and turn a new bronze bushing
#2597 The cam spindle is made from EN32A, case hardened to a depth of 20 - 25 thou. If it's that
bad, I would buy a new one - Mike Fotherby and others sell them for GBP11.
L #2770 I was just wondering if anyone has had any experience with a two piece magneto gear?
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#2771 Are you referring to the Criterion two-piece set up? If so, I have them fitted to two of my
engines and they are extremely useful in setting the ignition timing. You can even leave the centre
part attached, when removing the mag from the case and therefore never have to worry about it
moving on the taper. Criterion (Engineers) Ltd. Greenoak, Bishopstone, Swindon, Wiltshire, SN6 8QA
(01793) 790219
#2776 I have been running a Criterion 2-piece kit for a while now when running with manual magneto
and find it excellent - helps save a lot of fiddling when it comes to mag timing etc. and has no
apparent tendency to slip/wear etc.
L #3418 Does anyone know where I might get a pair of cam followers for a Thruxton that I'm
rebuilding?
#3420 If you’re in the usa dave smith will regrind them. He`s doing a set for me right now not very
costly. His phone num. is 815-254-3998
#3466 Thanks for the contact. I phoned Dave Smith, Dave grinds the profiles on the inlet and exhaust
followers based on the same location of the centre (but a different radius, of course) and swears it's
OK. I spoke to Nick Payton today and he said that he's traced these out in the past and inlet and
exhaust profiles were machined on different centres. Maybe it's not too sensitive to that variable. The
other comment that Dave Smith made was that Venom followers in a Thruxton do not perform well.
#3469 I had venom cam followers in my endurance engine. I changed the top end to thruxton parts,
the timing for cam to valves didn’t seem right when I set it up and when I ran the engine you could tell
they were not right.
#3450 I've recently been in contact with a Velo specialist who has given his opinion that the lower
rocker skids were ground to the same distances from the pivot shaft and that the difference between
Thruxton and Venom rockers was only that the Thruxtons were ground to a larger radius for quicker
lift. This prompted me to prepare a profile comparison of the three types of lifters MAS 118 (MSS/VM),
MAS 118/2 (Thrx Exh) and MAS 118/3 (Thrx In) from lifters in my possession. An outline tracing with a
sharp pencil of these three types does show the differences among them with the difference between
Thruxton inlet and exhaust obvious to the eye. Inasmuch as the above evidence failed to persuade
him, I did a little research in the factory manual and spare parts catalogue and other published items.
In my reading of Velo information over the last 20 years, I've seen numerous references to the unique
Thruxton timing. Bertie Goodman was credited in a contemporary published article on the Thruxton
(which I remember, but cannot find) with the clever devising of the modified lifters so that they would
not have to create a new cam, but could continue to use the VM cam (lifted from the KTT MK VIII) with
the special lifters. If you'll take a look at page 13 in the blue parts book, pub. F.482/7R, dated 1 M
JULY 1981, you'll see that ref #42 shows P/N MAS 118 used on all models but Thruxton for both inlet
and exhaust, while P/N MAS 118/2 is used as the Thruxton exhaust and MAS 118/3 is used as the
Thruxton inlet. The assignment of different modification numbers indicates the difference in the parts.
Page 105 of the 'Red Book' factory service manual states under "Re-adjustment of Tappet
Clearances" that the lifters "are not interchangeable" and must be "replaced correctly" So if you are
buying new lifters for your Thruxton or especially if getting the old ones reground, you might want to
verify that they are ground on different centers. This is easily done by mounting them side by side on
a drill bit and comparing with the MK I eyeball. If they are the same, your Thruxton will be giving away
some horsepower. The inlet rocker is set nearer to the pivot shaft.
#3503 Anent the recent thread about Thruxton followers, and being blessed with possession of VMT
816RC, one of ten special Thruxton racing engines hand built for dealers by the factory, I decided to
assemble enough of it to check the valve timing. This engine was acquired by me in a disassembled
but unworn and otherwise unmolested condition. It was originally shipped to the shop of E A
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Lavington, a racing dealer and Technical Secretary of the UK club in the late 60s. The engine had
apparently been placed in a racer for a short period of time, as the clutch and gearbox have never
been used and there is no burned oil anywhere, the forged squish piston showing no heat under the
crown. I mounted the timing gear and valve train complete on a VM bottom end and used a 7" degree
wheel mounted on the LH end of the crankshaft, reading from a sharp sheet metal pointer affixed
between two cylinder fins and a dial gauge on top of a pushrod. I established TDC by use of the dial
gauge reading both sides of TDC equally and placing a pencil mark central between the two
aforementioned points on the degree wheel. The large wheel gives about .080" of circumference per
degree, so it's easy to be accurate. I double checked each valve event for accuracy, and here's what I
found: Inlet opens 45 ½ degrees BTC @ .053" clearance Inlet closes 60 degrees ABC @ .053"
clearance Exhaust opens 60 degrees BBC @ .052" clearance Exhaust closes 41 ½ degrees ATC @
.052" clearance. I read this as 87 degrees of valve overlap. It's actually a lot more due to the
excessive clearance for checking. Additionally, the Inlet Open event is advanced 4 ½ degrees and the
Exhaust Open event is advanced 2 ½ degrees from Venom timing. I then substituted a pair of
standard VM followers on the same setup for the following numbers: Inlet opens 41 degrees BTC @
.053" clearance Inlet closes 60 degrees ABC @ .053" clearance Exhaust opens 57 ½ degrees BBC @
.052" clearance Exhaust closes 40 ½ degrees ATC @ .052" clearance These numbers give 81 ½
degrees of overlap. My conclusions are that the VMT followers do have the skids ground with the
centers of the radii at different distances from the pivot in order to increase the overlap as well as to
advance the valve opening events.
#3515 Thanks for clarifying the matter of VMT cam followers...it needed recording. Your message
3503,in conjunction with Dai^s information message3480 will be of great help in upgrading
run-of-the-mill VMT towards "toolroom specials" provided to the selected few by the factory. My own
experience with VMT followers is as follows (1) I purchased a pair from Reg Orpin at Stevens before
VMT went on sale. These were faintly etched "in" and"ex" respectively, unfortunately they were
probably incorrectly marked. They were ground to a greater radius than VM followers, the hole pierced
in the web was smaller than the corresponding hole in my VM followers. Before fitting the Stevens
followers to my machine I ground and polished redundant metal from the parts only preserving the
portion that ran on the cam, it is difficult to estimate the radius of these followers in their present used
condition. I don^ think their presence made much difference to my sprint times. (2)Shortly after
Goodman took over Dodkins business I paid a visit and had a pair of Vm followers reground to "VMT
spec". Theses were reground to a greater radius but with no offset, swapping them over and
measuring valve events convinced me that although marked "in" and"ex" they were identical.
Reverting to case(1),these were sold with the warning NOT FOR USE WITH VM HEAD. The included
valve angle on a VM is 70 degrees. The included valve angle on a VMT is 67.5 degrees, the change
was made to accommodate the 2"inlet valve, the exhaust guide and seat being tipped sideways to
prevent valves kissing. Elsewhere Dai has mentioned slight variations in VMT valve stem dimensions
to"improve the striking angle".Further information on this topic would be useful. Goodman sold his
remaining "special squish engine",when I saw it stripped it had some special features... overhead
rockers solid spindles ,presumably for better torsional rigidity...cam follower and idler spindles reduced
in diameter to accept needle rollers, the thin spindles struck me as looking weak.
#3528 Quite a few late VM Club seem to have Thruxton followers fitted- retrofitted? I'm not convinced
that, in a Venom, this would be a good idea, not with a change in centres. Does anybody positively
know if the quick-lift type were ever fitted by Veloce, and if so, did they have the centres modified?
#3608 While I had VMT 816RC set up to check the cam timing, I decided to check a number of
additional points for future reference. I have an early 'Red Book' marked for VM 1248 that stipulated
that the timing figures be checked at .030" clearance, so I did that and then checked the valve timing
at .006" INT and .008" EXH. Then I wondered what the timing would look like with the early 3/8" radius
followers, so checked that setup at all three clearances as below: M17/8 cam with VM followers: Inlet
opens 41* BTC @ .053", 56* BTC @ .030", 53* ABC @ .006" Intake close 60* ABC @ 053", 71.5*
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ABC @.030", 33* BTC @ .006" Exh opens 57.5* BBC @ .052", 70* BBC @ .030", 46* ATC @ .008"
Exh close 40.5* ATC @ .052", 53* ATC @ .030", 55.5* BBC @ .008" M17/8 cam with M 9/3 3/8"
radius followers: Inlet opens 44* BTC @ .053", 62* BTC @ .030", 45* ABC @ .006" Inlet close 47.5*
ABC @ .053, 64.5* ABC @ .030", 40* BTC @ .006" Exh open 61* BBC @ .052", 77* BBC @ .030",
34* ATC @ .008" Exh close 28* ATC @ .052", 44.5* ATC @ .030", 65* BBC @ .008" The above
notes offer more questions than answers. The first that comes to mind is the different clearances for
timing between early and late workshop manuals. My guess is that the long ramps varied from cam to
cam due to inaccurate grinding, so the solution was to check at a point of greater lift in order to
achieve more uniform results. The second thing that struck me is that the valves don't spend much
time on their seats at running clearances, and therefore could be expected to run hot. Prolly the
reason for the change to Nimonic 80 material for the exhaust valve as well as the heavy 3/8" stem. I
have the idea that it might be interesting to do some mix and match with the followers, eg: A VM
follower on the inlet for long duration and a M 9/3 3/8" follower to shorten up the exhaust duration for
better torque curve. Other possibilities may occur to some of the heavy thinkers on the list.
L #3665 Somehow the notion of retarding the valve timing by one tooth can improve high speed
power output seems illogical ? As far as the inlet cam action is concerned it would seemingly give the
engine less opportunity to "breathe in" ? Flex in the valve train as mentioned by P.I. would only
compound this, wouldn't it ? Interestingly, I know someone who (intentionally) advanced his (Venom)
cam one tooth, and has been grinning from ear to ear ever since ! Anyone else tried this ? Can
anyone supply timing figures for the M17/6 cam by the way ?
#3667 Retarding the cam, thereby closing the intake valve later, allows more time for cylinder filling at
high rpm. Of the four valve events the closing of the intake valve is by far the most important. That
said, I generally run my Velo /8 cams advanced a tooth if I can get away with it. This closes the intake
valve sooner and allows for more compression at mid range rpms (the piston is traveling up on the
compression stroke when the intake valve closes) and a noticeable increase in mid range power. I
have never been able to detect any decrease in high speed power though theoretically it should be
there. Maybe I don't wind that high. If you are having that familiar 'it's just starting to come on the cam
when I hit red line' Velo phenomena though, you may want to try it. Two caveats: Advancing the cam
will decrease piston to valve clearance on the intake opening. You should have .060, I have run .040
without trouble. Stick some .060 solder in the spark plug hole (cold) towards the intake valve and turn
the engine over gently to squish it and see what you have. Second, the extra compression may cause
pinking in the mid range if you are close to it now.
L #3806 My Venom is down investigating engine noises. A new big end assembly is to be fitted
as there is a little clearance. On stripping I found that the axial clearance on the cam shaft gear assy
to be 8 thou and the idler shaft axial clearance to be 4 thou. This is well above the 1 1/2 thou
recommended in the book. This can contribute to noise they say. Looking at the cam assembly the
bushing fitted is exactly the same length as the cam/gear itself. Is there a fix to get the clearance back
to what is more acceptable. This also applies to the idler gear assembly. The radial running
clearances appear OK Any comments from the experts out there would be welcome.
#3807 On my Velo and other bikes I own the excessive play was eliminated by punching shims out of
brass or steel shim stock. Make the shims the same OD as the shoulder on the cam wheel.
#3810 If the engine is out of the bike heat the cases up to about 130 degrees C. Place two pieces of
0.0015" feeler blade under the cam and with a counter bored drift that clears the threads on the
spindle (but makes contact with the cam) give the drift a healthy thump. However, due to the helical
gears creating outward thrust, the camplate also wears a thou or two. So either get the plate surface
ground or live with it! If the crankcases are in the bike use a Black and Decker paint stripper to locally
heat the cases. Regarding the idler gear, the only solution is to rebush the gear or precision grind a
smidging of the end of the spindle.
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L #4616 It seems when I push on the steel magneto timing gear, and gently tap it into place
finger tightening the nut, the magneto shaft still just spins inside the gear. Is there a washer under the
magneto timing gear nut? How can I tighten this nut up properly without revolving the shaft of the
magneto and keep the timing in place? Why did it take 500 tons of force to get it off and wont tighten
on the taper even enough to stop spinning? And finally does it tighten by pulling the shaft out as there
is no more movement for the gear to tighten against the shaft because it is fully seated against the
housing?
#4617 First make certain that the nut will spin onto the shaft with no resistance, then use a socket to
drive the gear onto the taper. Then bring the nut and washer up to the gear rather gently to exert
some pressure on the gear. Tap the socket (that is large enough to fit over the nut) to further drive the
gear onto the taper, repeat, repeat, repeat. Or... make a puller for the shaft consisting of a substantial
cross bar drilled and tapped in it's center to accept the shaft thread, with two more holes drilled at 180
degrees and tapped to accept bolts that will press the gear onto the taper. If you're pulling the gear up
to the housing, either the magneto flange gasket is too thick or the drive end bearing is incorrectly
assembled in the magneto. The fully assembled gear must be free from the engine housing.
#4625 I had a similar problem assembling my 66 VMT. The steel gear was rubbing on the engine case
just so slightly, and the magneto shaft did not want to lock in the taper. I took a skim cut on the back
side of the gear removing ten or twenty thou to provide the clearance and reassembled the bits. The
gear has more than e'nuff face to turn the magneto after taking the light cut. That was about 8,000
miles ago. I suspect either a thicker gasket or a slight altering of the location of the armature inside the
magneto housing occurred after it was rebuilt.
#4628 Re mag tapers - it is amazing how much further onto the taper the mag gear will go if it has
been re-ground a few times. I have a couple of mag sprockets here that are scrap as a result because
the chains are out of line. Same happens on M series gear pinions.
#4621 There is an alternative to the magneto gear 'tap tap' ritual mentioned by Frank (which has
always worked for me as well). I'm fairly sure Criterion sells a vernier magneto gear, which eliminates
the problem altogether, and makes accurate ignition timing a snap. If the magneto gear slips when the
nut is tightened, its possible the threads on the mag shaft or the nut are damaged. Another nut is
usually a good test, and that's what a decent spares kit is all about. This is best tried before the mag is
installed, to make sure that the nut will turn freely all the way down the mag shaft thread; otherwise
you're screwed!
#4623 If, after trying what has been advised, you still cannot get the gear to "grip" the taper, it's
possible that it may have slipped in the past and a previous owner has used Loctite or similar (this
could explain your difficulty in extracting the gear). Concentric grooves or ridges on either the shaft or
gear tapers are an indication of earlier slippage. The usual remedy is to lap these away using fine
grinding paste but, if carried out to excess, could explain why your gear fouls the crankcase. Beg or
borrow another gear and see if that is a better fit. The magneto drive gear should line up fairly well
with the cam gear that drives it; if it doesn't - it's time to worry. If/when you get that sorted out, the
centuries old method of ensuring that shaft and gear stayput was to pee on the taper prior to
assembly. I'm not kidding! Huge wheels in cotton mills and mine winding gear received this "attention"
if they showed a tendency to come loose but note that the necessary delivery was the prerogative of
the Works Foreman.
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B.5. Oiling System -
L #143 I had a Venom Club, and from time to time, possibly connected with bore wear and
engine speed, it spat out considerable quantities of oil via the engine/oil tank breather. A friend, more
thorough than I, believed on his similar Club it was the oil frothing too much and thought he'd pinned it
down to a certain make of oil- we're talking of 25 years ago. The only result was I checked engine oil,
as a reflex, every time I stopped.
#145 I'm wondering if the MAC puts out less oil mist then the higher powered units, if the pump is a
lower volume pump then the venoms. If not it means I have plenty enough oil flow. Interesting thing;
when I run up the rpms, on the center stand with the oil tank cap off, the oil is seen to be flowing back
into the tank but not under much pressure, and in sort of a pulsing flow. Is this normal for the Velo? So
many details, so little time.
#146 This pulsing flow is very normal on Velo returns. According to the manuals it's due to the fact
that the return side of the oil pump has a greater capacity than the supply side-this is designed to
avoid the possibility of crankcase flooding. On matters like this I'm in agreement with Bruce's recent
comments- Velocette were not theorizing when they built their bikes ! How many TTs did they win ?
L #179 The modification to the 1960 V models uses two pipes and the length of both is
important, but probably not critical. The lengths prevent the Pressure/Vacuum from syphoning the oil.
Steve of R F Seymour, The Velocette specialist, will inform as my information has gone "walkabout".
Tel +44 (0)1 844 212 277
#190 Listed in the parts book the respective lengths are FA138 Engine to oil tank 21.375 inches,
FA141 oil tank to wheel(!) 27.5 inches.
#195 You are spot on, but I have never found whether this includes the coupling at the engine end.
The inlet to the tank is at the back and I will find the dimensions and inform. The vent from the tank to
atmosphere is from the rear and at the top of the froth chamber
#626 If your breather arrangement on the crankcase is correct and you are using the late spec oil tank
(or one modified to Keith's spec), the pipes should be as follows: 1.. Breather hose - engine to oil tank
(21.375" long x ½" bore) 2.. Breather hose - oil tank to rear of machine (27.5" long x 3/8" bore)
L #350 History- Top end rebuild about 6 years ago but to my knowledge the bottom has never
been touched. Symptom- The bike has been unused for about 2 years, so the sump had filled with
about 1 cup of oil in that time. After draining this and starting the bike the engine smokes for about 2
minutes then stops smoking and runs cleanly for appro another 15 minutes then resumes smoking
quite heavily. After re inspecting the sump I find about 2 cups of oil unscavenged back to the oil tank.
I have been told the Velo pump is fairly reliable a gives little trouble, I have investigated all the simpler
possibilities but to no avail. Checked and washed filters in the circulating system. Plenty of oil is
getting to the top of the motor etc Checked and cleaned return lines to tank, no blockage found.
Checked that the oil tank is not pressurizing (and ran it with the cap off there is a constant flow)
Checked if overflow was blocked or kinked. OK Has the pump had it ?,and were do I find a
replacement in Australia. or and I hope, could it be that the gear/shaft of the pump has warn a groove
into case endplate and on heating up the gap increases far beyond spec (which I don't know) an the
pump fails on the return. If this last point is a common problem could somebody let me know, and
would refacing the casing on glass with lapping paste solve my problem.
#351 I also have a smoking MAC, a 1952 Alloy engine. My Mac started smoking after winter storage
several years ago. It also accumulates oil in the sump, but after draining that oil it will continue to
smoke and oil will ooze from the exhaust port. It has been sitting in storage in my shop office trailer
ever since. Several people have told me, that my engine probably has a broken oil scraper ring. That
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it probably rusted to the cylinder during the winter. I did neglect to pour a small amount of oil into the
sparkplug hole before storage. I just bought a blue shop manual reproduction on eBay, that covers a
lot of motorcycles other than the MAC. Better than trying to go in blind I would think.
#352 Have you cleaned the filter PLUG at the bottom of the crankcase 7/16" BSW Spanner
#353 Don't know your full case but I would strongly recommend that you investigate the oil return,,,, it
sounds like the oil accumulating in the crankcases cannot be transferred back to the oil tank quick
enough !!!.
L #410 I'm having problems locating 40 grade oil for my Venom in Ireland. Does anybody know
the location of a supplier? I am reluctant just to top up with Multigrade as I don't know the history of
the engine vis a vis rebuilds etc.
#412 I wouldn't use a multigrade after a straight 40. Try www.castrolclassicoils.co.uk/ They deliver
free for orders over £30 in UK mainland. or you could try Silkolene who also do a straight 40
www.a-pp.com/ There may be other suppliers of Silkolene oils.
#482 We cured most of our oil leaks by changing from a modern multi-grade to Castrol GP50. Last
Sunday at the Tyne Valley Classic Motorcycle Club show we were informed by an IQ0 that Velocettes
were never designed to run on straight oils. He had so many modern reworked parts on his bike the
only thing missing were the Honda badges..
#733 I won't be able to resist having a go on it before taking it apart but feel I should at least change
the engine oil before I run it. I have Silkolene 30's and various modern multigrades. Any thoughts?
#736 Strait 40 at this time of year, in the engine, gearbox and chaincase. Drain and refill the gearbox
as water may have entered. Silkolene is a good choice.
L #542 I have a 1950 MAC that recently underwent a complete nut-and-bolt restoration by a
very reputable builder. Although I have not asked him directly, I assume this included a new or rebuilt
oil pump as well. On occasion, the crankcase floods with oil, presumably involving some sort of
problem with the return pump. This only occurs after I have ridden very close to 22 miles (but again,
does not occur in every such case), which would seem to indicate a possible mechanical distortion
arising from thermal effects. The problem appears to rectify itself when the machine is shut off and
allowed to rest for approximately 5 minutes. I have checked for obvious causes, such as air leaks in
the feed and return lines, or any obstructions in the suction plug. There are no identifiable oil leaks
from the suction plug, the oil pump base, any of the feed or return lines, or any of the fittings
associated with the oil tank itself. A knowledgeable individual opined that the pump is probably not as
pristine as I would like to believe. In such a case, it would not develop adequate suction to reestablish
prime should it be lost (this is plausible, since the last occurrence followed a long downhill stretch at
high RPM, which would presumably empty all of the oil from the crankcase and the return side of the
pump). Allowing the bike to sit would cause enough oil to drain into the crankcase and reestablish
prime, which is also consistent with my observations.
#543 Do you mean the crankcase floods whilst the engine is running ? If it does this you've certainly
got a problem with the oil pump (which should be able to scavenge a greater volume of oil than it can
supply). I think I'd take it back immediately to your highly-reputed restorer ! Presumably it didn't have
this problem before it was rebuilt ?
L #544 I have recently built a Venom engine out of parts obtained from various jumbles and
other sources. the oil pump has been checked and is in excellent condition and there are no obvious
air leaks. The problem is when I fit the ball valve no oil will feed to the rockers. Remove the ball valve
75

and instant feed is there. Anyone had this problem before??
#545 Probably too obvious, but have you put the ball and spring in the right way - ball on top of
spring. Also the seat for the ball needs to be almost a knife-edge for it to work efficiently. If you can
see a clear chamfer where the ball sits on the seat it is probably too worn. Also obvious check again
for air leaks, even a pin hole will upset it.
#546 Make sure you prime all the air out of the delivery oil pipe so that the negative pressure exerted
by the oil pump will suck oil past the feed valve. You can, initially, pressurized the oil tank to do the
same job. The elasticity of any column of air in the pipe will forestall this. We note the comments
about ensuring the ball is the correct way round in the valve assembly. We have never had any
"sumping" problems with any of our Velo's.
L #601 All this talk of oil levels / oil breathers reminds me of a story the late, great Phil Irving
used to tell. During his first stint at Veloce, he took it upon himself to point out to Mr Percy that the oil
tank transfers were misleading and impossible to abide by. When queried he explained that the
wording "Keep Oil Above this Level" literally meant that the oil tank had to have oil in the top and only
air below the line on the transfer. He was told to mind his own business. Later models had a subtle
change to the wording - something simple like "Minimum Oil Level". So one can presume that Mr
Percy took note of this comment, having slept on it. On the subject of oil level and its effect on engine
breathing, early experience with VMT 457 and many other late model Velos shows that if you overfill
the tank it will pump oil out the breather system until the level stabilizes at about 50 to 60 mm below
the top of the filler. So one soon gets an eye for the level which avoids excessive waste, with the extra
oil simply blown all over the machine, whilst keeping enough in circulation to cool and lubricate. By the
way, I've never been one to be too concerned about what oil goes in - sometimes special (expensive)
4 stroke oils, and sometimes cheap generic brand multigrade (as long as its API spec was SE or
higher) and they all seem to work - never a seizure and now completing the first major overhaul in 20
years with nothing more than a hone, new rings and fitting a better second hand Nimonic exhaust
valve (the original was pitted because it was only a KE965 to start with and obviously didn't survive
the degradation of fuel quality these past 4 years or so). Oh and I did do a bottom end overhaul as
well, not because it needed it, but because I didn't want to be having to pull the engine out again
within the next 10 years. And the engine was only sitting on the bench in the first place because I
needed to remove the gearbox - give me an iron MOV or MAC any day! And those who have toured
with VMT457 will vouch that its longevity has little to do with a gentle hand on the throttle.
#604 My good, and lamentably late friend John Anderson used to reckon you should just be able to
touch the oil with the tip of your finger. Saves looking for a depth gauge every time.
#605 I also had a '47 KSS ( why did I ever sell it??) that had a breather pipe extending to the rear
mudguard and never had the slightest problem with oil levels or usage - in fact I never had any
problems of any kind over the 8 years of using the KSS. My "new" '61 Venom has an unvented oil
tank cap but has the half inch breather pipe referred to by Pete C. In this case it is directed to the
chain just by the footrest/brake pedal ( Clubman rearset). I have tried overfilling the oil tank - to see
what happens! - and it simply blows oil out onto the chain , which ends up on the tyre, rim etc, until the
level in the tank is back to more or less half way between the max and min level, the level seems to
stay there then irrespective of whether I'm in ride to work mode or having a long thresh down the M4.
L #607 Interested in the comment, "if no froth tower is fitted to your tank you are very likely to
have a big problem with excessive external lubrication, since the function of the tower is to separate
oil from breathed vapour." Specifically, what is a frothing tower? Perhaps a failure in my British to
English translations skills is at play here? The return pipe in my oil tank does stick up about an inch
above the oil itself (setting aside the rather active dialog about where to properly set the oil level). Is
this the tube/tower that is being referred to? I was also fascinated by Pete's remark about the, "lead
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the pipe (whose length is specified in the parts book and is important for correct operation)." With due
respect, the pressure drop in a 1/4" line at the flow rates in question is relatively minimal, and I fail to
see how the exact length would matter whatsoever. We're not exactly talking about the reflected back
pressure wave in a tuned exhaust system here.
#620 the froth tower is the name given by someone in Velocette history to the inch and a half
diameter tube that rises from the top of the oil tank by about two inches inboard of the right hand
frame tube. Inside the tank there is a tube running from the top of this tower down to the back side of
the tank with about an inch sticking out, to which a flexible pipe should be attached and led to the rear
of the machine. This is the tank breather outlet. I believe that the purpose of the froth tower is to keep
the end of the tube inside the tank well above the level of the oil or any froth (air/oil mixture) and to
prevent oil from being discharged via the breather. I cannot tell you whether there is any additional
baffle incorporated in the tower, perhaps someone else might be able to enlighten us? When the later
type engine breather system is fitted, the pulsations in the crankcase are transmitted into the oil tank
via the ½" bore pipe, and yes, there is a tuned length to the system. The factory worked out the
lengths of the pipes and if correct, the system is quite effective. If not, the system has been known to
pump oil out and lubricate the rear tyre. The return feed to the oil tank from the engine enters the
bottom of the filter chamber which is about 2 inches diameter, and runs up the inside of the Aluminum
tube that surrounds the through stud retaining the top and bottom caps on the chamber and prevents
unfiltered oil from returning to the crankcase through the scavenge side of the pump. Oil flows then
through the filter and returns to the main body of the tank through the short tube to which you refer,
just below the filler cap.
#623 having read your detailed description of the frothing tower, crankcase breather, vent lines, etc., I
can only observe that my '50 MAC as I received it does not have any of these features. It has a sealed
oil tank with two tubes entering at the bottom. One is the feed union, the other the return pipe which is
an integral part of the tank itself. That's it. I spoke with fellow who restored this machine, and he says
the tank, crankcase, etc. are as he received them (i.e. no vents anywhere). I did not think to ask him if
the unvented cap is a replacement. It's essentially perfect appearance indicates that it is most likely
not original, and may be incorrect in that it is unvented. I only began thinking about any of this when I
encountered a scenario wherein the crankcase floods with oil, but only after several minutes of
sustained, high RPM operation. Otherwise, everything appears to function properly. I noticed that
there are no vent lines whatsoever on the oil tank itself (or anywhere else for that matter), and that the
oil tank cap is unvented as well. In looking further, I noticed that a vented cap is available, which
reinforced my notion of the possibility that the tank is probably pressurizing. Unfortunately, my
scheme [notice the overt use of English phraseology] to explore this theory by temporarily replacing
the cap by a stopper with a reasonably large (1/4" or so) hole in it has been thwarted by the loss of
top gear. I have disassembled and carefully measured every part in the transmission, and everything
looks just as it should. Figured I would think a bit more about the situation before posting this problem
for others to offer their useful comments. [At present, I am leaning towards the possibility that there is
enough play in the camplate that it tips sufficiently to allow the actuating pin in the upper fork to slip
from its slot, jamming the camplate into the actuating pawl and binding up the shift lever]
L #614 Oil filter tube , If the fibre gear strips it will certainly block up the oil return , I've had it
happen in the past and a friend had it happen only a few weeks ago on a club outing , the pump
pressure split the return line . I do NOT recommend removing the tube from the Filter , When the
engine stops all the muck in the filter will drain down with about a half pint of oil back into your crank
cases , a) it makes it difficult to start with all the oil drag ( especially cold), over-oils the engine till it all
clears , c ) think of all the grit ,swarf and silicine that is in there ! Nots /bolts for the MOV . I don't know
of anyone who does Kits , but the VOC have many bolts sized according to listed part number/length
/thread .
L #638 While on the subject of oil tanks, I strongly recommend the fitting of the VOC oil filter kit
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in place of the original. The cartridge filters are so much more efficient at straining out contaminants.
On early oil tanks it fits without any modification, on later tanks you need to file away about 1-2 mm of
protruding tube. If you do this put the tank cap on and block the tube off from the inside with a small
piece of rag to avoid iron filings in the oil tank. Details of the kit can be found here
www.velocetteowners.com/sparesco/specials.htm
#639 Problems to translate, what do you mean "to file away 1 - 2 mm of the protruding tube" ?
#641 On later Velos, the plain hole from which the oil flowed from the filter chamber back to the oil
tank was replaced by a very short piece of tube. The tube enters the filter chamber and stops the oil
filter cartridge from fitting easily, so it needs to be filed away to allow the filter to fit into the chamber.
L #640 A more general question about oil filtering. In disassembling the oil feed tube on my '50
MAC, I noticed that it did not have the "gauze filter" described in the owner's manual (it did have a ball
check valve which seems redundant, since there is already one in the crank case). It occurred to me
that some sort of filter would be in order. In discussing this with some more knowledgeable people,
they essentially told me not to bother, as long as I was vigilant in changing my oil regularly. There
rationale was twofold: I) the tolerances in the pump are rather large by today's standards, so small
particulates will essentially pass through the pump anyway, and ii) any filter with even a small
pressure drop across it will prevent the oil pump from doing its job properly, since it is a volume (not
pressure) based system, and will not tolerate significant pressure drops. They further opined that the
gauze filters were suitably porous that they didn't do an effective job of filtering the fine particulates
anyway. Apparently, the filters under discussion here are meant for later [and different?] machines.
Regardless, should I be pursuing the installation of some sort of filter on the input line?
L #659 What's the best low-tech method of sealing the poly tubing to the copper tails of the
banjo(etc) connections in the oil system?
#660 Take them to a hydraulic hose or lorry parts company and get them crimped.
L #761 I've got a couple of questions which I hope someone can answer. The oil filter in the
tank has been taken out and an external (RGM) filter fitted on the return line. Is this a real advantage
or not? I'd really rather not have the external one on, simply because I don't like the look of it. If it were
a real advantage I could (just) live with it. I would have thought that the original filter is adequate
providing oil is changed regularly. Any views welcome.
#762 A few years ago while changing the filter in a BMW twin I found it fit the Velo oil tank quite well,
so that's what I use. It's a paper cartridge filter. All that's needed to fit a Velo is a couple big o-rings or
washers to center it in the bore. Some tanks will need to have the small tube trimmed back to let the
filter slide by. Framm and Purolater market this filter if you don't feel like frequenting the local Beemer
shop
#770 On the oil filters, I wouldn't worry too much about a bypass valve. Since it's on the return side
the worst that can happen if the filter plugs is too much oil in the sump. Never seen it happen.
L #774 I plan to modify my "old fashion" oil tank to the more recent standard. The crankcase
having been modified by the previous owner, I would like to "recycle" the oil coming out from the
crankcase breather. My first series oil tank being already fitted with its own breather outlet, coming
from the froth tower down to the outlet tubing coming off the inside face of the tank, if possible, I
would like to know the exact location and dimensional information of the additional tubing to be fitted
to receive the 21.375 in. crankcase breather pipe.
#785 Weld in a piece of half inch od tube about 1.5 inches long at the top of the rear of the oil tank.
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Make sure it clears the down tube when fitted. For a better pipe run, you can weld the tube in angled
towards the front.
L #783 has anybody converted an engine to the later oil drain from the timing chest to the
bottom of the motor. I think this mod came in about 1964. it looks like an external rib. I believe you
can do this but you have to plug the crankcase in the bottom of the timing chest to stop oil draining
into the motor internally. I was going to this some years ago but hit a problem with clearance
between the motor and the frame, to put a union on the bottom of the motor was going to foul and I
decided not to bother, but having thought about it I could come in at an angle and tap the hole and
then screw in a tube much like the later breather tube under the mag. has anybody tried this ?. it
would then be straight forward to connect to the tube, and then to the bottom of the timing chest.
velocette did some tests and discovered that when the engines were running, oil was backed up to as
much as three quarters of the timing chest as it was unable to drain into the bottom of the motor fast
enough due to the flywheels stopping the oil going down the internal drain hole. this was one of the
reasons why they did a revision of the crankcase. you should end up with a better crankcase than the
later ones with this mod because the earlier cases have the restrictor in the oil passage way to stop
debris going into the pump and the later cases do not have it. any feedback is welcome. Regarding
the later breathing arrangement, I read that people are doing this and breathing into the oil tank, I
hope that when they are putting the tube under the mag into the timing chest that they are also
putting a hole from the timing chest into the crankcase otherwise it is a complete waste of time,
because with out the hole from the timing chest to the crankcase the air cannot be expelled. just my
two cents worth. thanks for taking the time to read this. cheers.
#899 Having done that, throw the tube away! I did that over 40 years ago, and have never missed it!
Then you have permanent peace of mind, at least as far as a blocked return goes
#784 I have added the oil drain line to the timing case. I used two 90 degree 1/8" US pipe fittings, one
tapped in at the bottom of the timing chest and the other at the bottom front of the side of the case
(thinking the oil level would be lowest at that point while running). This is a tight fit in the frame as the
frame curves near the case at that point (swing arm frame). To do over again I would put it further
back where the frame rails are straight as I can't remove the fitting with cases in the bike. A side
benefit with this mod is that with clear tubing I can always see how much oil is in the sump when
sitting. I did not plug the old drain hole figuring it would now function as a breather between the crank
case and timing chest along with several others holes I added. Wet sumping while running has not
been a problem even with pump spinning 50% faster than stock 2 start (1/4 vs. 1/6 crank speed). I'm
getting ready to test pumping additional oil to the exhaust rocker box for cooling which may create a
drainback problem, we'll see.
#941 Do it that way and you won't be able to take it apart easily to clean it when you do a filter
change. The Velo factory guys weren't stupid, their way is still fairly well thought out most of the time,
personally I would leave it the way they intended or replace with the cartridge filter conversion.
#900 If you dispense with the tube inside the filter, the entire contents of the filter chamber will drain
back through the oil pump into the crankcase when the engine is stopped. NOT a good idea to
remove it.
#902 Entire contents? The whole half cup-full? As I said, I have never noticed any deleterious effects
whatsoever! Maybe you would if you are one of the traditionalists who insist on using SAE50 oil, but
not with the recommended 20W /50.
#907 And all the crap that has been pumped up into the chamber on the dirty side of the filter? I think
I'd rather leave that in the filter and not draining back through the oil pump whatever oil I use!
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#918 I'd suggest that most debris from the oil is already well embedded in the filter felt, and any oil
which does drain back will do so slowly that any metallic pieces large enough to cause damage will
settle to the bottom of the filter chamber. The 'drain' hole (the cross drilling) is not at the extreme
bottom. The oil returning to the sump has to dribble through the .001" clearances in the oil pump, so it
will hardly gush! Having experienced a blocked return due to the existence of this tube, and losing all
the oil as the result of the return pipe subsequently blowing off, I MUCH prefer to dispense with the
tube and risk a little debris returning from whence it came, rather than a complete engine seizure! By
the way, if all the blocked return does is to cause a build up of oil in the crankcase, there is a serious
weakness in the oil pump. The pump cannot revolve at running speed and not pass more oil than
could possibly squeeze through the pump clearances. You will therefore get a very high pressure in
the return pipe and excessive wear on the pump drive gear and worm (creating damaging debris in
the sump!!!).
#911 Both my bikes came without this mystery oil filter tube. Can someone please spec one out so I
cam make one?
#915 Part number A293/2 is what you want - sorry I can't give you dimensions without taking my oil
tank to bits! As I remember, it is a piece of alloy tube which is a push fit over the LE547 filter cap
adapter shoulder below the cross drilling. The OD is just about the same size as the hole in the
bottom filter cap and it is long enough to come to about an inch short of the top cap when fitted. The
¼" stud runs up inside the tube. It's not unusual for the tube to come off the adapter, perhaps when
changing the filter and either thrown away or simply dropped back on to the stud without being
properly located whence of course it will not do the job it was meant to!
#925 The tube is 0.500 od, 6.850 in length made of aluminum. The wall thickness is approx 37 thou.
The tube is a heavy push fit, light press fit over the fitting at the bottom of the studding; you can
clearly see the step it fits over on the fitting. Bore a piece of ali tube or bar out so that it fits. For what
it's worth I would fit the tube for the following reasons. 1) the filter holds quite a quantity of oil, and this
together with the oil left normally in the bottom of the crankcase may make starting more difficult 2) If
you fit the club filter kit which I recommend www.velocetteowners.com/sparesco/specials.htm you will
need it. 3) if it serves no purpose, Veloce would have saved the pennies by not fitting it I agree that it
is unlikely any debris above a thou will find its way past the oil pump, I just don't like the thought of all
that debris dropping back down.
L #936 When my piston "holed" it also bent things in the oil pump making me rebuild that as well
as needing now to take the engine apart to clean everything out. Would this new filter have saved
me?
#938 Unlikely, as the filter is after the pump not before it. What it does is strain out the very fine
contaminants that cause wear in the engine.
L #1055Here I am spannering my Venom racer, trying to reduce all the leaky areas ... I've fitted
a much larger bore to the engine breather - ok. I've drilled the timing case to crankcase hole - ok. But -
I undid the pokey leaky external (1/8 bore !) pipe and fittings to see that the fitting in the crankcase
shows me the side of the flywheel ... now this type of mod is a 'good idea' isn’t it ?! Well, surely if it
lets all the oil out straight onto the flywheel it's going to cause drag ?
#1058 I assume you are talking about a drain mod from the timing chest to crankcase? - There is no
technical article that I am aware of. If you think it through the oil supply to the timing chest is constant,
so you are going to get the same amount of oil through to the sump, it just takes a quicker route to get
there. The scavenge rate is greater than the feed, so when running most of the oil is scavenged from
the crankcase. The cupful or so that you get when you drain the chain case, is the oil that makes its
way from the rest of the engine when the pump has stopped.
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L #1275 I'm seeking info on the oil pump as fitted to the mid 60s Venoms. Can someone shed
some light on the pump rate or volume for supply side pump?
#1285 I'm not sure why you want this information or it's accuracy, but using SAE20 at room
temperature to replicate normal engine oil at operating temperature, a pattern pump delivered 1.07
pints per minute at 1080 rpm with a pressure of 18 psi. This information came from Fishtail.
L #1282 While looking at options, before I stuffed a brand new oil filter comprised of wire mesh
and felt into my newly restored oil tank, I slipped a BMW airhead oil filter into the tank's recess. Wow, I
suspect many folks figured this option out years ago but it was new to me. With the addition of a
simple adapter turned up from aluminum bar stock in about 2 minutes, the BMW 11 42 1 337 572 filter
is a perfect fit. Together with new gaskets cut from a sheet of 1/8" nitrile replacing the fiber gaskets,
I'm expecting a neat oil tight oil tank.
#1283 There is also a smart oil filter kit available from the Velo Owners Club in the UK, fits inside the
tank and its leak free! Doesn’t stop oil leaking from everywhere else though.
L #1367 It might be not important to my velo. But I can not stop wondering, how Mrk8 oil tank
inside like. Because it seems to be just box with cut out for down tube and cab. But it should have
something inside as I can see the cylinder shape marks appearing to the side of tank. What is it? I
would be glad if someone supply the sectional drawing of tank. It might be secondary tank mentioned
in Velo saga book for warming up oil quicker for racing?
Thank you
#1368 There is nothing special inside the Mk VIII oil tank. The pressed pieces are just to make the
sides stiffer. There is a mesh oil filter and a return pipe, that's all!
L #1391 Got the bike running over the winter and did about 50 miles with no problem. Then last
weekend I set off on the first club run of the year and when I started the bike I had an oil leak from
under the disc at the top of the filter on the top of the oil tank. The leak was not a drip but a
continuous flow. I tightened the nut (and the locknut) which sorted out the problem. I put it down to a
new gasket bedding in. The run was about 200 miles and I had no problem so I thought I had sorted it
out. Yesterday I started the bike again and had the same leak though a bit slower than before. I
removed the nut, washer and disc and found that the gasket had been cut through by the rim on the
oil tank. Maybe me overtightening the nut? Didn't have a spare gasket so bodged it by using silicone
sealant. Started the bike this morning and there is no leak from the disc/tank joint (probably because
of the silicone) but oil is leaking up the stud and out under the nut. To me this indicates a very high
back pressure from the filter. I'm running on Silkolene 40, the filter is new, there is a good flow back
into the tank. Any ideas?
#1392 When you put the new filter in, did you take off the alloy tube that goes over the stud that bolts
the whole assembly together. there is a cross drilled hole in there and it can block up with debris
coming back from the motor. If the motor has stripped the fibre teeth off the magneto wheel in the
past, the oil pump will pass it back to the oil tank but they are to large to get out of the cross drilled
hole, or even gasket sealants or bits of metal will do the same thing. I have heard of bikes blowing
their oil line off on the return side due to this problem. If it cant blow the oil line off the next thing would
be a pressure build up in the tank. I might be wrong but it is worth checking out. cheers.
#1408 If the alloy return tube or the cross-drilled hole were blocked the oil line might blow off but there
is now way this could result in a pressure build up in the tank, since no oil can find its way into the
tank, or even into the filter chamber. However, if the return stub from the filter chamber into the main
body of the tank were blocked then there would be a distinct possibility of the contents of the filter
chamber trying to exhaust themselves from the filter chamber cap gaskets or stud seals. The things to
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check, apart from making sure the holes and tube are clear, are that the filter itself is not clogged
solid, the cap gaskets are either new or in very good condition (these are quite a thick and solid
material and if the chamber flange has cut through them it might hint that the wrong material had been
used) and the adapter at the bottom and the nut and steel washer at the top have fibre washers fitted
under them (Dowty seals can be used if you can find the correct size). The alloy tube MUST be fitted
and should be a good push fit on the return adapter to prevent the contents of the filter chamber from
returning to the sump when the engine is stopped. When the machine is reassembled make sure that
there is a good flow from the filter chamber back into the main body of the tank - with the engine
warmed up for a few minutes this will contain a fair amount of air since the scavenge side of the pump
has a greater capacity than the feed side and attempts to keep the sump "dry".
L #1694 Wet Sumping: Ever since I bought the bike about 9 months ago, oil has disappeared
from the tank into the crankcase. I tried the "recommended" application of a copper hammer to the
ball to form a new seat but with no success. A few days ago I decided enough was enough and
bought a new ball, spring and seat. Fitted them and the problem, if anything, is worse. This morning I
found an oil puddle under the bike because the oil had filled the cases so much that it leaked out
through the main bearing. Despite this it started well (thanks partly to the new carbs). I really can't
accept this as OK so am looking for some advice. Should I call the supplier of my new bits and
complain? Should I accept that it's going to wet sump (surely not), or is there something I can do? Lap
the ball/seat with fine valve grinding paste? Any other suggestions?
#1695 As you guess, you shouldn’t have to tolerate this. Your course of action sounds ok to me - its
one of the things I'd do - making sure I'd cleaned everything off before reinstalling of course ! But first
- check the spring is the right one/length etc - this should be a 'truncated conical' shaped spring
approx 1.25 inches long. The thin end of the cone presses against the ball (obviously). Check the
spring is holding the ball on its seat ok - best done off the bike. Sorry if this is obvious, but in my
experience springs (of all applications) are the things pattern parts manufacturers most often get
wrong
#1696 I always put the ball valve seat in the lathe and using an end mill or slot cutter in the tailstock
chuck, just skim off the existing seat. A very, very light tap with a soft hammer recreates the seat.
Using this method I have found that no oil passes the ball valve.
L #1713 I have been told that non-detergent oil is preferred for the older machines which do not
have oil filters. Does anyone have any experience with Aeroshell aviation oil? Their "100" is the
equivalent of non-detergent 50W.
#1717 The non-detergent aviation oils are only for break-in. Even aircraft reciprocating engines have
gone to detergent oils once the rings are seated. The detergents in aviation oils are formulated to
absorb the products of combustion of aviation fuel, not the lamp oil we're being sold as gasoline. I
think you may have your viscosity indexes backwards, the way I recall it is that a 50wt aviation oil is
the equivalent of a 100wt automotive oil. Check this out from a couple of sources to be sure. You can't
go wrong with just about any good quality 50wt motor oil (40 or 30wt in cold weather).
#1723 I am a pilot. Aeroshell 100W is a 50 weight non detergent oil. Works fine in a motorcycle but
why would you want to pay such a high price for oil? Most modern 50 weight oils will work equally well.
I have used Aeroshell in my Sq4 with no adverse affects. I used the Aeroshell because after I sold
one of my planes I had an extra case gathering dust so why not use that expensive oil in one of the
motorbikes? Aviation "break-in" oils are mineral oils that are specific for aviation break-in purposes.
It's a long story but aircraft engines are slightly different from automobile/motorcycle engines and
require a different break-in procedure and oil.
L #2015 I wonder if any of you velofellows out there could help me with a problem I have had
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with my 56` MSS. At any speed over 50 mph oil is coming out of the vented oil cap breather hole and
around the cap itself. I have checked the breather hole and it`s fine. Any thought`s???
#2017 Over-full or if the oil cap is like the gas cap the two holes are offset, to prevent this. it is
possible that someone drilled a non vented cap straight through. Probably over-full.
L #2054 When starting my cast iron MAC, it smokes significantly from the tailpipe for about
fifteen seconds, then stops. This occurs if the bike has sat for several days or more. It runs
wonderfully, and does not consume any measurable amount of oil from the perspective of the level in
the oil tank. I let the bike sit for a week, then pulled the crankcase drain plug. Approximately two
ounces of oil drained out. It is not clear to me whether such an amount would typically accumulate by
settling, or whether the ball check valve leaks. I am inclined to think it is the former, since the amount
of oil that drains out does not increase with time (specifically, if I let the bike sit for a month, the same
two ounces of oil drains out). Could the observed smoking at start-up instead be attributable to oil that
has accumulated in the rocker boxes, and then drains down into the cylinder? If so, would this imply
that I have sloppy valve stem clearance?
#2056 Your diagnosis is correct. If you remove a rocker cover you will find the spring cup full of oil.
Reduced valve to guide clearance will reduce smoking, but not stop it. There are two solutions - fit
auxiliary oil drains or wait 16 seconds before you look backwards.
L #2136 In previous messages regarding oil tanks/frothing towers I don't seem to see an answer
to this one:- In the collection of parts which I acquired to build my MAC were two oil tanks, both with
frothing towers. Naturally I fitted one of these. The only visible result was a serious oil leak where the
polythene pipe fitted on to the outlet spigot, despite being a good tight push fit. No oil ever issued
from the poly pipe. I have since swapped one frothing tower type for a plain tank, and am considering
fitting this. The question is, which models were originally fitted with which type of tank?
#2150 Froth towers were introduced in 1959 the MAC was discontinued in 1960. Therefore the very
last models may or may not have froth tower oil tanks, depending on how Veloce used up existing
stocks. Velocette Springer oil tanks had quite an evolution during their life. Original had a long filler
neck Later the neck was shortened Mounting brackets strengthened (but not strong enough) Froth
tower introduced Pipe fitted to accept breather from engine Rubber mounted Thruxton variant
Brackets strengthened again by using one piece of steel to run from top to bottom mountings. Veloce
also produced a small number of drive side mounted oil tanks for special applications.
#2155 Thanks for the chronology of the oil tanks. Using this info I'll fit the plain oil tank. I've since
discovered that the oil leak from the froth tower tank was not from the outlet breather but from a
hairline fracture at the bottom bracket weld.
#2140 Mention of Velo frothtowers brings to mind a common (?) problem with oil tanks on RIGID
models fitted with the towers. If you own a KSS or a MSS that has a tower, & appears to have a small,
but persistent oil cap leak that cannot be cured, investigate the area on the top of the oil tank between
the vertical top mounting strap & the tower to tank joint, which is also the point where the 2 pressed
halves of the tank are originally gas welded. If you have the 'incurable' leak, you will find a minute
hairline crack in the enamel, which indicates a welding stress crack underneath. This occurred in the
original welding process & may, or may not have been completely cracked originally, but vibration may
(?) have eventually caused the leak. I am not sure that it's a good idea to attempt to repair by welding,
as excessive heat may restress the area. In the several cases that I have found, I just grind out the
small crack, & repair with a small spot of 'bronze', keeping the temperature as low as possible, & as
far as I know, it has remained an effective repair. I would be interested to know if anyone finds this
fault ? - check any unused tanks that you have !
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L #2472 Is it necessary for me to remove my Thruxton type oil tank from the bike in order to fit
renewable paper filter system which I got from VOC? (The frame loop gets in the way upwards and
the swing arm pivot downwards)
#2475Yes you will need to move the oil tank.
#2473 I am converting to paper element system and am at a loss as to how I get clearance to remove
wire and "army blanket" style filter The frame interferes upwards and the swing arm pivot downwards.
Any tips out there?
#2474 If you replace the oil filter, you will need to drop the tank off first. This also allows you to wash it
out to remove any debris inside.
#2479 On later tanks you also need to carefully file the short piece of tube inside the filter chamber,
otherwise you cannot get the filter in. Stuff the tube with a tiny piece of rag from the inside before you
file and push the rag through into the filter chamber, so that you don't get iron filings in the oil tank.
#2482 Hi I spoke to Castrol's technical group, regarding corrosion and gumming when using Castrol
R. As part of the conversation they forwarded me the attached:
TECHNICAL BULLETIN - WHAT IS ENGINE OIL 02/12/2002
What does it do? Engine oil does more than simply lubricate, in fact there are five basic functions:-
Lubrication: Prevents metal to metal contact between moving surfaces and reduces friction Protection:
Protects against corrosion and wear caused by the results of fuel and lubricant decomposition.
Sealing: Acts as a seal by filling the gaps between the piston assembly and the cylinder wall. Cooling:
Transfers heat away from pistons and bearings to areas such as the sump where the heat can be lost.
Cleaning: Maintains by-products of combustion finely separated until they are removed by filtration
(dispersive action). Resists black sludge formation (detergent action). What does 15W-40 mean? The
numbers, such as 15W-40, are the viscosity rating of the oil. The viscosity of an oil is a measure of its
thickness or resistance to flow. Thin oils are good for cold starting, especially in winter but are too thin
for high speed driving in summer. Thick oils are good in summer, but too thick for starting in winter.
The Society of Automotive Engineers (SAE) defined a classification system for viscosity (see table
above) Obviously, for all year round use, an oil which combines the cold temperature viscosity of a
winter grade with the high temperature viscosity of a summer grade is required. This is achieved by
adding viscosity index improvers (VI) to the base oil to create multigrade oils such as 10W-40,
15W-40 or 15W-50. What does API SL/CF, ACEA A3/B3 mean? As engine technology develops
there is a corresponding increase in the demands placed upon the engine oil. New performance
standards are introduced which supersede the previous standards. Therefore, even the latest ones
e.g. API SL, will be superseded at some point in the future. There are two major bodies setting
standards: the American Petroleum Institute (API) and the Association des Constructeurs Européens
d’Automobiles (ACEA). There are different standards for petrol and diesel engines. The most recent
standards are listed below, NB these are not equivalent eg SG does not equal A1! These standards
are based on a series of engine tests, often referred to as sequence tests. Each test measures a
different aspect of the engine oil's performance, such as camshaft wear. Only when an engine oil
passes all the tests can it be labeled with the standard e.g. API SJ. What's in it? About 80% of an
engine oil is the base oil which may be mineral, synthetic or a mixture. The remaining 20% consists of
additives which give the engine oil its performance. What's the difference between mineral and
synthetic oil? The mineral oil used in engine oils, although highly refined, still contains undesirable
compounds that limit the performance of the engine oil. Synthetic oils are very pure, only containing
compounds required for lubrication. This enables the production of very high performance engine oils
that offer significant benefits over mineral based engine oils. Although synthetic engine oils were
originally developed for high performance racing engines, their benefits are just as important for
standard engines fitted to passenger cars. These include very low wear levels, increasing the engine
life, increased engine efficiency for more power or fuel economy and easier cold starting. Will they
84

mix? All Castrol engine oils will mix with each other, even fully synthetic Formula RS and standard
Castrol GTX. Obviously, to obtain the maximum benefit from fully synthetic engine oils they should not
be diluted with mineral engine oils. Castrol engine oils will also mix with any other manufacturer's
engine oils. The only exceptions are specialist competition oils containing castor, such as Castrol R,
that should not be mixed with any other type of engine oil. Interpreting manufacturers'
recommendations Interpreting the vehicle handbook can be difficult because the information is often
out of date. In general, later standards can replace earlier ones, so SJ can replace SG, SH etc. It is
important to keep the recommended service intervals to maintain the engine in the best possible
condition. It is also important to do this to maintain the vehicle warranty, whether this is the
manufacturer's or a third party insurance policy. What's different about Castrol? Castrol has always
seen the API and ACEA standards as the minimum requirements for an engine oil. These standards
are often based on tests in old engines that have little in common with today's engines. To overcome
this problem and to ensure that Castrol engine oils protect today's technology engines, Castrol has
developed a number of special tests. ALOFT measures the actual oil film thickness between the
camshaft lobes and camshaft followers, the most heavily loaded engine components, whilst the
engine is running. BOFT measures the actual oil film thickness between the crankshaft and bearing
shells while the engine is running. Castrol 500 mirrors a standard engine test but uses a modern
technology engine to ensure that Castrol engine oils lubricate today's engines effectively. As well as
these specific tests, an extensive fleet of test vehicles is constantly on the road ensuring that Castrol
engine oils protect your engine throughout the life of your vehicle. Any questions? If you need any
further information then consult the Castrol Technical Help Desk on 01793 452222. Health and Safety
information sheets are available for all Castrol products from the address below. Castrol International,
Pipers Way, Swindon, Wiltshire SN3 1RE, England, Telephone: Orders/Enquiries (08459) 123011,
Technical Enquiries (01793)452222, Fax (01793)453750 .\
L #2552 I am trying to fit the VOC filter kit into my Thruxton style oil tank . I would like to know
why the filter assembly seems too long for the tank. I am having difficulty putting the upper cap on (the
lower cap seems to be fixed in place). Does the alloy tube that fits over the central long stud extend
so as to cover up the two lateral apertures at the bottom of the stud assembly ;or does it just sit
loosely on the ridge above?
#2553 On closer examination the alloy tube appears to sit on a machined ridge right below the oil
feed. I am led to believe that the alloy tube should be a tight fit over this machined ridge, the
instructions stress this and even suggest lactate. It seems to me that considerable force or reaming is
going to be necessary as the alloy tube has a smaller bore.
#2558 A light tap with the hammer is all that is normally required to locate the tube on the bottom
union - often they are slack. Perhaps your tube has been distorted. Before you fix the tube make sure
the stud does not screw too far into the bottom union and obstruct the oil holes.
L #2784 I recently received a replacement tube from Grove. It is steel whereas the tube at
present is aluminum alloy. The steel tube sent by Grove(U.K.)is 4 and5/8ths long but the alloy one is 6
and 7/8ths.This component is referred to in the parts list as A293/2 and is described as "Oil tank filter
centre tube".Being keen to do this right I am asking if any Velo person can assist. I am considering
shortening the longer tube to the 4 and 5/8 length.
#2789 The alloy tube in my oil tank is 6 and 3/4 inches long. This brings it to about 5/8 inch from the
top of the felt filter. When I've assembled this in the past I've thought that since the tube is a fairly tight
fit within the filter, the vast majority of the oil must be passing through the top inch or so of the filter. I
have sometimes had a small weep of oil from under the top nut which seemed to me to indicate a high
back pressure (which you would have if only part of the height of the filter were in the flow). Previous
posts on this site indicate that the 6 and 5/8 length is correct. Personally I think the filter's performance
would be improved if the tube were shorter but others with far more experience may well disagree
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(and be right!). As part of my current rebuild I've bought a paper filter kit from VOC spares. Not used it
yet but the filter is well clear of the tube and the whole thing looks very well engineered.
L #2785 I am getting towards the end of a 1964 Venom rebuild, and one of the things left is to
position the oil tank level, and the chain guard transfers. I thought it would be a novel idea to position
the oil tank transfer at the level at which the oil should. Since the oil drains to the crankcase with time
(I'm guessing this will happen even with the new ball valve), let's define oil tank level to be "the level
seen, immediately after stopping the engine". So with this definition where should the transfer be
placed? If there is another definition of oil level - let me know. Looking at period pictures, placement of
the transfer at best, looks to be pretty random. Some bikes appear to have the transfer placed below
the center line of the tank. There must be an explanation here .. Anybody know? On the subject of
transfers, the chain guard transfer also seems to have been also placed at random angles. There is
no obviously logic here either. The angles used do not seem to line up with anything.
#2786 One of my friends in the North American Velo club gave me the best advice on oil levels. This
was after several episodes of over-filling the tank on my '66 Thruxton. This is exciting as the oil comes
blasting out of the breather onto the pavement as the most embarrassing time. On that model, the
transfer is essentially under the carbs and not visible while looking into the tank. His comment was
you should just be able to touch the oil level with a finger with the bike warm and on the centre stand.
This assumes you have the standard hand, with standard dimension fingers, traceable to NIST
(formerly the Bureau of Standards). This has actually worked well for me as I usually have a number
of fingers with me while I'm out riding and wish to check the level. One additional note, 1/4 liter of oil
seems to change the level in my tank about 5/8 of an inch.
#2788 My understanding is that the oil tank transfer height depended on whether the tank had a froth
tower. The froth tower allowing a larger volume of oil to stay in the tank rather than on the back wheel!
I don't know about exact heights, but I put mine on so that my British Standard finger just touches the
oil when it's near enough half way between the max and min lines.
L #2787 The only job I'm not looking forward to is fitting the oil pump. I've read the red book and
previous posts about the amount of heat needed, it sounds a bit daunting. I was wondering about
getting the whole lot up to say 150C before I start then if I have to use more heat, the rest won't be as
much of a heat sink - any views?
#2790 When I recently built up a bottom end I did as advised but used a freezer to cool the pump for
24 hours, I wouldn’t say it dropped in but it was a damn site easier than the removal, plus I had a nice
mix of third degree burns and frostbite to amuse the locals.
#2792 Assembly is always easier than disassembly due to the fact that the oil pump hasn't been
heated as it is during the disassembly process. Further cooling of the pump may make things easier
still, but personally I have never found this necessary. If the cases are heated generally with a suitable
heat source - I use a good hot air gun, NOT an oxy-acetylene torch! - up to "spit and sizzle" point, the
pump will slide in easily and still allow enough time to line up the screw holes. This method ensures
the cases are heated sufficiently, but not to the point at which the material properties change. I would
think 150/C is far too high a temperature, spit will sizzle at not much over 100/C.
#2793 I always bolt both halves of the crankcases together when heating to prevent any distortion.
#2794 I had assumed that this went as read. On assembly it is necessary to have the crank
assembled into the cases and the joints sealed and bolted up fully. The timing side crank pinion, oil
pump worm drive, locking washer and nut should also be assembled, but that's all - any more and you
will unnecessarily be wicking heat away from the cases.
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#2799 Good news - the oil pump's back in. Thanks for the various bits of advice. Assembled
crankcases in oven at 120C, oilpump in freezer at -18C. Went in with a few very light taps of a hide
hammer. I'd cut the heads off a couple of old screws to make studs and fitted them to the crankcase
before fitting the pump. This made lining up the holes simple. I'd cut screwdriver slots in the end of the
studs to get them out after fitting the pump but they came out by fingers to let me fit the correct bolts.
L #3034 A mate of mine has the following problem: He primes the oil lines, starts the Viper,
which quickly drops about two inches of oil level in the oil tank. Once the return starts feeding back
into the oil tank, it flows fairly heavily and continuously from then on. Upon inspection, the crankcase
is then full with way too much oil, almost to the crankshaft bearing height, which floods the piston,
flywheel etc. flinging oil all over the internals. He has replaced the oil pump with a new one previously
as he though this may have been the problem, but this has had no effect. He has removed the oil filter
in the oil tank, the tank is well vented, and oil lines seem to be in good condition. Any thoughts
#3037 Are the feed and return pipes connected correctly? That is the feed to the feed side of the
pump and visa-versa.
#3067 The tube is in place, so there goes another option. My last thought at this stage is that he has a
double speed drive on the pump which in my experience causes major flooding to the point where the
exhaust port is full of oil, along with the top end etc! Both John Jennings and I had the same problem
and reverted back to the single worm drive - no more problems! I had suggested this to my mate last
year when the symptoms first appeared after his engine rebuild and thought he had already done this,
but apparently he had not. As he's just about torn all his hair out trying to find a solution whilst
retaining the double speed screw, I reckon he may well change it this time!
#3041 Feed and return lines crossed over?
L #3256 I have a problem getting oil to circulate after a rebuild. I have just finished re-building
the bike, although I didn't touch the bottom end of the motor except to blow and clean out all oil feeds.
I seems as though the oil pump doesn't have the strength to pull the ball valve off its seat. Remove
the ball and oil circulates - replace it and it does not. I have primed the pipe as per the handbook (4
times). I carefully sealed the pipe unions as per BMS service manual. When it last ran (admittedly 27
year ago) it was ok. Anybody got any ideas. I am using Castrol 20-50. How do I figure if the ball spring
is the correct strength? Return feed (scavenge) seems really strong.
#3257 It has been known for the ball and spring to be replaced upside down. However to pinpoint if
the ball and/or spring is the, problem take both out and see if the oil circulates. By the way general
consensus is that SAE 40 oil is better in a Velo engine (although this will not stop the oil circulation.)
#3258 You are probably sucking air. Did you make sure the oil feed line was primed i.e. filled with oil,
from a can and with no air pockets. One method of "force feed" is to seal the top of the oil tank (Flat of
hand) and blow down the breather pipe. It worked on an A7 BSA but we have never needed to do it to
the Veloplonk. Once the pump "takes up" all should be OK.
#3261 Check the ball valve & see its assembled correctly. Then - whilst its clean - suck on the bottom
to see if you can lift the ball of its seat (thats about 3psi) if you can , the motor will lift it OK but if not it
probably won't.
#3262 The oil valve spring is pretty feeble, if tried by hand. The ball should be nearest the oil tank,
with the spring below it. The sucking test is best, taking care not to get oil in your mouth. But
assuming the valve isn't gummed shut, and the ball isn't the wrong way round, and the spring is really
a Velo spring, the damned thing has to work. Problem of air in the line is physics: air can be
compressed but oil can't. If you blow a little compressed air into the oil tank, engine running, don't
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overdo it. If all the above seems OK but it still doesn't work, could be the feed side of the pump. But if
it works well with the ball out, then it isn't the pump, it is the ball valve. I presume that you have the
alloy tube in the centre of the oil filter, as otherwise, filling the filter chamber before you see the return
will tale even longer. Sometimes, due to that, it takes time before you see the oil ejaculating into the
tank, and your nerve may crack before the oil starts returning, causing you to stop the engine. Another
way is to take the little screw out the big end quill, and run the engine (but not too long). Engine oil
should squirt out there if the feed side of the pump is OK and there is no problem with your ball, or air
in your plumbing. But this starves the big end of oil, so should be done for only a few seconds. I
presume the feed pipe hasn't gone hard with age. Lot of riders use clear braided plastic, which doesn't
last long, and isn't really made for the job, but does allow you to see if there are any air bubbles. You
sometimes have to insist, but not too long.
#3264 We always "crack" the Rocker oil feed pipe bottom union nut to verify flow.
#3263 John I doubt many of us feel confident running a 'new' motor waiting for evidence of oil
returning to the tank. A few seconds seems like hours. Try the Nick Payton method of spark plug
removal and walking the bike in gear.
#3268 I would like to thank you all for your fast responses. This group is great. The oil pipes are new
and are made up of clear plastic, so its pretty easy to see when the return feed is working. Every thing
looks good here. The feed to the engine is filled with nice clean engine oil and its difficult to determine
visually if the oil is flowing. I am relying on the cracked rocker feed pipe to determine if the oil is being
sucked in and been circulated. Without the ball everything looks OK. With the ball oil doesn't circulate.
The spring in my old union was a bit mangled and since I couldn't buy a new spring separately, I
bought complete unit - ball, spring and housing. I actually tried both units, and oil did not flow in either
case. Anyway you have given me a few things to try. I will let you know what happens
#3270 When I reassembled it I pored oil down through the rockers to check the return feed (I did this
after following the "smoking Velo problem" discussed a couple of weeks back) so when it was started
it for the first time there was oil in the crankcase
#3271 I don't like to disturb the oil pump unnecessarily, and would recommend that the crankshaft is
removed through the timing gear and worm drive rather than removing the pump, but I had a Venom
that was reluctant to take its oil. I decided to remove the pump to check it, and it virtually fell out when
the 4 screws were removed, either the hole in the crankcase was too big or the pump was too small. I
cured this one by replacing the ball valve with a tap, which has its own dangers!. Also a MAC I still
have would circulate its oil when cold, only to seize up after about 20 miles, when the oil had stopped
circulating. On examining the pump I discovered that the body of the pump had a countersink
machined where the 2 gears meshed. I checked every other pump I could find and no other had this
feature. I replaced with a pump without this countersink and have had no more trouble.
#3272 With clear oil lines. already primed, it should be simple to detach the line at the outlet of the oil
tank, remove e'nuff oil to create a void of about 1 or 2 inches at the top of the line and re-attach. Start
the engine and observe the level of the oil in the clear line. As the pump pulls 1 cc out of the pipe, 1
cc of oil should come through the ball valve. As long as you do not allow all of the oil to be pulled from
the line, the pump will not be starved and the engine will not be harmed. In a moment or two of
running, you should be able to see if the ball is being pulled from its seat and oil flowing as designed.
In essence the oil line will become a drip feed sight glass. After the test, refill the pipe.
#3276 As you'll realize I've thought a lot about oil circulation recently (Smoky Venom). I've also learnt
(again) that often the problem is basic and not at all complicated (K-Tec). It seems to me that if you
have a good oil return when the ball valve isn't fitted this must mean that you have a good oil feed
when the ball valve isn't fitted which must mean the pump is OK. If the return stops when you fit the
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all valve it must mean there is a problem associated with the ball valve.
L #3288 I know you gentlefolk have discussed this before but that’s what you get for not keeping
all e mails ,I have 2 Macs and one I s being restored and I have just had a look in the oil tank and
cannot for the life of me find any info on the length of the alloy scavenger pipe, and what length it
needs to be from either the top or the bottom, can you help
#3291 You mean the pipe up the middle of the oil filter? The oil filter is sealed top and bottom. The
tube is a force fit over the central union, at the bottom, so that the oil rises into the filter chamber. The
tube cannot go to the top, or the oil could not pass into the centre of the oil filter. So the tube stops
short- by how much? Not critical, maybe 0.5" to 0.75". Thought of the week- below the filter, there is a
closed-off part of the filter chamber. It fills with oil. I see no way how that oil circulates.
#3294 Something which I think happens at times with new owners is that when they first change the
filter, they throw away the alloy pipe with the filter. I've wondered why it wasn't made to fit from top to
bottom, with some holes to let the oil into the filter. But normally, Velocette knew what they were
doing. But that "slug" of dead oil under the filter?
#3298 I have an alloy pipe on my VM approx 6.5 inches long ,it was loose so I contacted Grove(uk)
who sent me a replacement steel tube approx 4.75 inches. So then I was really confused so
counterbored the ally tube and used loctite to attach it to the return oil flow spigot -seems to work but I
wonder why the oil only flows into the filter in the top inch or so --this would seem to be inefficient use
of the filter. Something about the arrangement does not seem right. That said using common sense is
often a mistake when applied to machinery. Do have to second guess what Veloce had in mind or
does someone actually have the lowdown on this one?
#3300 . I met a guy with a Thruxton who in one breath was telling me about how he had modified this
tube to make it more efficient, in the next breath was complaining it was as smoky as hell when he
started it. The penny dropped when I pointed out the two are connected, drilling the tube causes all
the oil in the filter (and gunge) to drain back into the crankcase when the engine is shut off!
L #3951 On the KSS /Viper I fitted the non return valve to the feed at the oil tank. I now have a
doubt as to whether the pump can pull oil past the ball on its spring. The valve has the advantage that
you don't have to remember to close it at the end of a ride and, more important, open it before you
start the engine. The KSS has a spring valve on the supply side and I am told the KSS pump is
smaller than the Viper pump. As always any advice welcome.
#3953 The pump is the same size as the MAC uses, which on the later ones manages to draw oil
through the ball valve,(earlier ones had a ball valve in timing case one the pump outlet), also the KSS
pump turns at ½ engine speed which is much faster than the MAC or Viper turns it. If in doubt, check
the circulation when good and hot, if you have used the bike much, I guess you would have found out
by now if the oil stops circulating. My KSS/RS hybrid has a tap and a reminder (dymo) stuck on the
steering damper knob, and I live in fear of forgetting one day! -
#3959 You can use a waterproof micro switch attached to an oil on/off valve to insure safety. Just
install the micro switch to your oil valve so as it will ground out your magneto unless the oil valve is in
the "ON" position. If you forget to turn on your oil valve all that will happen is that your leg will
eventually get tired.
L #4055 Rode my Velo about 100 miles in light rain yesterday -- gutsy move for a 6v Lucas bike,
but all faired well. Each time I go out I lose a couple of fasteners. I suppose this will happen until I
eventually get everything locktighted. Yesterday I lost one of the screws that holds the oil pump into
the case. Does anyone have a thread specification for this screw? I took another one out and it
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doesn't match any of my thread gauges for SAE or Metric, so I'm guessing it's a British Whitworth or
other?
#4058 They are 3/16" British Standard Whitworth, as are the ones around the timing cover. The
original ones have a plain screwdriver slot, if they are replaced with allen key headed ones, don't do
them any tighter than you would turn a screwdriver, they are easily stripped!
#4068 The reason you are losing bolts will be one of two - either they are not tight enough so that the
required preload is not there to keep the bolts in tension, allowing the nuts to run off the thread, or the
fasteners have been overtightened causing the assembly to go into the preferred failure mode which
is that the bolt breaks at the first engaged thread, just under the nut. I'm not a great lover of Loctite,
except in a few particular applications, but believe that properly tightened and occasionally checked
fasteners, fitted with the appropriate shakeproof or locking washer, Nyloc or other appropriate locking
nut, will normally stay put. Overtightening can also cause premature thread failure (stripping) in some
cases - Helicoils are the best cure for stripped threads in alloy in my opinion, but must be correctly
installed. The alternative solid inserts sold by some places are not worth a light.
L #4160 Hello all, after fiddling with the oil lines, and reading the stern warning on the oil tank
about ensuring that the oil pump is primed before running my 1954 MAC, I thought I should know how
to carry out this procedure. What is the best way to make sure the oil pump is primed and all will be
well?
#4163 I use the old fashion thumb operated oil can, undo the feed line(oil wont come out of the tank
due to the sprung valve) pump oil into the oil line, if you hold the spout hard on to the oil line you will
actually be able to force oil into the engine oilways once the pipe is full. You will see when the oil lines
are full or if you don’t have translucent pipe you will feel the pressure build up on your thumb pumping
the oil. Just replace the oil pipe and your ready to start the engine. With the engine started keep the
revs low whilst watching the oil level in the tank, it should start go down, if it does not stop the engine
and find out why. After a while you will see the return oil spurting into the tank, you can now breathe
again, all is well. It always takes just that bit longer than you think before the oil returns to the tank, it
has to go round the engine collect in the sump before being pumped back where it then has to fill the
filter chamber first so don’t worry as long as the oil is going down, your engine is being supplied with
oil. All in all not an onerous task.
L #4290 In am ready to refit the oil pump into the crankcase on my KSS. It came out using the
1/4 BSF tapped holes into two of the retaining holes, fitting two screws and tapping out from inside the
case. The case was heated pretty hot but it was still reasonably tight and I get the impression that it
isn`t going to slide back in easily. I am concerned about the gears coming out of the pump body
during reassembly and can see that the job ought to be done upside down which is a little impractical.
Any ideas out there from people with experience.
#4291 Fit four lengths of 3/36 BSW studding for the pump to run along - back into the recess. Heat
the case up, possibly cool the pump in the fridge/ freezer. Holding the cases vertically, the pump will
slide down the studs and into the housing with no bother. The gears do not fall out - a little oil to hold
them in if you are worried. Once the pump is in the case check to ensure its seated right home - don't
forget the brass seating shim - tap the pump home if needed and fit the screws ASAP.
#4295 I've done this a couple of times on my Thruxton. Put the pump in the freezer overnight with the
sliding surfaces covered in grease. Heat cases well as suggested fit some guide studding. The
difference comes now - I didn't find that it just slid in easily..... line up and THUMP IT. If it tries to seize
THUMP HARDER! it WILL go!
#4299 Always bolt the two halves of the crank case together and heat as a unit. To prevent differential
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distortion.
#4303 It should NEVER be necessary to deliver more than a light tap on the inner end of the pump
body to REMOVE the pump, and refitting should involve no more effort required than SLIDING the
pump back into place. If the cases are heated sufficiently (and cooling the pump might help but is not
really necessary) then the pump will slide into place very easily with no effort. Thumping it into place
could cause the faces to score or pick up in the bore causing irreparable damage probably to the
softer material of the crankcases. I've said this before in previous postings - the proper method is to
heat the cases, ideally in an oven, but careful general heating with a blowtorch or a good hot air
blower will do equally well, just don't concentrate the heat in one spot. Heat until spit just starts to
sizzle off on contact, no more, and the pump will slide in or out perfectly. No damage will occur to the
cases by overheating when using this method, I can assure you.
L #4316 As I appear to be spending a bloody fortune on my MAC I think I would like to fit
Stainless, braided oil pipes. Anyone know where I can get these please. I just had the front brake
skimmed and oversize linings fitted to the front. Lovely job by SRM Engineering but really expensive
as well £105 !!
#4317 This may help - www.goodridge.net They make braided brake pipes and I think they make oil
lines as well, but you will have to check for correct thread.
#4319 Hello all, I have not had any experience with Goodrich, but I have used a company called
Baker Precision in Signal Hill California. I redid all of the brake lines for a vintage Ducati. I gave them
the desired lengths, and about two weeks later I had very beautiful crafted lines, with all the correct
banjo fittings etc. They indicated to me they had most all of the strange British threads and sizes; and
yes I can really relate to spending a small fortune on a MAC.
#4320 Can anyone tell me the correct lengths for these pipes please? I have the fittings but no pipes.
I can send them the old ones as a pattern but will need to make up the correct lengths.
#4351 The return hose is 19" long. However I would make up the oil pipes on the bike with cheap and
nasty clear 5/16" or 3/8" tubing and just wire the hose on. You can then send these as complete
patterns to whoever makes your hoses, as even being a quarter of an inch out spoils the line of the
pipe. You will then be assured that they will fit when you get them back. You can try Autohose in the
UK on 01782 542486 as they are old bike specialists.
#4353 That's exactly what I did - made up pipes with some bits of piping I found and marked them
with the internal bore that was needed. I sent them to Goodrich but if there are any problems I'll give
Autohose a call.
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B.6. Crankcase Breathing -
L #143 I've seen some weird systems with standard chaincases. One, probably practical but not
too pretty, was to weld a "blister" down the bottom of the chaincase, to increase the capacity. Another
guy put his engine breather into the chaincase, not the oil tank. Some schools of thought say to take
the engine breather, the one under the mag, straight out the back of the bike. This, they claim, avoids
re- cycling sulphur-laden oil back to the engine. This breather can be retro fitted. Stay around long
enough, you'll hear everything from the brilliant to the dangerous in mods. As you say, if there is a
real need, probably something can be done nowadays. Somebody over here says to take the alloy
tube out the centre of the filter. The purpose of this tube, as fitted by Velocette, is to stop the oil in the
filter going into the crankcase when the motor is stopped, and the Velo attitude seems to me correct.
Never assume you know better than Hall Green: they were pretty practical fellows. Bruce
#170 I'm in the process of adding crankcase and timing case breathers to my race viper and venom.
The viper had a small bore breather (1/8 in) on the timing case and the rocker inspection cover which
were obviously far too small to do anything useful. I've now added a 3/8in hole from the timing case
into the crankcase and a 3/8in bore breather fitting under the mag. I think these should be enough to
stop the piston pumping oil out the main bearing on a 350. The venom only had a 1/4in 8in bore
breather fitting under the mag, which I judge as woefully inadequate. This is being uprated to 3/8in
bore too, and I will put a 1/2in breather hole from timing case to crankcase. These are essential mods
for race bikes - or road bikes used in anger ! If you don’t screw the throttle, you wont pump much out
of the main bearing ! The side benefit that noone seems to discuss is that these breathers should
also allow the timing case oil drain work, as the piston will not be pumping oil back up it all the time !
Tony Finley has a specially made garter seal on his main cos he races hard ! BTW - there is another
belt manufacturer - Ray Thurston's son - who fits a seal as standard on his kit..
#178 Just to add to your comments, and I agree with your observation that Hall Green had a pretty
good idea what they were doing! Regarding engine breathing: updating the engine to the latest Velo
spec is about as good as you will get. This involves drilling through the back of the timing chest into
the main crankcase and fitting a breather outlet adapter in the back of the timing case underneath the
magneto. A pipe should lead from here to the oil tank which doubles as a separator, the oily stuff
stays in the system and the acidic gases then escape to atmosphere via the tank breather pipe which
should lead out to the back of the bike. This should NOT be returned to the chaincase or led in a
misguided attempt to lubricate the drive chain. Either of these options will result in premature failure
of either chain due to the corrosive effects of the breathed gas. This system is very similar to those
used on many modern machines and in racing, the only real difference that nowadays the gasses are
led back into the air box to be taken through the induction system and burnt as part of the emission
control system. If everything in the engine department is in good condition you should find that the
machine remains pretty well clean and dry, and there should be little or no fluid around the end of the
tank breather pipe. If the breather under the mag is led simply out to the rear of the machine you will
find it very quickly covered in oil!
L #181 I used with great success on my Thruxton a Moto Guzzi Le Mans Mk1 breather collector
box fitted under the seat at a greater height than the oil tank. The crankcase breather pipe ran into the
tank via a one way valve in the box, another pipe ran into the oil tank and a third pipe breathed to
atmosphere. The box needs a bit of modifying, but is well worth the effort. Royce Creasey described
the box in an article on engine breathing several years ago in Motorcycle Mechanics.
L #422 An article in a Fishtail some years ago mentions a Crankcase breather alteration. It
described how to do it, but had no technical info with it. It says, Drill a half inch hole behind the
camwheel from the timing chest into the crankcases. Drill a 1/4 BSP hole below the magneto and
insert the adaptor M275. I would quite like to do this, but would like perhaps a few more accurate
measurements before I attack my valuable cases with the pillar drill. Has anybody done it? or can
provide some measurements. The article was written by James Plant.
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L #584 As told previously, I got some noticeable quantity of oil coming off the crankcase
breather line. As seen in Parts List, would that help to drill a vent hole in the oil tank filler cap even
though there is already a breather line fitted to the oil tank ?
#596 The hole in the filler cap is about 1mm in diameter so it has a marginal effect on breathing,
however if it's like my Venom the hole will ensure that your leather trousers will require little in the way
of preservative. A fellow VOC member who has researched the topic of oil levels has recommended
the level to be 55mm below the top of a short necked filler cap.
#597Having previously posted a question relating to occasional crankcase oil flooding in my '50 MAC
(only occurs at sustained high RPMs), I now suspect that it is attributable to pressurization of the oil
tank. When I obtained this bike, it had no vent lines of any sort, and an unvented cap. Unfortunately, I
am currently prevented from verifying this theory, since having lost top gear two weekends ago, the
internals of the transmission are adorning my workbench. Hopefully, I will fix the latter problem, and
have a more definitive answer shortly. Ironically, while looking at a '47 KSS that a friend recently
obtained, I noted a tube that emerged in the vicinity of the rear mudguard and remarked, "What's that.
I don't have one of those." So it does appear that properly venting the tank/return leg of the oil system
is critical. My question relates to how much venting is required. Apparently, most [all?] bikes equipped
with a vented cap had a vent line as well. Is a one millimeter hole in the cap really adequate, or should
I add a vent line to the oil tank? I believe the originals were on the order of 1/4" I.D.
#598 Having similar problems with a 54 MAC- flooding the crankcase after a reasonably hard run, I
have no additional breather other than the 1mm hole in the oil tank cap either. However my main
intermittent problem which may be related has been -getting far to much oil into the combustion
camber at start-up. Obviously splashing up from the crankcase literally heaps of white smoke for
about-10-15 minutes far to much and long for just a guide wear draining back issue and yes my valve
guides and rings are tired). I have fitted a new ball/spring/seat in the one-way valve to no avail and
have checked for air leaks the pump is also returning a good flow, which is basically constant. Being a
novice looking for advice, and not knowing the correct oil level for the tank-I have been experimenting
and found that lowering the oil level in the tank to just below half and changing to a straight 30 grade
oil seems to reduced the problem considerably. Is there a correct ration re oil- tank volume and
engine/oil line capacity that determines the correct oil tank level or have I been basically overfilling the
tank ? What is the approximate volume of oil that should be left in the crankcase after standing
overnight? Like to know more about additional breather set-ups.
#599 The breathing system on older Velos is a bit marginal to say the least, and if no other breather is
fitted to the oil tank other than the 1mm hole in the cap it's no wonder that at times the cases will
flood. My Venom always had a breather on the back of the oil tank which internally went up to the top
of the froth tower and externally was led via a 3/8" bore pipe out to the back of the machine to
atmosphere. This always provided adequate breathing even when the machine was modified to the
later engine breathing system where an adapter is fitted to the back of the timing case below the
magneto and the ½" bore pipe leading from this breathes into the oil tank. I don't have a vented cap
and have no problems with excessive amounts of oil smothering the machine or my leathers either!
The engine does still breathe into the chaincase through the hole in the drive side mainshaft as well
and although this has recently been a bit excessive and necessitated regular draining of the case, I've
recently had the oil pump overhauled properly for the first time in its life and hope that this will cure
that particular problem. I think that a 1/4" bore pipe would be a bit too small to do the job right, and
you should remember that if no froth tower is fitted to your tank you are very likely to have a big
problem with excessive external lubrication, since the function of the tower is to separate oil from
breathed vapour.
#606 One point I perhaps ought to point out re breather vent pipes is that they should NEVER be
routed to discharge on to the chain. Whilst it may seem to be a good idea to lubricate the chain with
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any vented oil, the breathed vapour is in fact acidic and will shorten the life of the chain and sprockets
if allowed to exit in this way. The best place I have found is to lead the pipe (whose length is specified
in the parts book and is important for correct operation) out of the rear of the machine by ty-rapping it
along the underside of the nearside rear mudguard stay
#608 Do you mean that a pipe shall be routed from the crankcase oil breather the small tube at the
bottom inboard side of the oil tank ? I expected this small pipe being a breather outlet ?
#609 The small tube at the bottom of the oil tank must be blocked and takes no part in the breather
system. A hole is drilled and tapped into the crankcase just under the magneto. A screwed hose
adaptor is positioned and a 12mm plastic pipe attached. A hole is drilled into the back of the oil tank
and a 12mm tube brazed or silver soldered to place. The dimensions and angles are fairly critical. (I
have them somewhere) A second hole and tube at attached to the top, rear, of the froth/foam tower.
The tube from this is lead to atmosphere. The dimension of the lengths of the two tubes are critical if
the pulsations created by the positive and negative pressured in the crankcase or not to cause a
pumping effect and evacuate the oil. Also the vent hole in the oil tank cap should be blocked.
#619 You are right to say that this is the breather outlet. For the original
Venom/Viper/Endurance/Scrambler/MSS/Clubman tank this is, if I remember correctly, a spigot for a
5/16" bore pipe, 11" long which is clipped to the rear mudguard in front of the rear wheel - a positively
diabolical place to locate it if you are prone to overfilling the tank! I do know that you have had some
details from Keith about the later crankcase breather mods so I won't elaborate on these other than to
say that the position of the outlet on the back of the timing chest is quite critical and there is only a
very small space to fit it! There is a cast wall which surrounds the bottom circumference of the
magneto pinion inside the timing chest, below which is a small almost triangular area which is the
target to aim for when you drill through from the back of the case. If you drill above this the hole will be
shielded by the pinion which will then proceed to pump oil out at an alarming rate. In addition a ½"
hole should be drilled through the back of the timing chest into the crankcase. I'm not sure of the
exact location for this and since my engine is currently in one piece I do not intend to take it apart to
find out! I do believe however that it is documented in back issues of Fishtail.
#624 looking to my Venom, (because I've read that someone has nearly the same problem for a MAC
and may be this would make some difference) I already have a breather adaptor on the crankcase
with a tube fitted to it going no-where, but no other tubing on the oil tank than : the tank breather itself
(only 5 or 6 in. long) and the engine feed and return pipes. If this is a standard arrangement, how long
shall be the oil tank breather tube, and the engine breather tube ? or how can I have the tank modified
so the engine breathes into the oil tank ?
#625 Since your oil tank has no other form of breather I think you would be correct in thinking that you
should have a vented cap, and the flooding scenario suggests that the build-up of heat during
sustained high speed operation is causing the tank to pressurized and prevent the return of oil to the
tank from the engine. The simple solution would be the vented cap of course, but I don't think that a
hole as big as 1/4" would be necessary and may result in a well lubricated right leg! Your engine will
breathe through the 1/8" diameter hole that runs through the drive side mainshaft into the primary
chaincase via the channels cut in the inner diameter of the engine sprocket. This system was found to
be inadequate for higher performance engines and was eventually developed into the alternative
system as I described, and incorporated in all late models, I think from about 1967, but I stand to be
corrected on this. My own Venom is a 1962 model which originally had only the mainshaft type
breather and the oil tank was fitted with a filter chamber as I described earlier, and only the 1/4" bore
tank breather tube from the rear. I have since fitted a Thruxton spec tank which sits a little further
rearward than the original to give room for the longer inlet tract (or a decent length of velocity stack),
and have modified the crankcases to bring them up to the latest spec. So far I've retained the original
system of breathing into the chaincase as well, since this must help to lubricate the shock absorber
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cam, sprocket and primary chain, but it still suffered from what I considered to be excessive breathing
into the chaincase. Following advice from the good people at Seymours, I've just had the oil pump
overhauled for the first time in the machine's sometimes hard life and hope that all will now be perfect
enough to report soon that the chaincase remains reasonably dry. We shall see! Shall be interested to
hear what you find on the gearbox front. We happen to be on common ground here since mine too is
dismantled at present for renewal of the sleeve gear bush in an effort to restore efficient clutch
operation. I sometimes think that we old bike fans would be lost if we weren't tinkering with bits of
machinery!
L #761There is a breather from the inside of the timing casing to a stub (3/8 bore) at the top
inside of the oil tank. I can't remember this from my last Venom, though it is a long time ago and it
seems a reasonable thing to do. The oil tank also has a stub pipe (1/4 bore) on the inside at the
bottom. This has no pipe leading from it. It seems to be a breather with an internal pipe leading to the
top of the tank. Is it? If it is, why does it come out of the tank near the bottom? Should it have a pipe
on it and if so should it just exit somewhere convenient or should it be piped to somewhere in
particular?
#765 Regarding the additional engine breather. Apparently at certain rpm it was found that crankcase
pressure prevented adequate draining of oil from the rockers / cylinder head. An additional breather
was added from the timing chest, underneath the magneto, to the top of the oil tank. This then vented
via a tube from the froth tower to the rear of the bike. This was introduced in the mid sixties, but it is
an often found modification - my machine included. I believe prior to this normal crankcase venting
was through the chaincase. A previous owner of my machine even vented the chaincase via a snazzy
little breather tube arranged from the chaincase inspection cover. I think the small 1/4 bore pipe at the
bottom of the tank was a breather which was also used to lubricate the chain (this being blanked off
on my machine). A cartridge conversion is available via the Velo owners club which replaces the felt
filter with a paper cartridge type. This fits in the original filter tube and is spring mounted which allows
oil to bypass the filter if it becomes blocked.
#766 Reference to previous postings will yield a lot of info on the breather subject and in general what
Brian says here is correct. However, I can see no advantage to the breather tube from the chaincase
since this is already very free to breathe due to the huge hole through which the shock absorber
spring protrudes, and secondly, the 1/4" bore pipe at the bottom of the tank really should not be led to
the chain in an attempt to lubricate it. This is the tank breather which should vent to atmosphere well
away from the chain since the acidic gasses that exude from this pipe will help to cause premature
corrosion of the drive train. Mine is led along the rear subframe and simply vents to the rear of the
machine where it can do no damage.
L #828 My apologies for taking so long to get back to you on this one. My oil tank is one which
began life as a standard Venom tank and has been modified to Thruxton spec including relocating the
mounting position rearwards to provide clearance for a long velocity stack or inlet manifold, and is now
also chamfered on the inner rear corner to clear the rear mudguard, so the actual position of the
breather pipe connections may not be quite where you would want them on your machine. However,
the 21.375" crankcase to oil tank breather hose is 10mm bore reinforced PVC, pushed on to a 1½"
long stub of fairly thin walled tube which I think is 3/8" ID. Off hand I can't remember the dimensions
of the crankcase connection but the hose is a good fit there too. The tank connection is welded about
½" from the top of the tank, just behind the filter chamber in a position which will clear the frame down
tube. The tank breather is also relocated about 2" below and 1" to the rear of the engine breather
connection in a position to clear the rear mudguard. This is ¼" tube and extends up inside the tank to
the top of the froth tower, and has a length of ¼" ID reinforced PVC hose 27½" long venting to
atmosphere at the rear of the machine.
L #1223 Many modern engines employ a one-way check valve in the crankcase breather
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system. Wouldn't a 500cc Venom engine benefit from a check valve in the breather system? Can
anyone here supply any info on past efforts to use such a valve?
#1224 I have fitted to my Thruxton a Moto Guzzi Mk11 Le Mans breather as advocated by Royce
Greasy in Classic Mechanics and it has being very successful. The box and pipe outlets needed
alteration plus a couple of outlet pipes blanking off, the box contains a one way valve and I found it
"cleaned up" my Thruxton brilliantly. It must be fitted so it is above the oil tank so excess oil drains
back into the tank but with a little thought this is easily achieved.
#1235 I have not seen the breather article either but I have been using a reed valve in my Thruxton
breather for some time. I might add this works most effectively if you have fitted a seal to the end of
the drive side mainshaft. Otherwise air is just going to be pulled right back in at that point. Interesting
that the KTT engine is fitted with a timed breath (same effect) but Velocette did not see fit to add it to
later models.
#1237 Good point about the shaft seal. I'd not realized the size of the opening. I've intended to use a
reed valve from a airhead BMW. The valve is an aluminum disc approx. 25 mm in diameter with a
reed and stopped in the middle. The disc will be inserted in a aluminum cylinder turned up from some
bar stock and finished with a couple of barbed nipples for the breather hose. It will cost me about an
hour of time to build it and 7 bucks for the reed valve. The whole affair will be about 1 inch in diameter
and 1 1/2 inches long. What did you use for your valve? I may be able to beat the size and buy one
off the shelf.
#1248 A few aftermarket companies make one way breathers, especially for Harleys. Try Spyke.com
for one. I've also run, with varying degrees of success, automotive PCV valves, smog (gulp) valves
and power brake booster valves. Bring your girlfriend to the auto parts store and have her find one
that blows a lot of air in one direction with least effort to open and nothing the other way. Sealing the
mainshaft is tougher. Only way I've found is to put the case in the lathe and open the hole out to
1.875 for a .188 wide lip seal. One could easily make a tool to do it in situ. I've heard of lubing the
shaft and squirting silicone seal in there to make a seal of sorts. Might work, might make a mess.
#1249 I have been using a breather intended for a certain American motorcycle for two years now. Its
available from www.dohertymachine.com. I don’t know if it’s worth installing, had quite a lot of work to
get it operating properly. One problem which is not finally solved yet is to plug the mainshaft breather
hole, haven’t found a reliable way to make a plug stick and it seems to work better when that hole is
plugged. Another problem is that there comes quite a lot of oil from the below mag breather outlet and
that must be taken care of somehow so now I have a hose from below the mag to the oil tank and the
breather valve is installed on the oil tank breather outlet. This tends to pressurize the oil tank so my
only engine leak is now from the oil filler cap. I still have problems with oil leaking from the gearbox
into the primary chain cover and eventually out from there in the usual places. Third problem is the
sound, the description oink oink is quite accurate. Have tried several ways of insulating the breather
valve but its still audible if You listen for it. It did cure the problem though of very small oil leaks from
several places on the engine especially after a hard ride but the system still needs further
development.
#1255 Surely if a valve of this type is fitted it should be in the breather line from below the mag to the
oil tank? This would prevent tank pressurization due to the positive pressure required to open the
valve and consequently prevent leakage from the tank cap. The tank will still act as a separator/catch
tank to catch any oil returned through the engine breather and the tank breather will still work as
intended and vent only dry(ish) gasses.
#1257 I just happened to fit a drive side oil seal, because I use a Watson belt drive and oil always was
pumped into the primary drive up to the point when it exits through the felt ring after 200 miles. Now
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we in Europe are strangled finding the correct diameter size seal. And the seal must be of tiny
proportions anyway that it can be fitted. The nearest solution was a metric seal with 35 mm inner
diameter, and this is not a proper shaft seal with an inner wire spring, just a lipped seal like for fork
stanchions. For fitting the crankcase has to me machined with a recess, in my case the top hat bush
was the victim, and the boss and recess of the primary sprocket as well to get it down to 35mm. I
plugged the breather whole in the crank and used silkone gasket on the slots in the sprocket facing
the flywheel. To lubricate for the rocking motion when the shock absorber is acting, I filled the inner
recess in the sprocket with grease. If the whole system works I can not say yet.
#1262 Thanks for info. I will try that this summer. I thought there would be a risk that the hose would
be filled with oil after the breather valve.
#1266 A little oil may collect in the pipe but it should be of no consequence. If there were no valve in
the pipe then any oil there would either lie in the lowest point of the pipe or drain back into the
crankcase when the engine is stopped, but if the breather adapter under the magneto is in the right
place then the amount of oil finding its way into the pipe is quite small, the main purpose is after all to
breathe gasses, not liquid. There is of course some liquid content but this is separated out in the tank.
The majority of this liquid is carried into the tank while the engine is running, and only a minuscule
amount which drops out onto the walls of the pipe actually remains there when the engine stops.
L #4066 At long last my '55 MAC is getting a long overdue rebuild (to my usual standards!) I
have flattened all joint surfaces in a bid to slow the leaks, and have drilled and fitted a breather under
the magneto. The question is what do I do with the pipe? Can it be just run to the back of the bike or
must it go via the oil tank? The MAC tank would need some pipework welded in to do it properly, but it
has no froth tower, just a raised filler cap. Any suggestions would be most welcome.
#4069 The crankcase breather must breathe into the oil tank since it will carry a lot of oil out with the
breathed vapour. This is normally separated out in the tank, and the froth tower system keeps the oil
in the tank and only dry (ish) vapour out of the rear breather pipe. If you don't have a froth tower you
can only hope that not too much oil finds it's way out of the breather hole in the tank cap, but this hole
really isn't big enough to allow the engine to breathe correctly and I would recommend that you invest
in having the tank modified to incorporate the full late breather system plumbing.
#4072 There are two critical lengths for the pipes to balance the natural frequency of the engine.
Without them it is said that the oil will be evacuated. Someone will tell you the correct lengths, or if not
we will find the information in the Veloplonk draw and respond.
#4086 The adaptor to oil tank pipe should be 3/8 bore 21.375". Oil tank to wheel 27.5"
#4088 Please advise where exactly do you take these measurements from? They seem very tight
tolerance!
#4092 You don't take the measurements from any point to any point, they are just the length of the
pipes.
#4070 Agreed, I have tried several times to vent the timing chest breather directly out to the rear of
the bike, even going as far as putting a baffle inside the timing chest in front of the outlet hole. All in
vein, there is just too much oil flying around in the timing chest. In desperation, during the summer
rally, I routed the hose into the side of a plastic bottle, the air free to flow out the top. This worked fine
except I had to empty the can back into the oil tank at every stop! You mentioned you drilled the
breather tube hole under the mag. Make sure you also have the required holes leading from the crank
case to the timing chest.
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#4111 My first attempt to correct excessive oil breathing on my VM (aka "The Torrey Canyon")
involved fitting the standard BSP hose connection under the magneto and piping it to a small cast
alloy box mounted on a bracket under the dualseat. The other end of the box was piped to the general
area of the rear number plate. I ran a flexible quarter inch pipe from the bottom of this box through a
hole drilled in the top of a scruffy old oil tank cap and stuffed the box with pot scourers. There were
BSP stud couplings everywhere but the installation was fairly tidy and it just about worked. Until, after
about 3000 miles I looked inside the alloy box to find a disgusting mixture of mayonaise and rust - no
sign of the pot scourers. That's what happens if you get the breather pipe lengths wrong. Since then I
have done the proper job as outlined in Rod Burris' book but I've only piped to the oil tank; no external
pipe to the rear. The timing chest / rocker box behaves as a plenum chamber and, to a limited extent,
so does the oil tank; hence the reduced oil loss to the rear wheel when the tank is half full.
#4105 I reproduce here exactly Les's article. It appears that I am mistaken in that over the years Les &
I discussed, (mostly by mail ) various ideas on breathers & other things, & while I am sure that at one
point he was playing with some sort of timed 'valving' ideas, this article & the only drawing that I have
which is listed numerically, has no corresponding 'valve' drawing as I mentioned in my last mail, & I
have to draw the conclusion that this 'valve' is nothing more than an oil trap & drain idea that he
discusses in the article. The idea behind it's success being no more than the use of a large diameter
vent which he states should be routed well up above the unit, & the fact that any oil picked up remains
in a chamber & large capacity outlet tube of relatively static, though pulsating air, from which it drains
back to the bottom of the casing, & eventually back to the crankcase. Any 'timing' is no more than
striking a situation where pulsating air flow is reduced to minimum movement, - or even made static, at
which point oil has the chance to settle on the surrounding surfaces of the breather chamber, as well
as the inside surface of the large diameter vent tube & drain downwards. Further to this one would
deduce that as RPM rises, the oil would tend to settle out closer to the timing case, while if the engine
was running at low RPM, the fluctuations in the air direction would move towards the outlet vent tube,
whatever, theoretically if the point of comparatively static air can be kept within the confines of the
'valve chamber' 100 % of the oil held in suspension, should drop out & drain.!
ENGINE BREATHERS 'M' SERIES VELOCETTES - By Les Diener.
Over the years much has been written, & many designs of crankcase breathers used on various
machines, & without doubt the single cylinder engine presents the greatest challenge, due to the
amount of 'suck & blow' on each revolution. The greatest problem is to provide sufficient means for
the c/case to pass air only during the breathing cycle, & not a mixture of air & oil which, unless
suppressed, finishes up on the rear tire with possible disastrous consequences, & generally leaving a
mess in the process. The problem becomes rapidly worse with increasing engine speeds, & also when
flywheel assys. are more snugly fitted into c/cases, both situations demanding almost complete
evacuation & refill of the c/case voids during each revolution, whereas with slower revving engines, &
those having oodles of space around the flywheel assy. there is a form of 'cushion' on which to act.
Reflecting back over the years it would appear that in most cases c/case breathers were too small, but
a notable exception will be detected on most Italian machines. Moto Guzzi, Benelli, Morini, & others
always had huge c/case breathers which were mounted in a vertical position at some convenient spot
on top of the c/case, & with some form of 'trap-& -oil-drain' provided to separate oil & air. In later years
one Japanese example of this design was featured on the little CR 93 Honda, & whilst this was only a
125 cc racer, a huge breather tube of some 20 mm I.D. hose went out along the upper frame member
to the rear of the machine, preceded by a large 'trap' housing, which no doubt would have contained
some form of baffle which would have allowed the oil to drain back into the sump. Timed breathers
which have been used on all KTT engines & others, have been reasonably successful but are not
altogether foolproof as the engine RPM goes beyond 6000, firstly because the orifices through which
the air must pass is so small,& also that very positive seals are required to allow the breather valve
function to operate efficiently. Disc or 'clacker' valves are much the same. So, in summarizing, the
Italian concept would appear to be the best compromise, in that BREATHERS must be 'BIG'. The
design shown is what I have on the 'ELDEE' classic racer, & whether by luck or coincidence, has
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turned out to be the most efficient breather that I have ever used, for even with the engine running to
9000 RPM, not one drop of oil leaves the trap housing, & this is evidenced in the 3/4 inch I.D.
transparent plastic vent tube. The 'trap' can be fitted to all the earlier M series without problems, but
on the later 'domed' timing chest covers, a small 'platform' must be built up by tig welding. First it is
desirable to drill 2 additional ½ inch holes between c/case & the timing chest. Then drill a 7/32" hole,
on an angle, underneath the timing side main bearing, into the c/case, this is to always keep the
timing chest free of oil build up. This is only possible on later model c/cases, which have a large radius
cast below the T/S main bearing. Next drill a 5/8 " hole through the timing case cover in line with the
magneto spindle, a 5/16" hole is then drilled 11/16" below the centre of the 5/8" hole. (it may be
necessary to skim the surface of the timing cover at this point to provide a flat surface ) The housing is
then mounted to the timing cover with the 5/16" hole directly in line with the annular groove in the
housing & immediately below the 3/8" wide drain slot. Drill & tap the 4 mounting holes, & fit the
housing with jointing compound. ( At this point I have checked photos of the ELDEE & noted that Les
actually used 6 screws instead of the 4 shown in his drawing ) Take the 3/4 inch clear PVC hose
straight up as far as possible & route to the rear under the seat to the rear of the machine, & if my
experience is evidence, you have a breather that works ! Signed Les Diener.
#5417 It seems that there is room for comment here ? Re. Les Diener's experiments. As I remember
it, he started with the idea of a 'timed' device, & with this in mind, he machined a flat spot on the
outside of the timing case centred on the magneto spindle. The idea was to have a light circular body
that was ported internally, & vented back to the 'catch tin' via a hose in the usual manner. A light
rotary valve arrangement to be supported on the magneto spindle, but with ample running clearance
to the body of the valve, no contact whatsoever ! The idea being that despite air leakage via the
clearances in the device, the ports closing off at a critical point in the engine's rotation, the pulses
moving out through the outlet pipe, would be reduced to a minor steady flow, where with the
centrifugal force of the spinning valve & the construction of the body would induce most of any oil
laden air to drop the oil in suspension on to the inside of the body, where it would simply drain back
internally into the timing case. I believe he opened up the hole from c/case to timing cover to reduce
the pulses in the c/case somewhat also. Some of this may be in his writings somewhere ? He kept me
informed of his ongoing progress, at one point stating that the timing of the porting was extremely
critical both in the timing & the size of the ports. I must have missed the end of the story, as I was
surprised to find that the end result of all the experimentation was just the original simple chamber,
with no valve whatsoever, but working simply because he had come to realize that the device
equipped with a VERY LARGE BORE outlet hose, running up as high as possible, - & eventually to
the catch can, was in fact working in a harmonic fashion after the style of a 'tuned' exhaust pipe. The
action of the original timing device body having been re-worked to act as an efficient oil trap in a
convenient & efficient point in the system. All this is apparent in his detailed drawing, & according to
him, it worked perfectly, one would assume , best at racing RPM ! Les has been gone for more than
10 (11?) years now, & I still haven’t located his original ELDEE engine drawings, or his casting
patterns, someone out there is sitting on them I guess ? -- on the other hand, - maybe they were just
burned by someone who never considered them valuable .
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B.7. Racing and High Performance -
L #35 The easiest way to get your Viper to go faster, is to fit a Venom barrel and head. Better
yet, a Thruxton barrel and head! I have a Viper clubman, and it won't do over about 90, with a fairly
fresh motor. But, I remember at Montlhery several Vipers, and in discussion with their owners, they all
claimed to get over 100mph out of them, with no great trickery. Any thoughts on this, fellows? P d'O
#54 Try shedding some pounds. This is easier to do to the bike than the rider. A 50 pound reduction in
stock bike weight should be close to trying to gain 5 hp on a Viper. I have a Venom based racer that is
down to 240 lbs with fuel and oil (non-stock frame). It makes a big difference A box of clean spark
plugs and a selection of sprockets will do wonders. Spend the time dialing in your carbs and ignition.
Make lots of high-speed runs and immediately take those plug readings. A crisp running engine can
add an easy 5 mph to the top end
L #36 I am taking up sprinting using a 1937 MSS running on methanol with an 1 3/16 inch
10TT9, running on a standard M18/2 with standard followers. The clutch is to Thruxton spec. In my
first year my key objective is to be able to slow the beast down, as currently it has a rigid MAC 6 inch
hub (frame and forks are MSS/KSS). I seem to have been spending the last month converting a cast
MAC/MSS 7 inch front hub to fit the webs. Turned up lots of 5/8 inch to ½ inch spacers (in titanium),
and converting a 5/8 inch diameter spindle to having ½ inch BS Cycle ends. Titanium is a funny metal;
do you know you can get it to ignite when you turn it? I have been researching the subject of speed.
First thing is to speak to all the fast Velo boys at the meetings; they are only too pleased to be of help.
Secondly there have been some excellent articles on tuning Velos in Fishtail and Fishtail West by Nick
Vann, Dennis Quinlan, Bill Melville, Marin Violette, Robert Gussman, peter Witman and Laurie Nunn.
These appeared in a reprint of the technical articles in Fishtail, by our American cousins.
#59 While you are busy tossing the weight off your frame, think about getting some serious weight off
your valve train. That will help you raise the rev limit. Velos breathe fairly well with the 17/8 cam.
Problem was they tangle valves just over 6200 rpm (Venom). Actually they seem to be pulling hard
until then which indicates that power is still being made. Lightening the valve train will allow the revs to
increase. There is a problem with this though, as the revs increase the stresses on the crankcases
built substantially. As such, at the same time you lighten the valve train think about using parallel roller
main bearings or machine a steel top hat reinforcement piece for the drive side main bearing if you
stay with the taper rollers. The drive side case is definitely a weak point. I run a 9.75 to 1 compression
ratio, Sommerton polydyne cam, and my rev limit is 7,500 rpm (self imposed). I have run it out to over
8,000 rpm (undergeared and I wasn’t going to let that Manx get past me on the long straight) and the
bike is still pulling hard. I wouldn’t try go to this level without extensive engine work. I have lots of
mods, titanium bits and extensively reinforced engine cases (and even they have cracked). Many
bikes tend to run out of breath as the revs increase. The Mac, for example, with its mild cam just tends
to let you know that there is no gain in wringing the throttle any more, time to shift.
L #64 I am a member of the local WA Historic racing Club and have a '38 Mac. I'm having
trouble with second gear, it broke and I am advised by those that know that this is a common problem
and the best way out is to replace it with a pre-war MSS box, or it will just continue to happen. Any
thoughts? I am having great difficulty in finding a replacement 2nd gear in Oz. The Mac has close
ratio gearset and close ratio sleeve gear, SW springs, triumph front wheel, and runs on Methanol.
The barrel has had the cast iron fins removed and replaced with shrunk-fit alloy roundies for better
heat dispersion. I was using Castrol "R" but due to the difficulty in obtaining it and the high cost, am
flushing out the system and replacing it with a 50w oil, any suggestions on what to use given that it
does not get very cold over here and we do a maximum of about 6 laps per race, three races a day
plus 2 practice sessions. 4 others from our local Velo club are also racing this year having built up
pre-war 350's to come and play! We are trying to encourage other pre-war machines as this class is
just me at present, so I'm looking forward to solving a few minor niggles before the season starts.
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#65 I have checked the spares lists of the major suppliers in the UK and no one has this gear
available as new old stock. Probably because they break!
#66 Hello MT, yes, if the power goes up on your MAC, the second gear will continually be a source of
trouble. I don't know whether it's cheaper to have a batch of gears made or replace your 'box with
one from a K or MSS, as you'll have to make frame mod's as well. Probably the cheapest way is to
source used MAC clusters and expect a gearbox teardown frequently. If your average race is only 6
laps and you're running on methanol, I would think synthetic 20/50w oil should be plenty for your bike;
you might even get away with straight 20 or 30w synthetic, and I know several vintage racers who
use this. NSU used pre-heated 15w in their GP racers, and that was 1950's oil. I doubt your engine
will get hot enough to really thin the straight 50, so you'll be losing hp to drag. People use straight 50
to keep film strength in a really hot engine, but I think in your case it's just a hindrance.
#78 Strangely enough while a close ratio gear cluster was never listed for a MAC, it was for a GTP!
(Owning a GTP, I can’t think why). The alternative that some of the serious racing carry out is to grind
Venom gears to suit.
L #75 Can anyone help me with this one? My Mac racer (pre-war) has Iron head and barrel, with
fins machined off and aluminum fins shrunk fit, running methanol. Should I run a copper head gasket
as per later models, or just lap it in as per earlier ones? At the moment the exhaust valve is just
marking the piston and rather than reset it, I'm thinking that the extra clearance gained by using the
copper gasket might be a better option. Any thoughts?
#76 I think the copper gasket is essential in this case unless you want to start machining things like
piston crowns. If fact, you could pretty accurately measure your piston/valve clearance by varying the
head gasket thickness (it will compress slightly when you torque the head bolts). Especially as it
seems about at Zero at the moment; a good starting point! Just out of curiosity, what sort of CR are
you running with that piston?
L #283 Over the last ten years or so I have been planning to build a MAC sprinter. During that
time I have been researching what I need to do to tune the engine by reading about and speaking to
everyone that races iron Velos. In the end I opted for a 1937 MSS, which is very similar to a MOV.
Some of what I have described, I have carried out – some I will carry in the near future. Crankcases.
The MOV/MAC crankcase is as thick and strong as a Venom, it also has less cylinder overhang. David
Holmes and Nigel Lines who have produced the fastest iron pushrod Velos have not reinforced the
crankcases, so I doubt if you will need to. One of our fellow club members has converted his main
bearings to roller mains, but I am not sure what best solution is in this area. My MSS has been
converted to post war specification that is taper rollers similar to a Venom. Polish both the inside of
the crankcase and the crank to reduce drag. Also polish the con rod to reduce the likelihood of the rod
fracturing. I am not sure what the balance factor is best so I would leave it as it is. - Cams – The ideal
cam for a MOV is a M17/6 similar timing to a Venom but slightly less lift. Unfortunately they are very
difficult to find. Use a M17/8, but you will need to remove about 3mm. from the valve spring cup and
the bottom of the rocker box where the rocker touches when on full lift. Finally if you can’t get hold of
any of the above, you can use an iron MSS cam M17/2. - Valve Gear. Lighten the rockers, cam
followers and pushrods as shown in the attachments. There is also an oiling mod to supply additional
oil to the guides, but it is difficult to describe in print. - Carbs – for a MAC a 1 3/32 inch TT carbs is the
most appropriate and as big as you should go. However a 1 1/16 inch Amal 276 will do a similar job.
Increase the induction tract length by fitting a one inch spacer between the carbs and head. You can
use a larger inlet valve up to 1.5 inch. Ideally use a Nimonic 80 exhaust valve from a Viper and turn it
down to fit. The exhaust valve needs to be a loose fit in the guide to avoid seizure. Ideally you should
remake the guides out of aluminum bronze. - Valve springs. Use light alloy collars and springs
available from Nick Peyton. Approx cost £ 38. You could also consider fitting rocker return springs
available from R. F Seymour, although the jury is out on the benefits of this. - Pistons – methanol
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pistons although rare do exist. However the most common solution is a high compression Triumph
piston. It will need some fettling to make it fit and to obtain the correct compression ratio. - Oil system.
Replace the single worm oil pump drive with a double drive worm from a 86mm Velo. While you are at
it, fit a 86mm cam steady plate with the cam oiling jet. This will involve silver soldering a boss onto the
existing timing cover feed pipe and drilling into the pipe, not the easiest of jobs. If originality isn’t
important use a Venom / Viper timing cover and save yourself all the extra work. If you have a
crankcase with the rear cylinder oiling jet you can blank this off by using an ordinary bolt, rather than
the oil feed bolt. Then drill two small holes the same size as those found in the cam oiling jet in the
feed to the back to the cylinder – this is tricky to get them at exactly the correct angle to spray oil onto
the cams. Finally silver solder two one eighth inch bore pipes near to the bottom of each of the valve
spring cups to help drain the oil away. Use of flexible tube to connect this to a Venom type pushrod
tube. Finally buy a copy of Phil Irving’s book “Tuning for Speed”, it’s packed with practical and useful
information. Perhaps some of the MAC racers in the group can comment or add to my note May be
vibrations or force makes to flax the crank shaft? What I think is, primarily chain sprocket have to be
run as close as crank centre to reduce effective distance of shaft. This mean sprocket as close as
crankcase? The end of shaft there is a shock absorber. I think they have to go as they are hanging a
lot! This mean have to use rear hub like Triumph (with absorber inside) or convert to the primarily belt
drive?
L #257 1961 Venom with fairing and 3.9:1 top gear = 110-112 mph Standard Venom top gear
ratio 4.9:1 = 96 mph.
L #560 I got a 58 Venom since two years now and try to get it to its 100 MPH told capacity. By
now, the Lucas Racing magneto has been overhauled and the carburettor is a new Amal Monobloc
(checked and re-checked by my workshop), fitted with a 330 main jet. Test after test, the engine is
very smooth, but the power "flattens" when reaching 75/80 MPH with only 3/4 throttle with some
impressive vibration. Looking for any possible reason, I would like to know if this 100 MPH
performance can be reach with the standard 18 teeth sprocket, or if I need to fit a 19 or 20 teeth
sprocket in order to be able (may be) to get the bike to 160 km/h ? Regarding the vibration, may be
the wheel chain tension is too high, and I will correct that as soon as I got time. Another question is
that it seems that the engine oil is "jettisoned" through the oil breather tube. I got a recovery bottle
(half a litter), fitted with its own breather tube facing the road to limit the spillage. What is interesting is
that the bottle is full after 300 or 400 km, but when oil drops comes out of the forward outlet tube, the
oil consumption is then ridiculous. I had in the past a Ducati Darmah. In the oil breather line, there was
a restrictor dedicated to prevent the oil breather to act as a jet pump (or a jettison as we call in my
job). Does the oil breather adaptor mentioned in the Velocette Parts List contain a restriction or shall I
fabricate one in order to be sure that only oil "smoke" only goes through the breather line ? The fact
that oil consumption comes back to normal figures when the bottle is full tends me to think I shall.
#566 You will need minimum 19 tooth sprocket, or an enormous rear tyre with an 18 tooth sprocket to
pull the ton on your Venom, assuming 6200 rpm rev limit. For an Avon 100/90x19" rear tyre gearing
charts show these speeds per 1000 rpm and maximum speeds in top gear for the commonly used
gearbox sprockets. All speeds quoted are mph: 18 T 15.389 95.412 At 6200 rpm 19 T 16.244 100.713
At 6200 rpm 20 T 17.099 106.014 At 6200 rpm 21 T 17.954 111.315 At 6200 rpm
#567 Earlier posts discussed top speed of a standard Venom and in my opinion a well set up Venom
with the rider sitting upright will do about 85 mph + - 5 mph. The 100 mph in past road tests, were
when riders were flat on the tank. Why? Due to the petrol now available, most Venoms have to run
with compression ratios of 8;1 rather than the 8.75: 1, which reduces the power by approximately 2
BHP. Amals tell me that a TT carbs only flows 3% better than a Monobloc so it’s not that. Finally I
think as riders we are all presenting greater wind and frictional resistance as a result of maturing! How
can you make it go faster? Apart from setting the engine und the rest of the bike up well, short of
fitting a Thruxton head, probably you could get your Venom head gas flowed. Has anyone noticed
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that some Venom heads are stamped G or OK on the cylinder face, anyone know what this means?
You could also fit a spacer between the carbs and head to get the induction pipe length to resonate at
somewhere between 5-6000 RPM (if you have room between engine and oil tank). Lightening the
valve gear will only really allow you to rev quicker and safer. The M17/8 is the best readily available
cam around. Even at 85 mph a Venom does not normally vibrate to any noticeable degree. Check the
following Head steady fitted and tightened Engine bolts tight and holes not worn. Check your petrol
and oil tanks are tight (I spent days worrying about excessive vibration, only to find I had not tightened
the petrol and oil tank bolt) Check ignition and cam timing. Check the carbs is set up OK
#571 Don't forget the most important part needed for a ton-up Velo, as used on the 24 hour record
bike - a good racing fairing! Worth at least 10 mph, given proper gearing.
#572 regarding vfr 232 a 1960 venom clubman which was a very fast bike. it was fitted with a 12r
box. I was reading one of the posts regarding max rpm and top speed with a 19 tooth
sprocket, which was about 100 mph. I know for a fact that vfr 232 was cable of a bit more than that. it
used to show 105 on the straight with me lying prone. the question I have is, was there three top
gears. one for mss one for venom and one for tt close gears. 26 teeth seems to ring a bell. if a bike
was fitted with a higher top gear, it surely must give it more top end. my bike was always good for 90
in third. I still have the bike, although it hasn't run for some time, but if someone wanted a go on it to
prove its output, I wouldn’t be against it. did a tt close box have a higher top gear than a standard 12
box ?
#573 Top gear ratio is all in the sprockets, not the internal ratios of the gearbox, as I've never heard of
an internal top gear ratio other than 1:1 in a Velo. The options on sleeve gear and (I think) first gear
are what differentiates the suffix R from the standard series 12 box. A close ratio sleeve gear in any
box will leave top gear at the ratio determined by the final drive sprocket (or custom combinations of
any of the other sprockets for that matter) but it will bring all of the intermediate gears closer to top -
for instance a 17 tooth sleeve gear (in place of the standard 16 tooth) in my MAC racer left me with
1:1 top but overall drive ratios of all the other gears were higher by the equivalent of almost two
gearbox sprocket teeth, when compared with the overall ratios available with the standard sleeve
gear. So if you'd like to run a 19 tooth sprocket for your ton and a bit Venom, but have first, second
and third the same as if you had a 21 tooth sprocket, then go close ratio sleeve gear, which for series
12 gearboxes means an 18 tooth sleeve gear as the standard sleeve gear in the series 12's is a 17
toother to start with. For sidecar use go 16 tooth sleeve gear - it will have the opposite effect, and was
used in the wide ratio series 14 boxes. And of course whenever you change sleevegear the layshaft
pinion needs to be changed accordingly (from 16/28 to 17/27 to 18/26 and so on). Read the chapter
on gearboxes in Burris - it’s a good explanation for those wondering how the hell to calculate these
things called gear ratios.
#575 thanks for the info regarding sleeve gears, mine has a 18 tooth fitted, it is a genuine 12r box.
these boxes make a world of difference for performance on a venom, but are a pig to use in traffic.
they are definitely for the open road. regarding fitting a thruxton cyl head to venom, if you don’t
shorten the barrel by 90 thou it will be as flat as a pancake. I considered trying to buy the venom cyl
head patterns and having my own head made. thruxton valve angles are at 39 degrees whereas
venoms are at 45 degrees. if I had some venom head blanks I could have the valves at 39 degrees
and keep the stock venom valve sizes. a thruxton inlet valve at 2 inches is a bit on the heavy side,
and a venom inlet valve at 1 inch and three quarters is a better bet for higher rpms. any feedback on
this is welcomed. when fitting a thruxton barrel to venom head and tightening up the valve to piston
clearances, these bikes transform into a fast bike. dialing in the cam is a must for performance as is
accurate ignition timing, it needs to be set at 38 degrees, and on the money. I seem to remember
that Taylor Gue of Stroud in the sixties made a venom very fast and that when they were doing a
road test of a thruxton in motorcycle sport in 1966, they also tested his bike to compare it with the
thruxton and found it to be a faster bike. dig out your old copies and have a look.
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L #223 At last year's Stanford Hall Rally my Venom did not want to start. After I had exhausted
myself a volunteer from the inevitable crowd that were watching finally managed to get it going. On
kicking it over, it had now developed a habit of spitting back enough neat petrol for it to be seen
running down the oil tank. It got me home OK and ran well at higher revs. After repeating this
performance a couple of times I tackled all the obvious things, plug, BTH manual magneto points,
pickup etc. with no joy. I then changed the carburettor, from monoblock to concentric. This was
easier to start but ran lumpily at low revs and this time spat a small quantity of neat petrol back
through the carburettor on each firing stroke; again it seemed to be OK at higher revs. Getting more
desperate I have removed the cylinder head to find no problem with the inlet valve or seat. I have
taken off the timing cover and found the cams, followers and gears all to be in apparently excellent
condition. What next?
#225 I had the same problem on my 58 Venom, after fitting a new Monobloc. Spitting back at low
revs indicates richness, which is controlled for the first quarter of throttle movement by the Pilot Air
Screw. Try screwing it out a little at a time (to weaken the mixture) until the spitting stops. You may
have to adjust the throttle stop afterwards to obtain a satisfactory tickover.
#228 One of the major reasons for a Venom spitting back is due to the large amount of valve overlap
that a M17/8 cam gives. If you check out most Venoms after a run, you will find petrol and oil debris
on the oil tank that has been jettisoned from the carbs. A MSS with a softer M17/7 doesn’t suffer from
this. Check your valve timing, remembering to use the increase valve clearances. You will find that the
timings will not be spot on mine were 65–39–50–55 rather than the 65-35-45-55 as specified. If yours
are out you can spread the error by moving the cam a tooth either way to see if it helps.#943 if all fails
should I fit a compression plate to lower the ratio if so what size, where should I get it from (It’s a
thruxton standard bore).The Piston in there now came from Goodmans. Is there a superior piston out
there that can handle this problem?
#945 The Velo tech website (thanks again Dai) has the formula for C.R. vs. compression plate
thickness. Plates normally come in 0.030" and 0.010" thickness, I'm running 0.050" under my
Venom's similar barrel (it came with these plates from the factory). It never pinks now, even on our
watery U/L premium, as long as the fuel mixture is adequately rich. Plates are available from the
Usual Suspects - oops I mean Sources, check the List archives. As a Velo rider, you will soon be on
a first name basis with them. And I strongly recommend that you join the VOC and VOCNA; the
VOC's Spares Service is excellent. See the VOC website for links. I assume you have an Omega
piston, I have had some trouble with them seizing but never had one fail structurally. There are few
alternatives in any case, unless our Aussie mates have made some more? Pretty please? But before
I detuned my VMT I'd double check the ignition timing, make sure you haven't fitted an extended tip
sparkplug (such as NGK BP7ES instead of B7ES) and that the fuel mixture is adequate. There must
be no blocked jets or air leaks.
#959 I might make another suggestion since most of the logical things have been mentioned, if you
want to take advantage of your compression and use the highest available octane, install a cam with
more overlap and a even little more lift (commonly referred to as "hotter")if you feel cheeky. This will
effectively lower compression by opening the valves longer during the cycle and give you the power
that the compression is there for and should stop the pinging if everything else is standard settings.
The shim plates are poopy in comparison.
#961 Increasing overlap gives more time for the fresh fuel/air mixture to cool the combustion
chamber. It will also reduce low rpm power and fuel economy; there is no free lunch here. I have two
modern, 4- valve per cylinder motorbikes that suffered intake valve damage from inadequate cam
overlap for their higher-than-original compression ratio. The symptom is that the intake valve
clearances close up over time. Interestingly, the seats are harder than the valves these days. The
cure in one case was to change the cams, in the other a reduction in compression ratio is needed - it
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already has a hot cam. The easiest way to increase overlap on a Velo is to increase the radius of the
cam followers - oops Veloce already thought of that! The difference in power characteristics between
MAC and Viper illustrate the difference perfectly.
#962 I meant to mention that this cam change should include a duration and timing change as well
(this goes with high performance cams as a matter of course), which will require a regrind. It is
definitely true that changes like this are detrimental to low end performance, you will get a lumpy idle
and less grunt off the line, but in the mid range and up, it will be sparkling! I like regrinding because
you can get a higher lift without a taller cam profile from centerline (the backside of the cam is
ground down to give the higher lift), thus avoiding clearance problems.
#1020 I have my race venom in bits just now, so I will measure the pipe for you. It is more than
thruxton spec, so I think it classifies as 'tuned' ! I run end-cans on the venom and viper for racing that
seem to do enough silencing, and will measure those for you too. In general terms, if you are going to
sprint, you will obviously get a bit more power if you run an tuned straight pipe, but you always lose
out if you think in absolutes ! The answer is usually a compromise, and reverse-cone megas are
exactly that.
L #1030 I have now spent the season experimenting with a variable exhaust pipe extension and
settled on 45 inches along CL. This seams to resonate with the induction length at about 5500 RPM. I
knew I got it right as for the first time the bike wanted to over rev, the valve hit the piston and the rest I
am sure you can imagine.
L #1959 Hi Does anyone have a table of drill sizes to drill out main jets. I have a table up to 500,
but need information above that size. Even better if anyone has any surplus main jets above 1000,
that they would be happy to swap with me for smaller sizes to save me butchering them by drilling
them out.
#1960 What bike needs a jet size of 1000? You running methanol?
#1962 Yes in my race bike - in my experience a much nicer fuel than petrol. Only problems are: - you
use 2.25 times as much as petrol - when it's cold it can be very difficult to start - virtually impossible to
take a plug reading - contaminates and washes the bore of oil - can rust the inside of the engine But it
runs cooler, will give you between 10 - 15% increase in power, and allows you to raise the CR to give
you the same increase again.
#1975 My MAC runs happily on a 800 main, it starts very easily and revs right through to 6000 without
a problem. To improve the starting add 1% Acetone to your methanol, it improves cold starting.
L #2486 As I am building an engine now that will not run for at least six months, My query was
what lube to use when assembling engines to run on R. I spoke to both Castrol and Morris, they said
the same - only use R to oil components on assembly and not to use any other lubricants as they will
not mix. Basically their advice was to try to keep the engine in a warm dry atmosphere to avoid
condensation. They reckon corrosion is no more a problem with R than mineral oil, the problem is the
amount of methanol swilling around the engine. Oxidation is only a problem when the engine has run.
There is a company that sells an additive to add to engine run on dope and R that inhibits corrosion,
but I have not tried it as it appears very expensive (during the season I change oil every couple of
weeks.)
#2487 I think Morris sells a special oil for grasstrack and speedway engines, this oil is supposed to be
for use in methanol engines.
#2488 Oil of castor type for use with methanol is Castrol M. This should not be mixed with R or you
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will get a very pretty purple sludge!
#2489 I use Morris MLR40, which as it says on the can, is designed to be used with methanol. Even
has a picture of a speedway bike on the front! Still drains out purple with a nice bronze sheen to it
though.
#2490 I'm curious, did either company say much more about the advantages or disadvantages of
using 'R' compared to a good modern monograde? I spoke to both asking advice on what oil to run an
OHC Velo with and couldn't get a clear opinion either way from both companies.
#2497 No I didn't ask that question as I run on methanol. Regarding lubricating dope burning engines
on mineral oil, one grass tracker I know uses mineral oil but extends the feed pipe some 4cm into the
oil tank. Between races he undoes the oil tank drain plug and drains off the separated methanol that
settles below the oil.
#2494 I don't think there is any particular advantage to using vegetable based oils in petrol engines -
the advances in lubrication technology over the last 60 years or so mean that modern oils have far
superior properties than before - but if you are running methanol then it's a different matter. Dope will
degrade mineral oils severely due partly to the diluting properties of the fuel but mainly to the fact that
a considerable quantity of the fuel finds its way past the rings and into the sump. Vegetable oils are
not degraded by methanol to the same extent so are preferable in engines running this fuel. I think
you will find that the majority of speedway and grasstrack and some vintage competition engines run
on "R" for this very reason.
#2499 I firmly believe that castor oil still has the edge in extreme air cooled situations. In particular
consider a MkI cam box with iffy lubrication and high point loads. Castor has still the highest film
strength. Other oils work very well under higher flow rates and in the case of synthetic for longer
periods. The drawbacks are non-detergent, hygroscopic tendencies and the goo! If you want the
motor to last though, frequent oil changes and acceptance of the goo factor is a price well worth
paying. As an aside, multi grade oils do not suit air cooled engines. As synthetics are generally thinner
I presume they would be even worse?
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C. The Electrics
C.1. Ignition and Timing -
L #129 Have just finished restoring a 1956 Mk II LE, and heard today that the correct timing was
with the timing marking holes coincident (TDC), and the points just opening with the auto timing
device weights fully extended. Surely this is incorrect? When I set mine, I set it with the weights
closed (retracted) and it starts and runs OK. Thanks for any advice.
#177 (LE Model) The timing settings for all engines I know of are quoted as "full advance" i.e. with the
ATD springs fully extended. This will give a setting which when using the design intent fuel will
produce an approximation to maximum available torque at all engine speeds, while keeping clear of
damaging detonation limits. If you set your ignition timing on full retard i.e. with springs in closed
condition, the effect will be for the engine to run with excessive spark advance which may improve
torque, but only if the optimal spark timing has not already been reached. The trouble is that the
increased advance may also cause the motor to run past the detonation limit at some speeds.
Modern pump gasoline (even unleaded) is generally much improved on the equivalent available in
1956, so it is possible that the LE might stand a little more advance, but the only way to tell for sure is
by running spark sweeps on a dyno. Remember too that ignition systems of this era were very
primitive by modern standards and are only capable of a small amount of automatic advance which
will retard spark at low engine speeds and reach full advance at around 2500 - 3000rpm. With
modern engine management systems it is possible to calibrate the system to run the ideal amount of
spark advance for all running conditions e.g. speed, load, throttle opening, engine temperature, air
temperature, even making adjustments automatically for whichever gear you happen to be using!
With our old things spark timing can only ever be a compromise, and was specified to provide the
best performance while keeping within a safe running condition. In light of this, unless you have the
facility to find out otherwise, stick with the factory recommendation and set up with the ATD wedged
in the full advanced position. Happy riding, Pete C.
L #182 Looking at page 3 of "Tips" on www.le-velocette.co.uk/info.htm I read the following:
(Quote) "1. When setting the timing on Miller systems, bring the flywheel into alignment of TDC by
setting the hole in the flywheel central to the hole in the mounting back plate. Adjust the cam unit to
just opening the points, in a clockwise direction, with the bob weights in a FULLY OPEN POSITION.
i.e. fully advanced. This is not clearly stated in the workshop manual." (End of quote) Surely this will
give a large amount of retard at starting, and will only advance the spark to TDC at full revs? I have
assiduously studied all the manuals and documentation I can find, and nowhere do they give a degree
figure for the fully advanced setting for the LE Miller set. They all tell me to set TDC with the holes
referred to in alignment (TDC) and fit the ATD with the points just opening. This would be fully
retarded at TDC, and presumably the degree of advance is set by the operation of the bob weights, of
an amount not specified. I will do a little experimenting/measuring to find just how much the ATD does
effect an advance, but nowhere have I been able to find a figure
#187 your interpretation of the instruction appears to be correct in that you are told to set full advance
at TDC. I can only assume that the engine is extremely det limited if this is the correct method. If on
the other hand the method should be to set to full retard at TDC, i.e. with bob weights closed, then
the only control on the critical full advance setting is the amount of advance provided by the ATD,
again a fairly primitive device which was likely to have had a tolerance of a few degrees of range
even when new, never mind after half a century's use
L #313 Has anyone got to hand the Valve timing figures for a MK8 D.O.H.C. works engine?
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#444 My 1967 edition of the Red Book lists 30 thousandths checking clearance in the Data section
(p.7), but the Sports/Clubman Preparation section (p. 102) states that "Greater accuracy of reading is
obtained..." using 53/52 thousandths, with identical cam timings. Anyone care to comment? There is a
shortcut, though - courtesy of a "Molegrips and Hammers" article in an old FT: For fairly obvious
reasons, both valves should be equally open at TDC (of course, one is actually closing). That is, at
TDC the rocker arms are lifted equally, which is easily verified. The actual limit on accuracy is finding
TDC in any case. This has worked acceptably with the /8 in my Venom, not needing adjustment in
25,000 miles.
#446 Quite obviously something wrong here. Greater accuracy may well be obtained by using a wider
clearance when checking because you will be on a steeper part of the cam, but the timing will of
course be different - with wider clearances the opening time will be later and the closing time earlier. It
is for this reason that I prefer to check the peak lift point when checking cam timing. If you assume the
cam to be symmetrical, which they normally are, then this is easily worked out. As regards finding
TDC accurately this can be done easily to less than half a degree if you use a positive stop for the
piston when setting up the degree disk. An old plug can be easily modified to do this by carefully
cutting round the steel body just above the hexagon and removing the insulator assembly. remove the
outer electrode and tap 10mm x 1.25 through the body. Fit a 10mm bolt around 60mm long into the
body and file or grind its end to a nice rounded profile to prevent damage to the piston and you have
the tool. Remove your spark plug and rotate the engine so the piston is in the lower half of the stroke
and fit your new tool in the plug hole, tightening gently. fit your degree disk and pointer and rotate the
crank slowly until the piston is hard against the stop and take a reading on the disk. Turn the crank
back until you are hard against the stop in the other direction and take another reading. Using the two
readings set the pointer to read equally either side of TDC when the piston is against the stop and you
have a very accurate setting which accounts automatically for any.
#448 It seems obvious that increased clearances change timings, but as we all know, the Red Book is
never wrong! M17/5 and /7 cams are fairly symmetrical, but the /4 and /8 are far from it, with a much
gentler opening ramp. The beauty of the "Rastus" trick is that it requires no degree wheel. I have a
tool that measures piston position, it is a sliding scale in a holder that is threaded for the spark plug
hole. It makes finding TDC to within a couple of degrees quite simple. One tooth on the cam gear is
four degrees; no better accuracy is available unless you are willing to disassemble the cam from its
gear. This may make your racer a tiny bit quicker but is not needed on a street machine.
#449 My Red Book (for the swingarm models) shows a 10 degree difference between /8 cam timing
at .030 and .052 lift. One tooth changes the valve timing 8 degrees at the crank, where timing is
measured, and it is certainly noticeable. Careful with piston clearance, particularly the intake valve
when advancing. The lever action followers create much more action on the opening side, so
although the ramps on the cam are different, actual valve rates are probably much closer to
symmetrical than it appears, I've never graphed it though. If timing for split overlap gives correct timing
when measured at .030-.052, then the valve action can't be symmetrical. On a /8 cam, assuming the
timing was symmetrical, lobe centers based on the book would not be the same, more like 95 and
105 degrees..
L #850 At 38 degrees btdc what is the exact imperial measurement that a Venom piston is from
the top of it's stroke. I will use this to time the engine with a dial-gauge.
#851 A word of advice: use a degree disk, this will be considerably more accurate than using a dial
gauge and does not necessitate the removal of the head to do the job. If you use a positive stop
method to find TDC this is the most accurate method of timing. My positive stop is a spark plug body
with the insulator carefully removed - just run a fine hacksaw cut around the shoulder above the hex
and the insulator will drop out - run a 10mm tap through after removing the earth electrode and fit a
10mm allen bolt or similar with the end suitably rounded to prevent damage to the piston and long
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enough to stop the piston before it reaches the top of its stroke. By rotating the crank back and forth
to the stop (slowly and carefully), TDC can be found by splitting the difference between the readings.
The result is an exact TDC setting which needs no compensation for backlash.
#852 From 36 to 38 degrees the piston drops 20 thou per degree, so this is a more consistently
accurate method of setting timing than messing about with degree wheels. And certainly more
convenient, you can even do it by the roadside. But the measurement is taken along the bore
centerline, so a dial indicator that screws into the spark plug hole will not yield accurate
measurements, due to its angle and the probability that the point will move on the piston as it drops.
Use a small steel rule, this will give more than adequate accuracy. So here are the numbers - 36
degrees is 0.3957" BTDC and 38 is 0.4384". Keep the rule vertical as you measure. I use 0.040" and
0.4375" (7/16"). I marked an old spoke with a file and keep it in the toolkit.
#855 Back of an envelope and IE6 calculator stuff (scratch scratch) Venom stroke is 86 mm, right?
(not sure - I am an LE man) I reckon piston rise = (86/2)-(cos 38 x (86/2)) = 43 - (0.788 * 43) = 43 -
33.884 = 9.116 mm = 0.359" or 23/64" in Imperial. You did ask for "exact" and my IE6 calculator works
to 33 decimal places,
#856 I have an alternator on the end of the crank and have it degreed so I use a strobe light. And I
always find no matter how carefully I set the timing statically, it's always a few degrees off when
running, presumably due to gear lash, bearing float etc. That said, a few degrees off, unless over
advanced to detonation, is hard for me to notice in the seat of the pants. Could make for a hot piston
though, and we all know what happens next
#861 After a recent engine rebuild I established TDC with the positive stop through the plug
hole/degree plate system, then tried two others, purely out of interest. A sensitive dial gauge,
anchored on a rocker cover bolt, through the plug hole, got me within one degree every time (read off
the degree plate, still in place). Slightly more accurate (here comes the heresy) was a fine pointed
scriber inserted through the plug hole and held against the piston top with the fingers pressed tightly
against the plug cavity. Rocking the piston back and forth either side of TDC, then judging the
moment of no movement consistently found TDC +/- less than one degree.
#866 I think the equation is d = S/2 + L -S/2 cosX - L sin {cos (power -1)(S/2L sin X)} where; d =
equals distance before TDC S = Stroke L = length of connecting rod X = angle before TDC in degrees
You can still ask your granddaughter to work it out though, as I haven't used log tables since I was
forced to give up engineering 24 years ago! By the way, for those of you that don't want to drill / chisel
out the centre of a spark plug, Seymour's sell the correct graduated tool for the job at about £5
#868 if you're stuck on the road re-time the mag to open the points at TDC on full retard. Its good
enough to get home.
#869 38/ BTDC is the correct timing for the old leaded fuel. 36/ is more likely to work with standard
leaded fuel without preignition.
#871 I have tried a few different methods and I have heard about the positive stop method, but for
me, I find that I need to go through my own method. firstly remove the gas tank. then remove the
dynamo outer cover and pull out the split pin out of the crankshaft. then unscrew the dynamo pulley
off the crank. then slacken the dynamo strap and undo bottom mounting for inner dynamo cover. pull
the inner cover forward and turn clockwise to about 20 to the hour. then push it back and tighten the
dynamo strap. this now puts the inner cover out of the way and gives access to the crank. next, get a
thin piece of wire and slacken one of the primary screws and make the letter u at the end and put it
under the screw and refit it and tighten it up. bend the wire so that when the degree plate is on you
will have a pointer. you will need a timing disc, a plastic one is fine. make sure that the hole of the
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disc is comparable to the crank. now, you will need two big penny washers, they need to be not too
thick and have a hole comparable with the crank. now, take the castellated nut off the two dynamo
discs and sandwich the disc between the penny washers and put on the crank. then put on the
castellated nut and tighten up. this serves two purposes. one. it makes the degree disc strong and
flat, and two, you can now kick the bike over. next remove the spark plug and now you will need a
dial gauge. a draper one works well. now you will need to find the compression stroke. put your finger
over the hole and turn the motor over until it starts to hiss. you are now on the compression stroke.
bring the piston up to the top of its stroke and then slacken the castellated nut and set the degree
disc to twelve o’clock. i.e. zero at twelve. now the trick is to find an accurate tdc. with the piston at
the top of its stroke, screw in the adaptor for the dial gauge and then insert the dial gauge. you may
need to screw an extension on it. let the dial gauge down until it just kisses the piston. this is
important. now what I do next is to get a trolley jack and put it under the frame on the l/h side where
the mainstand would be, as I don’t have a mainstand. I then lift the bike so the back wheel is off the
ground. put the bike into first gear and now you can operate the crank via the back wheel. if you have
a mainstand fitted that should work good as well. turn the rear wheel clockwise to turn the motor
backwards to take it off tdc. now bring up the piston up to tdc again and watch the dial gauge needle
and slow down as the piston contacts it. set the gauge to zero by turning the outer on the gauge, as the needle starts to lift, keep
zeroing the needle. this has to be done very slowly as it blips the needle quickly. when the needle
starts to drop, stop and bend the pointer back to zero on the degree plate. Look straight at the degree
plate as looking at it to on side will give a slightly different reading. now, your dial gauge is showing
the piston starting to drop away after the rock on the crank at tdc. turn the rear wheel anti clockwise
very slowly and watch for the needle stating to move again, when it does stop, and look at the
degree plate. check the amount of degrees of movement and split this in two and that is tdc set very
accurately. turn the motor back off tdc by turning the rear wheel backwards to past 40 degrees. then
bring it to 40 degrees and set the points to just breaking, a cigarette paper is spot on for this. make
sure that you have pre set your points gap. get your paper between the points until it will just pull out
but there is still a little resistance. I find the next step is to have two people to do the job, as with one
it is just about impossible. have one person hold the points in the mag with his hand as it is breaking
at the points and have the other person put the magwheel on the other side and tap it smartly with a
deep socket and a hammer to put it on to the taper. I guarantee that if you set the degree plate to
38, you will end up with 36. been there, done that. when set at 40 you will get 38 when it is rechecked
don’t ask me why, but I always get 2 degrees of movement. the motor is now set at an accurate 38
degrees. super unleaded is a highish octane and with silkolene pro-boost added with it you wont get
detonation provided that the motor is not running too lean of course. I hope somebody can use this
info. regarding setting the timing at the roadside, I have never had to do it as I make sure that nothing
will slip when doing assembly. if the magwheel is foreign to the magneto shaft, lap it on to the shaft
and when it is pulled up it will never slip. remember that when assembling, that doing it wrong ends
up in failure sooner rather than later. if the mag fails when you are on the road get the yellow taxi
home.
#874 I use a stiff metal degree wheel, drilled out to just slip over the threaded part of the drive side
mainshaft. Then I replace the nut which holds the generator pulley (after removing the shockabsorber
spring and pulley), tightening it onto the disc, which abuts the slotted part of the mainshaft. I
then turn the crank with a wrench on my timing side mainshaft (Thruxton - I check the valve
clearances at the same time), using the positive stop method to find TDC, and remembering to move
the crank 30 degrees or so when trying (again!) to get it all right, in order to accommodate any
backlash in the timing gears. By the way, I time at 38 degrees, and have had no problems with pinking
or melted pistons.
#891 I have formed a golf ball sized piece of Bluetac (plasticine) around a thin nail, then
pressed/screwed it into the plug hole far enough to achieve a gas tight seal. With the nail withdrawn, a
depression formed around the top of the resulting hole and a drop of washing up liquid in the
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depression, bringing the piston towards TDC results in a growing bubble. As TDC is passed the size
of the bubble diminishes. The bubble is very sensitive to small movements.
#896 A very novel idea! this cannot fully account for the backlash caused by running clearances at
the big and small ends and piston rock due to both the taper of the piston and the piston to bore
clearance. The ONLY method that will accurately find TDC irrespective of these factors is the positive
stop method. It will however, still be necessary to account for backlash when setting the ignition timing
by only ever turning the engine FORWARDS to the timing point so the backlash in the timing gears is
taken up.
#897 I still reckon that by using a dial gauge and a degree plate you will get as near as you can get to
get an accurate tdc. to allow for slack in the small and big ends, I can see where you are coming
from, but when you use the dti like I do, you can work to a minuscule fraction which has to be more
accurate than the positive stop method. as for timing back lash, velos have fine helical cut gears and
any backlash can only be minimal compared to a triumph or BSA which have corse cut straight gears.
I was always told to take the timing past 38 degrees and then bring it back to take up any lash.
without question you have to time at 40 degrees to get 38. I have tried forever at 38 and when
rechecked it is 36. beats me why but it is.
#898 At the end of the day, if you have found a method of timing which gives good repeatable results
then stick with it. The Velo will never be as critical as regards ignition timing as a modern racing twostroke,
so this argument is largely academic!
#901 what is the positive stop method?
#905 The positive stop is a method of setting up the degree disk accurately prior to setting or
checking ignition or valve timing. First obtain a suitable degree disk, these are available from most
good tuning part suppliers or classic bike part dealers. You will also require a piston stopper tool,
these are available commercially although may be harder to find - I have made mine by modifying old
spark plug bodies, since I regularly work on a variety of engines I've made a set of three to suit
engines with 10, 12 and 14mm plugs. These are made quite simply by running a hacksaw cut around
the steel body where it is crimped over just above the hex and withdrawing the porcelain insulator
complete. Cut off the outer electrode and run a suitable sized tap down through the hole. I found that
6, 8 and 10mm threads respectively worked well. Take an Allen cap head bolt of a length which will
run through the plug body and protrude about 25 - 30mm through into the combustion chamber and
round off the end so as not to cause damage to the piston. You could also file a flat on one side of the
bolt to allow air to escape as you turn the engine over. Screw the bolt into the plug body and Loctite in
place. Remove the dynamo pulley and shock absorber spring and fit the degree disk on to the end of
the crankshaft using the pulley nut finger tight for the moment to retain the disk. Fashion a pointer
from either a piece of sheet metal or stiff wire - I use 16G welding wire bent in such a way that it can
be mounted on the sprocket cover mounting studs and triangulates up to the edge of the disk and
doesn't move unless I want it to but any suitably solid mounting point will do. Remove the timing cover
and with the spark plug removed, turn the engine over with a ring spanner or socket on the timing side
crankshaft nut until the piston is roughly at the top of the stroke - at this point you will be able to feel
for the piston with a small screwdriver inserted in the plug hole. It doesn't matter which stroke you are
on at this time, the stopper will not foul the valves. Loosen the pulley nut and turn the disk on the shaft
until the zero mark lines up approximately with the pointer and tighten the nut finger tight once again.
Turn the crank back or forward, it doesn't matter which way, by about 90/ and fit the piston stopper
tool to about 10 ft-lb torque. With your spanner, turn the engine over either way slowly until the piston
stops against the tool and hold it tight in this position while noting the reading on the disk. Turn the
engine over the opposite direction until the piston once again stops against the tool and take another
reading. You will now have two readings which should be fairly close to each other, e.g. 35/ on one
side and 45/ on the other. By splitting the difference you should now reset the disk or pointer to read
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in this example 40/. If you now recheck by turning the engine back to the other stop, you should have
the same reading, i.e. 40/ on the other side of zero. Now remove the stopper tool and by turning the
crank until the pointer is on zero you will have true TDC. Now you are ready to start your timing
checks. Ignition should be set at 38/ BTDC fully advanced for 98 RON or better fuel. I would say that if
you can only get 89 - 92 RON then this could well be the cause of holed pistons and audible
detonation (pinking) would be horrendous with 38/ timing. If this is the only fuel you can get I would
strongly advise to retard the timing by a significant amount. You could try 34/ and see how it goes -
retarded ignition timing will cause the exhaust temperature to rise and consequent blueing of the
exhaust downpipe is probable together with a loss of performance but this may be inevitable if you
want to prevent engine damage. Ideally you should try to find higher octane fuel, in the UK our
premium unleaded is 95 RON which I consider too low for the Velo. Super is rated 97 RON, but pump
average is in the region of 98 - 99 depending on supplier. I don't believe that unleaded fuel will do the
engine any harm.
#906 on an old banger such as the Velo - no disrespect intended - accuracy to this degree is
unnecessary. Having said that, I prefer to use a good old fashioned Rizla Blue cigarette paper
between the points
#910 One more question pops to mind. How many degrees of change does the manual\retard
advance lever make? Can it solely be used to retard the engine from say 38 to 36 degrees with any
kind of practicality?
#914 Sorry I can't answer this - perhaps someone with a manual mag might comment? But while it is
possible to back off the ignition slightly with the lever, most of the time you would want to run fully
advanced simply for ease of riding - at normal engine running speeds even an ATD will be at full
advance - the ATD and the manual lever are only an aid to starting really. To trust that you did not
over advance the lever I would suggest to be a bit risky. However, you could use the lever as a test,
gradually increasing the amount of advance until you identify the point at which excessive pinking
occurs, leave the lever at this point and check the timing to establish the exact figure. Ideally this
would be done on a dyno by running spark sweeps over a range of throttle openings to establish the
MBT (Minimum spark for Best Torque) and BDL (Borderline Detonation Limit) curves, to give the
technical terms, but more practically for the average enthusiast, a good degree of patience and feel
coupled with a lot of trial and error will get there in the end!
#917 The magneto, if set up correctly, will produce its best spark only at full advance, but I doubt if 2/
will affect it significantly. The problem would b e to move the lever only enough to give you 2/
retardation.
#923 I checked this a few months ago on my MSS sprinter and from memory the manual mag control
allowed a variation of between 4 to 38 degrees. Originally I marked every degree as I wanted to try to
check what advance gave the most power. I gave up on that idea as the greatest variable was the
consistency with which I coordinated the clutch and the throttle.
L #2123 Hello all, Can anyone tell me if ATD units are interchangeable? If I have a 1951 MAC
and see a spare one for sale from another model, will it fit? Or do I have to look out for particular
models/years?
#2130 With the exception that the control spring has a different rating I believe, but can't fully confirm
that they are identical, . This is certainly true for VM and VR as the Lucas part numbers are different
47576A and 47545B respectively, differing only in the spring part number.
L #2315 Folks, My Thruxton is a late, 1970 model, and fitted with coil ignition. I've read good and
bad about the coil ignition, but have a problem I could use some advice or help with. The velo started
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making a mechanical clatter, which was traced to the distributor gear, with the help of a long time velo
man. It seems the distributor bushing or bearing, (not sure yet) has given up. This seems strange, as
the bike has less than 6,000 miles on it from new. Anyone have experience repairing the distributor? I
haven't removed it yet, but wanted to get some ideas on how to dissect the thing.
#2330 If I remember correctly, my distributor (69 MSS) probably got crappy with not many more miles
than that on it. At that point, I got a Bosch conversion done by a Canadian.
#2347 The Lucas distributor was a great idea but the wrong execution. The needle bearing and shaft
were prone to rapid wear. It is almost impossible to set the timing on a worn unit as the points return
spring causes the shaft to deflect which results in a point gap that varies but not in any sort of
controlled or predictable manner. When this happens you will find the bike hard to start, near
impossible to idle smoothly, and generally a poor performer all around. I built a Bosch points and coil
conversion about 20 years ago to get rid of the magneto problems on my Thruxton and sold a few to
friends. Nowadays it is much easier with the availability of electronic ignitions to cure these
distributors. The short term and cheapest fix is to throw the Lucas advance unit in the trashbin, install
an electronic ignition such as the Boyer Bransden, and the engine will start and run a treat, without
fixing the bearing and shaft problem. The pointless magnetic pickup is not affected materially by the
wobbling shaft so the timing will be as set. Ideally though, a proper fix will require you to remove the
distributor and have it bored to accept 2 deep groove ball bearings and the shaft altered to suit. While
you are at it have a small lip seal added on the timing gear side to minimize oil blow by. You will find
that there is a huge improvement in performance. The built in electronic advance curve will help with
starting and give you a nice boost in mid-range power. You will find that ‘pinking’ will also decrease.
The Boyer unit has a rather rudimentary advance curve similar to the stock Lucas advance unit but it
works. If you really want to maximize performance get a unit that allows you to program your own
curve. I have a modified Lucas unit with a Boyer unit on a ’54 MSS that works fine. My 20 year old
homemade Bosch points and coil unit has my own advance curve of 32 degrees total advance (twice
that of the Lucas or Boyer). I have had one kick starting and a Thruxton that will tolerate city traffic
and pull hard from 3,000 rpm. The best part is that I can burn mid grade gas (89 octane) if I have to
and still get virtually no pinking on 9.2:1 compression.
L #2664 I am not sure how to use the manual advance lever on my Viper, what is the most
efficient position to run it on, I know how far to retard it to start but what then?
#2665 Run it at full advance. If properly timed, full advance will give the most efficient operation. If
your engine is at idle speed, running very slowly, or on low octane fuel, it may run better with the very
slightest amount of retard. If the idle running is irregular at full advance, you can experiment with
various amounts of retard to create a smooth regular idle.
#2673 I also knock back the timing a little when pulling a long hill in top gear, or when the engine
seems like it would be laboring, as when two-up pulling a hill and the revs can't be brought up. Haven't
melted any pistons this way, yet.
L #2667 Talking about timing I run a Mac with an auto advance and for timing purposes the
manual (haynes) instructs to jam the auto adv unit into fully advanced position what does this mean??
I am running my mac with a Daytona piston and wonder wether this affects the usual 38 degrees
btdc?
#2668 It depending on the year of your MAC, Lucas specified one of two auto advance units: 47522A
or 47545A/B. These units provided 16 ½-18 ½ degrees or 11-13 degrees respectively. These auto
advance devices have two bob weights which swing outward when being driven by the gear train (I.E.
centrifugal force takes effect) and in doing so, advances the ignition timing in a smooth timing curve
under the influence of two coil springs on the bob weights. At rest or at low engine speeds, the timing
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is automatically retarded and the auto advance unit will only achieve full advance when spun at
engine speeds approaching 3,000 RPM. This provides the rider with easier starting and a more
tractable engine. A good thing, no? Since engine timing is really only critical at higher speeds (I.E.
generally > 3,000 RPM for most engines) the maker tells one to ensure the ignition timing is correct at
FULL ADVANCE and in this case, you are told 38 degrees before top dead center. This makes sense,
since this is the engine speed most of the time while riding the bike. Since the auto advance unit at
rest is at full RETARD, not full advance, you are instructed to manually move the bob weights to the
full OUT BOARD position (full advance) and hold them in that position with a wooden wedge or scrap
of rubber. Should you attempt to set the engine timing without manually forcing the auto advance unit
to full advance, upon running, the engine will move from 38 degrees to 51 degrees (assuming the
later 47545A/B auto advance unit is used). The effect will be difficulty in starting, an engine with a
reluctance to achieve low idle speeds, and severe pinking under light loads. A holed piston may result!
As to your question about the "correct" advance for your bike with the Daytona piston, I can only
comment that you should start at 38 degrees and use the highest octane fuel commercially available.
If the engine easily pinks when under a load, retard the spark two degrees and try again. Depending
on the compression ratio with the Daytona piston, you may have to either retard to 36 degrees or add
a few compression plates. Caution: If this engine has been run with the Daytona piston a few
thousand miles and has created any ridge at the top of the barrel, you must not reduce the thickness
of compression plates without absolutely removing any ridge or sever ring/piston damage may occur.
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C.2. Sparking Plug -
L #217 I have a standard 1960 Venom which has had the piston rings and valve guides and
valves replaced. This was only about 100 miles ago. I am having problems with the spark plug oiling
which may be due to the guides and the slightly rich mixture. However it did that before I rebuilt the
engine. I have used Champion N3C and NGKB8ES plugs although the NGK ones seem better.
However, even that let me down coming away from a classic bike show, about 30 seconds after I had
started the bike. Very embarrassing as I was being critical of all the competitors who were loading
their bikes onto trailers. A fellow competitor lent me a plug which had a centre electrode that
protruded more than the plugs I normally use. It got me home and still had a big fat spark when I
checked it out. Does anyone have any suggestions as to whether I should use a hotter standard plug,
go for an equivalent plug with the protruding electrode or try to deal with the cause (if there is one) or
the symptoms.
#218 In my 67 Venom I have had excellent performance from NGK B7ES and BP7ES, the latter has
the projected electrode. Unlike some other brands, you can decipher NGKs as follows: B means
17mm threads P means projected tip 7 is heat range, higher is colder E means long reach (iron head
MAC takes H) S means standard materials (not platinum, etc.) At high altitude (over 8,000 feet) I have
also used B6ES successfully.
L #553 Sparking plugs KLG FE70. Lodge HLN ChampionNA8 & Bosch W.175/T1 all seemed to
be unlisted nowadays all the above are probably unsuitable now days with unleaded fuel anyway, the
plug in it is a Bosch WW4DC that tends to carbon up a bit which suggests it's a bit on the soft side.
what do you guys recommend for a standard MAC
#554 NGK B6ES is the equivalent plug to the FE70
#669 My Venom was having the sulks and simply was showing no signs of life on the kick starter. So
we tried a NGK Iridium IX spark plug type BR8EIX. I interpret this to mean it is equivalent to a B8ES
except it has a resistor in the plug. It was like throwing a switch, an immediate response from the bike
and it started on the second kick. What is the experience with NGK Iridium IX spark plugs and Venom
/ Vipers? On the basis of this experience they may well be worth the price.
#670 1. What other new plugs did you use as a comparison, before opting for the Iridium plug? 2. Are
you running a mag or electronic ignition? 3. If you are running a mag, I thought I read somewhere that
you shouldn't use resistor plugs. 4. How many miles have you done since fitting the plug and does it
still start perfectly? Either way I hope it keeps going for you.
#671 My Venom has a recently reconditioned "standard" Lucas magneto. I have been running NGK
B8ES and recently NGK B7ES plugs. I had been trying a softer Bosch W7CC that day, I've been
using this type of plug with some success in my Viper (it has a slappy piston, burns some oil and
runs on lead replacement petrol). In terms of the Venom's recent starting behavior, all plugs have
been the same. Yes, I'm also puzzled about that resistor. I'd appreciate feedback from others who
may be running this NGK Iridium IX BR8EIX type of plug.
#672 Sorry, but I just have to ask....what gap are you running? Perhaps the iridium plug had less gap?
Mags can use as little as 18 thou, which definitely helps starting. I've tried both platinum and iridium
plugs in Velos and moderns with no real advantage. They do seem to last a bit longer in the moderns.
Also, adding a bit of leaded racing fuel to my VMT's tank definitely improved starting.
#673 VMT 260 has been running the same factory-spec KLG FE 220 for about 2400 miles, with no
problems starting or running. I've always used these plugs for the VMT, and there seems to be no
problem with longevity or fouling, even when the bore was clattering and the valves tockling away in
loose guides. Perhaps some plug trouble is experienced with the 'aperturus restrictus' syndrome.
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Open those throttles wide once in a while; Velos can take a spanking!
#819 Accessory Mart has KLG FE 220 plugs, standard fitment on Thruxtons, on sale at $1.80 ea.
currently. They are at 513 871 6682, in Ohio. Part # 06-00384. I've had the same plug in my Thruxton
for three years, and it starts first kick.
#935 Is there an alternative to the NJK plug; what is the best plug for the totally standard Thruxton
running on the poorer octane unleaded gas.
#939 I run an NGK B8ES. The equivalent Champion is N3 but I found NGKs a lot more reliable. Either
should be OK or you could try a B9ES if you ride particularly hard.
#957 Interestingly three of us have been experimenting this summer with using softer plugs in our
Venoms. Two of us have moved down to B7ES, giving noticeably improved starting, and one has
even gone down to B6ES. Probably most of our rides are only 50 or 60 miles, albeit pushing close to
the legal maximum speeds (!), no holed pistons to report yet.
#958 There are as many spark plug preferences as there are plugs. I suggest reading the spark plug
article in Dai Gibbison's website (and just about everywhere else one looks) by the late Gordon
Jennings. This is widely recognized as the bible for engine tuning via the spark plug. After reading,
take his advice and get a projected nose plug for your Velo. I run NGK BP7ES. You will have the
benefit of a hotter plug for starting and idling, plus a cooler plug at speed when the incoming air
charge (especially with the Velos hemi head) will cool the plug. I noticed the improvement in low
speed operation immediately in my Thruxton. Additionally, timing may be able to be retarded a
degree or two with the faster burn having the spark occur further into the chamber. Don't worry about
piston clearance, I have run them at 10.5:1 compression.
L #975 Any experience with what a resistance plug will do to a BTH, or a Lucas mag? I
understand that a wider plug gap puts an increased load on any magneto, but I don't know of any
correlating information on air gaps vs internal resistance of a high tension system.
#989 For interest how/why do non resistive plug caps and leads help with a magneto?
#993 Resistor type plug caps, leads & plugs introduce a resistance into the ignition set up. Using any
magneto it is a distinct advantage to reduce the resistance as far as possible hence leaving more
power for a decent spark. This is the reason for the smaller plug gap which encourages a fatter spark
over the smaller gap.
#995 I should add that certain resistance plug caps may increase resistance over time and with wear.
A 30 year old resistance plug cap that started at 1000 ohms could test at ten times that or more today.
L #3547 Should the spark plug cap on my '55 MSS be of the resistor, or non resistor type? The
current one is the black plastic KLG variety and it was acquired 30 years ago. It is marked 15K ohms
but measures 20K ohms.
#3548 If using a magneto, you require a non-resistor type plug cap.
#3562 Mags aren't that robust to gross overvoltage. Probably the best thing you can do is have a
smaller plug gap. The rotating-coil mag as built by BTH, Lucas etc was a stupid design for the
1950s'/60s. The reason it was done that way was that when mags were first made - early 1900's? the
magnetic materials available were very poor and needed a long magnetic path between poles. So
these early mags had big horseshoe magnets - you must have seen pictures of them. But by the late
30's much better stuff was available - alnico permanent magnets. Rather than fix the coil and spin the
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magnet they saved money on redesign and just ced the big horseshoe magnet with a short cast-in
one. Lucas made a few spinning magnet mags for Matchless, and they were much better. Why is the
spinning-coil so bad? Because it means you need brushes and pick-up rings working at thousands of
volts. It means the coils are very limited in size - look at the size of a standard car coil and compare
with the armature of a mag! and so can't be insulated nearly so well or have as many coils.
Abomination though they are mechanically, the mags on magdynos are a bit better as they have a
larger diameter armature.
#3574 Having parted with real money (£.s.d.) in 1965 to obtain a full drum of "RIST" carbon fibre
cored suppressed HT lead plus the special tool required to crimp the little spiky widgets on the end, I
am not about to dump it all in favour of copper cored lead. With suppressed cable you do not need
the resistor plug cap and you put an end to mean green copper corrosion misery. After 10,000 miles in
all weathers what caused my KF1 to fail? A botched solder connection to the capacitor by the last
"restorer", that's what.
#3576 A scientific answer: www.ultralightnews.com/enginetroublshooting/resistorcapsandplugs.htm
looks like no resistor (cap or plug) is the way to go....unless you have an electronic ignition system
that requires it, then the lower resistance the better.
L #4535 Hi, Having recently returned to 'Velo' ownership - a Viper - after a bit of a gap (nearly 40
years) I am having to relearn some old skills like getting it to start with the most economical use of a
right leg that is not getting any younger. Starting is not a major problem, am pretty confident about
mag condition and carburation so I'm now looking for refinement hence the interest in spark plugs.
Coincidently, whilst sorting some of my Dad's stuff, I have just come across an NGK V-Plug
conversion chart. Does anyone have experience of 'better starting performance' by using a B8EV
rather than a B8ES and also for better cold starting in winter is the hotter B7ES / B7EV an acceptable
alternative i.e. won't misfire too readily at higher loads.
#4536 All you want to know about different plug electrodes can be found here www.ngkspark.com.au
Running a B7ES/V will give you easier starting and no problems - well that's my experience anyway. If
you are doing mainly motorway mileage at 80+ then stick to B8ES/V
#4549 I've been using an NGK platinum plug in my Viper last 2500 miles runs ok and starts easily
even in cold weather last few days.
#4550 Plug grade I've been using is BP7 EVX
#4552 In the UK B7ES is fine all year round, unless you are doing long motorway runs. B7EV is even
better - well that's what I and others use anyway.
L #4609 Hi all, I'm having some running issues with my '38 MSS and would like to eliminate the
old (Lodge I think) spark plug as a possible cause. Can anyone recommend what the equivalent in a
modern plug might be, and if one brand is better then another?
#4610 I use NGK B6HS in my 1938 MSS. It was recommend in the Nicholson Brothers book. They
have a chart showing several plugs from several manufacturers, and their equivalents. Let me know if
you want a copy of the chart. I've been using them for 5 or 7 years. They seem to work fine, and are
easy to find at the automotive shops. Every so often on one will be bad, right out of the box though
(maybe 1 in 20). Luckily my bike doesn't foul plugs too often.
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C.3. Dynamo, Magneto and Battery -
L #112 By the way, are there any sources for good used or rebuilt Lucas K1F mags, or is this a
cry in the dark. Even though I have electronic ignition and 12V sparks for the lights, I'd like to have a
standard mag in reserve.
#157 Would it be possible to get the names and contact info regarding the Lucas K1F mags we
talked about?
#159 Sorry for the delay in getting back to you. Below you are the telephone numbers of UK suppliers
of reconditioned mags, I have not used them so I can make no recommendations. Some may only
provide exchanges. Dave Lindsley +44 (0) 1706 365838 FTW +44 (0) 114233 6269 Independent
ignition supplies +44 (0) 1237 475986 Dynamos only P Dunn +44 (0) 1782 856839
#165 I am sure many people are familiar with Dave Lindsley. There was an article on him in FT 310
which describes his attention to detail. He has reconditioned both my mag and my dynamo and I am
very pleased with the results. Independent Ignition supplies have a website at www.magneto.co.uk
L #346 Don't know if people are generally aware of this, but a modern alternative selfgenerating
magneto ignition system is being developed by Rex Caunt Racing using the BT-H trade
mark. The results can be seen by following the links from www.rexcauntracing.com . Rex makes
ignition systems for classic racers which are considered to be one of the best. The magnetos are not
cheap, estimated price on his web site is £500, but it might be worth it for a reliable system and a
weight saving of over 3/4lb over a Lucas K1F. Base mounted units already in production for
AJS/Matchless etc are available with a choice of 2 advance curves built in so I would guess that they
can be run without an ATD - another positive point for those who want to run a tacho drive from the
timing cover but don't want the hassle of manual advance.
L #592 Just "lost" the battery retaining strap on my '61 Venom this morning on the way to work
.Found the old-type black battery cover on my left foot at a set of traffic lights! Retraced my route with
special emphasis on the gutter - found the retaining strap but no sign at all of the bolt. Question -
what is the size and thread type of the bolt?
#593 The bolt is a 2BA thread, I think about an inch and a half long. There is a trick which might
prevent future losses - fit a nut to the bolt before running it through the threaded trunnion, as you
tighten the bolt it will trap the nut between the two strap ends and act as a lock nut, and if the bolt
should come loose after this the nut will usually help to retain the bolt and plain trunnion in the strap.
L #652 Spent part of the weekend investigating a low / zero charging rate on my '61
clubmanised Venom. The Miller ammeter was showing a very intermittent or zero charge. Dynamo
drive is a vee belt and no sign of slipping. I discovered that although I have a Miller headlamp switch
and ammeter I have a Lucas dynamo - I thought that these did not come into use until '65? I couldn't
make out any model number on the casing - but I assume it must be an E3L? If this is correct can I
get 12 volts from it? I discovered a Lucas RB108 regulator fixed under the seat but the bonded
rubber mountings had parted and hence the regulator was held in place only by the wiring. Does
anybody have any experience / tips for repairing the bonded rubber mountings ? I have done a quick
fix of taping the regulator body to the mounting bracket but clearly this is not a long term solution!
The various tinkerings seem to have solved the charging problem - a nice steady 7 - 8 amps all the
way to work this morning.
#656 Rubber mounts normally go. Answer - Super glue
L #674 I've just had a magneto overhaul and refitted it and done all the business with TDC
finders and degree discs. My problem is with refitting the auto advance mechanism. It came off fine,
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the bolt loosening and tightening as it drew off the taper just like it says in the manual. Putting it back
on, the fibre gear meshes perfectly and the bolt screws on but goes solid about 3/8" before the bolt
head buts against the mechanism leaving the horseshoe washer and the round plate that locates on
the 2 little pins totally loose. I took the mag off about 3 months ago and I've never messed with an
auto advance before so it may be that there is something else under the bolt head I've forgotten. I
also wonder if the auto extraction (can't get my head around how that works) in reverse means the
bolt goes tight early and then loosens but I'm reluctant to apply too much force without asking first. I
can't see how I could have put the mag on wrong. Any thoughts welcome!
#675 Forget about the Mag. With the ATD in your hand / on the bench, screw the bolt in until it slops
about. Your then past the self extract thread and can get on with the fitting.
#678 your advice was sound and the ATD is on and the timing done. A couple of lessons I've learnt
which may be of use to other ATD virgins: on manual advance mags I've tended to hold the gear or
sprocket on the taper by finger pressure whilst tightening - if you try that with an ATD you push the
ATD body too far in ahead of the bolt so the mag thread and the extractor thread can both engage
locking everything up. Basically refitting the ATD and setting the timing are 2 distinct operations, my
main mistake was trying to do both together, best to get the ATD on first and then set the timing.
L #709 Anyway I now have an early Venom and am considering upgrading to electronic ignition.
My question - does anyone know where I can get a waisted 3/16 box spanner to remove the magneto
#712 if you are such a heathen (like I am) as to fit electronic ignition, why not go all the way and just fit
an allen headed bolt, it makes life oh so simple. It's fine if you are not regularly taking it off, (then a
stud would obviously be better - so you don't wear the hole in the crankcase).
#713 Fit a BSA "long magneto nut" and solve the problems. Autocycle Engineering sell them at £4.99.
L #751 I was led a merry dance by a carbs spitting problem at kickstart/low revs. The culprit
turned out to be the ( peripheral ) slip ring in my manual BTH magneto; there was a section missing!
Presumably, at higher revs the points operating arm jumped the gap.
#788 it dawned on me that I had made a foolish mistake recently in claiming that I had traced
starting/spitting problems to the fact that a section was missing from the cam on my manual BTH
magneto. Of course the cam is steel and easily inspected. It was the brass HT pick-up ring that was
found to have a section missing.
L #768 A tip for other electrical know-nothings like myself. I've a very pretty, obviously reconditioned,
model of one of these which I was considering setting up on the bench to see what joy I
could get from it. However, along with the stampings E3LM-LO 6v etc.,came an arrow pointing in the
exact opposite direction to what I needed. A quick phone call to Dave Lindsley(see prev msgs)set my
mind at rest. His first comment was that the whole caboodle was a re-con job ,and that the laminated
case was from another model, but it would be perfectly O.K. To check(on neg earth bikes),join 'F' and
'D' contacts together, run a wire from here to the pos. terminal of 6v battery. Run a wire from neg.
term of batt. to the case of the dynamo and the dynamo should run as a motor in the correct direction.
If it doesn't, just reverse the brushes(with wires).
#806 I have added a copy of an excellent article explaining, how and why to uprate your dynamo to 12
volts to the files are on the group site.
#808 Here are three short answers to your electrical system questions. 1. The dynamo can operate in
either direction, this is determined by connections and polarization, as described in Dai's articles and
the literature that accompanies the electronic regulators. 2. Operation at 12V reduces losses in the
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wires and connectors, giving brighter lighting. Sealed headlamp units are also commonly available in
12V. 3. The original Lucas regulators shatter at the mountings (takes about 10k miles). The various
electronic ones do not. Also, the contact points in the Lucas reg can stick, burn out, etc. etc. You
could adjust a Lucas reg to give 12V if you wanted to, but most owners take the easy path and fit an
electronic one.
L #797 As soon as I'd sent the e-mail earlier I had a thought and explored the insides of the
"RB108" regulator. All is not what it seemed! Mounted inside is a solid state 12v voltage regulator
made by TEB Technology. This still doesn't explain the dynamo marked Lucas E3LM-LO, 6v and
running in the opposite direction to that marked on it. The system is positive earth if that is relevant.
#818 The insides of an RB108 are essentially the same as an MRC2. Someone replaced the original
guts and replaced it with some solid state thing. Best solution, use a Podtronics from Kizer.
L #821 The lighting system I'm building up on my MAC is Lucas. The voltage regulator I have,
which looks in good nick, has a flat base with two bolt holes at 3 5/8" centres. It's not obvious to me
where it's meant to be fitted.
#823 that one is usually somewhere under the seat. Often bolted to the rear mudguard. Recommend
you throw away the 'innards' and install a new electronic regulator into the box. I'm told that the
Podtronic device is 'The Best'.
#834 The original position for the regulator was on top of the dynamo, it was moved in 1958 to the top
of the rear mudguard. You can just about see it in this photo.
www.velocetteowners.com/photogallery/machinesworks/xvenomusts.htm
L #991 Does any body know the size of the front holding down bolt on the dynamo strap mine is
1/4 o.d but I don’t know what thread.
#992 This bolt at the bottom of the strap is part number SL8 15 which is 1/4inch BSF x 7/16inch bolt.
The bolt at the top of the strap is SL9 22 which is a 1/4inch Whitworth x 13/16inch.
L #1253 Where in the USA to get the proper size 6v battery for my 1948 MAC (I brought home
from England/Beaulieu last year) It has the hard rubber battery box now. I'm not sure if the battery
replaces that or is meant to just go inside.
#1256 I have been told the hot setup is to: I) purchase a dummy battery box, then ii) insert into it a
sealed six volt conventional motorcycle battery. Having previously purchased an original-type
replacement with vented caps, I now also have the unpleasant experience wherein the escaping and
subsequently condensed vapors have corroded my nice, chrome battery strap. The dummy boxes can
be purchased from Groves in the U.K., or here in the States from Ed Gilkison. Others may have them
as well. Sealed 6 volt cells are easily obtained from almost any motorcycle dealer or accessory
provider.
#1258 You can get 6V rubber batteries that cost about $60 in the UK, but I wouldn't waste your time.
If you are running 6v, buy a 5ah sealed battery from www.burlen.co.uk . It's a fit and forget, the lights
still work even after a winter lay up, no need to charge during this period. However, you do have to fit
it inside a dummy case.
#1260 Just one thing to be aware of on this - would also recommend the 6V Burlen - but I have found
it a very tight fit in some of the dummy battery cases on the market. (Needed to cut part of the bottom
out of mine) - externally this doesn’t notice if you are careful. And it may not apply to all dummy cases.
The battery is well worth it though.
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L #1759 I have a Miller dynamo transformed to 12V with electronic voltage regulator (don`t know
the maker..). I have a very small 12V battery inside that rubber case what Grove sold. Now the
dynamo popped and is completely dead. It worked well about 100 miles. Question: how big the battery
has to be, how many amperes that it takes all the charge and won`t cause any damage to other
parts? I think mine was too small, I don`t know it`s amperes but I can't risk to use it after dynamo
repair if it possibly breaks it again. There are obviously lots of other reasons why the dynamo breaks
but this is my main problem.
#1762 Sorry to hear about your problem with your dynamo. The size of the battery is not critical, but
bigger is better. In most cases, finding a battery small enough to fit inside the black rubber case will
limit you small lead-acid battery in the range of 3 - 5 amp/hours. This small size is OK. Your dynamo is
probably rated at 60 watts. A watt is a volt amp. When the dynamo was used as a 6 volt generator it
would produce 60 watts or 10 amps @ 6 volts (10x6=60). Now that it is being used with an electronics
converter, it still will only produce about 60 watts but at 12 volts or 60/12 = 5 amps. Batteries are
storage devices, like water tanks. You can not have them too big. A 5 amp, 12 volt battery will become
completely charged with your existing dynamo in 1 hour, if you do not run with the head light on, or
use any electricity. A 5 amp battery will light your headlight and tail light for about 1 1/2 hours with the
engine stopped. Common small lead acid batteries are best for this application, although, there are
some other forms of batteries that may work such as nickel hydride or nickel cadmium. Too small a
battery can be a problem.
What size and type battery did you use?
#1765 I agree, having a small battery shouldn't cause the generator to fail. I'm running on 12v with a
6v generator and a small battery in a Grove box and have had no problems. The only downside is that
you need more revs before charging starts so if you were to ride in traffic all the time, particularly with
lights on, the battery might become discharged. There is an article on the group site under
\files\electrics which explains why it's OK to run a 6v generator into a 12v system, it is well worth
reading. It seems the most important thing is to control the rate of increase of charge rather than to
limit the maximum voltage. This is what the black box regulator does. The most interesting part of the
article to me is that a 6v 60Watt dynamo when run at 12v will produce around 100 Watts (theoretically
120W but losses reduce this). This means that you can run higher wattage headlight bulbs etc.
Obviously you don't get something for nothing and the biggest one is that charging starts at higher
revs than before. Other people might be able to give you some ideas about why your dynamo has
failed, but I'm sure it's not been caused by having a small battery. You say it lasted 100 miles. Is this
100miles on a new(reconditioned) dynamo or 100 miles since you went to 12v? If it's 100 miles on a
new dynamo I'd be speaking to whoever supplied it!
#1766 Here`s more info: Battery: small 12V and about 3-4amps. Dynamo: history unknown, but can
be more than 10 years since conversion to 12V,we did all the tests described in service manual and
nothing worked, it won`t spin with outside battery and meter shows nothing when running. So maybe
it`s hours are up... Regulator: metal box under seat in top of rear fender, painted grey "hammer
laquer",main fuse on the right side 15a and next to it green led which lights when charging, so what
make is that? It had broken diode which I replaced (kept burning that main fuse). Box has lid which is
detached with four small screws. My friend has left over Alton generator from Gold Star single and I`m
gonna try that one soon as I can get a pulley machined to suit Venom. Any experiences with Altons?
Does it rob much power because it feels so stiff compared to Miller?
#1767 For a number of years I have lived with unsatisfactory 3.5ah 12 v lead acid battery in a
hollowed out battery case. It never had the capacity to smooth out the fluctuations in current
requirements to provide steady lights. Also, every year I had to replace it, as even when trickle
charging during the winter it never fully survived. Two years ago I replaced my lead acid battery for
two 6 v 5 ah Cyclone batteries in series www.hepi.com/monobloc.htm They hold their charge really
well, and work perfectly even after laying idle over the winter. You will need a replica case and not a
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hollowed out case to fit two batteries, as they are a tight fit. For six volts either wire them in parallel or
use the 6v 8ah version. While you are at it fit a Xenon headlight bulb and get 30% extra light for no
extra load.
#1770 The UK distributor is DMS Technology Ltd, www.dmstech.co.uk located in Romsey, Hampshire
(just round the corner from me). Unfortunately they have a minimum order charge of 100 pounds.
They suggested that I go to RS components. A quick look at their web page rswww.com/uk shows
that the 2v 5A/H (p/n 591-483) cell is 6.25 GBP each (plus VAT) or the 2v 8A/H cell (p/n 265-1947) is
9 GBP (plus VAT). At those prices, a 12v 5 A/H battery would cost 44 GBP and a 12v 8A/H would cost
63.45 GBP. Another solution would be for a group of like minded people to get together and place an
order greater than 100 GBP direct from the distributors?
#1772 Hi I buy my Cyclons as Kempton Autojumble approx GBP 12 for the 5 ah and GBP 15 for the 8
ah. If you can wait, I will get his phone number when I go later this month. Alternatively call CMES who
sell them all be it a little more expensively. However they will give you excellent technical support as I
have heard they have an excellent reputation on rebuilding dynamos. Their number is 01454 323434
#1773 If you go back to Fishtail # 324 page 20 I gave some details of a Cyclone battery 'contact'. I
presume he still does it.
#1775 For those of you w/6 volt lighting and Mag ignition, I recommend using a sealed lead acid gel
battery. These are available for emergency lighting and a 4.2 amp/hr unit fits perfectly in a hollowed
out Exide black rubber case. You could use 2 to create a 12v source. I have a connector wired into my
loom so that one I am not using the bike the battery is on a charge. Because the battery is sealed
there is no worries about boil over. I've been utilizing this set up for about 15 years and it works great.
#1778 I've just finished making a slightly larger battery box from sheet steel, complete with a curved
lid and bolting it to the original battery platform. It will now house a conventional lead acid battery but
also have the capacity to take a choice of others when the time comes. Once powder coated the
whole job will appear to be in the spirit of the machine. I've obviously kept the original straps etc so I
can revert if I wish.
L #1829 Having only recently finished the restoration of this Thruxton and completed about 800
miles over the last couple of weeks, I'm learning its personality. The dynamo belt seems to go slack in
rather short order. Say 200 - 300 miles. I can tell I've a problem when the amp meter shows a
dramatic jump from near full charge to near full discharge on a Lucas 8 amp gage. This seems to
occur at around 3,500 RPM. I'm running the Miller 60 watt device on a JG converter with a new wiring
harness and new 12 amp hour lead acid battery. After finding the dynamo has rotated under vibration
of the engine, I've re-tightened the clamp bolt to 12 - 14 Ft./Lbs., and drawn a pencil line on the
dynamo to observe any movement. I've fitted a new Gates brand 2210 v-belt and tensioned the belt to
what seems normal for a drive this size: perhaps 1/8 - 3/16" deflection mid belt under 5 - 10 lbs. force.
I've checked alignment on both pulleys and have both angular and groove alignment within about
1/16". Pulley grooves are clean and bright and no evidence of the belt "bottoming" in the pulleys. After
my most recent setting, the belt was slack e'nuff to allow some slipping which was detectable by
turning the dynamo pulley by hand. Yet the dynamo had not rotated under the clamping screw
pressure. Something is causing the belt slip and belt wear. The engine is rather oil tight and there is
no evidence of engine oil being blown in huge clouds into the belt housing. So how does one keep
these belts working for their keep? Any thoughts would be appreciated.
#1830 Try the toothed belt conversion from the VOC. The complete kit is £55 and the belt does not
have to be too tight and is resistant to the slightly oily atmosphere it occasionally encounters.
L #1953 My magneto has suddenly lost its spark. I have checked the points, cleaned the
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earthing brush, high tension pickup and contact breaker assembly but still no spark. Does anybody
know how to test the K1F magneto to determine what is wrong? What about temporarily converting to
coil ignition?, I would like to have the bike running before next weekend as I am due to attend a rally
on the Yorkshire Moors Railway. Finally, if all else fails, can anybody recommend a magneto repair
company?
#1954 I have used FTW recently with good results, they are based in Sheffield - 0114 233 6269
#1956 Did you check the connection between the spark plug lead and the mag pickup and/or the
spark plug lead and the spark plug cap? Any foreign material between the points will also render a
magneto mute. Check the timing and see if it's slipped, too.
#1964 I would try Dave Lindsley if you are in the North West or are willing to use a courier. He once
offered to lend me a dynamo to get me to the TT when I was in a similar situation. As it happened he
rewound my own one in good time and Lucasised it too. Also check that the little key on the back of
the CB assembly hasn't flattened and slipped, likewise the cam ring in the end of the mag. both have
happened to me in the past!
#1966 I had mine rebuilt by Bell in Wheaton Maryland--great job.
L #3431 I'm trying to reinstall my recently rebuilt BTH magneto to my '46 MAC. I am setting the
crank to 4 deg. before TDC on the compression stroke and the points just beginning to open. The rub
is, when I torque down the ATD, the magneto rotates and the settings go out of whack. What is the
trick to keeping the mag from rotating? I hate the thought of just wedging something in there to stop
the rotation. With the Lucas Magdyno, a "U" shaped "keeper" kept the gears in sync when reinstalling
but I don't see a similar option with the BTH.
#3433 Most folks simply place a deep socket over the magneto shaft, up against the drive gear and
smack the gear onto the taper. Then tighten the nut. The "U" shaped "keeper" you mention is intended
to allow the rebuilder to set the slip friction to 4 - 10 Lbs./Ft. to keep the fibre gear from shedding its
teeth, under the greater resistance of the dynamo's mass. There is no need to synchronize the
dynamo to the fibre drive gear as there is nothing to "time" between these two devices. Since the
magdyno needs to have the outer cover in place when installed, the holes for above mentioned "U"
shaped keeper could not possibly be used to restrict the magneto from turning once the magdyno is
mounted 4 degrees BTDC sound a bit late to this reader. Is it possible you are setting ignition time
with the ATU bob weights in the "at rest" position? As most engines spend the bulk of their working
time at full advance, there is great advantage in always setting ignition at full advance, I.E. bob
weights wedged in the "out" position.
#3446 I too recently faced the problem of trying to stop the mag from rotating while setting the ignition
on a '46/47 MAC which I was bought for Christmas! (same age as me). I simply held the contact
breaker fixing bolt and tightened as much as I dared; it has covered a few miles since with no
problem. However, the timing was approximately 35 degrees too far advanced when I had checked it,
so it may well slip again. If only I had the sense to solicit advice from this forum at the time ( thanks
"Doctor" ). I can confirm that the 4 degrees before TDC fully retarded is correct according to the
manual. The advance-retard mechanism on these machines does not use conventional bob weights.
L #3470 --Re topping batteries. I use a gel battery off a modern bike, no acid to spoil paintwork
while breathing and no need to top up as its sealed after the initial filling.
#3472 I don't know the reason why but these modern gel batteries are not recommended for bikes
with magnetos/dynamos, read it recently in one of the monthly classic mags, would be interesting to
know why as I know many that do use them without problems..
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#3493 The reason is that the old electrotechnical regulators were set too high in volts. With a normal
battery this just meant they gassed off a bit, so you had to top them up with water once in a while. Gel
batteries can't be topped up, so if you overcharge them they lose water and eventually don't work.
Electronic regulators can be set accurately below the voltage at which this happens, so no problems -
when did you last top up the battery in your car?
L #3476 I'm planning on using wheel bearing/high temp grease on the magneto bearings, any
suggestions of a better lubricant? Also, is the points cam follower oil wick effective or should I use light
grease there as well?
#3483 Almost any NLGI grade 2 grease specified for disk brake applications should be fine. The CB
end will definitely benefit from both oil and a dab of Bosch or comparable contact breaker grease,
especially of the ring cam still has both felts still in place. If the bike gets ridden in the rain, you might
want to use boat trailer (water resistant) grease on the control spring and plunger, and a fresh rubber
boot (Lucas #458731) to keep things dry.
#3484 Only one wick hole in my mag cam...it has the auto advance/destruct mechanism. I'll replace
the wick. Do you think it's advisable to put some kind of removable coating on the armature windings?
I've read where the shellac eventually turns to goo, deposits itself on the armature, and locks up the
magneto. I appreciate the help.
#3488 Anything you put on might do the same - specially if it's 'removable' - what did you have in
mind?
#3490 I was hoping a modern plastic coating had been found and used. By removable, I mean non
permanent that could be taken off without damage in case the windings needed to be redone. On
more thought.....I should do it the right way....rewound and a new capacitor. I'm planning on total loss
battery arrangement and will be relying on the mag completely.
#3487 Look carefully Grasshopper, is there a round felt in the hole, or just a rectangular felt in the
recess at the bottom of the mag housing. Unless both are present, there is no way capillary action will
"wick" (pun intended) the oil thru the cam ring and lubricate the breaker. As to the armature, your
question leads me to believe this armature has not been rewound. If that is the case, I trust you have
a plan for hauling your bike back home when the magneto fails. They all do! The 50 year old windings
will fail sooner or later, and the ancient capacitor will fail to restart the bike when the magneto is hot.
This always occurs when you have just come out from a store after a brief ride, some fellow is
admiring your bike, and tells you he had one in back in 19XX, and wishes he still had it. He will tell you
about his travels while you get red in the face trying to start yours. Bite the bullet and get the mag
rewound.
L #4062 Hi, Does anyone know the procedure for testing Miller Dynamos in situ? Mine is on a
Rudge, but I'm sure Velo's use the same Miller parts.
#4063 From page 74 of the Red Book: "The dynamo can be checked quickly and with very little
trouble by removing the driving belt, and the commutator cover, and pressing the cut-out points
together. If the dynamo does not begin to run as a motor from the battery current there is a fault in it.
"This is not a 100% check, as in some circumstances a dynamo with a faulty winding may 'motor,' but
by testing in this way a lot of time can be saved."
#4075 Doug is bang on.. but shorted turns in the field or armature can allow the dynamo to motor but
still not charge. Measure the field resistance - should be 2.5-3 ohms. The armature is best tested with
a 'growler' - see an old fashioned motor rewinder in your area. Obviously check all wiring is sound and
that the brushes are in good condition and move freely. Might be worth cleaning up the commutator -
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if badly worn trim up in a lathe taking as little off as necessary. My experience with miller setups is that
the dynamo is less likely to be faulty than the regulator.
L #4749 Hi Does anyone know where I can obtain dynamo brushes for my Miller dynamo, mine
are getting low and the spring pressure is becoming ineffective, I don't mind modifying substitute
replacements.
#4750 Dave Lindsley in the UK has them as his part number 404.
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C.4. Lights and Horn -
L #381 My recently acquired '61 Venom Clubman has original Miller electrics - all working v well!
But - it has a Cibie head lamp unit that has no provision for a pilot/parking light. It has a current MOT
but my local testing station is telling me that I need to have a pilot light. The Miller light switch clearly
has pilot and main beam positions. Any thoughts/advice??
#383 Change the sealed beam unit. Remember the pilot bulb assembly. Contact R F Seymour Ltd. 01
844 217 277. They will sort it
#385 The Cibie light unit makes a big difference to your headlight at night. I assume you have the
concave lens that was fitted in the seventies. I have a Cibie fitted with a pilot, but they are now have
convex glass. You should be able to get them from M & P in the UK cost £ 33. M & P part number 525
334.
#398 If you have converted to 12 volts I recommend buying a Hella H4 headlamp lens and specify
the one fitted to early Minis. This had a sidelight.
#399 In your case you will be absolutely correct, and this may be a way round the problem, but I don't
think that was the way the switch was intended to be wired up originally. I think you will find that the
first position was intended to be wired to the pilot light, but somewhere in the machine's past it has
been wired directly to the dip filament in the headlight instead. In this configuration the dip beam does
in fact become the pilot light, since it is independent of the dip switch and satisfies all the criteria of
the test, albeit a bit grey in terms of being a separate light bulb. When you move the switch on to the
headlight position the power is routed through the dip switch before going to the headlight, so you
then of course satisfy the criteria for the headlight. What you lose however, is the failsafe position that
should the dip filament fail (a very likely scenario!) you do not have the pilot light to enable other road
users to see you without being blinded by your high beam. I agree that we seldom if ever use the pilot
light through choice, after all what chance have you of seeing anything beyond the glow on the front
mudguard, but the general principle is that, as stated in the regs, "The light must be visible from a
reasonable distance," indicating that the idea is not to see, but to be seen.. .
#419 Miller lights in good condition are impossible to get hold of. If you are lucky you may be able to
get a NOS Lucas, the correct item should have the words “motorcycle” and “700 Headlamp”
embossed in the glass. If you want to use a halogen bulb (recommended) try your local Enfield India
dealer who should sell them to fit (they may even sell Lucas light units). The bulb is not the same as
the modern halogen bulbs. Alternatively buy a Cebie light, which are excellent and no one will notice.
You can do what I did on my MSS to keep it original; bought a light unit, smashed and removed the
original glass and used silicon sealant to bond the existing Miller glass into the unit..
L #553 want to get a few basic spares that do not seem to be available through the velocette
spares. 1. 24w/24w 6v SBC double filament bifocal. (pre-focused type) Lucas168 or Philips 6722 are
not listed any more. emailed Grove Classics 2 weeks ago but got no reply's, the bulb in the Miller
head light is a Stanley 6v 18w18w SBC which is a bit of an odd one?
#554 I fit a 6v halogen bulb which will fit strait in to the Miller / Lucas headlight unit. They are made for
Indian Enfield’s and I usually pick them up at auto jumbles for £5. Try calling +44 (0)1454 323434 who
sell them for £7. I would phone Grove classics rather than e mail, when you will receive excellent
service.
#557 A 30w main and 24w low beam is available from Walridge Motors. It is their P/N BULB 312. Lots
in stock $5.67ea Canadian. I do notice that my supposedly optimally functioning Miller dynamo still
does not keep up with the 24w low beam at low rpms. Thus the 18w Stanley bulb is an interesting
possibility.
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L #978 By the way does anybody have a horn for sale or know where I can get one.
#986 Try Taff Isaac at Swansea. He will advise you on which horn you should have, He prefers it if
you have an old one that he can restore for you but does have some that he has already restored. His
email address is found at www.velocetteowners.com/techinfo/electrics/electrics.html
L #2008 With the Miller headlamp shell and rim? Can anyone in the UK recommend a
modern(ish) unit that will accept car bulbs? I have an Alton dyno conversion and would like to fit the
best possible headlight.
#2041I bought a modern halogen unit, carefully smashed the glass and replaced it with the Miller
glass. A thin smear of my favorite silicone between glass and unit seals it from the weather.
#2072 I do not know the size of the headlamp on a MAC but for my Venom I bought a new Lucas
combined reflector and lens with separate 55/60 Watt bulb, Halogen I think from Goodman when he
was in business. I expect Grove Classics have them. The Lucas is an H4. I converted to 12volt with an
Alton too.
#2083 For many Velo owners the favorite headlight unit is the Cibie. Unfortunately they are difficult to
get hold of. However M & P sell them, go to www.mandp.co.uk/ then products, no need to register,
click on the catalog button and enter code 535334. I know it fits a Lucas unit, but I am not sure about
a Miller unit.
L #2118 Hello group, I'm looking for information on the type of horn my 1948 MAC would have
had when new. I'm not sure if should look for a Lucas or a Clearhooter or just what. I have a nice MAC
and like to show it but the cheap repo horn sticks out like a sore thumb. Anyone have such a horn to
sell or can point me in the right direction to locate one?
#2122 Look under horns, here www.croesus-consultants.co.uk/v-tec/ Velos around about this time
had all sorts of parts fitted, but I believe it was a Clearhooter.
L #2228 I am trying to ascertain whether I have the correct headlamp for my '50 rigid MAC. The
chrome rim is roughly 8" in diameter, and everything else on the bike is Miller, so I assume the ring is
an MIL118 (this number taken from Groves most recent parts list).The reflector and the glass are a
single unit, sealed together with a steel band of some sort. The glass itself is flat, and has a pebbly
texture (what we refer to in the States as bathroom glass). This assembly could possibly be a MIL148:
Miller 8" Light Unit (Glass and Reflector). Personally, I think it looks a bit odd, and people often ask me
why I have a piece of bathroom glass for a headlamp, but that's a separate issue. I notice that Groves
has a 138 Glass 8" domed, and a Glass 8" flat, but I could not find a corresponding 8" reflector that
would presumably be used in conjunction with either of these.
#2229 I have a 1950 rigid MAC, also, it came with no headlamp on the Dowty forks fitted to the
"basket case" machine bought a lot of years ago. Like you I wasn't sure as to the correct fitment. My
investigations revealed that at the very end of the rigid MAC production the factory used up a load of
"out of date spares" some of which were 8" miller headlamps. I've since fitted that size of headlamp to
my machine complete with the bathroom glass, it looks brilliant, 'need to find out how it performs on
the road. My glass and reflector came from separate sources and are therefore separate in their own
right, no steel band etc, so can't advise further on that bit
#2230 The Miller catalogue indicates that MAC 47 - 53 was fitted with a 7" lamp, that used a domed
moulded glass non sealed beam type reflector. The unit you describe sounds like a 7 ½" unit fitted to
later MAC/MSS, it too should have a domed glass. This unit came with both separate reflector and
glass, and as a sealed beam unit.
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L #2340 Being a newbie and used to riding a Beemer, I'm wondering if the vibration of my
Venom/Thruxton is the culprit. I've blown two H4 halogen bulbs in short order (at $10 a pop, I might
add!!)and now the taillight bulb has gone, as well. I replaced the halogen with a standard sealed-beam
headlamp and so far so good. Are there rough-duty taillight bulbs available? If not, any suggestions
for brands that have proved less sensitive?
#2341 Might be worth checking the system for excess voltage first - no more than about 15V with
engine running at or above 2500rpm or so - if over this then the regulator is up the Swanee. Bad
switch connections could be causing power spikes which bulbs won't tolerate for long, fitting a relay in
the system to minimize the arcing in the dip switch when changing between full and dip beam will
help. Also make sure the earth wiring is good and secure and that the lights are solidly mounted, not
shaking about in their mountings. On this side of the water several outlets are retailing a LED bulb
which is a direct replacement for the standard offset pin 12V 21/5W stop/tail light bulb. At around £9 a
throw they aren't particularly cheap but should last forever and if my experience is anything to go by
their brightness doesn't seem to be affected by fluctuations in voltage.
#2342 If I'm getting spikes with switch operation would I see that on a digital multimeter while I flick the
switch, or does it happen to fast to register?
#2343 I don't think a digital multimeter would show spikes particularly well - you might just be lucky to
see the numbers change momentarily but its unlikely. An analogue meter would be a much better bet,
but better still would be an oscilloscope if you can get access to one. The trouble is, you're looking for
something which may not occur until the machine is traveling, but strapping a scope to the tank and
trying to watch it as you ride is not a practical proposition. There is equipment available which can
record the performance of any movement or electrical signal - usually in use by most of the higher
level of racing teams nowadays for data logging if you have the contacts and want to take this route
as a last resort. But I would just try connecting an analogue meter across the bulb to start with and
watch the needle as you flick the switches on and off and between main and dip with the engine
running to see if it jumps excessively high.
#2355 I had a similar problem that resolved itself when I changed the piddley little 12v 3 amp hour
battery for two cyclones with a higher ah rating.
L #3856 'What is the "correct" Miller tail lamp face for a '54 MSS? I have seen the "STOP" and
"DIAMOND" available. Was the "STOP" ever put on bikes exported to the colonies?
#3863 The road test in The Motor Cycle dated the 15th July 1954 show a "diamond" type Miller rear
light.
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C.5. Electric Conversions -
L #23 I also converted the shaft of my distributor of my 1969 VMT to ball bearings some ten
years ago. Plus the fitting of Boyer electronic ignition and 12Volts by JG unit and careful
stroboscobing, I have not touched the ignition setting since 10 years and 15000 miles. It is clear to fit
a sealed bearing towards the CB room of course. If you use a Boyer (pre digital) ignition, be careful
with the coils. I have a collection of burned out coils. Especially the thin 12V ones ast only 1000 miles.
Ernie Brandsen gave then the advise to fit the genuine thick Lucas 6 V coil with a Norton Commando
ballast resistor in series. Till today it does the trick !
#27 I've had no luck with electronic systems, probably not sufficiently convinced to persist long
enough to clear up all the problems. Means going to 12v which I have on only one of my Velos. With
my ball-bearing conversion, I couldn't find an oil seal which fits, so the outer bearing is sealed on one
side.
L #88 am in the process of installing a Boyer ignition on my 1970 Venom Clubman, keeping the
bike at 6V. I'm wondering if there are any other electrical mods I should make at the same time to
improve reliability. Should I replace the original Lucas voltage regulator? How about the coil? Does
static ignition timing work well on these bikes, or should I strobe it? Also, I'm assuming this bike is
positive ground, since all the pretty red wires go to the frame :)
#89 You can stay at 6v, but if you intend riding much at night, why not look at alternators? There are
two on the market at least, my preference going to the one which looks most like the old dynamo. The
dynamo style one comes with control gear, as does the Lucas alternator version. You can use a
cheap voltmeter, a useful bike tool anyway, to check polarity. Personally, I have never had much luck
with electronic ignition systems, and still use points. As the Velo does not have a fixed mark for
strobing, the result you get depends on your skill setting it up. Which also applies to static timing.
#91 I have my doubts if you will succeed with 6V and a Boyer ignition. I have a Boyer on my Thruxton
since 13 years, but, as far as I am aware of, it only works with 12V. I converted the dynamo with a JG
unit to 12V and the system works reliable. If you convert to 12V here is one good tip (from Ernie
Brandsen, the electronic wizard himself) : Use the old 6V ignition coil with a Norton Commando ballast
resistor in series.
#92 I did purchase a 6v Boyer unit, so theoretically it should work. It's turning out to be a bit more
involved than I initially thought, since I need to replace the coil (the original coil is 2 ohms, and the
unit requires one in the 5 ohm range. I'm also going to switch to a solid state voltage regulator while
I'm at it
#93 Most electronic devices (semiconductors) need roughly 4.5 VDC minimum for function. In any
wiring system there is a voltage drop across each of the numerous connections. When you include
the effects of time and weather it is very unlikely that your Boyer will have sufficient voltage to operate
reliably in a 6V system. This is also one reason that 6V lights tend to look dim, even if the power
rating (wattage) is the same. OTOH, you could solder up all the connectors - but this makes repair a
bit difficult! I agree with Herr Patek, the JG has been 100% reliable on both my 60W Lucas (Venom)
and 36W Miller (MAC) dynamos. The Venom has 30,000 miles and 12 years on this setup. I cannot
think of any good reason to stick with 6V. Also, both bikes have magnetos, and after towing a couple
of dead Velos equipped with coil or electronic ignitions I would not use anything else.
#99 I am very surprised to hear that Boyer offers now a 6V electronic ignition unit. Those Boyer guys
are excellent in technical respects, but quite bad in marketing their products. Who knows the exact
difference between a MkIII and a microdigital unit ? Instead of running their identical advert in all
magazines, they should describe their products closer. The only draw back I always had with all Boyer
units were the coils. An A65 twin worked perfectly with two 12V coils parallel, the Commando only with
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two 6V coils in series. The 12V converted Thruxton, blew about six 12V coils of different makes on the
most uncomfortable places (single repair lane of motorway on top of a bridge with no escape lane, big
fun !) till my desperate call to Ernie Brandsen revealed the secret of using the original 6V coil with that
mysterious Norton Commando ballast resistor in series. Why not telling the customer in advance ? I
agree with Tom Ross that the most reliable ignition is a magneto, and in this case a BTH. Once you
have a rewound armature and everything checked over, you should have no problems. On my Venom
I use a manual TT BTH magneto with a steel geared Lucas ATD and this offers the best of both
worlds. Reliable and smooth tickover, and the possibility to adjust at full revs when the engine pinks a
bit. I have 8 old bikes and long winter months (lay up periods) and compulsory daylight riding. So I
converted all magneto ignited ones to battery less systems, because I don’t want to buy several
batteries each year. I short cutted the cutouts and adjusted the voltage to about 7V at full revs. The
light switch stays permanently on, and from a little over 1500 revs, I have lights which can be seen,
though this does not say, that I see anything at night with a 6V Miller 30W system, for instance. One
word to the praise of the JG units. It seems they work perfect on Velos, but we tried four (4) on three
different Goldstars, with the effect of boiling batteries, burned bulbs and 3 exploding dynamos !!! A
very expensive try ! It appeared it has something to do with the high revs of the magdynos on the
Goldies (the dynamo rotates with 10500 rpm at full revs). We all reverted to conventional mechanical
regulators then. Fitting an electronic ignition to an original coil equipped Velo is the easiest (and
cheapest) way to overcome the sloppy distributor spindle. For the Boyer unit it does not matter if there
is a bit up and down clearance on the spindle once the rotor stays between the poles. But you always
need to watch the healthy state of your battery, be it 6 or 12V.
L #95 When my dynamo burnt out I was toying with the idea of fitting an alternator or converting
the dynamo to 12V. The Alton alternator looks more like a dynamo than the Criterion but I preferred
the bike to at least look original. I tend not to ride the Venom at night as the VFR seems much more
suitable for this. In the end I had the dynamo rebuilt (cheaper than an alternator) and replaced the
KTec (part of the reason why the dynamo burnt out) with a 6V JG regulator. The only modification with
this was to convert from a positive earth to a negative earth. Another useful modification was to
replace the dynamo V belt with the owners club tooth belt, which requires less tension and puts less
strain on the dynamo bearings. I have also had my magneto overhauled (extensively) and it seems to
give a hefty spark, so I am also in favour of points
#97 I got a dynamo rewound to 12v, and the fellow who did it wasn't happy. He claims there is
physically not enough room to put in as much copper wire as should properly be done. He also says
there will probably be some inferior rewinding jobs around. May be that he's a perfectionist. As long as
a modification is easily reversible, I have nothing against it.
#98 Electronic regulators (and 12 volt conversions) have been around for a couple of decades now.
The conversion requires no rewiring or other mucking about with the dynamo (assuming it is in good
shape to start). There were some problems with very early JG units, but they are quite reliable now. If
you run electrical accessories such as heated clothing, better buy an alternator. My vest draws 60W
by itself, which would not leave anything for the lights. Up to now I've toughed it out, but advancing
age will soon force me to install an Alton. Procedure: (tip o'the hat to FT and Ed G.): 1. Examine
machine for magneto. If found, proceed with step 2. If not, purchase 12V coil or (thanx Johann)
Commando ballast resistor. I am not sure if you need a 12V condenser, wouldn't hurt. 2. Purchase
12V JG electronic regulator, plus suitable battery and bulbs. The horn will be fine unless you live in
Cairo. 2. Polarize dynamo per red book or instructions packaged with regulator. 3. Install above listed
items. VERY IMPORTANT - install a main fuse on the battery (10A should do it). Ride away. On my
Venom the ammeter shows charge at anything over 40 mph in top. The MAC (even with it's wimpy
little 36W Miller) performs similarly. The only dynamo problems I have had with either was when the
screws holding the mounting plate backed out (Lucas). Oh, and the brushes stick once in a while.
Concerning cosmetics, the JG is small and silver in color. It's not visible under the seat of the Venom,
and on ZUMAC I painted it black. This has not kept ZUMAC from earning a trophy every time I have
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shown it. I use a full sized Yuasa motorcycle battery, wrapped in self-stick pebble-grained black vinyl
film made by 3M. It is used on auto bodies and a good paint shop should be able to get it. You have to
be within 10 feet - and know what to look for - to notice it. Others have cut open an old black-case 6v
battery and placed a small 12V one inside. I saw a reference to a metal cover somewhere, too. And
the sealed type batteries are black already, if a bit dear. There is one on my Honda XR650L - I think
it's called a Dominator in the UK. Personally, I like having lots of battery; the Venom has been used
for campsite illumination during late night work sessions on VOCNA Summer Rallys. This is the best
reason for sticking to a mag - battery condition doesn't affect engine operation. When it finally
becomes so discharged and sulphated that the dynamo field windings can't function (no charge even
when revved), buy a new one. Plus, if you leave an ignition coil powered up for very long without
airflow for cooling it can explode and spray tar everywhere. Happened to a friend's Clubman...
#100 To all of you considering of fitting either a JG or Ktec voltage regulator unit : There is one major
snag with all those electronic regulators. Once your battery is completely flat (after winter lay up) or
because the idiot riding it forgot to switch off the lights, the battery is not charged at all after a restart
(only possible with a magneto), no matter how hard you rev the engine. We experienced that there
must be sufficient voltage in the battery left to get the whole system working again. At least halve
charged ! No manufacture of the those units state this affair in their descriptions ! A mechanical
regulator instead also provides a charge to a completely flat battery
#101 I disagree that a mechanical regulator will charge a fully discharged battery. The field coils of
the dynamo must be energized first before the dynamo can function. However, the mechanical
regulator will function at a slightly lower battery voltage; the threshold voltage required by the
semiconductors in a JG (about 0.7 VDC) must be overcome. This means that a battery too flat to fire
up a JG might still work with a mechanical regulator. I remain unconvinced about no battery at all.
#102 I understand that the magneto system is much simpler, and when properly set-up is very
reliable, but, it seems to me that if the battery is kept up by regular running, and the coil(s) are of good
quality, and considering that millions of vehicles of all types use coil/battery ignition systems, if the
quality of the Boyer system is good, what would the problem be, aside from the dynamo being
required for double duty, ignition and lights? My Mac has the 12V JG unit in place with a B-B ignition
system installed in a K1F body by Dave Smith and seems to work just fine, though it has not had a
great deal of usage as yet,
#103 I recently converted my '56 MAC to 12V lights and ignition. It required rewiring the Miller
Dynamo to 12V, using the excellent JG Electronic Regulator, but I left the old regulator box on the
dynamo to look "right". I got a Boyer Bransden 12 V electronic ignition unit very nicely installed in a
K1F Lucas Mag body with new shaft and sealed bearings by Dave Smith Classic Motorcycles here in
the US, along with the required coil, a small German made unit that seems a good one. I got a
10amph battery that is a bit small but works well. Except for the required extra wiring to be properly
installed, and retiming according to the clear instructions, that's it. The mag on my MAC needed
rebuilding, so I opted for the Electronic ignition and she starts up 2nd kick every time and often on the
first if I do my bit. Of course, you could just convert to 12V lighting and make sure the 6v mag is good
shape for ignition. My lower back is pretty bad, so any guarantee of less kicking over is happily
appreciated
#108 I have tried JG's K-Tecs, dynamos with little success. I also have a Criterion type alternator
conversion. In my opinion the best solution is the Alton. It is easily fitted, well engineered, has great
performance and is aesthetically pleasing. I have had mine for 3 years, I did have a strange
mechanical failure outside the warranty period but they replaced the unit, just for the cost of the
postage. Its performance is superb - and even when you point out that you have an alternator fitted,
the most common comment is "I can't see one. I have uploaded the information files in the file storage
area of the group site, within the "Electrics" folder.
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#117 The Alton was designed by a French Vincent owner, Hervé Hamon; For those who don't know
the Alton, it simply bolts on, in place of the Miller/Lucas dynamo and is belt driven as per the original.
If you wish later to go back to the standard instrument, this is simple, other than the rest of the bike
being 12v equipped.
#121 All the details on the Alton have been uploaded to the files section of the Velocette e group. Try
this link. http://groups.yahoo.com/group/velocette/files/Electrics/
#124 Unfortunately you cannot use your JG with an alternator, as it was designed to regulate a
dynamo. There are sources within the UK that sell reconditioned KIFs but I have no experience of the
quality, so I could not recommend a supplier. If it’s just names and contact details you want I can
provide these
#341 I have run an Alton alternator now for about 4 years and have had no problems. It does come
with a hefty fully encased regulator unit and the strap will have to be changed for a more substantial
type. Their is a strong magnetic pull compared to a dynamo I also run it with a club supplied tooth
belt. The only criticism if any is the vents on the body (water ingestion maybe on the exposed position
on a Velo). Moreover, as it was designed for the Vincent some maybe supplied with a parallel keyed
shaft for a magdyno not a taper a la Velo. They are expensive but are a clever bit of design also by
the time you've had a dynamo overhauled bought a new electronic regulator you're half way to
buying the Alton with 150 watts.
#344 I purchased an Alton direct from the manufacturer in France about six years ago. My views are
as follows; The Alton is simple to fit; the most difficult task is removing the front engine plate to get at
the1/4 BSW bolt that holds the dynamo strap on. You need to do this to fit the substantial slotted strap
that comes with the unit. The rest of the installation took about 30 minutes.
#347 I have heard from a "reliable" source that the Altons are hard on bearings, and have a life span
of 10,000 miles or so. How many miles do you have on your second unit? Even if true this would
probably not matter to most owners, but for a machine used regularly it could be a concern. I should
also point out that my Venom has needed new bearings in both dynamo and mag during its 33,000
mile history. The screws backed out of the dynamo end housing, apparently a common complaint.
#348 I have completed just over three thousand miles with the Alton, and unless it stops raining soon
I won’t be adding many more miles this year! A friend has a Criterion and has had to change the
sealed bearings in that after approximately 3000 miles
L #530 Could you please tell me where I could purchase a 6 volt Boyer Ignition system for a
1961 Venom Clubman?
#532 I bought mine from Dave Smith Classics
L #743 I have just acquired a 12 volt 110 watt criterion alternator which comes with Zerner diode
and heat sink. the bike it came off used the mk one venom clubman/ mss/ viper type battery platform
which had a 12 volt 14 amp hour on it. I plan to put it on my bike which has a mk 2 toolbox come
battery holder. < same as thruxton > the problem I have is that the battery which goes inside it is
quite small, a lot less than a 14 amp hour. I am a bit concerned that the alternator might overcharge
the battery with dire results. should I look to relocate the battery and fit a decent amp hour size. any
feedback on this welcome.
#792 If the alternator/Zerner is operating properly, the battery will not overcharge no matter what size
it is. On the other hand use the largest battery that will fit and use a sealed one is even better.
Podtronics makes a good alternator cum regulator that should do better than a full wave bridge plus a
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Zerner diode. Keep in mind that Zerners come in all limits and there are manufacturing tolerances,
even if the Zerner says 14 volts, the actual limiting voltage can vary by a few tenths. The state of your
battery will depend on the type of riding you do ( daytime, nighttime, fast and long, city trips, etc.).
Many problems can be traced to negligence of not keeping the battery topped up. That's why I
suggest a maintenance free type.
L #778 I have just fitted an electronic ignition on starting, the bike it stopped charging. I have
sent the dynamo for repair and I am informed that it is burnt out due to the electronic ignition and it
has been suggested that I go back to Magneto. Have you any thoughts on the subject please, also
any thoughts on converting dynamo from 6v to 12v while it is in for repair.
#779 IMHO, I don't see how the ignition module could "burn out" the dynamo (generator). Those are
big wires in there. The only way I know a generator could "burn out" is through a massive short circuit,
that heats up the armature and the solder melts and is thrown out. The ignition module only draws a
couple of amps. You should have some seriously melted wiring if you had a short of that magnitude.
BTW, I would convert to 12V if you can. Much more efficient.
#780 The Boyer ignition module draws less than a tenth of an amp, it's the coil that uses two or three,
same as a regular coil/points setup. I'm with George, it takes a dead short to burn out a dynamo. I
have had excellent results from electronic voltage regulators made by "JG", even the little 36 watt
Miller on our '56 MAC maintains a charge at any speed over 40 mph in top, with lights on. We have
them also on Zuma's 1950 MAC, and my Venom. These regulators "trick" the dynamo into producing
12V by raising the cutout voltage. Although the '56 has a Boyer, I still prefer magnetos 'cause I hate
the sight of all those wires! Simple is best. But I would look for another specialist for advice re your
dynamo and ignition bits.
L #840 I've got a 1951 MAC, with a new 6 volt battery and bulbs - but it won't charge. I'd prefer
to hide the regulator unit in the old Miller case above the dynamo as it would be too visible sited on
the mudguard, (separate seats) I've got a 12 volt JG unit (which won't fit in the Miller case) and also
the converted 60 watt dynamo which worked perfectly last time I used them on my Venom - about 17
years ago. Is it best to use the 12 volt system although it would mean buying a new battery, bulbs
and headlight(and horn?). I've heard of K.Tec and now I hear about Pod Tronic. From real
experiences, which is best and where do I contact the various companies and how much do they
cost?
#843 The Lucas MCR2 voltage regulator I have looks in good condition, but as indicated in recent
messages it seems like a 'Podtronics' item maybe a better long-term bet. So, where can these items
be found in the U.K., and at roughly what cost?
#845 SRM Engineering have recently started importing the Podtronics regulator. SRM Engineering
Unit 22 Glanyrafon Industrial Estate, Aberystwyth, Dyfed SY23 3JQ
#849 For anyone else interested in similar technology, here's the reply I received from srm1@s... :-
'We have choices of 6v & 12v conversion Podtronics, both available in pos. or neg. earth. Units are
wired in same manner (FADE) as standard regulators & so are simple to install; comes with diagrams
anyway. Units are(here I guess they're talking about the model I asked about) £64.88(incl p&p and
VAT.'
#867 I am uniquely qualified to give you advice on dynamos an voltage regulators. I have tried to get
them working on three Velos and failed every time. Having spoken to others 12v dynamos are better
than 6v, but they need to run at greater speed to maintain a charge. Anyway here's my input K-Tec -
cheap aprox £25, available from lots of classic bike dealers. I've never got one to work and there is
absolutely no technical support. JG - more expensive larger, and if you buy it from the right place you
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should get technical support. Still need a knack to get them working. I have heard lots of good things
about the support and product made by CMES in Bristol, telephone number +44 (0) 1454 323434, but
I have never used them myself .
L #109 in nearly 15,000 miles of Velo rallies here in the US, the most common breakdown I've
seen is due to a non-standard coil ignition failing, due to either a flat battery or fried electronics,
followed by fibre gears stripping on Lucas mag's.
#110 Both my Velos have the original magnetos, and I have had good performance from them.
Indeed, the Venom's 35 y.o. K1F needed some work a couple of years ago - not the standard
capacitor-and-remagnetizing, just new bearings and insulators. It was then demonstrated to produce
a 1/4" spark when turned by hand. It's a shame that the Works couldn't get mags by the late 60's - I
read somewhere that toward the end they would send a runner with cash for one or two at a time. A
coil system is relatively "cheap and cheerful." The problems I have seen with coil and B-B type
systems have usually resulted not from faulty product but with the installation and maintenance. Bad
connections, batteries shorted from vibration, and not installing proper fuses result in being stranded.
Obviously this is not a concern with a mag. Most roads where I ride are very lonely, often lack mobile
phone coverage, and vultures circle overhead. And I am not eager to win VOCNA's booby prize - the
highly non-coveted Crock of S!#t Trophy awarded to the Chase Truck Queen on our Summer Ride. I
should point out that, unlike some areas, daytime lighting for old bikes is not a requirement in my
home state (California). All you need is a brake light. Also, I have several bikes and am constantly
charging flat batteries. Being able to hop on the Venom and ride off regardless is a real pleasure. As
long as the battery doesn't fall off onto my foot, as happened with a mate's Velo once! Also, the
added current draw from a coil or B-B will raise the rpm required for a dynamo to produce a charge.
This could be marginal on a 36W Miller on a slow revver like a MAC.
#115 I ride the MACt three times a week, for at least 20-50 miles per trip. The Miller is converted to
12V so in effect it now puts out 72 volts, though that is a technical rating. It seems to charge up quite
well between 4-6 volts cruising along, but I will always keep an eye on it,.
L #337 Having had some mildly worrying times on dark country lanes due to fading Miller
glimmer, I have been wondering if the grass would be greener with uprated electrics. I have enough
bits to change to a Lucas 6 volt late model 60W dynamo and appropriate regulator as the BMS book
suggests Or.... The JG unit has been around for a long time but am I being over cautious in
mistrusting electronic boxes on vibrating British bikes? I am not keen on the Criterion alternator
conversion, preferring the appearance of the dynamo, so is the Alton unit the (expensive) answer? Is
its accompanying regulator just another electronic box? I have been a VOC member for two years so I
haven't got the relevant fishtail articles on Alton and 2CV alternator conversions. Can anybody give
me their real life opinions of these conversions and their reliability on wet winter nights.
#338 Re alternators etc. These comments are based on my own experience. I ran my Thruxton for
many years with a J.G. conversation with no reliability problems. The drawback was despite a first
class dynamo, with the headlights on the battery would eventually drain and the lights. (output
checked by suppliers of dynamo) I decided during a bike rebuild to convert to electronic ignition,
(Boyer). I had used it in the past and was impressed with its performance and advantages. Since the
slow running problems with the J>G> an alternator conversation was I thought necessary. I was
impressed with the unobtrusive looks of the Alton but thought the Criterion was a known, proven and
made in Britain. I ventured on the side of looks, but was unable to make contact with the
manufactures of the Alton so the Criterion was purchased and fitted some years ago. Initially I used
a Zener diode and rectifier with no problems. I later fitted a Boyer power box with does away with the
Zener and other ancillaries, this was several years ago and to date has given no problems. Electrics
are not my strong point but find wiring a electronic ignition system and the control box as simple as
wiring a three pin plug.
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L #1120 The Miller DVR dynamo on my 67 Velo is shot. Is there a recommended source for
rewinding in the US or UK?
#1121 In the past I have used FTW in the UK 0114 233 6269, but perhaps the most knowledgeable
person I have come across so far is a Mr P Dunn, on UK 01782 856839. I have had good results with
both. But this sounds like a good time to buy an Alton to me......all my dynamos now sit on the shelf !
details from Paul Hamon in France, BP49, 29480 Le Relecq Kerhuon, Brittany FRANCE 00 33 298
283575. Paul speaks good English. Alton comes with 2 year warranty and looks very neat and
unobtrusive, and very much like a dynamo - and so doesn’t spoil the bikes appearance My only
criticism (so far) of the Alton is that it really needs a toothed belt rather than the std V-belt Toothed
belt is available from the UK VOC - a very simple machining job is needed to get it to fit. It would be
interesting to hear of anyone else’s experience with the Alton - mine has done over 10000 miles with
no problems - it is one of the current models - there were some problems early on with these I believe
?
#1123 A "usually reliable" source has told me that Alton bearings have roughly a 10K mile lifespan,
possibly due to the fact that they are geared to spin much faster than in a dynamo. This opinion is
from experience with older production. Has anyone else obtained more than 10K with one? And is
your Velo mainly used to putter down B roads or is it frequently on the motorway? The latter is an
unfortunate fact of life in my area. Many machines are ridden gently, perhaps only a few hundred
miles per year, these owners may not find a 10K lifespan a problem. I have obviously been thinking of
getting an Alton myself, but my dynamos have been more than adequate so far, running magneto
ignition helps. Still, our Boyer equipped '56 MAC ran 1000+ miles with all lights on last summer, and it
still has its original 36W Miller, converted to 12V via JG.
#1125 Hi
I have owned an Alton for a few years now. My first Alton failed, in of all places France. Paul replaced
it free of charge (the shaft had sheared). The new one has been fine.
I am a fan of the Alton. My only complaint is the version I have has a steel body, painted black that
has started to rust. I did however have to change over to the Club toothed belt drive as belt slippage
at high output was a problem. Fitting the toothed belt drive was not a problem, all you have to do is
bore out the centre of the pulley and cut a keyway in it.
#1128 Hmm, your experiences really don't seem to indicate reliability equal to most dynamos. I've
never heard of one failing totally early on, yet you report this in 2 of 4 Altons. In around 50k total miles
on various Velos we've had one failure, when the screws holding the end plate on a Lucas came out
after 25,000 miles (easily prevented with a few drops of Loctite). I could have bodged it by the
roadside, but with magneto ignition all I had to do was remove the belt. Repair cost less than $100.
IMHO, for 350 euros plus shipping the Alton should not rust or need machine work on a pulley to
make right. Do overseas customers have to pay French VAT? The order form includes this in the
pricing with no further comment. My "source" is a major U.S. importer and distributor of Tri/BSA/Nor
parts, he based his comments on the experience of his customers. Again, this was some time ago.
Perhaps the tension required by the v- belt accelerates the bearing (and shaft) failures. Andrew, if you
had fitted a toothed belt, what do you suppose would have happened when the brushes seized the
shaft? Until California starts requiring daytime "lights on" for vintage bikes, I think I'll stick with my
dynamos for now. Unless someone else weighs in with happier tales? One of our French group
members, perhaps?
#1129 As I said I am a fan of the Alton. At a evening vintage bike meet, it was even commented on
how bright my lights were. (By the way, I recommend Zenon bulbs, c 30% extra output for no extra
power drain.) My first Alton was a very early version, Paul has constantly refined the design to iron out
the problems, e.g. bodies won't rust as they are once again aluminum. Regarding having to fit a
toothed belt kit, that was my choice as I ride with my lights on all day and only run a very small battery.
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L #2196 I'm curious if anyone has experience with a self generating type ignition like a pvl on a
velocette? We've had problems with the magnetos on the racing Thruxton, and would like to upgrade
the ignition. any help appreciated.
#2198 I am using a self generating ignition supplied by Tony Harris of Rexton Ignitions and can highly
recommend it, although I am not into racing. It has the benefit of being able to power a strobe light
and is provided with slots rather than holes and an O ring instead of a gasket to allow adjustment with
out stripping the machine. (once timing marks are transferred to whatever.) The advance and retard
can be either fixed or electronic and there are no pick ups to fail. They only moving parts, I believe, is
a disc holding the magnets and two good sized bearings. It looks like a magneto and Tony insists it is
a magneto and bears the markings "BTH". He is into racing and can advise better than I can. Only
down side it the cost, but if for a Thruxton? Tony Harris can be contacted at
www.excelsior1.supanet.com/. There was little wrong with my Lucas magneto but I couldn’t resist his
magneto.
L #2957 My Viper shows a charge of 8 amps on the ammeter going down to 3-4 with lights on,
it's a 1955 model with a 1961 engine fitted but don't know if a Miller or Lucas dynamo is fitted it's
negative earth and I'd like to do away with the regulator and go transistorized i.e Podronics kit or
whatever is best, will gadget fit either a Miller or Lucas or do I have to get specific one? And is it a
simple job to fit or should I be looking for an expert, going to Bristol show tomorrow so hope to buy
what I need there.
#2959 I'm sure a quick look will tell you if you d-mo is Miller or Lucas, 'cos it says so on them ! The
Podtronics reg works on either BUT... If you have a Miller unit it will need internal re wiring to "Lucas"
operation ( Not difficult ) It does sound as though what you have works ok.
#2960 There is an article on the files section of the site that explains all you need to know about
dynamos and regulators http://autos.groups.yahoo.com/group/velocette/files/Electrics/
#2971 I use CMS on my Venom (Miller)and 31CSR (Lucas) without problems so would recommend
CMS. Nice guy to talk to for info. also.
L #3022 I have recently purchased a 1955 MAC it has a good 6v battery (exide) which I have
charged and the charge has held OK for a week the ammeter shows discharge when the lights are
turned on. When the engine is running and reved the ammeter shows no charge. It has a miller
dynamo which appears to have the cut out removed at least that what I think should be in the space
next to the armature, the voltage regulator is a little black box on top of the dynamo and this has a
little black box within which doesn't look very Velo.
#3424 Sounds like someone has rewired the dynamo to look like a Lucas and fitted an electronic
regulator - there are several on the market these days.. it might be broke or there might be a wiring
fault or the dynamo may be faulty.. 'fraid you've got a bit of detective work to do 1) motor the dynamo
- i.e. connect the field and armature wires together and attach to a battery of the correct polarity with
the drive belt off - it should run as a rather pathetic motor. Check the brushes are in good order and
can move freely . Check the field winding resistance - about 3 ohms. Check the armature - should be
near a dead short. Does anything looks burnt? Is the commutator clean? 2) Check all wiring carefully -
sounds like it should be wired like a Lucas setup. 3) Check the little black box - who made it? Send it
back to the makers or find someone who can. K-tec's units are in a little black box, but there might be
other makers .... got any documentation?
#3427 I found the problem eventually (after buying a new regulator)the original was a K-tec so I
bought another one. The dynamo was wired correctly(Lucas style) after a fashion but the earth brush
had insulated it's self, believe it or not it had motored and on occasions I had measured 13-15v just
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above tick over.....anyway after taking it all a part cleaning continuity checking all the contacts I put it
back with the old regulator and all is fine. I'll not send the regulator back as soon as I do the old one
will go bang.
L #3818 Hi, Has anyone ever taken an Alton apart? Mine appears to have stripped an internal
reduction gear and I'm not sure if the drive-side alloy is a screwed or pressed fit in the steel body. It's
impractical to send it back to the factory from Australia so if anyone can help, I would be very grateful.
#3820 I have one of the first Altons that were available almost 15 years ago. It's screwed together but
LEFT threaded, i.e. opposite to a normal thread. Inside it there is a gear made of plastic with
something that looks like it is intended as a slip device, about the same as the slip device in a
magdyno. It worked for about 10 years until I installed the clubs toothed belt. Maybe the original belt
was more flexible or it might just have been worn out. Mine is still in pieces. If You find a supplier of a
new gear/clutch assy please make it known.
#3822 You can e mail Paul Hamon, I too had a similar problem and he was extremely helpful.
Otherwise call him on +33 2 98 46 57 74. Paul's English is better than my French, but like all French
British bike owners he is fluent in the key words of communication. (e.g. knocking big end, flooded,
misfire, clutch slip, leaking oil, etc.)
#3823 Interesting point about the toothed belt - I too have fitted one and I believe the damage may
have been caused by the motor kicking back as it sometimes does with the electronic ignition on the
first attempt. Certainly there is no slip or flex in the belt so it could be a problem with the Alton drive
system as you describe it. Maybe Veloce knew a thing or two about driving dynamos? The Alton
requires a lot of power, hence my fitting of the toothed drive. Bruce, thanks for your kind offer - I will
attempt to unscrew the "gearbox" end and see what I require in the way of new parts.
#3825 Harvé Hamon is the one who does Vincents at 56 Aurey. His brother, Paul, is at Brest and
does the alton alternator, tél.02-98-46-57-74. Paul should be able to fix you up for spares.
L #4109, I've a sick 6 volt to 12 volt JG Unit electronic control. Might anybody on this list have
any technical knowledge about adjusting the parameters on this device or know how to contact the
maker?
#4110 The JG Unit is still manufactured and therefore probably still repaired in England by Dave
Lindsley, 196 Pilsworth Road, Heywood, Lancashire OL10 3DY. Tel (00440 01706 365838 Fax (0044)
01706 627500
#4122 I used a JG unit many years ago before going over to an alternator. It seemed a bit fragile and
eventually failed. It does not like a fully discharged battery, a condition often met with classic bikes.
My unit was "potted" with a silicone substance that prevented easy repair, I don’t believe anyone
would offer a repair service. I was persistent and dug out the rubbery/silicone stuff. I found that the
field coil of the dynamo was controlled by a flimsy micro relay about the size of a small capacitor, and
this is what had failed, I replaced this with an external relay which kept me going until I got the
alternator. Since JG are still in business the circuitry must have changed as everyone I knew with one
had this trouble sooner or later. My recommendation would be to put your money towards an
alternator rather than a replacement, you will then have good lights and power to spare, Podtronic
make alternator controls that I have fitted and was impressed by, one box, three leads in (from the
alternator) and two leads out + and- just earth the one you want. This replaces the Zerner diode and
rectifier (diode) pack at a price less than the Zerner alone. Dynamos are getting old now and although
many people will swear by them 60 watts (yes a bit more converted to 12volts) maximum output is just
not enough. Criterion conversions now have an outboard bearing under the pulley and are much
better than the old overhung ones that used to fret around the poorly designed tiny inboard bearing on
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the end cap. If you have access to a lathe build your own, enrol in a college if not and use their
machines, I have diagrams if required but you can just buy a billet of alloy and turn it down until the
stator fits. It certainly is not beyond anyone who can tinker with Velos..
#4123 Largely agree. 12v dynamo conversions work, but you've a trade-off - either you limit the field
voltage to 7-ish volts, as in the original 6v electrotechnical regs, with a resultant cut-in speed of about
3000rpm - or you allow full 14v to appear across the field, over-dissipating it 4x causing overheating
and early failure.. I never stripped the gunge from a JG to find out what was underneath, but
measured one to discover it did the latter - as do the other 12v conversion controllers I've come
across. Modern alternators ought to do much better. But I hate the zener crude controllers that eg
Criterion used to use ( do they still?) Dumping the full power of the alternator generates less whatever
the bike uses as heat. Wasteful, and if the Zener fails, burnt out bulbs and boiled batteries. I wrote to
them offering to build a decent efficient regulator for them for a commercial rate ( my trade is
designing electronics) many years ago, but no reply.
#4124 I was under the assumption that permanent magnet alternators (Lucas) had the same engine
load and output regardless whether the current went to the coil, zener diode or nowhere. I did see
something about an after-market Harley (permanent magnet, single phase) regulator that was able to
save engine power by regulating the current in some fashion (I think they called it a serial regulator).
Do the coils in the stator create a stronger pull the more current that goes through? Is the zener
arrangement just a cheap way of regulating? Do the regulators on permanent magnet Japanese bikes
work on the same principal? I've had a Lucas E3L 6v generator running with a 12v VW Bug
mechanical regulator ($20 at the auto parts store and available everywhere) for some years now. Had
to convert the generator from 'A' style to 'B' style by switching the brush wires around. It's never given
me any trouble but I don't ride with lights on very often.
#4126 The Podtronic regulator that I fitted for a friend seemed just the job, price from memory was
around £24 but I know some places charge more. Ill dig up the source if anyone wants it. The
regulation was really good at around 14 volts, very stable. I shall convert mine soon and get rid of the
Zerner and rectifier, indeed some high output alternators call for two Zerners to be fitted, even more
expense and messing around with the wires. Has anyone used the podtronic in anger for extended
periods, I know this USA regulator gets good comments in the USA press
#4130 Sounds a bit like the old Ducati thyristor-switching regs I mentioned in my previous. I properly
done should work very well. Less load on the engine, almost no wasted power so nothing gets hot.
regards
#4128 Permanent magnet alternators look pretty much like current sources - the faster they go the
more current they supply up to a limit set by their leakage inductance and the revs - the higher the
revs, the higher the frequency and the more the inductance limits the current. Above certain revs this
means they generate a constant current and the voltage is undetermined - could be quite high - 40 or
50 volts. Unregulated lighting sets as used on bicycles ,cheap mopeds etc rely on this constant
current designed to feed their quota of bulbs correctly. But if one bulb blows the current remains the
same and the volts go up, so you'll blow the rest pretty soon. You're quite right about
Zerner-controlled alternators such as the old Lucas design - they generate power proportional to
engine revs ( i.e. constant current and volts proportional to revs) , and the power is distributed
between the Zerner and the various bike loads. They were cheap and simple, but wasteful of power
and didn't control the battery volts very well- an old triumph of mine always had to have it's battery
topped up regularly. And of course if the Zerner failed you boiled the battery thoroughly and blew the
lights the moment they were turned on. Early Ducati twins had a permanent magnet alternator like
Lucas, but used a clever thyristor regulator such that each cycle of the ac output was only turned on
for long enough to hold the battery at 14 volts. With no load this took very little time on, with heavier
loads more. It's this style of reg I offered to design for Criterion. I don't know what Harleys use(d).
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Might be a simple series pre-regulator but this misses the point as the inductive reactance is lossless (
approx) . Don't know - can only guess. Modern bikes use wound field alternators just like cars, with
similar control units. Glad your VW regulator works OK - but if designed for 12v it won't limit the field
voltage and hence you risk over-dissipating the field and burning it out.
#4132 A brief follow up on the JG Unit. I called Dave Lindsley this morning and had a long chat. The
problem I'm having is with a E3N 48 watt short generator mounted in a, wait for it, a 49 AJS. (the JG
Unit in my '66 VMT works Great!!!). The JG Unit will frequently fail to "wake up" and begin to charge
unless I blip the throttle and really boost the revs, like 4K RPM. Mr. Lindsley walked me thru the
control strategy and gave me great ideas for locating the problem. His view is the air gap may be too
wide on the newly rewound armature. Large air gap means the residual magnetism in the pole shoe
man not be sufficient to begin exciting the field coil unless the dynamo is spun faster than normally
required. The difficulty in correcting the air gap problem lies with either replacing the armature with a
"newer" armature that may not have been skinned after rewinding, or shimming the pole shoe. Either
option require removing the entire primary drive and tin ware to pull the dynamo out of an AJS. (I
know, I know, this a Velocette list). I've a PODtronics 6-12PE unit on hand and may swap out the JG
Unit before removing and stripping the dynamo. I'm seeking the path of least resistance! I've some
testing to do. In any event, I really appreciated Mr. Lindsley's patience with me and help in finding
some resolution. This is a vendor I will continue to support! One of his answers may be of interest to
the group. The JG Unit does send approximately 14 volts to the field coil but limits the current to avoid
over heating the field coil and the possibility of reducing the life of the field coil.
L #4161 My MAC is getting nearer completion and I have an Alton Alternator to fit. I have fitted
some neat little indicators and want to use a larger, more modern headlamp. I have a Honda
Superdream unit that fits OK but my query is, do I need the ammeter? No modern machine has one
and if the Alton is all it is cracked up to be, why would I need an ammeter at all. I am using the
handlebar switches off a 1960's Honda CB250 and although I know it's not original, I want to be able
to use it in the dark. I have the original bits to refit if I choose. Can I ditch the ammeter?
#4162 It certainly wont hurt to ditch the ammeter, if you think you need an indication of charge then a
voltmeter will do the job just as well but will not affect the electrics, if it goes faulty, as its in parallel
unlike the ammeter, where you loose all your electrics as its in series. As you say modern cars and
bikes don’t have ammeters now and once you ditch the dynamo you can rest in peace with lights you
can see! My ammeter is more affected by vibration than the current going through anyway, it just fills
the hole in the headlamp.
#4169 Keep the ammeter. When, one bad day, it wacks over to 8amps full charge even when you
know that the battery is OK, then you will have the classic indication of regulator failure. It's happened
to me twice now. I guess that MCR-2s and RB-108s or whatever just don't like the vibes given off by
86x86 and yes, I have tried all kinds of rubber mountings. In the end I capitulated and fitted a V-Reg II
- end of all the problems.
L #4667 When I bought my '58 Venom 3 years ago it was running a coil ignition system with a
solid state regulator at 12v in line with the "Dynamo Uprate" article on the site. Last year I went back
to magneto ignition but left everything else alone at 12v. All went well for about a year until last month
when I noticed I had no charge. The cause is clear - the solid state regulator has a molten metal
"blister" on the side. I've checked the dynamo and all seems OK. My first thought is to simply replace
the regulator - I've read the various views on the different manufacturers. Then I had another thought.
I hardly ever ride at night, the only uses my lights get are if the day is particularly dull/raining and the
very occasional short trip at night and whilst it's nice to have bright, 12v lights I wouldn't want to do this
at the cost of shortening the dynamo life. I'm not an electrical engineer but I can't help but think that
running the "6v" dynamo into a 12v system will put addition strain on it. My choice is - a new 12v solid
state regulator or new 6v regulator, battery (probably needed soon anyway), and a set of 6v bulbs.
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Any experience out there with running a "6v" generator at 12v for an extended period?
#4672 The big advantage of 12v is to be able to use QI headlamp bulbs which are MUCH brighter...
but if you don't ride much at night this may not be important to you. Also 12v bulbs are freely
available, whereas you have to buy 6v ones from a specialist. My ( homebrew) 12v conversion has
run for 30 years and 160,000 miles without dynamo problems.
#4675 On my last Venom I ran thousands of miles at 12 v with a 60w Lucas dynamo and a JG 12v
regulator with no trouble. Soon after I bought my present Venom the 6v K-tec regulator went wrong
and the dynamo failed at the same time, coincidence? I fitted a re-con 6V Lucas 60 watt dynamo with
a CMES 12v regulator together with a small dynamo pulley. Running at 30 mph in top gear on
standard gearing I get a balance of charge showing with a 60/55w Q.I. bulb on dip. Speak to Sean at
CMES 01454-323434, he is very helpful and will explain everything in layman's terms if needs be.
#4681 I'm also running the same lighting kit - 60w Lucas CMES 12v regulator - with no problems.
#4683 Does the JG unit work ok with a Lucas dynamo? If it does then it may be that the Miller dynamo
wires have not been altered to suit a JG as is required,
#4684 I converted the wiring myself, the whole system worked fine for a couple of days then stopped
charging. I thought a wire may have come loose so checked it over but every thing keeps pointing
toward the dynamo so I checked to see if it would motor, which it does, I then earthed then F and
connected D to voltmeter, ran bike voltmeter shows about 12 volts,
#4713 I have used V-Reg II regulators, and have had no problems whatsoever with them. They come
in neg or pos earth, and regulate at 6 volts as supplied, but are converted to 12 volts by snipping a
small loop of cable that sticks out of the epoxy surface of the regulator. They are small enough to fit
inside the miller regulator case. Look on www.AOservices.co.uk I speak as I find and have always had
good service from them.
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D. The Carburetor and Fuels
D.1. Carburetor -
L #152 I am thinking about fitting as one inch and a half carbs to my Thruxton which has been
stroked to 580cc. I will be boring out inlet to suit and have been given a MK2 concentric to try. Has
anyone fitted a larger carbs to a Thruxton? If so what was the benefit if any?
#155 I have alternated between 1-3/8 and 1-1/2 GPs on my Thruxton (709cc). I have not opened up
the intake port in the head as flow bench testing revealed that with minor work around the guide area
and the best valve tulip shape netted 50+ hp flow potential with the 1-3/8 port. I would guess that
opening the port would only slow velocity and weaken the midrange (although some other 2 valve
street singles did come with the larger port, most in my experience will not outrun a good Thruxton,
particularly off the corners). Instead I have the 1-1/2 inlet manifold tapered down to 1-3/8 at the head
which is common practice on newer long inlet tract designs. I tested a bunch of carbs (GPs, Mikunis,
Delortos, Concentrics, etc.) and couldn't find anything with a needle in the middle that would match
the GP for all out flow. Others may help mid-range though with better part throttle metering than the
broom stick that the GP uses for a needle. I believe there are two different Mark 2 Amals, standard
and smoothbore. I think you will find a standard 38mm (1-1/2) Amal will not flow any more air than the
stock 1-3/8 GP. The smoothbore might a bit. The stock Velo exhaust port is terrible, you should
concentrate more effort there.... The seat of the pants difference between the two GPs on mine is
negligible. I'm going to be trying a 40mm Mikuni flat slide in the near future but the sight of that thing
sticking out the side where a GP used to be doesn't excite me any! Maybe the power will.
#156 Re: Stewart's question on larger carbs on Thruxtons. Paul Zell has a 1.5" GP carbs on his
720cc monster Thruxton, and it works just fine thank you. Mind you, his engine is a lot bigger than
your measly 580cc (MSS crank?) item - and as a consequence he's done a lot of work beefing up the
drive side of the custom cast crankcase. But not even a Manx used a GP that big, and made plenty
of power. But then again, Italian racing singles use monstrous carbs for top end breathing - they must
have been useless at low rev's. Don't expect a big increase in the top end unless you have a very
good tuner doing your porting!
L #212 I would really like to set up an airbox/filter for my '56 MAC which has the usual short
open bellmouth on the 376 Monoblock. Putting any kind of even light foam over the bellmouth breaks
up airflow and causes the bike to run lumpy. I live in the desert area around Carson City, Nevada, so
an airbox would probably add considerably to the engine's longevity. Any suggestions out there?
#213 I have a foam sock on my 52 alloy MAC, bought at a dirt bike place. Works, but you may need
to rejet. There is not a lot of room between the carbs mouth and the oil tank. The original Velocette
air cleaners had a rubber tube leading to the air cleaner between the back of the oil tank and the
battery. I don't see that this would give any better air flow to your mono block than a sock, but it would
probably look a lot better. I have seen variations on this, a rubber tube with a sock on the end.. I also
have a K&N flat round filter on my Endurance which is perfect.. just fits with some force between the
oil tank and the carbs. I had to reject for it as well, but it is like other K&Ns.. not much restriction. I
understand that these are no longer available, I got it with some parts I bought. I have seen modified
Triumph style filters fitted to Velos.... if you are handy with body work.. I think you need to start with
one with hole for the carbs in the middle. Mike Jongblood has one on his 500, you may have seen it.
#219 Thanks for the air filter info. I will be at the opener. I have come across one of the BSA/Triumph
pleated paper air filter elements, about 4 ½ inches by 2 1/4 inches. I have some great firm plastic
sheeting to adhere to both sides of the element, cutting an opening for a short rubber spigot to apply
to the 376 Monoblock after removal of the dinky bellmouth, which, aside from protecting the threads
on the carbs is probably technically useless on the MAC at it's normal driven speeds. I think it will
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eath quite well, but we shall see. Need a project right now, anyway. I have already dropped the
main jet to a 180 from the stock 200, which at this altitude of about 4700 feet cleaned up the mixture
nicely. Now, If I choose to open the throttle to the 3/4 to full open position, the engine doesn't bog
down. Must remember to rejet when I get closer to sea level. Running a B7ES.
#219b I run a small foam air filter on my Venom, yes it required minor rejetting. I run a main one size
down from the 270 specified for my Concentric. It has the spring. The light green Uni's filter better but
flow worse; I'm using a dark grey one. If you have never seen a stock air filter like the one Paul has
offered you would not believe that it actually flows enough air. There is a short rubber adapter
(

eamers couldn't open the jet? Ah, but who will risk his/her reputation and tell me the bore dia. of a
270?
#680 New jets cot approx. £2.50 in the UK don't risk it buy a new.
L #745 My Viper thruxton 500cc is fitted with a 32 mm concentric, is this a good choice. Im
finding that there is a spitting back in the carbs (really it is a small flame inside the carbs at idle or just
above idle)......what causes this? Should I fit the GP5 carbs? I do have the correct manifold on. I
have also noticed that there is a flooding of fuel into the head is this just a bad float needle or a bad
angle for this particular carbs?
#746 Spitting back in the carbs can be a sign of a weak mixture, although you do say that there is
flooding which would perhaps indicate enough fuel is getting through (unless there is a restriction in
the pilot jet leading to weakness at tickover, and the main jet / needle is oversize leading to flooding
when the throttle is opened ?. I would think that by checking the state of your plug immediately after a
run i.e. not letting it tickover before you check it, would indicate whether or not it's running rich? What
is the engines performance like when it's running above tickover?
#749 I was led a merry dance by a carbs spitting problem at kickstart/low revs. The culprit turned out
to be the ( peripheral ) slip ring in my manual BTH magneto; there was a section missing! Presumably,
at higher revs the points operating arm jumped the gap.
#752 The Plug was black and the engine runs very well past the tickover speed. The tickover passage
in the carbs was cleaned out thoroughly. In general should the VMT have a compression plate added
to reduce the chance of a holed piston?
#753 My Venom runs an optimized 8.75:1 compression ratio (measure the volumes to make sure), the
same as a Thruxton. Cams are M17/8 but with standard Venom followers, head and valves. Carbs is a
30mm Concentric Mk1 with a 3" long velocity stack (proper Amal turned type, with a blended venturi).
Getting the carburation exactly right was a bit of a pain, but it now runs quite happily at all speeds
and loads, with no more pinking than I would expect on a Velo (I do believe that they can stand more
than people realize). I run on either Super unleaded or Optimax (not yet sure if there is any advantage
to Optimax due to my experiments with carburation overlapping with the introduction of this fuel to the
marketplace), in either case Nominal RON value of 97/98. I always felt that the motor ran more happily
on unleaded than on LRP.
#762 Just fitted a 1036 Concentric recently, the air correction orifice (the center of the 3 holes)
needed to be opened from .080 to about .135. Make sure you have the 4 stroke siphon tube, the one
that is cut flat across the top. thanks for the info . Can you tell me why the air correction orifice has to
be opened and how? Also what is the 4 stroke siphon tube?
#770 The air correction orifice performs the same function as the air correction lever on a GP, it
allows some air to enter in the mix at the siphon tube, the brass tube that needle enters into first. Two
strokes need lots of fuel at low rpm so the air correction is small and the siphon tube is usually slash
cut across the top, four strokes are flat cut. To convert to four stroke use take the siphon tube (along
with the needle, needle jet and jet holder, also different, and whatever main you want to start with)
out of most any smaller four stroke Concentric. While you have the siphon tube out of the 1036,
match the size of the air correction hole (the center of the three that leads to the siphon tube area) to
the four stroke carbs you just cannibalized from about .080 to .125-.140 I believe, or you can see how
it runs and gradually open up the hole. You will probably need a 3 or so cutaway on the slide, you
can file it if it's a 2.
L #790 I am also trying to source an air filter.
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#791 Grove Classic Motorcycles on +44 (0) 1582 873066, e mail mike@g... has loads of original air
filters at a reasonable cost.
L #1143 I am having difficulty staring my Venom. The magneto has been overhauled and there
is a fat spark on kick-start. I think the Mk1 Concentric is suspect. There is noticeable play on the slide
in the body. I am looking at the tolerances and possibility of replacement slide . The literature tells you
how to set it up for running but mine is OK once going. Is there a procedure to set it for starting? I am
also considering a new carburettor. Has anyone any experience of modern alternatives. I know a
Mikuni has been used and a Del Orto. Any first hand experience of these, later Amals or others
welcome.
#1144 Usually a well-tickled carburettor will start just about all the time, a worn slide will produce an
erratic idle and the engine seldom settles down to the same idle speed twice. If you're still considering
a carbs change, though, I've had good luck with Mikuni slides dropped into suitably bored and
modified Amal concentrics. Here in Arizona I go through AMR in Tucson - couldn't tell where you are,
but they do mail order if you're on this side of The Pond. Personally, I like this approach because you
still have a tickler on the finished product. Nothing like the smell of raw fuel in the morning to get the
day started right.
#1145 Essentially all carburettors have two circuits as part of their design. The idle circuit is in play up
to about 1/8th throttle. Beyond 1/8th, the slide cutaway, the position of the needle in the needle jet
and finally the main jet all come into play. Getting all of these components to work in harmony and in
sequence is a bit of a chore if one starts from scratch. In so far as AMAL has published great amounts
of data, as have Veloce on the specs for a give model, switching to a Mikuni or Del O'rto may cause
you to become very frustrated, unless you have reliable info on how the brand X carbs should be
setup. You email does not state which model Concentric you have, or any of the specs. I can only
assume that the carbs is one Veloce recommended and is properly set up AND the bike has been
reliably started on this carbs by you or a previous owner in the past. Reliably started is defined by me
as "the bike will start with 2 or 3 kicks regardless of ambient temp or engine temp. Have you ever had
this degree of reliability with this bike? If the answer is no, two factors come to play. All bikes, most
notably English single has a "combination" in the starting sequence. Learning the sequence, and it
can be different for each bike, can be a bit tedious, but adds to the charm of the breed. When
properly set up, an AMAL concentric should readily start your bike on the idle circuit and require
almost no throttle till the engine lights up. Would you please tell the list the model of the carbs
stamped on the side, and the variables such as jets, slide cut away, etc. Is this a two stroke or four
stroke variant. There are distinct differences between the two carbs variations. I'm confidant someone
here can help you get this machine running in short order.
#1146 Having torn my cartilage trying to start my KSS with a worn carbs. I replaced it with a new one,
result starting first kick. Obviously you could still have problems with your magneto, starting drill, etc.
but a new carbs sounds sensible. In a discussion with Surrey Cycles who sole line of business is Amal
carbs, they recommended the Monobloc as better than the Mk1 concentric. You could fit a MkII
concentric, but you would probably need to have your oil tank moved back. New Monoblocs are
available.
#1147 The carbs is a Mk1 Concentric marked R29/930. The needle jet is 106,main jet 270 and air
screw out 21/2 turns. Jets and needle are all new. Float needle is new. These numbers agree with the
list from Frank Stafford in FT and printed in the batch of tech docs last year. It used to start in 2-3
kicks but has not been used for some years. I had a long spell of working away from home and other
less acceptable reasons for not using her till I took early retirement and carried out a refurb, mainly to
cycle parts and new electric's. Apart from the Magneto I have not touched the engine as the last major
work was to the head and valves. I cleaned the carbs several times and soaked overnight in fresh
petrol to remove internal deposits, but some passages cannot be reached. Performance when running
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appears good and progressive, although I have not tried extended full throttle yet
#1150 I had the same starting problem with my Gilera Saturno 500cc which for some reason is fitted
with an Amal Mk1 Concentric virtually brand new so no wear in it at all. This problem occurred after
the bike had been standing unused for some time. I ended up soaking the entire carbs in carbs
cleaner for about a couple of weeks & it seemed to solve the problem...as you rightly say in your later
posting, there are passageways in that carbs. which are inaccessible & you just have to rely on
solvent doing its job + a strong jet of compressed air. At the best of times Amal Mk1s like a lot of
flooding for cold starts as I've found out after fitting one to my Thruxton!
#1151 I bought a Mikuni kit for my Venom about 8 years ago from Phill Allen. The kit consisted of a
jetted carbs and an adaptor. I have used it since although I fit the correct carbs for special occasions.
My magneto and other related components are in good shape. The starting is extremely reliable. The
only way to not have a first kick start is to forget the fuelcock or completely ignore the Hall Green
procedure. I use my Velo almost daily and last summer it missed first kick 9 times (I keep count) and
that was my fault because when used to reliable starting you get sloppy, and it still needs a boot, but
not more than an ordinary moped. The tickover is reliable as a steam engine. The drawback with the
Mikuni is that it gives lower top end performance, the top speed is in the low 90s and if rh knee is not
tight to the tank it slows down to about 75. There seems to be an unfavorable airflow around the carbs
inlet on a standard Velo with a standard oil tank, of which Phill warned me when I bought the kit.
#1155 AMAL lists the R930/29 in their 1969-1972 carburettor Settings List as being the right carbs for
Venoms from 1970 on. This variant of the 930 differs from the R930/15 specified for the earlier
Venoms. The difference being the R930/29 does not have a replaceable pilot jet, like the number 30
specified for the R930/15. AMAL initially released the Concentric with a replaceable pilot jet but later
decided to build all 4 stoke variants with a pressed in bush for the pilot jet, while 2 stroke versions
retained the screw in pilot jet. This change made things difficult for folks wishing to tune Concentric
series for applications AMAL had not considered. I found that modifying an existing 1000 series to fix
my '60 Gold Star required changing it from a left hand model to a right hand model and drilling out the
pressed in bush. The change out to a replaceable pilot jet was a rather simple drilling and taping
operation and has made the Gold Star an easy starting and tractable bike. I've since made this
modification to other fixed bush Concentrics and am quite happy with the change. In your case, as
this carbs used to work fine on your Venom, I'd recommend you remove the float bowl, and the pilot
air adjusting screw and direct a stream of compressed air into the passage to blow out and
obstructions in the pilot jet bush. If the carbs is gummed up at all, some carbs cleaner squirted into the
passageway several times a day for 24 hours and then blown out may provide the cleaning required
to return the carbs to its easy starting ways.
#1149 If you are obtaining a good idle with the pilot screw 2 ½ turns out my guess is your slide is OK,
my experience with worn slides is they require the pilot screw be turned all the way in to compensate
for the extra air. Easy to put some grease on the slide to test though, see if it starts better. The Mikuni
slide is about .040 bigger than the Amal and a good fix, done it a few times. It's made of dissimilar
metal too so doesn't wear out the bore so fast.
L #1163 Does anyone know what a 1 3\16 GP carbs would have been used on, I happen to
have one. I picked it up thinking it could be put on a Venom.....any thoughts.
#1171 GP carbs were fitted to some Clubmans in the mid 60's both VR & VM then later on all had
Monobloc and lastly Concentric carbs. The GP is not so nice on the road as a TT though. (and the
Monobloc works just as well as a TT - even on the track!)
#1180 I guess I was attracted to the looks of the GP. I have to agree about the Monobloc they do the
job very nicely. I'll leave the small GP off the bike.
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#1168 I have a 1 3\16 GP carbs which I picked up in the hope it may fit on a Venom. I didn’t know that
they could be used for that. DO you have any settings that might apply to a Velo that has a Thruxton
head but other than that is still a Venom well actually viper.......long story.
#1195 The settings given in Burris for 1 3/16 GP are for use with a Venom with megaphone, so prob
no good to you. The Thruxton normally uses a 1 3/8 GP, not sure what effect a 1 3/16 GP would have
but doubt it would be beneficial, I have always stuck to the book with Thruxton motors since they go
well enough for my humble purposes that way.
#1251 Well, I promised to give the settings for my Thruxtonised venom racer ... Amal 1038 with 4 inch
manifold and 3 inch trumpet. 380 Main #3 slide 107 needle jet needle in the middle groove 30 Pilot
CR is approx 10.4 It goes very well, and idles reasonably
L #1616 On the newer Amal Concentric MK1 carbs the pilot jet is pressed in and not accessible
or even visible. How does one know what that pilot jet size is? Also, I notice that Monobloc's are
available new. Is there any reason to switch a '60 Venom back to a Monobloc?
#1618 Isn't a Monobloc the original fitment for 1960? My '69 had one but I suspect that my Dad fitted
it, as it was considered superior in design and manufacture back then. Recent postings have stated
that they flow better than the Concentric, too. There is a "new" (Spanish?) Monobloc on ZUMAC, it
seems to work very well. The offset float bowl is an interesting feature; when you lean it onto the side
stand the revs pick up, this can be useful at times.
#1620 Yes, Monobloc is original fitment for a '60 Venom but this has been replaced with a concentric
prior to my acquiring the bike. I'm therefore working with what I have. There seem to be a number of
monobloc's for sale on ebay. Can someone explain the numbering nomenclature to me? I wouldn't be
adverse to buying one and rebuilding it even if I needed to get it sleeved.
#1622 Don't waste your time - buy a new one from either Grove, Hitchcock's or Surrey Cycles. By the
time you have reconditioned a carbs it will cost you nearly as much as a new one. Incidentally the
numbering system defines the carbs body (first three numbers) and the numbers after the / define the
application i.e. the bike it is designed for with specific jets, slide, needles etc. If you speak to
Grosvenor Works (as was), Hitchcock's or Surrey Cycles they will tell you that the Monobloc is a much
better carbs than a Concentric, which was built to a price. Size for size its flow is only about 4% better
than a TT.
L #1665 I have freshly rebuilt Venom in second overbore, with Viper head (8,5:1 CR) and Amal
MkI1/2 Concentric (lever choke, no plunger) 30mm with air filter. What do you use as settings (needle,
jets...)? I know these are found in tech data base but do you use those? I set my carburetor according
that in data base but I think she runs lean and spits back when idling and dies and accelerates poorly
in my opinion. Maybe I just have to fiddle with pilot air adjustment. But I`m interested to know what
different settings do you use. Exhaust is Clubman style.
#1691 It's commonly said that the carburettor settings that were indicated in the Haynes book and
other technical books are now obsolete since we're all using lead-free petrol. It is recommended to
ride with a richer mix. I'm doing this with a MSS which has been equipped with the same carbs as
yours (pilot jet 270, as for a Venom), the plug is always OK and cold starting is second kick. If you
don't do this, you're at risk of overheating.
L #2013 I'm doing a tune up and other maintenance on a friends Venom Clubman. It has a worn
monobloc and my friend is interested in replacing the carbs. I had a mk1 concentric on my VMT, and it
was ok, but... Can someone suggest the best replacement carbs model and size and recommended
base jet sizes and settings. The machine has stock exhaust, 9:1 CR, BTH mag with manual control.
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We'd like something that will enhance starting and slow to mid range running, not WOT.
#2022 A non-technical response based solely on lots of miles on Velos / learning from my own
mistakes. Either new Monobloc or new Concentric Mk1 will give good performance for the road if set
up properly and the machine is otherwise OK etc. Set-up info, jet sizes and so on are readily available
in most Velo books - and prob in the archives on this site. The Rod Burris book on the M series is not
without errors but is readily available and gives a useful table of carbs settings etc. I’ve had a few
VM's VR's and a VMT over the years and find they all run slightly differently/better/worse on slightly
different settings - really I think it depends on just how worn out things are ;-) Best advice is to stick
with std factory recommended monobloc/concentric settings to start with and then fine tune to suit
your machine / your riding requirements - jets, slides etc relatively inexpensive. I think if I were starting
from scratch and had to choose one carbs only I might go for a new Monobloc but for real world use I
doubt there is much in it. (Make sure you’ve got a plug to suit the type of riding you do and of course
get that ignition timing spot on).
#2039 A number of the carbs settings in the Burris book are incorrect. I believe, but cannot confirm
that those on the technical site are correct. I have cross referenced them against original Amal lists. I
spoke to the technical manager at Grosvenor Works when they manufactured Amal carbs. He
confirmed the monobloc was the best all round carbs, providing you are not using it at silly angles.
L #2071 I have a 1961 Venom Clubmans fitted with an Amal Mk2 Concentric and I am unable to
determine where the hand lever should be for enrichment, should it be under tension or fully forward
for enrichment? Alternatively what position is off?
#2079 The Mk2 Concentric has a cold start system similar to most modern Japanese carbs, not an air
slide in the main throat of the carbs. The choke on these carbs is ON when the cable is pulled, i.e. the
choke plunger is lifted. For normal running the cable should be slack. This is opposite to the Mk1
instrument but similar I believe to the "Mk1½" which has no tickler but has the Jap type sold start
circuit in its place.
L #2209 Another very useful chemical available from Yamaha is their carburetor cleaner, P/N
ACC-CARBC-LE-NR. This is a powerful liquid cleaner that is diluted 1:3 with gasoline and placed
directly into the float chamber via the fuel line, then drained after one hour. It removes varnish and
other dried fuel residue. Also paint, etc.; I use a 50cc catheter syringe to minimize spills.
L #2303 My Mk I LE "Carburettor of Many Jets" has lots of brown discoloration on the outside.
Can anyone suggest any way of getting it back like new? It's a very small carbs with lots of crevices.
I've heard about some liquid cleaner you can buy. You drop the carbs in and let it bubble away for a
certain time. Another option might be to paint it. My MAC carbs is painted a sort of silver-grey. I didn't
do this so don't know what kind of paint it is. Is there a special paint for this kind of application? (Looks
like the same stuff that's on the cylinder.)
#2307 Here in the states we refer to it as "boiling" a carbs and you can pick up a carbs cleaning kit at
any auto parts store. It consists of a lidded one gallon can with solution and a parts basket. Costs less
than $10.00. I purchased one years ago when I was restoring a very grungy BSA M20 and found that
it was great for general parts cleaning, although I would be very hesitant to put a carbs back into it
after it was used for other parts. Stay away from any cleaners that contain phosphoric acid - you're
carbs will turn into something that resembles gelatin.
#2309 I have seen carbs that have been boiled in water with Ariel Biological Washing liquid (aka:
enzyme detergent), the result while not perfect was good. Vapour blasting is the only way to getting
your carbs to look as new.
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#2317See below - its from somewhere on the great WWW: Acid Cleaners Acids help remove hard
water deposits. Some acid cleaners help remove discoloration from aluminum, brass, bronze, and
copper. Other acids remove iron rust stains. Acids are typically found in toilet bowl cleaners, rust
removers, metal cleaners, and kitchen and bath cleaners that remove mineral products. White
vinegar, a weak acid, is about 5 percent acetic acid. It may remove hard water deposits from glass,
rust stains from sinks, and tarnish from brass and copper. b.. Lemon juice, another weak acid,
contains citric acid, which can be used in much the same way as vinegar. c.. Oxalic acid is effective as
a rust remover. d.. Phosphoric acid is often found in cleaning products that remove hard water
deposits. e.. Hydrochloric and sulfuric acids are sometimes used in diluted concentrations in toilet
bowl cleaners. Rust stains present a special problem on plumbing fixtures. Commercial rust removers
contain oxalic acid. If you purchase oxalic acid at full strength, dilute it with 10 parts water. Follow all
precautions when using oxalic acid, as this is a highly toxic product. A commercial product like ZUD
may be effective on rust stains because it contains oxalic acid. When surfaces have become rough or
pitted from repeated scrubbings with an abrasive cleaner, ZUD or a similar product may be mixed with
water to form a paste and left standing on the stain for several minutes, then rinsed off. For fixtures
that are not acid resistant, clean with trisodium phosphate to remove the rust. Cream of tartar, a mild
acid, may be mixed with water to form a paste rust remover.
#2329 "Wonder Wheels" sold in motor accessory shops works well on aluminium carburettor bodies
(tried and tested) but works best if all oily deposits are removed first. Oxalic acid is very good for
removing rust stains even on cloth, but chemists won't now sell it to the public. However a good
source is Teak Brightener/Cleaner which normally contains oxalic acid in enough concentrate for most
tasks (find in boats' chandlers or hardware stores- check contents on bottle)
#2306 The discoloration on the outsides of carbs, taps, & petrol things in general is easily removed by
using methylated spirits. As it evaporates quickly, apply liberally with a small piece of cloth. it is not
always fully effective on the internal parts. An old toothbrush is the obvious choice, but some electric
shavers have small bristle brushes, used for cleaning, an old one of these is good for getting into the
crevices.
L #2386 What does the number after the slash on a monobloc carb refer to? Say a 389/96.
What does the 96 refer to?
#2387 A code about the slide/needlejet/main jet that was originally fitted from Amal-factory.
#2388 So who has the code? Is it available? I see various motorcycle manufactures specifying say a
389/46 as original equipment. Is the code published?
#2389 Yes, an AMAL bulletin from the period will list all of the machines covered, and the
specifications for each one of the /numbers. Bruce Main-Smith and the usual suspects may have
these bulletins. A 389/46 will have been fitted as: original equipment on BSA A10 Super Road Rocket,
for 1960 & 61 using a 389/003 mixing body, 1 5/32" choke, 389/057 jet block, 420 main jet, 25 pilot,
#3 slide, needle in position #2, .106 needle jet, and tun less air cleaner. Date from AMAL list No.
601/3 for 1955 - 1961 motorcycles. Please note, any 389 carbs with a 1 5/32" bore, fitted with a 1
5/32" jet block can be assembled to become the same as the 389/46 as manufactured. For example,
a Matchless G80 built between 1955 - 1961, was fitted with a 389/1 with the BSA sized mixing body
and jet block, I.E. 1 5/32". In this instance, the G80 carbs with only a few parts changed would work
on the BSA A10.
L #2521 Does anyone on this list know where to get Gardner carbs, info, parts, etc?
#2522 Try Summerfield Engineering, they should have contact details or poss supply direct
(UK) 01773 835977
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#2557 I have just arrived back from the Australian Classic Racing Championships and spotted your
request. You can contact Ron Gardner as follows: The Gardner Carburettor Company Limited 12
Slimbridge Road, Burgess Hill. West Sussex. RH15 8QE. UK Phone : (44) 01444233485
L #2864 Hello, I am trying to complete my Velo project. I started with a 59 swing arm frame a 68
endurance engine, I bought a thruxton head and intake new amal con. carbs. I bought the correct
pushrods, set up the engine for 9to1 compr. did the valve timing following advice from dave smith. He
sold the carbs to me and said it was jetted very close. I have converted to electronic battery ignition
and timed to dave’s advice. This carbs is a 1036 on body of carbs. I have a correct velocity stack on
carbs. Starting the bike is quite the project, when I do get it running it runs very rich I took the jets out
of my 500cc bsa single and tried them in this carbs same thing. Any ideas would be helpful. Next
problem oil from engine fills the primary. I have Bought thruxton oil tank new lines filter conversion. I
have very good flow on return. In 5 miles of running it fills primary with 1\2 pint of oil. This bike project
is driving me nuts. I have worked on bikes for 30 years, I am a mechanic by trade and I always figured
things out this bike has me at a disadvantage. Any ideas?
#2877 Original Thruxton Conc 1000 series carbs should be R1036/4 (D Gibbison) Main jet 320, pilot
jet 30, slide #3, needle pos #1 and needle jet 106. Common reasons for rich-running are incorrect idle
mixture and worn needle/needle jet. When carbs gets worn it also affects the needle/needle jet with
resulting rich-running at part load. Countermeasures are dropping the needle (step one), and
replacing needle/needle jet (step two). Check that carbs doesn’t vibrate which might upset the function
of the floater needle and cause high level/flooding.
#2884 My VMT ( 519 )is fitted with a Mk 1 concentric stamped 1036 R1 on the body that came fitted to
the bike . I have the GP but have never tried it as I figured the Concentric would be easier to set up . It
has 320 main and 30pilot jets . a 2 ½ slide and 106 needle jet . There's no choke . I adjusted the
needle position to give the best pick up as in pos 1 it was hesitant under acceleration ( I have a feeling
it is on pos 3 , it's a new needle ) It was difficult at first until I found the 'knack ' to starting . From cold I
have to flood it really well and with Ignition retarded just a tad it will start easily . If it doesn’t fire I have
to flood it up again . Warm it starts first or second swing using the velo 'ritual '. In deference to my age
and maintenance , I fitted a center stand and put it on the stand to get a good swing . I've always felt it
is over rich at tick over/ just opening settings , and it took a while and riding adjustments to get it to a
setting where I'm satisfied .It ticks over OK if a little faster than a std Venom and if I set it to a too slow
tick over it will sometimes stop which is inconvenient. The Thruxton was meant to go , so I'm happy to
trade mid range performance against a good tickover.
#2886 If you open up the size of the air correction jet, you'll get rid of that slow speed richness. The
1036 carbs was made in Spain specifically for use on the big two strokes, which require richness at
that point. The air correction jet is directly under and parallel to the main 36 MM bore, the middle of
the three drillings, and you'll find that it is about .075" in size at the inner end and should be
.100"-.140" in order to allow more air entry to the upper end of the needle jet, thereby leaning it out.
Go slow with a set of number drills until you reach optimum results, as it's hard to replace metal that
you have been drilled out. This adjustment variably affects the mixture from barely above idle to about
half throttle with nearly the entire effect at the closed throttle point. It works in similar manner to the
pilot jet in that the jet is sized for a slightly rich condition and then air is added to adjust the mixture to
a more correct ratio, it being easier to moderate air flow than fuel flow.
#2901 Not only the air correction hole must be increased, also the following changes are necessary :
Spray tube must be of cylindrical type without cutaway, needle jet must have bleed hole, main jet
holder must be of longer 4 stroke type, jet needle must have 2 identification grooves at the top. The
story goes that there were never any 4 stroke 1000 Concentrics made. As I never found a 4 stroke
1000 series Concentric either, only 2 stroke types, I really wonder if the Velocette factory on their own
converted the 2 stroke types into 4 strokes. Was there a guy drilling by hand all the air correction
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holes and changing all the internals?? Or did they get them converted by the Amal factory ? Any info
would be appreciated.
#2907 Is this of any help? www.ingfatrygg.se/amal.html
#2911 A useful reference guide on Amal carbs. www.britishonly.com/tech/tips/mark1.asp
L #2921 I was reading the article in Classic Bike Jan 04 regarding carburetors. In the article it
recommends "where the flange has been bowed through over tightening .. then grind it flat on a flat
plate". It also says that if the body is distorted "bore oversize and sleeve". Well my Mk1 concentric
was suffering from bowed flange and distorted body making the slide stick. I took it to Rabers in San
Jose, and they were able to "straighten it" so that the flange was flat and the slider also moves freely.
It turns out that in many cases the two problems are linked. Rabers have very simple jig to correct this.
They charged a nominal amount and it took less than 30 minutes. I took a look at the jig and it
consists of two parts. One piece is an almost flat plate with a 15 thou concave dip with a hole through
the middle (about 3/8inch). This goes up against the carbs flange. The other piece is a round bar that
just fits fairly tightly within carburetor body. This also has a hole through which allows a bolt to be
pushed through throat of the carbs and though the hole in the middle of the flat with the concave
surface mentioned above. The procedure is to tighten the bolt and leave it for a few minutes – and
magic the whole thing is straightened. I hadn't heard of this before. I thought other might be
interested. The trick I should imagine is making the plate with the 15 thou concave. I have no idea
how this might be done, but I am not a machine shop expert.
L #3331 looking to fit a new carbs to my standard 62 Venom. Do I fit standard Monobloc or as
someone recommended a Concentric. Observations appreciated.
#3332 I fitted a new concentric and it transformed the bike! However a new Mono might have
improved things also because the old one appeared very worn on inspection. I suppose it depends on
finances( new concentric is cheaper) and how original you want things!
#3334 Common consensus is that a Monobloc is a much better carbs than the Mk 1 Concentric. This
was also supported through various conversations I have had with a number of people in the know,
including a one time Technical Manager at Amals.
#3345 I always figured that the Monobloc had to be jetted richer than the Concentric, by about ten
sizes, due to the greater distance that the fuel must be lifted from the bowl to the discharge nozzle.
L #5290 My Venom has a monobloc carbs with standard Venom set up. The bikes performance
is good with no problems running or starting etc. I'm using a Campion N3C plug, which is the same as
when I purchased to machine. The only thing is that each time I have removed the head (for various
reasons) there has always been a heavy build up of carbon. The plugs general colour would indicate
some richness in the mixture, but not excessive. I would think that only a small adjustment somewhere
would improve combustion. Should I drop the needle a notch (currently set at fourth notch) or would a
different plug help?
#5291Which kind of carbon is it? Hard carbon from Petrol or Soft carbon from Lub. oil.
#5293 Most definitely hard (used a needle gun, cold chisel and lump hammer etc. to get it off). The
bike doesn't smoke at all and the bore is nice and clean.
#5294 Suggest leaving the needle and using a N0. 4 or 4 ½ Throttle slide. We are on a 4 and have a
4 ½ available. We also run with a 330 main jet as the book.
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L #3688 I live at the beach/ocean in Southern California and want an air cleaner. My automobile
air cleaners trap LOTS of sand and I don't want sand in my bike intake. I can't find any standard air
cleaners for a '55 MSS Velo. Suggestions? I would prefer a 'standard' look but want to ride the bike.
#3689 Grove Classic Motorcycles had a number of these in stock a few months ago.
#3690 There were two versions of the Velo-built filter: "gasworks" carbs (i.e. pre-Monobloc) and
Monobloc. I've been told the pre-Monobloc fits the Concentric. Can anybody confirm this?
#3691 I have an Amal 276 type carburetor with the side float.
#3693 The 276 side float ("gasworks") carbs was normally not used after 1954, unless maybe Velo
had shelves to empty. So far as I know, the later Monobloc filter doesn't fit the Gasworks- I talking
about Velo-made filters which maybe aren't the best for fine particles. The Monobloc filter doesn't fit
the Gasworks. Nor (I think) does it fit the Concentric, but maybe perhaps the Gasworks filter fits the
Concentric.
#3704 I ran a K&N air filter on a 1036 concentric fitted to a VMT. The filter worked well. K&N make
many many sizes, and you should be able to get one that has a inlet flange that will clamp to the inlet
threads on the carbs. On the VMT the carbs is set quite a ways back from the head, and as a result is
close to the frame tube near the front of the saddle. I looked at a number of filter sizes and offsets
and found a tapered cleaner that fit nicely. The K&N is a modern device, designed for periodic
cleaning and reuse. If you find one with a black end, rather than the chrome ones, it doesn't look too
bad on a Velo, and will do wonders versus no filter at all. A good solution for a bike to be ridden.
L #3860 I have received my Thruxton just a month ago, and the mixture is much too rich the bike
is running with a GP2 carburettor. I have checked all the jets no: 25, 109 and 280), needle (position 4)
and slide no: 3) for correct size and also adjusted the float chamber to a little below the recommended
position. What can be the problem? The ignition should be a little higher, I believe. What is the correct
setting (timing). What is the correct position for the air control level on a hot engine? It seems that the
handle in forward position is giving the best result.
#3861 You may find that the carbs is weak not rich. If the air slide is closed (forward) this indicates
weak mixture. Is the slide worn? Ignition should be 38 degrees BTDC as book, probably 36 degs.
would be better on current fuel. Your carbs settings are as book. Check the float chamber level
carefully, this has a big effect.
#3866 When supplied new in Sydney Australia in March 1967, VMT457 and VMT458 were both fitted
with no3 slides. Dennis Quinlan, first owner of 458 soon changed to a No4 slide and the running rich
problem was solved. My Thruxton, VMT457 has run a No4 for the past 30 years of my ownership.
Dennis wrote to the factory and advised them of the problem but I don't know if they corrected it in
later bikes supplied with a GP carbs, or in any updates to the red book - apparently not. So I
don't think the carbs is weak - change the slide to a No4 by filing away the leading edge by 1/16" (I
think! can someone in authority please confirm) and the problem should be solved.
#3867 I agree it is 1/16, so a 4 slide has 1/4 inch cut away. My VMT would never run with a 3 slide
either, 4 and even 5 needed. Also too rich with the rich needle (has about 3/4 inch of taper) even on
the leanest setting and new jet. I used the lean needle which is straight for all but the last 1/4 inch.
This on US petrol.
L #4140 I am thinking of fitting a Mikuni carbs to my Venom. Information I received from the
supplier stated that the 3 gallon petrol tank needs to be raised by an inch and a half at the rear to fit it.
Has anyone carried out this modification and could they detail how the tank was raised and did it spoil
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the symmetry of the bike ? Also was there a noticeable improvement in performance ?
#4146 I have used a 30mm Mikuni kit for 6 years on my Venom Clubman with the big tank. There's no
need to change the tank in any way if a standard Venom head is used. I had a problem with the
airflow at the inlet, it's a known fact I think that the performance is dependant on the driver holding his
right knee to the tank. I fixed this with a homemade inlet extension of about an inch which is not
conical but cylindrical. The top end performance was not improved but it's always a first kick starter
and the idle is reliable as a steamboat.
#4149 I have just fitted a Mikuni, supplied by Allens, to my Thruxton. The bloody thing doesn't really fit
at all. I have had to squeeze it in and it presses with great force on the oil tank and underside of the
Thruxton petrol tank. It WOULD fit if the finned aluminium inlet spacer was not the full 4 inches long
that it is. Does anyone know how I can get hold of a slightly shorter inlet piece (say 3 inches?) Also, at
a standstill the petrol pours out of the little plastic breather pipes. Oh woe is me!!
#4158 4 inches - thats ½ inch longer than standard. (size matters) Not sure of the mikuni fitting but I
have a 3.5 inch inlet manifold going spare for a stub fitting Mk2 Concentric (i.e. rubber mounted as I
expect the Mikuni is) for a Thruxton. Its not an original cast item but a 'machined from solid alloy'
modern thing.
#4143 Now, raising the rear of a small tank and inch and a half would be atrocious! Fortunately that's
not necessary. My Venom had a 38mm Mikuni on it for some time that fit (albeit snugly) under the
small tank without raising. I have a 36mm (1036) Amal Concentric on it now which also fits fine.
L #4430 I recently bought a 1936 rigid mac now need to set the carbs (a new concentric) up as
it did seem to be running lean going by the colour of the plug, I had replaced the old mk1 concentric
fitted with a new one and need to set it up correctly this time!! jet size is 170 ,the new needle seemed
to be too short so replaced it with the original one but I do not know what the correct length should be
any advice on setting up would be appreciated thanks.
#4432 Be sure to use a .106" needle jet and a needle with two identifier rings above the three grooves
for the needle clip.
L #4416 I have a Venom fitted with an Amal 389 carbs of uncertain age (old). Whilst the bike
goes really well, tickover speed can vary and be a little unreliable when the engine's hot. I have toyed
with fitting a Mikuni to it, but am put off a little because the information supplied by Allens Ltd state
that the 3 gallon tank has to be raised at the rear by one and a half inches to clear it. Can anyone
confirm that ? If the Mikuni is not possible then I will fit a new Amal. What's the best advice-a
Monobloc again or a Mk 1 or a Mk 2 Concentric?
#4417 Just checked with a friend who has a Mikuni carbs fitted to his Venom that has a 3 gal tank.
He's had the underside of the tank modified rather than jack up the tank to provide clearance in order
to fit an air filter on his carbs. He reckons that if you are intending to use just a bellmouth then you
should get away without any need to jack up or alter the tank. I've used a Mk 2 concentric on my
Venom with very satisfactory results, but never tried a monobloc or Mk1 concentric, just that the Mk 2
came my way very cheaply, so I bought it.
#4419 I have used the Mark 1 Concentric carbs on my 1963 Venom Clubman for years and have
absolutely no trouble at all as long as the timing is spot on.
#4420 I recently rebuilt the carbs on my Venom which was the 389 type. I initially tried to cut the cost
by replacing jets and slide but this didn’t prove 100% successful as it continued to run on the rich side.
Eventually I succumbed and replaced the body and jet block too which basically meant I had a
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complete new carbs which transformed the running. The only problem I found was that to get it to run
OK on pilot I had to reduce the jet from a 30 to a 20. 25 was still too rich. Once this was done all
appears OK and it runs well now albeit I still think slightly rich on the needle. I am loathed to lower the
needle a notch as I have read with interest the cases of holed pistons and weak mixtures. I do note
that the small red Owners Handbook, mine being the 10th edition dated August 1967 says "Normally
the needle clip is in the middle groove" All my other publications including the official Service Manual
state the No4 groove. Starting is not a problem, second/third kick, sometimes even first
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D.2. Fuels -
L #180 I have not used my 1947 iron MSS (called "Eugene", after its designer) much in the last
three years or so since leaded fuel pretty much vanished. On pump unleaded (95) it seems to run
ragged at revs and much hotter (straw exhaust pipe for the first time ever - I do not thrash it as a
rule). Does any one out there have any experience of carburation with UL fuel? Do I need to re-jet?
The valve seat recession thing can be dealt with by additives and I cannot believe that I need an
octane booster with the MSS at around 6 to 1 CR! All ideas gratefully received.
#183 We Veloist here in West OZ have had all sorts of problems with the lead replacement fuel which
replaced the old "Standard" fuel. Plugs foul after only a couple of miles, engines run roughly,
impossible to time the engine - Yech! The only solutions we have found to work are either using the
combined octane booster/upper cylinder additives in conjunction with the highest octane rated
Unleaded fuel we can get, called Premium Unleaded down here, which works well. It certainly does
not work using the additives with "ordinary" unleaded fuel. The best solution and one that makes the
old girls run as sweet as can be is to use Avgas (100 Octane aviation/racing fuel) at a ratio of about
25% Avgas to every tank of unleaded fuel. This has worked for all our machines from pre-war to
Thruxton
#184 RE; the unleaded fuel debate. We in the USA have had unleaded fuel for about 12 years, and I
am happy to report that it required very, very few changes to jetting or valve seats. There was as
much fuss here at the time of the switch as you are experiencing, which all pretty much went away
with time. Yes, the octane is lower, so no more 10:1 pistons, we find 9:1 the limit on a Velo. Some
(VERY FEW) bikes have had problems with valve seat recession, in fact the only bike I ever
consistently heard with this problem are BMW R 100's of a certain year. I don't see why a bike with an
iron head and 7:1 piston would need Avgas, it will run hot certainly. Some unleaded fuel has extra
alcohol here, which can make some bikes run lean, a simple adjustment is all that's needed. Don't
panic, everything will be just fine.
#421 fill up with Shell Optimax, they make some ridiculous claims - however it has transformed my
Venom, no more pinking the acceleration and performance is back to what it was on 5*.
L #438 It’s a well known fact that petrol does go off rapidly, I find even two month old petrol will
hamper starting. There is even an additive to add to lawnmower petrol to stop it going off.
#439 Thanks for the note. I've often heard people say that petrol `goes off' but have never
experienced this. Even when the bikes have been sat in the garage over the winter they don't seem to
have any fuel problems. Maybe in the colder weather the volatiles don't evaporate so quickly. Anyway,
I'll get a fresh gallon tonight and see what happens. By the way, I've been using your Velo Technical
website a lot during the rebuild. Very useful site..
#440 Don't know if it is available in the U.K., or if you have your own version there, but there is a fuel
stabilizer here in the States called Stabil, which works well in diesel and pump gasoline. I have literally
used 6 month old gas that has been treated with it, and the vehicles ran fine. Might be worth looking
into. I have the feeling the quality of pump petrol in your geographical location is poorer in quality then
what we have here. My impression, at least..
#443 Here in the USA, if fuel is in a vented tank, such as a motorcycle tank, and sits a year of so, you
can't light it with a match! Fresh fuel and a new plug should do it.
L #908 In USA, and probably in Canada too, the quoted Octane number is (M+R)/2. Therefore
what is 92 octane in USA is probably a close equivalent to 95-96 RON= in UK, and the 97 (R+M)/2
must be around 100 RON or so. I thought you'd like to know that! It does cause confusion.
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#909 If that is correct then North American 97 grade fuel should be the stuff to use without a doubt. If
Michael has been running on the lower grade option without backing off the ignition timing then this is
highly likely to be the cause of his holed piston don't you think?
#916 Quite right. The top grade should be used in Vipers and Venoms. Lower grades are OK for
MACs and MSSs in standard trim, but their use with the higher CRs will cause pinking and eventually
holed pistons. Using the wrong spark plug can do this too, by causing pre-ignition. NGK B8ES or
harder is necessary for VM etc.
#919 I always run Sunoco grade 94 (they claim is the highest available in Canada) Is Aviation fuel an
option?
#926 Personally I wouldn't recommend using Avgas. Although the normal rating is 100LL (100 Octane
Low Lead) my experience with an Aprilia 250 GP bike demonstrated that this is not a cure all for
detonation problems. This machine was bought new direct from the factory in '90 for use in the British
and European championships and came with the usual amount of technical documentation and help
that one gets from an Italian factory - not a lot! Believing that we ought to be running high octane race
fuel which was unobtainable in the UK at the time and since the rules on fuel were being tightened up,
on advice from BP we began running the machine on Super unleaded 98 RON pump fuel (BP claimed
at the time that their pump average for this fuel was 99 RON). Since this was a two-stroke machine we
mistakenly believed that the lack of lead shouldn't be a problem. Within a dozen or so laps of Cadwell
on the first time out we had a holed piston. Consultation with people in the know suggested that
perhaps we ought to be running leaded fuel so the next time out we ran a 50/50 mix of 4* leaded fuel
and Avgas, a common brew in racing use at the time. This stopped us holing pistons but we continued
to have a small amount of detonation erosion on the top of the pistons and the rider always reported
poor carburation whatever jetting settings we ran. I gradually increased the proportion of Avgas until
we were eventually running 100% of the stuff but never completely got rid of the det damage and it
appeared that the carburation problem was getting worse. Eventually frustration led me to go to the
other extreme and I tried 100% 4* as a last resort and - hey presto! - no more detonation and perfect
carburation! This led me to believe that although Avgas is rated at a high octane it is not designed for
use at ground level but at several thousand feet up in the air where the oxygen content of the
atmosphere is lower. The "Low Lead" tag is misleading too, in fact Avgas has a higher lead content
than 4* leaded gasoline. However, as the regs regarding fuel have changed over the last few years,
most of the factories have produced racing machines which are designed to run on Avgas and have
combustion chamber shape and ignition advance curves altered to suit the burn characteristics of the
fuel. My conclusion was that in general Avgas was no help in tackling det problems in engines unless
those engines were designed for it in the first place. Better to alter the timing to suit the available fuel,
particularly when you can't get Avgas from your everyday petrol station. What would you do if you
went for a touring holiday on the bike - have someone follow with a tanker full of special fuel?
#932 In the USA Sunoco sells a variety of race fuels, their website is www.racegas.com There is a
dealer close to me that has 110 octane (R+M/2) leaded, they also offer unleaded up to 104. And
leaded up to 117! Also methanol if you are racing speedway or sprint cars. With a 50/50 mix of the
110 and the 91 octane U/L "premium" sold in our local gas stations, my VMT starts first kick, no
pinking. Since this bike is not intended for long-distance touring (rather for 100 - 200 mile rides on
Sundays), this works for me. All other Velos in our garage are timed at 36 - 37 degrees and run 8:1
CR or less. 30 years ago I thought my Venom had a rod knock, took it down to the crankshaft looking
for a non-existent problem, realized years later it was pinking.
L #934 What about so called octane boosters? Is any one brand preferred over another?
#940 Octane boosters are a waste of space.
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#942 Warning! Anything potent enough to raise octane significantly in small amounts will likely be so
poisonous and/or carcinogenic that you wouldn't want it in your garage, much less toolkit or tankbag.
Remember Dave Allcock.
#944 I have spoken in the past with a fuel chemist, and he recommended adding xylene at NO
MORE THAN 10% to gas if octane boost were needed. Toluene I would imagine is much the same,
but I wouldn't add 20% as this might bring new problems due to altered burn rate and excessive heat.
L #1035 On the question of petrol in the UK as an owner of a Lotus elan for the last 30 years
until recently. The Lotus twincam engine with 10.5 c/r & webers carbs, the drop in octane in UK petrol
has been a real problem! in starting & pinking. 95ron & 97 ron is not the same as the old BS octane
figure, that use to be on the British petrol pumps the MON octane is lower than RON, & LRP has not
even got a British Standard!! The FBHVC lead replacement testing was only carried out on a Rover
A series iron head low compressions engines @ 4 deg advance for VSR measurements, which is no
criteria for a high compression engine. But in the Lotus world we do know QED with Miller oils had
done engine power tests with QED dynamometer with Millers CVL. (Competition valve lubricant) on
the twin cam. Test showed that it produced considerable power increase using 95 ron unleaded fuel
at 300ml x 20 ltrs further inquires with Miller oils tech dept confirmed the results that CVL produces a
rise of 3 octane & Millers VSP a rise of 2. I used VSP in my Lotus for two years before I sold it to
great effect that I was able to advance the ignition back to 12 deg. from 10 deg which most of us had
been running at since the loss of 5 star petrol in the uk, I have been using it in the Velocette although
the MAC is not a Performance engine. I think it improves starting? The only problem with using
octane boosting additives is Millers is manganese, Castrol valvemaster is phosphorous and LRP is
generally potassium although individual oil companies will not confirm this? But what ever you use
you must stick to it as they do not mix, the other unknown factor is long term corrosion if any? Only
time will tell. Which as somebody has already said, makes Gordon Jennings, thesis on Plugs, a bit
old hat nowadays.
L #1732 My 1958 Venom has a manual advance/retard. I've set the timing at 38 degrees BTC at
full advance. I'm running on normal unleaded with Shell Valvemaster and Octane Boost. The problem
is that I cannot find a "balance" between loss of power and excessive pinking. Keeping the engine "on
the boil" by using lower gears helps to a large extent but doesn't solve it. I haven't looked inside the
engine since I bought it about 6 months ago and have not measured the compression ratio. The only
indication I have is that there are no compression plates between the cylinder and the crankcase and
the previous owner (who is not contactable) had a bit of a reputation for "warming up" engines. I've
read previous postings and the options about mixing avgas/petrol etc really aren't practical for me. I
need to be able to fill up with what is easily available when the tank is empty. I've used Optimax and
this does seem to improve things, though it's not necessarily available in the wilds of Cumbria where I
live. Normal unleaded and LRP are often the only things on offer. I've heard good things about the
Broquet catalyst but wonder whether anyone has any experience of it. www.broquet.co.uk/ for anyone
who hasn't heard of it and is interested. Any experience out there?
On a different topic I read the list of things which break with vibration with interest. The centre stand
can be added as I found last weekend - one side up (with the spring) and the other side dangling does
nothing for handling! Where's the brazing gear?!
#1736 It might be worth trying genuine 4 * petrol. I don’t know where abouts you live in Cumbria but
there is a garage at Thursby (West of Carlisle) that sell it. It is rather expensive though.
#1738 Might simply need a decoke. I just done mine and it cured a not dissimilar problem. On
additives - I have had good results with Tetraboost - which contains real tetra-ethyl lead. Dose is
100ml Tetraboost to 6.5 litres super unleaded (97 octane) - gives 5 star (100 octane). Not very
environmentally friendly though. Tetraboost are on 020 8870 9933 see also: www.tetraboost.com If
you want to try it I have plenty spare - comes in 1 liter bottles - let me know (or ask James Jacques
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who I think still has a drop or two I 'lent him for experimental purposes') On centre stands - Criterion
((01793 790219) used to do a 'special' alloy centre stand - no experience of this - but I'd bet there is
stuff in the archives about it.
#1996 Mine is running an optimised 8.75:1 on Super U/L or Optimax preferably, 38/ ignition timing
without any form of octane booster or other additive. It pinks slightly at high load/low revs as one
would expect, but is quite happy otherwise. Pinking tends to increase slightly as it begins to run low on
fuel and the level in the float chamber drops - a useful warning to switch to reserve before it slows up
rapidly with someone on your tail!
#1998 Pete, 1) you have stated THE most important thing to remember ... 'It pinks slightly at high
load/low revs as one would expect, but is quite happy otherwise.' 2) BUT, also remember that a weak
mixture will pink more than a rich mixture. My venom and viper racers both run approx 10.5:1
compression, and I run them both on super u/l, no additives (which is just about the only thing you
_should_ be allowed to run according to how _I_ read the acu regs) They don't pink 'cos they don't get
run at low revs ... Pinking is an issue with 'lugging' your engine, if it pinks, just change down a gear.
BTW - Shell Optimax does _not_ have a better octane rating than other manufacturers any more (if it
ever really did have).
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E. The Drive Train
E.1. Primary Drive, Chainwheel and Clutch -
L #151 I would be interested if anyone else sees this as a problem and also if anyone knows of
a cheap source of the large ballrace assembly. The last one I purchased was about £90 so I would not
want to replace it too often.
#154 I got mine from Grove Classic Motorcycles in Bedfordshire U.K. (+44 (0)1582 873066) as mine
was cracked and loose in the chainwheel. I checked the price list and they are currently listed at £95
#156 Re: clutch chainwheel bearing (not throwout bearing) life with a belt drive. There will always be
some oil in the primary from the engine breathing through the main bearing. I think we should ask
someone who's put some miles on this system, though, to find out if it's enough. Those bearings
sometimes are in short supply! And as a sidebar, on the throwout bearing, rollers are the only way to
go. Two sets of the ball type wore out in 3 years on my VMT before I got wise, and have never had to
change them since (this is 12 years ago).
#157 Some new chain wheel bearings are a thou or so undersize (not necessarily those from Grove
Classics), and have a habit of dropping out of the chain wheel. Check the OD of the new bearing
against the old before you fit it.
L #160 My Venom has traveled just about as far in 13 years with the original ballrace release
bearing. It is adequate when properly lubricated. I was slipping the clutch like a mad 125 GP rider on
the way up Pikes Peak last summer! Stinking SUVs... Simple geometry says that the roller setup
needs good lubrication too. If the heavily loaded rollers on a crankshaft skidded like they do in the
release bearing they would not last a minute. I agree that someone with experience with running a
"dry" primary should give us some hard facts about bearing life. Race bikes probably don't see the
long-term clutch abuse that a street Velo does. Perhaps
#161 Reference the clutch release bearing saga, I modified the brass cage on the bearing by filing it
to take 3/16th" rollers after reading about the mod in Fishtail in the 70's and never had to change any
of the parts despite using the bike as everyday transport for years
#162 When I had mt first Thruxton back in the late 60's early 70's it seemed to "eat" thrust race
bearings of the ball type. I now use the roller type and find in the 10 years of ownership of my second
Thruxton I am still using the same bearing
#164 I have been using bonded clutches and better quality steel plates for about 3 years now and
find them a great improvement. I find that neutral is easier to select, the gear change is smoother,
also when abused the clutch will go out of adjustment but return to its original settings when "rested".
I have found that the chainwheels made in Germany do not last long and seem to wear very quickly. I
have just had them relined at Safetex in Yorkshire, but to date have not had the time or the weather
to used them, has any one else used Safetex relined chainwheels or plates?
L #423 I have a 1954 MAC and I want to rejuvenate the clutch. I have a few bags of inserts from
Martyn Bratby, enough to do all of the plates and the chain wheel. Is it as easy as popping the old
ones out and bunging the new ones in? Or are there other things I should do as well?
#424 Plates must be reasonably flat. Tabs to be deburred, insert new inserts, put every 2nd one in
then reverse plate, and finish off. I have found that a dab of araldite holds the inserts in place , they
tend to become sloppy in use. finally , a gentle sanding,( 250 grade wet and dry on a flat peace of
glass). The main thing is to use FLAT plain plates, most become dished with use. A little extra throw at
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the lever ,till the clutch is bedded in will help eliminate the drag.
#425 I agree with Chris replace them alternatively from opposite sides; you will need to file the inserts
with a taper to make them fit the holes. (Use gloves and a mask). Inserting them will require some
form of press, I used a fly press but you may be able to do it in a vice. You will need to find a spacer
so that the insert can protrude through the plate –some people use wire. To calculate the wire
thickness, take the thickness of the plate away from the insert thickness and halve it. Remember there
is two thickness of inserts 0.195 thick for the seven-plate clutch and 0.155 thick for the nine-plate
clutch..
#428 Why not send them to Saftek, 1 Rawfolds Ind Estate,Bradford Rd,Cleckheaton, West Yorks.
BD19 5LT.Tel 01274 862666 Web site www.saftek.co.uk and have them bonded, saves a "pig of a
job"
L #451 I do have a running long term test question; I have had two of the new 'Canadian'
clutches (with bonded linings from an automatic trans - I think Goodman makes a version now) in my
bikes. They have failed within 3000 miles each, with proper adjustment even. Anyone else out there
have the same experience? My Thruxton, a week before our annual ride, has terminal clutch slip.
Time to go back to standard
#480 I think you will be surprised to find that the 'demonish' clutch you took apart is identical to the
one in any Venom, MAC, KSS, etc! All Velo clutches work beautifully if they are set up according to
'the book', and in this case you could use the Red Book (factory service manual for Venom etc) to set
up the clutch, or ask any knowledgeable Velo enthusiast; they could help you set it up in a trice, as
undoubtedly they have done it themselves many times. There are several sources these days for
improved clutch parts, i.e. bonded linings on the friction plates, slotted plain plates to obviate warping
(not so likely with such an, er, understressed engine as the model U), most of which were developed
to handle the power of a Thruxton engine on that same little clutch. As for you overhung crank, many
prewar two strokes used them, including Scotts, and while yours will likely do an 'end to end' run with
no problem, the advantage of this design is the ability to replace the rollers without removing the
engine! That's what that round door on your crankcase is for. Not your grandson's Yamaha... By the
way, after surfacing my plain and friction plates on my Thruxton's 'Canadian' clutch, it has improved
dramatically, and after some adjustment on the first day of our annual Velo rally here in Washington
stage, went perfectly the rest of the week/1100 miles or so
#481 I agree with Paul, with the exception of the thrust and chain wheel bearing you cannot use any
of the modern parts as the clutch while operating on the same principle needs components of different
dimensions..
L #529 I have a 1970 Venom Clubman, and could use some advice about the clutch. I've done
the clutch adjustment drill as carefully as I can, and my clutch still slips under power. Should I dig in
and take the clutch apart to see what's going on, or should I try adjusting it further to increase drag?
Since this is essentially a new bike, with just 12 miles on the clock, and sat for 30 years, could it
simply be that the clutch springs are sacked?.
#531 Now I don't know if this will help but I had bad clutch slip on my MAC after replacing the main
bearings (I also took the clutch apart). Turned out that I had replaced one of the plain plates the wrong
way round. That’s all it was. It was preventing the plates being sandwiched together.
L #1041 In this cold period, I decided to keep my sundays busy in replacing this felt seal on my
Venom, you know which I mean. Opening the primary case, I saw the following problem I never
experienced : The primary chain has seized links, some rollers are broken. The chainwheel is out of
alignment, outside 2.5 or 3 mm. There is no sensible end play on the sleeve gear. I'm puzzled as
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there is no provision to shim neither the drive pinion nor the clutch or the sleeve gear. Where could
this trouble could come from, and how to cure it ?
#1042 You have got something wrong. There is no way that the chain line will be out if all the parts
are as they should be. Is the chain wheel on the clutch the right way round? Which way is the chain
out? Is the tubular spacer behind the clutch the right length? Do you have a Venom engine sprocket?
Did the machine work OK before you noticed the damage? A bit more investigation will find the cause
(I hope)
#1045 That's why I'm puzzled !!! The chainwheel is too much outside; yes it was in the right way (two
friction plates inside, one outside), the spacer on the sleeve gear is the original one I use for years, as
well as the engine sprocket. Engine and gearbox have been rebuild, and the machine ran perfectly
well ! If no other idea, next step could only be to take the sleeve gear off, which I should have
preferred to avoid.
#1046 If everything in your clutch was fitted the right way, my suggestion is that the big threaded ring
that secures the main bearing loose and the whole clutch moved away from the gearbox because of
the force you put on it when operating the clutch. If the bearing sits relatively tight in the housing, you
won't feel any play. Anyway, if this is the case you should have encountered some clutch drag. Maybe
you adjusted it and some time later it occurred again and so on.
#1057 I have taken the bearing ring nut out, it was ok, and the bearing is snug fit in the case, so any
end play would have been noticed. Do you mean that's normal to have 3 mm or so out of alignment,
and is not why my "normal" chain has been destroyed ? The outside of the chainwheel teeth is worn
too (the chain wheel is outside alignment). So the only two other possibilities I consider are lack of oil
(there were very few in the case), or too tight a chain. It was ok when I opened the chaincase recently,
but I remember last year I found it over-tightened once. Just in order to check the sleeve gear bearing,
is there a way to take it apart without opening the gearbox ?
#1067 Just one observation that you probably knew about. When you checked your primary chain did
you check in five or six different places on the chain. Every primary chain I have checked has variable
tension depending on the concentricity of the chain wheel. If your unlucky it can vary between tight to
flapping about. It's also interesting to check (with a gloved hand) when everything is hot, I am
surprised how tight it gets on expansion.
#1069 Yes, I always check the chain tension in different places. For years, I always had it on the slack
side. But last time, I remember I tightened it more than usual, to the specified value (red book) ½ or 1"
free play cold, thinking it would get some more play when hot. This, added to dry case, could explain
the chain havoc. But this doesn't explain chainwheel misalignment. I checked all the clutch parts :
Chainwheel was true on the backplate, as well as on the sleeve gear. Thickness of all plates is right, a
bit less than new parts, a bit more than used ones. Some plates are not perfectly flat, but as far as the
clutch worked properly and didn't drag, I do not think this could cause a real thickness excess of the
assembly. Anyway, even without any friction and plain plate, i.e. assembled with backplate and
chainwheel alone, the later is still outside about 2 mm. The alignment was checked with a ruler on the
outer face of the engine sprocket (in different positions of the engine, and sprocket). The edge must
point at the outer face of the wheel teeth. It does at the middle of the tooth instead. I reckon this
measure must not be affected by the position of the box in the mounting plates, as far as the shell is
tight between them. Misalignment could be due to wrong spacer length. Maybe it has been like this for
the last 35 years (never checked it before), and the oil + tension revealed the prob. This would mean
such a misalignment is acceptable.
#1070 Venom Par no. B35/3, length = 11/16 inch. MAC/MOV etc. B35/2 length = 5/8 inch. The
primary chain normally tightens when it get hot.
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#1072 Both my spare parts list for MAC (spring frame model) list B35/3 sleeve gear distance piece for
the MAC. not B35/2 ? could this be the problem
#1075 I used the designation MAC/MOV etc. to relate to rigid gearboxes. You are correct B35/3 was
used on "Springer" MACS. Also check that the inner end plate, i.e the one closest to the gearbox, has
a 2 5/8 inch diameter recess that is 9/64 inch deep. This information comes from a Fishtail article
written by Dave Childs, which if you own a Velo is an absolute must.
#1071 Maybe your problem is due to warped gearbox mounting plates. During several decades of
hard work this might happen. At least my plates were warped when I stripped the bike although it was
fitted with the double plates at the drive side.
#1087 The B35/3 is the right one, the inner clutch plate has the correct 9/64" recess , the mounting
plate doesn't seem to be bent, as far as I can check it in the frame.
#1608 I bought bonded and plain clutch plates from Simon Goodman some years ago, which I think
are the same as offered by Grove. I seem to remember him telling me that the bonded plates were
thicker than standard, and the plain plates thinner, making the overall clutch the same width as
standard. Regards
#1689 I dismantled the clutch on my recently acquired Venom (which came with receipts for a new
clutch)which has Goodman's bonded plates and Goodman's plain plates together with a standard
chainwheel. As the inserts were very loose I had the chainwheel lined with bonded material by Saftek.
I fitted a new engine sprocket (same dimensions as the old one)together with a new Reynolds chain.
The result was a mis-alignment of the chainwheel and sprocket of about a sixteenth of an inch. The
engine sprocket was being pulled away from the engine. also the outer chaincase was now being
fouled by the clutch, so my conclusion is that the clutch is now appreciably thicker. With no oil in, it is
easy to here the chain clicking over the engine sprocket as it runs out of line (turning by hand of
course). It appears the only answer is to decrease the length of the spacer behind the clutch but there
is not a lot of room, or put a spacer between the sprocket and the main bearing. I have looked at the
last option and cannot see a problem. It wont seem to mask the breather (it has a crankcase breather
as well)but it will increase the shock absorber spring tension.
#1060 I have done quite a bit of primary chain (well belt in my case) alignment work. One thing I have
noticed is that if checking with a straightedge across the chain wheel the state of the trans in the
mounting plates has a significant effect on alignment measurements. This applies to rear chain as
well. The effect riding the bike has on the trans (notice how when you adjust the primary chain,
making sure to leave the jack screw pushing the trans forward, then go for a ride the primary chain still
tightens up as the trans gets pulled back on the drive side only) will change alignment. So you might
try moving the trans in the plates and see if there is any change. Also main bearing shimming will of
course change alignment by a small amount, as will clutch plate thickness.
#1051 Regarding primary chain alignment, they are usually out of line by about 4-5mm my friend from
holland has encountered this problem and I have fallen foul of it as well. The standard primary chain is
a bit weak if you tend to give the bike a bit of stick. you can fully stretch a chain in 1500-2000 miles if
you ride a bit hard. I was told to fit a 428H DID primary chain which has thicker side plates and is a
heavy duty chain. It’s a tight fit to the primary case but they are ok. I fitted one and ran the bike. I had
to take the outer chaincase off and to my horror the chainwheel was eaten away on one side very
badly where the chain was trying to align its self and pulling into the chain wheel because the
sprockets were out of alignment. It hadn’t done it with a standard chain but the heavy duty chain
showed up the problem. the chainwheel is a fixed item so any adding shims has to be done at the
engine sprocket end. if the engine sprocket is too far out, you can always let it down by using grinding
paste and a mirror. Remember that a mirror is flat because it is ground and a pane of glass is not. it
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seems that all the bikes that were made were not too well aligned on the primary side. He has
checked a lot of Velocettes and they all needed aligning on the primary side. I hope someone can use
this information. p.s. remember that if you do decide to fit a heavy duty primary chain always rivet up
the link as split links are a definite no no.
#1241 Some messages suggested to shim the engine sprocket to achieve primary drive alignment. So
the breather hole in the mainshaft will no longer be in line with the groove in the sprocket bore. What
do you think about it ? Will it cause any problem
#1053 I mentioned about primary chain alignment and I said that you either had to shim or let down
the front engine sprocket. I was lying in bed when it dawned on me that I should have said shim or let
down the inner cush drive, as that will determine the alignment and not the sprocket. my mistake. I will
give him a ring and ask him for some more input into this subject..
#1061 The inner 'cush' drive IS the sprocket! There is also a spacer on the sleeve gear against which
the clutch backplate abuts. This may be the wrong length, causing chain misalignment. Different
models had different length spacers, and sometimes the wrong one is inadvertently used.
#1062 PS: It is also possible that the clutch chainwheel bearing is worn, loose or missing (yes, I've
seen it missing!). Also, of course, the sleeve gear nut not being fully tightened would cause
misalignment.
#1068 When you stripped the clutch to check on the sleeve gear bearing was the chainwheel still tight
and central on the large bearing? I think he has the right idea when he refers to the clutch plates and
inserts wearing and misalignment taking place. Have you measured the inserts and the steel plates
and compared them with the thickness of new items? I have seen Velo clutches where it is possible to
rock the chainwheel even when the clutch has been adjusted perfectly, due to worn inserts. A
combination of the above and your own observations of little oil and tight chain could have caused
overheating leading to seized and broken rollers, culminating in the wear you noticed on the
chainwheel. As Geoff states the mainshaft nut in the box shouldn't affect the clutch, which should still
work and rotate even if the mainshaft is out of the gearbox, but don't try it too often as the pressure
exerted is taken by the unsupported clutch and bearing and may distort or crack the alloy of the
gearbox shell. you stated in your second reply that the bearing spacer was the original and the
gearbox bearing was still tight so I can't see what else could cause such misalignment other than the
above.
L #1140 In rebuilding the 7-plate clutch (inner end plate, outer end plate, chainwheel, two insert
plates, two plain plates) on my '50 rigid MAC, I came up with a few questions. For reference, I went
through David Childs' article, "Identifying the Right Clutch Parts," and the measured dimensions of all
the components agree exactly with his list. On that basis, it would appear that I have all the correct
parts. 1) Dai's list states that the correct clutch springs are C12/3. The free and bound length for these
springs are specified as 7/8" and ½," respectively. My measurements indicate that when the clutch is
fully assembled, the free length of the springs (i.e. when the clutch is engaged) will be on the order of
0.600." I measured the full travel of the thrust bearing (when the clutch lever is pulled completely up
against the grip) to be about 0.070." Therefore, the compressed length of the springs (i.e. when the
clutch is completely disengaged) is 0.530." The amount by which the springs are compressed is a bit
more than I expected. The processes of assembling the clutch compresses their initial free length of
7/8" by nearly 31%. Further, when the clutch is fully disengaged, the springs are only 0.030" longer
than their bound length of ½." Is this really how everything is supposed to be set up? 2) I replaced the
original ball-race type thrust bearing with the redesigned roller-type. The original bearing was badly
worn, so it is difficult for me to assess whether the grooves in the races are purely a result of wear, or
perhaps a groove was intentional when these thrust faces were originally manufactured. The end
result is that the new thrust bearing assembly is about 0.020" thicker overall than the original. When I
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pull the clutch lever hard up against the grip, the front face of the new thrust bearing actually touches
the surface of the clutch inner end plate. I don't believe this situation would damage anything, since
the end plate and thrust surface would already be rotating at the same speed. Is there typically some
amount of clearance between these two surfaces? I haven't checked the alignment of the engine
sprocket and chainwheel, but I suspect I could install a small shim between the distance tube and the
clutch inner end plate to add a small amount of clearance if it is advisable.
#1141 Your message re the 7 plate clutch had me checking my K model clutch which happens to be
in bits at the moment! The spring C 12/3 is .875" free length and .485" coil bound. The amount that
the spring is compressed when the sleeve gear nut is fully home is .300" Therefore the spring length
installed is .575" The maximum lift on the clutch is .125" which as 'on the tilt' and so equates to .0625"
at the centre. All the above works OK. Remember the clutch adjustment method is based on only a
slight increase in pressure above the 'just slipping' point. Therefore only a slight reduction in pressure
will let the clutch free. Now to the thrust bearing. The grooves are wear and the inner and outer rings
should be flat when new. How do you know the thrust bearing touches the clutch inner face? I would
suggest that you check the length of the thrust pins which should be .391" also check that the sleeve
gear nut is fully home. I would not fit any shims in the clutch assembly. If all the bits are correct it will
work properly. Dave Child's list of clutch parts is correct in all important respects and is the clearest
guide available.
#1142 I appreciate your response. As you observe, the length of the springs when the clutch is
disengaged is only on the order of 0.030" longer than their bound length. I found this a bit surprising,
hence my motivation for soliciting input from those more knowledgeable than myself. It appears that
everything I have is set up properly. As I stated previously, I checked the dimensions of all parts
against David Child's list (if no one has ever thanked Dave for compiling the list, I would certainly like
to do so). This included the thrust pins, which are 0.391" as you indicate. I know that the thrust
bearing touches the clutch inner face [when the lever is pulled hard up against the grip] for the
following reason. I made an aluminum cylinder that fits over the sleeve gear, and has the same O.D.
as the thrust bearing. It is also the same thickness as the clutch inner end plate (not the total
thickness of 0.875" as shown in David's specifications, but rather the thickness from the indent in the
back face, to the surface against which the sleeve gear nut comes to bear. For reference, I measured
this to be 0.603".) This cylinder slides over the sleeve gear, and is trapped hard up against the
distance tube by the sleeve gear nut, just as the actual clutch inner end plate would be. When you pull
on the clutch lever, you can measure the resulting clearance between the face of the thrust bearing,
and what is equivalent to the plane of the inner clutch face. In my case, this clearance is zero. When
the clutch lever is pulled fully to the grip, the face of the thrust bearing just touches the back face of
the clutch inner end plate. It's possible I do not have the original clutch lever, and may have slightly
more travel than originally intended.
L #1185 The clutch action on VM1958 is very heavy. I first fitted the clutch cable before I fitted
the petrol tank and when the cable was run freely between the lever and the gearbox (no petrol tank)
the action was light, so it's not a problem with the clutch itself. When I fitted the petrol tank the clutch
action became very stiff. I concluded that the run was wrong but I have spent a long time today trying
different runs without making things any better. Without the tank the action is still easy so I'm certain
that the problem is to do with the cable routing. The cable is new. Any ideas? Is there a "correct"
route?
#1186 I've found that the larger the curve of a cable, the easier it is to pull - clutch, throttle, brake, etc.
If the clutch cable is routed to pass under the tank on the left side of the steering head with one curve
and the other portion arcing down behind the engine it should be a smooth and easy pull. Of course
things get in the way. Monoblocs with float bowls on left or right (I've used both), concentrics with
single fuel feed or both can have fuel lines get in the way. Up at the top the back of the headlight can
push the cable out of the desired path, as well as other cables too. Keep at it, you'll find a way. An
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addition to the previous thought is that a cable can also be too long. In that case it will kink in the
middle of its curve and be hard to pull, too. There's always something else to check.
#1189 Re- clutch cable. I had exactly the same problem (& also with the valve-lifter cable).I daresay
there is a proper way to lead them, but I took the easy option & bought new ones from Johnson's (Ads
in OBM).Just ask for whatever extra length you require, how much free play on the inner cable, and
where you want the adjuster situated, and they'll oblige - all for £12 per cable. Just remember if you
want the clutch cable adjuster situated where it's accessible, you may also be allowing easy entry for
water into the cable & thence the gearbox.
L #1331 My clutch ballrace is bit wobble I suspect wear on the ball. Some one know the exact
size of balls and is it easy to obtainable?
#1332 It is normal for the ballrace to be a bit loose. It is likely the race itself that is worn, as the balls
are very hard. I have one that a local expert filled with balls from a Triumph's similar assembly, it is
really tight. I don't think it makes much difference in operation, this bearing only keeps the chainwheel
centered in the clutch assembly and a few thou of movement should not cause concern. It gets most
of its loading from primary chain tension, when the clutch is disengaged. Check the race closely for
cracks, I had this happen once. Unless they are seriously worn, the balls are easier to install than
remove, so perhaps you could measure the ones in your race and try to find some a thou or two
bigger.
L #1322 I have a 1953 MAC which is experiencing clutch drag after about 5 - 10 minutes riding.
Once the dragging has begun, it is impossible to move away from stationary and all I can do is to limp
home. I have adjusted the clutch according to the book, but to no avail. It feels as if something is
expanding or warping when it gets hot. Could it be the plain clutch plates warping? The clutch is the 7
plate type for which Veloce Spares Ltd do not sell a replacement. However, would the individual plain
plates from the 9-plate type clutch fit?
#1325 Are all the clutch bits in good order? Thrust bearing OK? The clutch plates on the 9 plate clutch
are thinner - on the friction plates - but the plain plates are the same. Try some new ones as they are
likely to be the source of your problem. Even the thinner friction plates will work if you don't have the
correct 'thicker' type. Have you got a clutch lever with the right amount of lift? with standard levers
there is precious little lift and hence the clutch will drag more easily. Check for lost lift through the
system as wear can reduce the effective lift too. With a MAC you should be bale to achieve the
sweetest easiest clutch which will work easily and last too.
#1334 The brass that contains the balls is high tensile brass. If you fit a replacement bear this in mind
because if it is just ordinary brass it will give problems. some replacement parts today just don’t cut
the mustard and are dubious at best.
L #2166 Can anyone tell me the exact dimensions of a clutch back plate thrust pin ( part no.
C6/3 I believe) as fitted to a Venom please ?
#2167 Follow the clutch link on this page www.croesus-consultants.co.uk/v-tec/
#2168 These are 3/16" diameter 0.453" long.
L #2758 I have just stripped my clutch to investigate movement in the clutch chain wheel. I have
found approx 9 thou clearance between the clutch ballrace assembly and the backplate. According to
the manual this should be a light push fit. Has anyone else come across this problem ? If so how did
you overcome it? Will I need to weld up the back plate and then turn it down to size? What should be
the measurement for the ID of the bearing? Mine measure approx 2.927 inches.
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#2759 That bearing is pretty much free of any load, as it only moves when the clutch is disengaged.
Later Velos used only a skinny bronze bush in there, so make one up and use that, pressed into the
wheel. Or affix it with two part epoxy such as Devcon or J B Weld or a few tacks of arc weld.
#2763 While not sure of the exact damage (?) to plate, I can suggest 3 small bits of 4-5 thou. shim to
stabilize the race in position, then use LOCTITE, I have used the 'WICKIN' grade for all sorts of things,
including really sloppy gear fits on shafts on stationary engines, also substituting it for silver solder
when fitting ends on Veteran guard stays etc. It's Bloomin Marvellous stuff & I have never had it let go,
& I can assure you that the only way to unstick such a joint is to heat it up to a considerable
temperature at which point it can be pulled apart, (if you are lucky ! ) It should be an easy certain cure
to your problem, definitely better than center punching the inner surface of the plate, (which is
common !) although this would be an acceptable way of stabilizing the bearing into the correct
position instead of the shims. Assuming that you are going to use LOCTITE, it is imperative that the
ball race is sealed off with light grease, it is best to do this before fitting bearing, & then cleaning off
the outer mating surface with petrol/cleaning solvent to ensure a good bond with the Loktite. When
you get everything set up, lay a piece of light plastic sheet, (a good shopping bag will do ) on a flat
steel surface, then tap the bearing & plate flat to the plastic to get a perfect alignment, then use the
LOKTITE, failure to use plastic will see the assembly stuck to the steel surface!
#2765 The inner diameter should be 2.922 +0.001"
#2769 Beware the "light push fit" with the chainwheel bearing. In my experience this needs to be a
loose fit on the back plate otherwise the inner part of the race binds on the backplate when you
operate the clutch (due to the initial tilting action) and the big bearing ends up working its way out of
the chainwheel assembly in short time. Many of those that were a good press fit in the chainwheel but
too close a fit on the back plate have ended up being tack welded to the chainwheel to keep them in
place, whereas the solution was to find a friend with a bin full of old ones and swap him your new one
for a serviceable used one which is sloppier on the backplate (as I did over 20 years ago, and Peter's
bearing is still in my VMT). Check for cracks at the notches if reusing an old one. The notches are only
good for assembly of ball bearings - I've never met anyone who has been able to get the balls out to
renew them. My 69 Clubman has the bronze bush that Frank referred to - the factory used a bronze
ring on the backplate as well as the ring in the chainwheel so that it is a 2 part chainwheel bush. It is
renewable at a fraction of the cost of a "pattern spare" chainwheel bearing, and far less trouble!
L #2761 I have seen for sale recently by a dealer, clutch back plates featuring 6 thrust pins
instead of 3. Has anyone tried 6 pins. Was there any difference/improvement to clutch operation?
#2762 Fitting 6 pins was a suggestion from many years ago. In the Velo design pulling in the clutch
lever pushes the "frying pan" against the pins. They push the spring carrier, which starts to free the
plates which supposedly separate in one complete revolution of the back plate, a form of self servo
action apparently. It was believed therefore that drilling the back plate to accept 3 extra pins would
speed up the process of clutch separation even more. Don't ask me if it helps, mine has only been
modified like that for the past thirty odd years! I never could find the time to try three pins against six
with all the hassle of refitting etc, to test the theory of which was better. I've still got 6 pins in my
Venom racer and it works beautifully in the Manx Classic race, but I haven't bothered to alter the back
plate in my MAC! For Lords sake don't let him charge you extra for one with six holes, he'll make a
fortune selling less back plate and 3 extra pins!!
#2766I drill my back plates out to accept three extra pins, the theory is that the clutch disengages and
engages more evenly. The logic is sound, but I am not sure in practice whether there is any significant
improvement in clutch action.
#2767 I think that the logic is NOT sound, but I don't see that the use of six pins will injure anything. If
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you examine the cross sectional drawing on page 28 of the Red Book for 86 X 86 Velos, you will see
that the pins (3 or 6) do nothing but hold the inner surface of the spring holder parallel to the outer
face of the thrust race such that these parts collectively function as one unit. There is no rotational
movement between the two flats separated by the pins, (3 or 6). This can be verified by examination
of the flats upon which the pins press, which will show no wear. The lifting of the thrust cup does
appear to apply lift to one side (forward) of the front plate, which would cause axial movement of one,
or possibly two pins followed by the other(s) during the first rotation, but the pins always remain in
parallel, as do the flats on which they press. The initial movement would create a 'diamond' cross
sectional distortion of the normal rectangular configuration of these components, but there is no other
relative movement. During the first rotation the rectangular configuration is recovered as the spherical
interface between the thrust race and thrust cup moves and aligns. Similar to a three legged stool, the
addition of three more legs would do nothing to change the relationship between its top and the floor.
#2768 There is a nice feeling about the 6 pins, but wishful thinking I am sure, but if so go for it.
However the reasoning (?) behind it must go back a long way, & to be honest I was quite surprised to
note that in later years, 6 pins were actually used (?) , of course I am not very familiar with anything
past '46 having only once owned a Thruxton for a very short time, & the only late model stuff that I
possess is included in my 53 framed & gearboxed , 48 'Cammy' special. - But , for years I have owned
a NOS plate of a smaller diameter that only relates to the earlier models, possibly early 'K' series, but
certainly also of the early two stroke era. I have always viewed this as a bit of a curiosity, it is certainly
a genuine early NOS part that could have lain on a dealer's (Frank Mussett) shelves for years, so
what was this intended for, a KTT possibly ?, Frank certainly had a lot of KTT stuff over the years.
maybe Ivan Rhodes or someone out there knows the full story ?
L #2820 Laying in bed last night after closing down my PC, I realized that I had assumed that all
Velo owners are fully conversant with the workings & correct adjustment procedure of the Velo clutch,
the fact is that some of the inquiries that the site gets, may well be from first time Velo owners, - even
some who have bought a completely dismantled machine, & with a good chance of a clutch that has
already gone through all the stages of neglect, maladjustment & ruin. As long time Velocette owners,
it is our duty to make sure that these newcomers to our marque, fully understand what goes on inside
the clutch at all times. Les Diener used to say, 'The average clutch is usually simple, but a Velocette
clutch is an engineering device, & it takes an engineer's reasoning to keep it in good order' There is
no guarantee that a newcomer has engineering expertise, or the instruction book with the full detailed
adjustment procedure ! So I say, if this is your first Velocette, get good detailed, on the spot instruction
from a LONG TIME Velocette owner, and DON"T interpret slack in the clutch cable, as the necessary
running clearances inside the clutch !!! this is almost certainly the biggest trap, the start of clutch
problems, & the ruination of countless thrust races. Probably 99.9% of the site readers know all this,
but if you are of the .1% you really have to know it ALL! This sounds like mindless repetition, but we
cannot assume that all new owners know the score !
#2831 You are right to assume that I am a first time Velo owner. Though I have had the bike nearly 18
months this is the first time that I have had the clutch off. When I bought the bike the clutch was
almost OK but dragged a little. A new cable and re-adjustment of the clutch as per the manual solved
this problem. The reason why I stripped the clutch was to investigate the chainwheel movement which
was causing a variation in primary chain tension. I noticed this shortly after buying the bike but don't
think it has got much worse in 2000+ miles I have ridden it. It does mean the I have to run the primary
chain a little slack though. If there are any LONG TIME Velo owners within 50 miles of Carlisle that
would not mind me bringing my clutch for a second opinion please let me know.
#2838 In mentioning that the clutch 'dragged a little', you have described the initial symptoms that
leads to the Velo's, (or any clutch for that matter) downfall, the difference is that agricultural, ( BSA,
NORTON etc) clutches can withstand this sort of abuse, a Velo clutch cannot !. This is the price you
pay for having a lightweight clutch , that when properly set up will remain perfect for ever. One rule
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with Velo's is that you should never just pull the clutch in & chat to your friends, everything goes down
hill from there ! You have to educate yourself to snick into neutral at all times before stopping, - even
for the traffic lights if it looks like being a long wait. To this day I do this on any bike that I am riding, &
also when driving a manual vehicle, it's a GOOD habit for many reasons, not all to do with the Velo
clutch! The dragging clutch is , assuming that all outer clutch components are in good order, almost
certainly the end result of lost movement between the clutch lever & the little pin coming out the end
of the gearbox, but one must be sure that the springs are of the correct length & not stuffed to the
point where they cannot give full compression movement, & are 'bottoming'. As for the internal
components, I have variously filled the worn & elongated pivot hole in the crank lever with bronze, &
re drilled it, or found a better one in the old spares box. There can also be the result of the pivot bolt
not being adjusted 'snug', & the lever kicking to one side has the pin off centre, & wearing the side of
the contact point - I have made new pivot bolts, the old ones which I have seen worn almost half way
through. There is also the problem of a clutch outer casing that has been pinched at the steering
head, & has a small section that springs in & out under the pressure of clutch lever useage, this must
not be ignored ! Non standard clutch cables can also be a problem, no hint of stretch can be tolerated,
the reason why Velocette have always had their own heavy duty cable assemblies, which can last
virtually for ever. I have made up cables using modern Japanese clutch cable assy.s & they work
really good if properly made up. All the above needs a thinking approach at every point, don't ignore
even the smallest indication of lost movement.
L #3653 I have a small bag with 88 clutch plate inserts (C25-2) that I bought from Lou Branch in
Los Angeles in 1974 (?). Price marked on the bag is $11.44 :-) The material is not cork, looks like
Ferodo and in great condition. What dimensions should I size them to before pressing them into the
clutch plates? Any suggestions on how to size them? I plan on running a dry primary case.
#3654 If these are the original parts, they will be only slightly bigger than the square holes they fit into.
Just press them in to alternate holes, turn the plate over and fill in the gaps. This helps to keep the
plate central as the inserts are then slightly oversize on alternate sides. When all in, assemble all the
plates in your hands, then squeeze the whole lot in a vice a little at a time turning the clutch in the vice
as you go. This will get all the inserts level with each other. It may pay to wear a face mask as I don't
know if these may contain asbestos. Should be OK running dry, but don't expect too long a life from
the chain ( or have you belt drive?) Good luck, Bob PS older clutches with 3 friction plates had thicker
inserts, The fact you have 88 suggests yours are the thinner 4 friction plate sort.
#3658 Yes they are slightly bigger so I'll just press them in (I'm sure easier said than done!)....I'm
refurbishing an MSS for city use and feel good chain lube should be sufficient for the lower speeds
and short trips.
#3660 In years gone by when Velocettes were in daily use, we had the ' 88 inserts' & they were
seldom replaced in normal use, as to chain lubrication, the primary case always seemed to be filled
with oil from the engine mainshaft leakage, & at times lubricating the rear chain with the surplus,
rather than needing more oil ! This situation varied with the model & the amount of wear/use. There
was also the problem (?) of washing the model every Sunday morning with the kerosine brush & the
garden hose, & this procedure invariably introduced water ( & kerosine), into the chaincase via the
openings , the result, after a few weeks there was certainly a pool of watery gunk at the bottom of the
primary case, with the lube (?) floating on top ! - If you were into riding through shallow creeks or
flooded roads, I had a local main road that often had 6 inches or more of water running across it
after a Winter downpour, - there was also the water intrusion problem. The answer to this was to fit a
drain at the lowest point of the outer primary chaincase, & I don't doubt that many of you have bought
a Velo with this drain already in place. (did any later models have this fitted ?) This meant that you
could drain the case at intervals & at least give the chain some good fresh oil ! As for clutch slippage
problems with the old type inserts, I can't recall ever having any, the clutch seems to keep itself free of
oil by centrifugal action, even if it became overfull, maybe we were lucky in those far off days, or the
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oil & the (asbestos ?) composition that the designers had arrived at from the 'suck it & see' method
was quite efficient, whatever, in years of Velo riding, - & side carring I can't ever remember having
clutch slippage problems that related to oil in the primary chaincase, - Maybe I was just lucky?
L #3714 What is the trick to removing the ball bearings from the clutch ballrace assembly? Is the
opening crimped in any way once they are all installed or do I just need to apply more pressure when
removing them. It feels like a piece of foreign matter is caught in there and flushing doesn't remove it.
Any suggestions are appreciated.
#3716 I have never found a way of getting the balls out of the ballrace, after all, they're designed to
stay in there! I would suggest however that if you can't sort out the problem by flushing and blowing
out with an air line, then the chances are that the races themselves are damaged and the only
solution will be replacement.
#3731 I have stripped a big race bearing. It was a little loose, and the problem was to line up the two
half-holes on one ball. I don't remember how I did it which normally means it wasn't too difficult. If the
balls are 3/16", this is 0.1875". An oversize 5mm ball would be 0.19685" but I don't know if you would
go through the hardening at that figure. A friend did grind oversize, just a touch, but used the original
balls. He Loctited the bearing into place hot, which tightened it up, but either he calculates better than
I do, or he was lucky. Seems it worked. I could get oversize balls but the price could be horrific- how
much does that bearing cost now?
#3742 I have a Venom with the bearing in the clutch plate which refuses to stay in place. The last
attempt to Loctite it in using "bearing fit" did not work. I have measured the bore of the chain wheel
and the outer diameter of the bearing and these are size for size at 3.812ins. i.e. no interference fit. I
am loathed to purchase a new bearing or chainwheel as I don`t know which part is incorrect. Does
anyone have the correct dimensions for both parts? Is there an accepted "fix" for my condition other
than the one in the BMS book by tack welding which is rather over the top as it buggers both parts up
for the future. The brass bushing solution seems a way out. Does anyone have information on this?
Was it a factory solution fitted to later models and does it fit in place of the ball bearing and does it
work? A brass bush will be considerably less expensive than an £80 ball bearing. Here`s hoping for a
solution to get the bike back on its wheels on the road.
#3745 You say that tack welding buggers up both parts. Here's another thought: With an OD size of
3.8 inches, the bearing/bore interface has about 12" of circumference. A tack weld has about 1/4" of
length, so four of them will use up about one of the twelve inches. Given that later removal of the
bearing likely would destroy that bearing, OR the chainwheel, and given that the chainwheel sprocket
is normally subject to damage from wear, what do you have to lose by welding? If not welding, how
about a two part epoxy such as JB Weld? I was told by Ed Gilkison that the OD of the bearing was
tapered such that when the smaller diameter was pressed in to the chainwheel it would tighten up.
#3750 Between the chainwheel and the bearing, I'd say that if one is worn, it is more likely to be the
chainweel, as it is softer. As you probably know, if you suspect there is a taper, try fitting first from one
side, then from the other. The taper would be more likely to be on the chainwheel, if there is one, but
in mechanics no possibility can be neglected.
#3752 Check for adequate clearance between the ID of the inner and the OD of the prongs of the
back plate - I tell you if it is too tight here the bearing will work out of the chainwheel no matter how
good a fit on the OD. Don't know if Dai has the factory tolerances but the inner needs to be a sloppy
fit (excuse the technical jargon) on the back plate. As to the big bush in lieu of expensive ball bearing
option, I suggest you find a friend with a late model machine and measure up - I loaned the
chainwheel and backplate from my 69 Clubman to a friend last year and for about AUD$25 he had a
bronze sleeve for the backplate and a big bush for the chainwheel manufactured to the same sort of
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tolerance as my partly worn example. When I got the bits back I threw the clutch together and the
original 1969 big bush is still there and working fine. I'm not aware of it causing problems after the
factory changed from expensive ball bearing to cheap bush - the only time it does any work is when
the clutch is disengaged anyway. I know of another 69 Clubman that has never had the clutch apart,
and it would certainly have the same clutch parts as mine, being only one engine no. apart.
L #3927 My 1970 Venom Clubman clutch slips, so I need to adjust it. I made the proper tool, but
the inner and outer race both turn together when I rotate the rear wheel. The manual describes a
technique where you place the trans in gear, and rotate the wheel the opposite way. This seems to
take advantage of differing rotation speeds of the two parts. My question is this: How fast does the
clutch adjust with this technique? In other words, using this alternative technique, what is the ratio of
wheel turns to the standard technique (when it works). Also, my bike only has about 200 miles on the
clock from new. Should I pull the clutch apart to see what's going on? (I'm not anxious to, but will if
recommended.)
#3928 Initially, depending on the degree of mal-adjustment, you may need to engage top gear and
with engine turned against compression a complete rotation or two of the rear wheel may be required.
(for safety sake, remove the high tension lead from spark plug). After clutch has been properly
adjusted, some miles racked up, and you are making a new adjustment to correct for settling, etc., 1/8
- 1/6 of a turn of the rear wheel will be sufficient find that I must turn the wheel forcibly and swiftly to
move the clutch sleeve without pulling the engine thru compression. I've a 20 spring clutch in my
Thruxton.
#3929 The adjustments are made in neutral. Make sure the clutch cable is removed from the clutch
lever. We pull (or push) a sidecar and do not have clutch problems or the need for frequent
adjustments.
#3931 Select an intermediate gear- 2nd? - not top cos then the clutch and final drive move together.
Put peg through final drive sprocket into a notch on the spring carrier - you may have to push back
and forward a bit till they align . ( Pull in valve lifter so the engine can turn freely .) Push forward
maybe half a turn of the rear wheel. Remove pin and try to see if the clutch grips. Repeat until it does,
then do adjustment as normal.
#3932 The lower the gear the greater the differential movement between spring carrier and outer plate
of the clutch - in top gear there is no differential movement. Except I'd take the plug out during this
operation as I find it hard to reach the valve lifter from a position squatting behind the back wheel. If
reading from the Haynes Manual, beware - the edition I have gives the wrong advice on which way to
turn the wheel. If doing it in neutral turn the back wheel forwards to create greater clearance between
thrust pins and spring carrier and hence cure a slipping clutch. If having to do it in an intermediate
gear then turn the back wheel backwards to achieve the same result. It's possible that after you adjust
it you can do future adjustments in neutral because a clutch that is badly slipping won't have enough
friction to hold the front plate still while the spring carrier turns. But in other cases the damn things are
just tight and you have to use the intermediate gear technique all the time.
#3934 Had exactly the same problem last night on my Venom after reassembling the clutch. I found
about half a revolution of the rear wheel with the transmission engaged took care of both parts turning
then I could adjust in the normal manner, i.e. out of gear. Remember the cable.
#3968 Thanks to all for providing advice on the clutch adjustment. Once I used the "in gear, rotate tire
backwards" method to break it free, I could adjust it as normal in neutral. I was amazed that 1/8 turn of
the rear wheel produces nearly 1/4" of cable play, so it doesn't take much once your in the right zone
on clutch adjustment. In any event, the clutch doesn't slip or drag, and shifting is great.
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E.2. Gearbox -
L #9 Being new to my 1956 MAC, what are safe max upshift speeds on this machine? I have
been shifting at about 15, 30, and 40 miles per hour, taking into account the relative accuracy of the
Smith's Chronometric Speedo.
#10 Proper shift speeds for a MAC are 'before the valves bounce', preferably. The mph would
depend on your gearing. As Velo's are fairly unburstable, I don't think it's much of an issue to worry
about. I usually shift when the model is no longer accelerating under full throttle. just one man's
opinion.
#12 Torque is fairly low down on the MAC, and on the wide-ratio gearbox, buzzing it won't do a lot.
3rd. is at 75%, remember. Always remember, don't slip the clutch
#14 The ratios are as follows with the standard 21 tooth final drive sprocket: 1st- 14 to 1, 2nd- 9.6 to
1, 3rd- 7.3 to 1, and 4th is 5.5 to 1. These don't seem to be particularly wide ratios. I do find, though,
that when I shift at an indicated 40 mph, speed drops enough so that I need to run a fairly wide
throttle to build up acceleration again to cruising speed.
#16 Over here, we work out gear ratios as percentages, so what you have is the 10- box, which has
the wide-ratio gears the same as the MSS. I don't think the actual pinions are the same, I think the box
is a bit lighter being drawn from the MOV rather than the "heavy" bikes. This on the MSS is called the
14- box, and not all MSS had it, some had the Venom 12- box A 5.5 ratio on a MAC is unbustable,
that is, you can rev as far as you like, you are not likely to get into the red zone. But on a 7.3 third, 70
mph is already too much for sustained use, 50 in third the same, and 40 in 1st. is about 7,400 rpm- we
are talking racing speeds here. You tell us how many rpm you consider reasonable. To give you an
idea of how wild a Thruxton is, the high 4th. gear (4.4 on a 20 tooth sprocket) is to try to limit revs in
4th. gear- usually we can get to the maximum allowable, 6,200, in all four gears without trying too
hard, which is about 105mph in top. On the Mac, you could go to 20mph in first, 30 in 2, 40 in 3 and
you would be revving to about 3,800 or so in each gear. I don't know peak power on a MAC, but it is
likely to be around the MSS figure of 5,000 rpm. You would have nothing to gain revving beyond
5,000.
#288 Judging from the way that ZUMAC ran up the hills in top, I think that a 20 tooth gearbox sprocket
would improve things on both your S/A MAC and Zuma's iron head rigid. The Book says yours came
with a 21, ZUMAC with a 19. BTW Dai Gibbison, your spec page lists all 86mm 500 Velos as having
18T gearbox sprockets as standard - the Red Book sez VMTs came with 20. Of course, it also lists no
standard sprocket at all for scramblers.
#576 hello, a 21 tooth sprocket is very very tall, and a bike would struggle to pull it. my venom has a
19 tooth fitted and it works spot on. I fitted a 20 tooth and it was too tall. fitting a 21 tooth would be
way too tall for a 500 and a 350 would never pull it. I guess the demand for a 21 tooth is next to zero,
that’s why they are probably not listed.
L #197 Just a quick comment on the use of 80/90 gear oils in Velo gearboxes - DON'T!!!!
Especially if they are Hypoid type oils - REALLY DON'T!!!! The recommended oil for a late Velo
gearbox is a 20W50 multigrade engine oil - Hypoid oils will attack the bronze bushes in the box and
cause eventual seizure - the sort of increased friction you can do without.
L #199 First comment is to correct the statement re non-listing of c.r. gears for pre-war
MAC/MOV. When iron MAC first came into the family in 1978 I copied a parts book from old Joe at
Allparts, Sydney, (sadly no longer trading, although sister company, Modak, in Melbourne is still
going strong and does excellent mail order service for things like 3/16"x3/16" rollers for clutch thrust
race conversions, .001" oversize rollers to revitalize tired drive side mains on pre-war Velos etc).
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Anyway this book is marked "12/39 G.D." and lists B6/2AS sleeve gear (bushed) 16T (standard ratio)
& below that B6/3AS ditto 17T (close ratio). These pair with B86 layshaft driving gear 28T (standard
ratio) and B86/2 ditto 27T (close ratio). Now, Mick T's MAC definitely has the 17/27 combination (I
counted the teeth when he had the layshaft with the broken 2nd gear on the table at the January
Club Meeting here in Perth) and they are as rare as... easiest way to go close ratio is to get a
standard ratio MSS sleeve gear and driving gear, grind down to suit MAC/MOV width, then make
suitable changes to the various spacers, sleeve gear nut etc of the clutch so it will still operate
correctly, as I think the protruding threaded portion of the sleeve gear will be different length to a
MAC. Oddly enough, the MSS parts book of that era lists 2 ratios, the 17/27 (BK8/2AS & BK86/2)
being "standard ratio" and the 16/28 (BK8/3 & BK86) being listed as "wide ratio"!!! At least this
explains why there are a lot more 17/27's around for MSS gearboxes. Only other source of new c.r
gears for Velos I've found are the 18T KTT sets available from Bob Jolly in Adelaide, but these would
need grinding to fit a MAC and I'm not sure we need 3rd and top to be THAT close. If enough of us
got together we could have sets made in Perth from EN36 - enquiries have been made with the man
who makes the gears for most of the V8 Supercars (Ford and GM Holden tintops), but price for only
2 sets is prohibitive. If I'm swamped with positive rehouses we'll include 2nd gear layshaft in the order
as well, to help get Mick back on the track and to fit to our racers to ensure that bogey stays at bay.
#207 I for one would be very interested in c.r. gear set for MAC. To be viable I guess they need to
cost less than the swing-arm grind-down method. I haven’t been able to check how easy(how hard?)
this would be as I don’t have a later g'box to look at...(I have owned three different swing-arm 500s
but now there's only the wee-mac). Maybe someone happens to have both types in bits and could
compare dimensions. Many years ago when I first had the Mac, someone told me that c.r. gears were
available in Sydney. I wonder where they ended up, or if the info was even correct, seems it may have
been if the parts were once listed. I cant imagine many Macs would have been other than 'standard'
ratio at the time when they were new, as for a general- purpose machine and perhaps with a pillion as
well they would be struggling with anything else. I'm not under any illusions about making the Mac
into a 'racer', but for the use I give it, the c.r. box would be a real improvement.
#208 CR 27T layshaft gears (B86/2) are available new old stock from the UK Velocette Owners Club
spares scheme, cost £ 8.30 plus postage. I have just bought a new 17T B6/3AS sleeve gear for £
36.00 plus postage. The Velo dealer that I bought it from probably has more; if any one is interested
please e-mail me direct (not via the group) and I will check this out and get back to you.
#209 Strangely enough I think you will find that B86/2 and B3/3AS was originally listed for the GTP as
it appears in the GTP spares book but not the MAC spare parts book.
L #265 in FT319, the letter from Mr John Watson is very interesting for me. Because the gear
box shell I ever look at in the autojumbles have problem there. Good one seems to be non-existing.
In the letter, He made the oversize retaining ring with the left hand thread. I would be very interesting
to hear that is such a conversion is expensive business (I have to send out to the engineering firm in
UK)? Someone out there has ever done this? Where, how much was it or do you know how to
contact to Mr John Watson?
#266 Identification of gear cam plate I supposed to have cam plate from prefix 4. But no parts number
on it. I do not know I can use it for the rigid MSS shell, etc. My MOV racer is from totally bits of parts
and still it is. And I am no way to test it.
L #556 During a discussion with Don Chesson this morning the subject of a weakness in the
normally robust series 12 gearbox came up. Don is Perth's elder statesman of Velo folk lore, having
begun his racing career on a Velo just as WW2 was ending. If you refer to any list of bearing
numbers for Velos you will see that all the sleeve gear bearings B22 are the same from MOV to MSS
to VMT. Same for the layshaft bearing B22/3 or BK22 for cammies - one bearing fits all. But when it
comes to the mainshaft end cover bearing the series 12 shares its bearing B23 with the MOV/MAC
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whilst the iron MSS and cammies use BK23, a larger bearing. Consequently it has been known for
this bearing in the series 12 gearbox to fail or for the relatively thin bearing housing to crack, with
disastrous results. Don has recently obtained a butchered series 12 end cover and is presently using
it to make a pattern to cast a few series 12 endcovers with enough meat around the main shaft
bearing to take the BK23 type bearing of the iron MSS and cammy style. The strange thing is that I
can't recall ever reading of this weakness in the design and have personally never had a problem in
over 25 years of flogging VMT457 around the best biking roads in Australia. But I've seen the results
and know of a couple of people who are currently looking for series 12 endcovers to replace broken
ones, so this isn't a figment of someone's imagination. The recommendation is to replace that little
RLS4 in the endcover of your series 12 before it lets you down. They are cheap, readily available at
bearing shops and easy to get at for replacement. And while you've got the endcover off, pull first
gear off the mainshaft, get your Maglite and take a real good look at the gears, particularly the load
bearing side of the teeth. At this age, there must be many chatty gears still doing service inside the
trusted series 12 gearboxes of our Velos. I've had 3 apart in the last year and I was hard pressed to
make up one "good" set of gears out of the three of them, such was the state of the hardening,
particularly on first second and 3rd gear layshaft and the double sliding gear. Not surprisingly the
gears with the most teeth seem to survive longest! Has anyone else out there had a series 12 main
shaft end cover bearing collapse?
#558 I too have a stack of #12 gearbox end covers that are cracked around the mainshaft bearing
area. Two of them I know are the result of gearbox blowups. And the good ones mostly have loose
fits in the bearing bore. I'll bet if you walk up to any Velo and yank in and out on the countershaft
sprocket you will find many with end float due to a loose mainshaft bearing bore. On my VMT I have
eliminated the circlip and use a sleeve that is held in by the end cap to hold the bearing in tight.
Haven't had a bearing itself go bad. All in all a good gearbox though and easily serviced. Count me in
on one of the new castings
#559 VMT 457 had a sleeve behind the inspection cover to locate the mainshaft bearing (in lieu of the
circlip) when we bought it in 1975. Rebuilt it with new bearings in 1982, ignored the onset of tooth
wear and got another 20 years out of it. Oil changes only and made sure water was kept out (using a
distributor cap rubber on the clutch cable entry - a must). When rebuilding as a 5 speed this year, I
noticed that the bore of the bearing housing was threaded, same as iron engine gearbox endcovers.
So I had a threaded sleeve nut made up, like the pre-war gearboxes, and now have positive control of
end float. Sometimes, winding back the clock can be an improvement!
L #562 During pull-down for rebuild of my 68 Venom Clubman I discovered that the gear change
internal assembly of two yokes (GC56), connecting link (GC58) plus clevises was missing in my
gearbox, replaced by a short length of twisted strip steel riveted at each end. I assumed this was a
temporary bodge fitted by some previous owner, until I ordered all the bits and pieces from a supplier
and received - a short length of twisted steel with rivet holes at each end! Did Velo decide, after years
of the complex assembly, that a steel strip was just as good? Should I chase the 'real thing' according
to the parts book, or refit its simpler alternative?
#563 The piece of twisted steel works fine and there is no real need to replace it in normal use. If you
want to reduce play in the linkage though I would suggest that you obtain a pair of 1/4" "Rose" joints,
one with a male thread and one with a female thread, and an appropriate locknut. Screw these
together and adjust to the same length and orientation as the ends of the piece of twisted steel. It may
be necessary to shorten the threaded end on one or both parts in order to get the required length.
Lock the assembly together with the locknut and a drop of loctite if you want to be doubly certain of
things staying together and use a couple of button head Allen screws and nylok nuts to replace the
original rivets and Bob's your uncle. If you're using a rearset linkage you can replace the external
clevis
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#564 The length of twisted steel with pins inserted can easily be replaces by 'rose' joints (or Heim
joints), as I've done on my VMT. The twisted steel is fine for a while, but eventually the pins wear out
their holes and sloppy gear changes result; a shame on such a nice gearbox. A retrograde step from
those early robust linkages, just as John Jennings found with the earlier end covers! Imagine finding
a length of twisted steel in there, surely a bodge!
L #574 In the following for gear shaft nut please read sleeve gear nut. I've two clutch spring
holding assemblies, #1 is a one piece unit, max depth 5/8", with four sets of four spring holding holes,
with springs presumably 3/4" long when new. #2 is a two piece unit max depth 7/8" with a separate
spring holder containing 16 equidistant holes. No springs. When I ordered a set of clutch springs for a
7-plate clutch from VSL they turned up at 1 1/8" long. I've only one gear shaft nut which is 7/16" long. I
can get the nut on to set #1 and the clutch works in this mode; but to try to get it on to set #2 I'd need
to be Britain's Strongest Man. Is there a gear shaft nut with a longer thread, or have I been sent the
wrong length of new springs, or what? Both sets would seen to fit behind the gearbox sprocket with
sufficient clearance. Why is a 21t gearbox sprocket as indicated in the Spare Parts Catalogue (SL
94/1) not listed in any of the current main suppliers catalogues(it is listed under Viper bits);has it been
found to be unsuitable? Finally, the gearbox nut locking piece. When countersunk mine has the
thickness of a fag paper, so what does the little 1/8whit csk screw into?
L #650 Please someone tell me the parts number of the gear box end cover ball bearing for
prefix 5.
#651 I am not familiar with all of the various gearbox serial numbers and their potential
similarities/differences. I can tell you that this bearing in my '50 MAC is a FAG LS5. Readily available,
at least here in the States.
L #681 Could you please suggest any remedies for an oil leak from the kick-start ratchet box, it
appears to be coming from the shaft. Is there any way of fixing it apart from buying a new box?
#682 Try here www.velocetteowners.com/qanda/gb008.htm
#683 I used a 19-27-4 single lip seal obtained from Bearing Services Ltd., fitted into a 4 mm deep
recess carefully bored in the outer face of the kickstart housing. The shaft was carefully deburred and
its diameter cleaned (if it's pitted or damaged the seal will not last long) and eased through the seal lip
so as not to damage it with the flat for the cotter pin. The lever was fitted as normal, being careful that
it didn't slide back through the seal during assembly, and the whole assembly then fitted back into the
end cover as per the manual, but with a thin smear of Three-Bond silicon sealant on the mating face
to seal it. This part of my machine has been totally oil tight ever since.
#685 There are people who will do an exchange or conversion with an O ring seal fitted to stop the oil
loss. Colin East on 01522-810029 does, I'm sure there are others too
#686 Some years ago, I tried to cure such oil leaks and followed the advise found in FT Hints and
Tips. So I get the housing machined to fit an O-ring. This proved to be an improvement for a while, but
seepage came back, although less than before, as 0-rings are not designed to cope with repeated
rotations, and they wear. Especially if there is some wear in the assembly. I'm now considering to fit
an oil seal instead.
#694 A quick remedy to ameliorate the oil weep from the kickstart housing without recourse to
machining it, is to epoxy-resin a thin oil seal 1x3/4x1/8 imperial obtainable from a good bearing
stockist for maybe £2.00,to the outside of the housing cover over the kickstart shaft. This may sound
a bit of a bodge but it does work without interfering with the kickstarter engagement.
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L #1086 Have some of you experienced another way to secure the sleeve gear bearing retaining
nut than butchering the g/b shell, each time at the same places, which I hate to do ? Is Loctite safe
enough ?
#1088 I've a very worn thread on my gearbox plus a worn sleeve gear bearing nut on my Venom I've
used Loctite but a retainer not a threadlock type. With normal threadlock I've had a problem, but with
a high strength retainer I've experienced no problems, though I must admit my threads are very worn.
I might also add I've had no difficulty in unscrewing the nut after I've used the retainer.
L #1969 After my 500 racer jumped out of 3rd gear several times at the last race meeting, I have
the gearbox apart. (And the road venom's gearbox for comparison) It runs a tt top gear and std 1st
gear. 1) The tt top gear with the sleeve-gear dogs looking very sorry. Does anyone out there have one
available ? 2) Any opinions on using a std sleeve gear plus tt 1st gear ?
#1974 You can use any sets of gears from a heavyweight box provided the total sum of the mating
gears on the main shaft and lay shaft add up to 44. There was an interesting article published by
Bruce McNair in Fishtail some years ago, which thoroughly analyzed combinations of using Prefix 12,
12R and 14 ratios. Unfortunately I cannot tell you which edition of Fishtail it was published in. If you
get desperate I will scan the article and send it to you. You can therefore play with gears to ensure
that the engine stays within its power band for any particular combinations of gears. John Jennings
from Australia also developed a spreadsheet that calculates RPM and speed in gears. If you want I'll
check with John to see if he minds me sharing the spreadsheet.
L #2218 I have a gearbox which is literally in pieces. I have the KSS spares list to identify parts
and the owners manual but need more info to assemble the parts. Is there an exploded view of a
gearbox to help with assembling the selectors and gears. Any advice appreciated.
#2222 The assembly of the MkII gearbox is largely similar to the VM prefix 11,12 or 14 boxes. You
should also have a look at the Venom service manual - still no pictures though! I can't think of an
exploded view. Anyone else help?
#2224 Thank you I have the Red Book and Bruce Mainwaring published book.
#2223 Mike, I had the same situation with my gearbox for the KSS, a couple of bags of rusty things
and a gearbox housing !! I searched all over the place to find a proper assembly drawing for the box,
and although not perfect, came across the following............ "service series No 11" from the magazine
'MotorCycling" dated 11th June 1953. It's entitled "Gearbox restoration routine for the MK11 348cc
overhead camshaft KSS and KTS Velocette" It gives a pretty good exploded view of the box, I found it
useful in conjunction with the KSS service manual. There are two other parts to that service series,
one from April 30th 1953 covering the restoration routine on the engine, and the other from July 16th
1953 covering the restoration of the cycleparts. All the articles cover mostly what is already in the
service manuals but include other small tips and those very useful exploded drawings. All these can
be had through the Classic Motorcycle as photocopies for a couple of quid or eight.
L #2376 I have a series 12 gearbox end cover with damage to the mainshaft bearing support. I
need to build up with weld and then machine the bearing housing. Can anyone give advice on the
appropriate weld material or method to build up the damaged area please.
#2378 A more expensive but permanent solution is available from long time Velo fettler Don Chesson,
here in Western Australia. Don has cast up 3 or 4 series 12 end covers with the area around the
crappy little 250 sized mainshaft bearing beefed up to take a slightly larger ball bearing - not as big as
those used in the pre-war heavyweight gearboxes but a better thing just the same. Phone him on + 61
8 95731286 if you want to discuss price and mailing costs with him. We are GMT + 8hrs, just so you
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don't phone in the middle of the night.
#2381 Here's a little caveat while working on your gearbox: A friend who shall remain nameless had a
loose locking ring at the back of his gearbox, the 'punch' method having failed to secure it properly
(and who would be surprised after a 50% horsepower increase!). He logically decided to Loctite it in
place, problem solved. During our 'British Singles Run' the other weekend, (and yes that was my
squish head Venom clubman two-up, passing two Gold Stars on a fast run -thanks Dave Smith), said
fellow noticed gearbox oil exiting the 'box at the clutch side, and he can tell this as he has a belt drive
primary. Another primary strip down, and lo, the excess Loctite had pooled and blocked that little drain
hole at the bottom of the bearing assembly; it seems to be there for a reason! What's worse, when he
tried to remove the locking ring, he found that the red Loctite is the type that really doesn't want to
come loose! One buggered ring. That's lesson number two, or is it three?
#2384 Probably teaching my Grandmother to suck eggs here, but a great way of removing Locktite
secured bearings and threads is to play a gas torch over the area. Long before you do the metalwork
any damage - the Locktite will let go. Parts should be separated while still hot.
L #2612 I am in the middle of restoring my Venom back to a standard footrest and handlebar
arrangement from the Clubman guise it sported previously (rear set footrests and swept back
exhaust). I fitted the new (standard) foot rests last night, and was surprised to note that the folded kick
start position seems to interfere with the right leg. Now I know there are two types of kickstart crank
(my understanding that the clubman/thruxton crank was different), but I am unsure of which one I
have, and whether a different crank would provide additional leg clearance. How can I identify the
crank that I have? Would another crank provide a worthwhile difference to leg clearance?
#2613 There are three types of kick-start cranks fitted to spring framed Velos: BK12/5 fitted to prefix
MACs with prefix 11 gearboxes BK12/6 fitted with spring foot piece retaining blade BK12/7 fitted with
spring plunger foot piece retainer If you used rear sets previously your kick-start is either BK12/3 or
one of the others that has been suitably modified.
#2614 If you used rear sets previously, your kick-start is either BK12/5 or one of the others that has
been suitably modified.
#2617 Allow me to offer an alternate answer for the part number impaired: I have S/A MAC, Venom,
and VMT in the garage. There are three different S/A kickstart cranks, as follows: Early S/A MACs
with the narrow gearbox (prefix 11) used a crank with approximately 1-1/2" of offset. You definitely
don't want this one. Venoms, VMTs and later MACs with prefix 12 boxes used one with only about
3/4" of offset. There are two styles of these, the later one has a ball and spring detent and allows the
pedal to rotate inward, away from the ankle. The older style has a flat spring and the pedal points
straight forward. This style was used (up) on some later Clubman and VMT models, but some
judicious grinding will allow the pedal to rotate inward. This modification has greatly reduced the
kickstart ratchet noises when Zuma shifts 2MAC.
#2618 My kickstart is the one with the flat spring. Since I have just had the thing chromed and bought
new shiny stainless bolts and spring, the "judicious grinding" option looks like the approach to take. I
was blown away with the news that the spring type rotates inward. I checked all of my velo books and
not one shows the pedal rotated into an inward facing position. I never realized. Mine is a 1963 model,
which according to the records was built as a VM.
L #2833 The gearbox in a racer I've been working on tends to miss the upshift from 2nd to 3rd.
It’s a Thruxton engine in a 60s springframe with standard gearbox with the close ratio set installed.
I've stripped the box to bits several times, but have not found the cause. The rider is an experienced
one, so I place the blame on the box, not the rider. It doesn't happen on every attempt, but with
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sufficient frequency to be a problem. The only thing not standard inside the box is the linkage, having
been changed to a short rod with heim joints, in place of the pressed steel plate that normally
transfers the movement. The shift forks are straight, and the shafts are shimmed to minimum end
play. I did try deepening the 3rd gear slot in the shift plate, with no change. Any suggestions as to why
this is happening, or any suggestions on where else to look would be appreciated.
#2834 I have the same problem on my Thruxton. It has been suggested to me by another club
member that the problem is due to wear in the Striking Pawl ( doesn’t rotate the camplate far enough
for the indexing pawl to drop into the third gear notch). As I'm pretty busy workwise, I have learned to
live with it and take a couple of stabs at getting 3rd gear if necessary. Usually however I can get the
gear by giving the lever a good sharp prod. I think this gives the camplate enough momentum to
rotate far enough. I can see why this wouldn’t work on a racer though.
#2841 I think that you will find that whoever suggested the pawl not engaging properly it spot on, this
is one of the most common causes.
#2844 I experienced similar problems, and several comments offered by Mr. Ed Gilkison were
conceptually reasonable. More to the point, implementing his suggestions resulted in a gearbox that
now shifts accurately and reliably. The first issue relates to the internal actuating lever itself
(apologies: I don't have my parts book in front of me, so my exact nomenclature is probably off), and
in specific, it's figure-8 shaped hole. The extents of this hole limit the travel by virtue of coming up
hard against the pin on which the cam plate and indexing hub pivot. With all of the gear shafts and
dogs removed, I could observe when actuating the foot shift lever that the cam did not fully rotate to
the next indent position. It is important when doing this to put a load on the cam plate, since you will
otherwise observe the misleading result that the cam plate rotates further when there is no load
placed on it (I just applied pressure with the palm of my hand). By slightly grinding the extrema of the
figure-8 shaped hole, I was able to get the cam to fully rotate to the next index position when under
load. This required enlarging the hole by about 0.040", noting that different amounts were required in
both the upshift and downshift directions. Grinding away more than necessary is clearly
contraindicated. In doing any of this, it is first important to carefully inspect all of the external linkage
elements for wear or play, and insuring among other things that the foot shift lever does not bind
against the exhaust pipe (or anything else). Ed also noted that polishing the edge of the cam plate
itself helps quite a bit, a notion that apparently was brought to his attention by Graham Rhodes. In my
case, this definitely helped. I also noticed that the point on the indexing pawl was worn considerably,
and the spring seemed a little weak. In this case, it was easy to simply replace them. The actuator
pawl and indexing hub were also worn, and I replaced them as well. In terms of the former, both the
teeth and the pivot hole were worn, which was clearly obvious when comparing them with the
replacement. All of these features conspire such that the cam plate does not fully rotate as desired. In
the end, I now have a gearbox that works exceptionally well, and unquestionably shifts more smoothly
than before. Parenthetically, I found it slightly humorous to read in my original owners manual that
none of the parts comprising the actuating system have ever been observed to wear or need
replacement. This was certainly not true in my case.
#2850 Missed Gears ! I had loads of problems with my racers last year - I ended up getting a 5 speed
cluster for one of them - which did not turn out easy to get going properly, but eventually provides a
delightful set of ratios. It turns out that the quaife cluster has _much_ tighter tolerances than the velo
clusters ... and that most of our gearboxes are running with a very sloppy fit for many of the parts, but
still shifting ok. This is, of course, in line with the standard velo factory policy of rejecting as few parts
as possible ! The moral of the story is that your gearbox does wear quite considerably, but you will not
notice it at first, but when you do, and you fix the first problem you find, you will also find that a
number of other parts are worn - like the shafts, which bend when you use the power ! (even a racing
viper can do this !) So, if you upgrade to a quaife cluster, be prepared to replace few remaining velo
parts too !
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L #3074 Being fed up with the brown burnt oil stain on the downpipe I intend to fit an 'O' ring in
the kick-start ratchet housing. I know we've covered this thread before, but I'm at a loss to find the
responses. I know some of have already done this mod and that a standard 'O' ring is available. Can
anyone point me in the right direction for the 'O' ring and dimensions of the groove to be machined in
the housing? Secondly I'm in the process of tidying up the Velo' and carrying out those little bits of
maintenance before the summer season. As part of this I'd like to tidy up the oil lines and petrol feed
pipes. Does anyone know where I can get some nicely made up steel braided pipes for a Venom or
where I can get the appropriate fittings from somewhere so that I can do the job myself ?(UK, West
Midlands area)
#3079 HMP Grease in the kickstart housing stops the leak and is cheaper. Mine has lasted 18 months
so far.
#3088 Forget 'O' Rings; for them to work they need to be retained and that involves fine machining of
grooves etc. Instead, fit a proper Oil Seal as described by Tom Ross in FT234. He gives a National
No. 240735 for the seal and maybe this means something to a bearing supplier. Personally, I use an
LE Primary Shaft Oil Seal (Veloce Part No. LE431) and machine the Kickstart Housing about
0.020"dia. undersize as the seal is rubber coated on its outer diameter. If you have difficulty pressing
the greased seal in after removing all burrs then turn off another 0.005"dia. and try again. The 21mm
ID of the seal is a correct fit for the Kickstart Shaft. This would be a good opportunity for you to join
the LE Velo Club (What! you don't have an LE? How many would you like?) and enjoy their truly
delightful "On The Level" magazine which averages more technical articles than most club journals.
Failing that, the number marked on their LE431 is: W11907915R21/29. Basically, the seal is 29mmOD
x 21mmID x 5mm thick. For your braided hoses try: "AutoHose", 7b Bagnall Road, Milton,
Stoke-on-Trent, ST2 7AY Tel: 01782-542486; though you will have to make up the copper/brass
unions at each end yourself.
#3091 I used a 19-27-4 single lip seal obtained from Bearing Services Ltd., fitted into a 4 mm deep
recess carefully bored in the outer face of the kickstart housing. The shaft was carefully deburred and
its diameter cleaned (if it's pitted or damaged the seal will not last long) and eased through the seal lip
so as not to damage it with the flat for the cotter pin. The lever was fitted as normal, being careful that
it didn't slide back through the seal during assembly, and the whole assembly then fitted back into the
end cover as per the manual, but with a thin smear of Three-Bond silicon sealant on the mating face
to seal it. This part of my machine has been totally oil tight ever since.
L #3080 I have a swingarm MAC and she seems to lose a lot of oil into the primary cases, what
can I do to go some way to slowing this down or even preventing it happening, can I use grease
instead of oil, when the oil level has been renewed she changes gear like a dream and the oil will then
flow quite antisocially to the point of altering the gear change reliability I will then have 5 or 6 neutrals
and difficulty engaging gear the oil loss is excessive and needs to be resolved, any ideas?
#3082 You have a problem. The main seal between the gearbox and the primary chaincase is the two
shims either side of the sleeve gear bearing. If these have slipped or not been put in you will loose a
lot of oil. Also, have a look at the state of the sleeve gear bush, this may be worn oversize on the
bore. However, you are not likely to loose so much that way. Take the primary drive off and have a
good look at the gearbox casing while you're there in case of any other holes, cracks etc. Grease is
not recommended. The oil should stay inside the box for a long time with usual checks for level.
L #4027 A query for the technically wise out there. For the past 2 seasons the lightweight
gearbox in my '39 MAC racer has produced a constant stream of bronze in the oil whenever drained.
The source was from 3 places: First gear mainshaft bush - caused by the gear wanting to move
inwards and thus wearing away the end of the bush on the raised portion of the mainshaft. Cured by
changing for another first gear (assume the gear was not cut true or the bush in the original not bored
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parallel); Second gear layshaft; Third gear layshaft. Both of these constantly run towards each other
wearing large amounts off the face of their bushes in the process (like 12 thou in 2 race meetings
when last checked). Have changed double sliding gear twice (thinking that if it isn't cut true maybe it
could cause some lateral force in the mating gears below) and rebushed these gears with careful
parallel boring of bushes twice. But still it persists. In desperation I have dealt with the symptoms by
installing a 20 thou thick hardened shim between third gear and the raised portion of the layshaft (as a
trial), with a similar amount taken off the face of the bush to maintain correct gear location and end
float (about 5 thou). Thinking like Frank, I figure that all this wear takes place when the particular gear
is freewheeling on the layshaft. Yet third gear is the most frequently used at our home track, so most
of the time it is under drive load and there is no differential movement between it and the layshaft. But
it sure does itself some harm for the two short periods when I grab top gear. By the way, mainshaft is
new and true and layshaft is not bent . Anyone else had this problem?
#4029 A word of warning - EP oils should NEVER be used in a Velo gearbox. As you say Steve, the
sulphur content of these oils attacks the bronze bushes and will eventually lead to seizure. Most likely
the first thing you will notice will be a difficulty in selecting gears, and inspection will show the first gear
bushes to have seized on to their shaft. Straight or multigrade engine oils are what was recommended
by the factory and these work well. You could also try one of the modern racing 2-stroke gearbox oils
which should be suitable for use in boxes with bronze components and in wet clutches, although this
isn't an issue with pre-unit motorcycle boxes.
#4034 Your problem is that the EP Hypoid Gear oil that you use is chemically eating the bronze
material used for the bushings. Use SAE 50 and that will stop. I always use a bit of molybdenum
disulfide powder in the gear oil to inhibit wear. This problem affects both my Velo and Royal Enfield
gearset bushings, but not the B50 or Commando bushes. I've always assumed that there were
different confections of bronze used by different makers. I first ran into a similar problem in about
1984 when I attempted to cure a leaking crankshaft seal in my Guzzi by addition of a Casite
(Hastings) product sold to dry up weeping seals. Lost the gudgeon pin bushings in about 150 miles,
replaced the rods, changed the oil, and lost the second set in another 150 miles, apparently from the
residual chemicals . I then installed bushings for a VW rabbit which did not dissolve. Once warned by
this experience, I took notice when my Velo and RE boxes showed the lovely golden glint in the oil
when using the hypoid concoction, and reverted to my SAE 50/Moly mix for no more trouble.
#4035 I've heard horror stories about using EP oil, but what does the EP stand for? If you can tell me,
then I'll check my supply of oils to make sure that I don't use it. Is it called something else in America?
So what good is a gear oil that eats bronze? Why is this stuff made? I can't think of an application that
has lubricated gears, and doesn't have any bronze or brass too.
#4036 EP = Extreme Pressure. Developed for gearboxes where the tooth shape increases the
pressure but runs more silent. It was often branded as Hypoid.
#4037 In USA gear oils are GL rated. GL-4 is non EP, GL-5 is EP. Norton Commandos call for EP in
the gearbox as do some others with yellow metal. I buy GL-4 by the gallon and use it in everything just
to be safe. It stinks just as bad as GL-5 so it must be good.
#4038 I did some searching on Google, and found out about EP oils. EP stands for Extreme Pressure.
Some gear oils have EP additives, some have a little, some have a lot, some have none. The oils to
avoid are designated API GL5 and API GL4. The GL3, GL2 and GL1 have decreasing amounts of EP
additives, and will not harm brass, bronze and other yellow metals. Classification --API Designation
Like motor oils, there is an American Petroleum Institute (API) designation for gear oils. Unlike the "S"
category for motor oils, the gear oil categories do not necessarily supersede one other. For example,
API SL motor oil can be used in all prior gasoline "S" classifications. The API designations for gear oil
are API GL-1, GL-2, GL-3, GL-4 and GL-5, where the "GL" stands for "gear lubricant" and the number
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indicates the level of extreme pressure (EP) additives in the formulation. Extreme pressure additives
give gear oils their infamous smell and protect the gears from sliding wear. GL-1 gear oils do not
contain EP additives. GL-5 gear oils (recommended for hypoid gears in most axles) contain the
highest level of EP additives. It is important to follow the manufacturer's recommendations for the API
designation, because, depending on the application, too high of a treatment of these additives might
hasten component wear. In other words, more additives are not necessarily better when considering
gear oils. One must select the proper level of additives to maximize component life. A case in point is
a manual transmission with bronze or brass synchronizers. Higher concentration of EP additives in
manual transmission oils might cause the softer "yellow" metals (copper, brass and bronze) to wear
out more quickly. API GL-4 contains approximately half the additive treat rate of GL-5. API GL-3
contains approximately half the additives of a GL-4. So which is better -- GL-1 or GL-5? Again, the
answer is neither or both. One must always select the recommended API designation for each specific
application. A gear oil product meeting API GL-5 SAE 80W-90 is commonly recommended for both
manual gearboxes and conventional differentials in cars pick up trucks and sport utility vehicles
(SUVs). This fluid provides the full protection of an SAE 90 under high temperatures and hard driving
conditions, while still providing the fast flow characteristics of SAE 80W when the unit is cold. Likewise
API GL-5 fluids may also be recommended for use in industrial gear units. However, a typical GL-5 will
contain approximately twice the amount of Extreme Pressure (EP) additive as that of an API GL-4
gear oil. When an API GL-5 fluid is used in an API GL-4 application, the additional EP additive may
have a negative reaction with the yellow metal components (brass, bronze, etc.) used in some
transmissions. The EP additive can contribute to chemical corrosion, etching or excess wear of yellow
metals over time, which may shorten the life of the transmission components. Always be sure that the
correct fluid with the proper API service designation is chosen for the application. Another common
gear oil used is a product meeting API GL-4 SAE 80W-90 which also provides the viscosity of an SAE
90 under hard driving conditions while providing the low temperature flow characteristics of SAE 80W
that are necessary during cold weather start-ups. EP and antiwear additives are added to minimize
metal to-metal contact wear, but at approximately half the amount used in API GL-5 products.
Likewise, an API GL-4 product is commonly designed for both transmissions and differentials found in
certain models manufactured by Audi, Hyundai, Nissan, Porsche, Suzuki, Toyota, Volkswagen and
others. Always remember to double-check that the proper fluid has been chosen for the application.
Although not as common as other gear oils, some products are formulated to meet the API GL-3
classifications and have limited applications. Currently the most common application is in certain late
model jeep vehicles. This fluid is available at your local Jeep dealer's parts department. API GL-1 SAE
80W-90 is a non-EP, straight mineral oil. It contains no active extreme pressure additives that may
contribute to chemical corrosion, etching or wear of yellow metals such as brass or bronze. API GL-1
is specifically designed for use in manual transmissions, transfer cases and final drives in on-highway
trucks and off-highway equipment which require an SAE 8OW-90, non-EP, API GL-1, straight mineral
gear lubricant.
#4039 Now that you've been through all that, back to the Velocette application! The manufacturer's
recommendation for Velocette singles is to use exactly the same oil you use in the engine, whether it
be a straight 40 grade or 20/50 multigrade engine oil, the exception being if you chose to use Mobil
oils when they recommended their Monolube GX90 product which was presumably a 90 grade
non-hypoid gear oil. The distinctive smell of EP oils of most grades is attributable to the sulphur
content of the EP additive which is as you say, present in all grades but GL-1. It is this EP additive
which does the damage - if it is present at all it will still do the damage, it will just take a bit longer if
there is less additive. The only answer is to avoid EP Hypoid oils like the plague!
#4040 Thanks for the feedback, group. I let this one run for a while because the funny thing was I
didn't say what oil I was using in the initial post. Following investigation and a phone call to Shell, I'm
satisfied that even their hi-tech synthetic gear oil is the most likely culprit (GL-5 - ouch!)
#4042 A number of people had recommended that I put Mobile 1 synthetic gear lube in the tranny. I
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pulled up the specifications on the web, and it states that it does in fact meet GL5 standards. Would
the potentially detrimental additives being discussed also be likely to be present in synthetic gear
lube? The same specification sheet says nothing specific about any additives, potential problems with
certain metals, etc.
#4043 I too have seen reports that 'modern' GL5 is yellow metal safe. Is the risk worth the reward? As
others here have stated, Velo boxes have lasted this long on motor oil and rain water.
#4045 I called Mobile 1 Technical Support. They confirmed that their synthetic gear lubricants do, in
fact, contain the higher levels of EP additives that were previously mentioned. They further agreed
that these additives can be harmful to certain yellow metals, and stated that this product would
probably not be a good choice for this reason.
#4044 I, too, put synthetic 80/90w gear oil in my Venom this summer, and my main bearings failed...
Actually, I looked carefully at this oil before using it, as its fairly well known (but not enough, clearly!)
here in the States that 'hypoid' gear oils eat bronze. There was no 'hypoid' on the label, but I'll check
for GL-5.
#4046 It may (or may not) be of interest to recall that Ralph Seymour always used R40 in his
gearboxes. It is of course well known that castor oils are far superior to all this synthetic stuff!
#4077 The effect of EP additives on bronzes may vary according to the type of bronze. I assume that
Velo gearbox bushes are phosphor bronze. Many car synchromesh gearboxes used something called
"aluminium bronze" for the synchro rings (or baulk rings, blocker rings if you prefer) with few problems
but not all manufactures specified EP80 for the 'box. Ford always specified EP Gear Oil (from about
1954 anyway) and even blanked off the gearbox drain plug to stop misinformed garages from draining
it and refilling with straight 50 grade.
#4079 It is the Zinc that is attacked and the more Zinc the worse it gets. Gunmetal (LG2) has 5% Zinc
(LG4 and Admiralty NES 830 have 2%). Phosphor bronze has the smallest amount of Zinc. Aluminium
bronze is a hard erosion resisting metal and not "normally" suitable for bearings, it resists Seawater
attack. It is sometimes used for Wormwheels under great load. In short the less Zinc the better but
then we get into the area of Tribology and have to decide whether we want the bearing to wear or the
shaft.
#4080 Velo gearbox bushes have a material specification of PB7 - do you know what the material
specification is, and its modern day equivalent?
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E.3. Final Drive, Chains and Cases -
L #20 The only thing I want to do now on the MAC, aside from regular proper maintenance is to
find a relatively decent cure for the primary case leakage, which is pretty massive, even after a new
seal was put on. May resort to black silicon sealer.
#25 Most pin type p/chaincases distort finally, so you'll hit this problem with second-hand cases. I
wonder if belt primary drive might not be the solution, for Velo singles in general.
#28 I've been let down on the side of the road on a Velo have been primary chains, and both times it
was my fault. The second was trying to run an open case using spray chain lube, when I lost the oil
drain plug on a long ride. Au revoir to chain and clutch chainwheel both
#31 I was pondering that very thought recently, but though I have seen belt drive units for several of
the more popular parallel twins, nothing for anything so esoteric as a Velo single..
#34 There are two manufactures of belt drives for Velocettes one is by a guy called John Watson
telephone +44 (0)1768 898599, the other is Kevin Thurston telephone +44(0)1525 404699 – both I
have seen, but not used and look well engineered.
#71 I recently fitted a belt drive cum clutch kit onto my Venom. As the space inside the primary case is
very crammed, a bit of machining of the pulleys was required to get the required clearances. But
otherwise the kit was of unusual high tech quality and fitted straight forward and the back up help from
the manufacture was more than excellent. Clutch action is better and sharper, and neutral can be
found at standstill too. But do not expect a complete dry primary case. I recognized oil still collecting
in it as the crankcase blows always a bit into the p.c.c. and also some oil from the sleeve gear bush
dribbles in it. I fitted the belt kit because I got tired of cleaning the rear wheel and the garage floor
after a fast blast. I assume the Mac case and clutch is similar to the Venom, but Mr. Watson will know
upon these details.
#133 I've been in touch with Dave Smith of Dave Smith Classic Motorcycles, in Illinois, and he handles
the John Watson belt primary drive system. He is going to get back to me on my MAC, regarding
pricing, because there is little call for this system on the MAC, mostly the Venom, and I would need a
different ratio compared to the Venom, of course. Supposedly a good quality unit with no major
obstacles to installation besides replacing the clutch plates as the new basket will have friction
material as produced, so new plates would help guarantee proper function
#135 A word on belt primary drives. As we all know, the mainshaft breathes some oil into the primary
chaincase. But neither the belt primary drive, nor the dynamo/alternator belt drive really appreciate oil.
The primary chaincase also stops oil from getting at the generator drive. This should be borne in mind.
#137 Most of these primary belt kits come with a complete new clutch. A Velo clutch will work dry, or
wet, but not both ways in alternance.. From experience, the best pressed-metal primary chaincases
don't keep oil well enough, Velocette or other. The same chain, inside a good, oil tight alloy chaincase
gives no great problems. Years ago, I met somebody who had cast up an inner Velo primary
chaincase out of alloy, but retained the pressed steel outer. I meant to follow this up, but for some
reason didn't.
#139 Glad you brought this up. I have wondered how the generator/alternator v-belt is kept from
slipping with the engine breathing oil mist into the primary case. The belt primary drive I am thinking of
is of the notched tooth variety, and some oil shouldn't affect it too much, especially as these new
plastic/metal core belts don't stretch basically, keeping potential slippage to an absolute minimum.
#140 I guess the cast alloy back half of the primary would keep it somewhat more leak proof holding
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normal warpage over time to a minimum. Was this a pin or band type case? You see, this is one of
the things I love about owning this dear old MAC. While I can appreciate wanting to keep these fine
machines absolutely pristine, it is most enjoyable to figure out practical ways to improve on a good
basic design from an earlier time, while keeping the overall feel and "character". I plan on coming to
the Spring Opener of the VOCNA, and plan to ride the several hundred miles there, alone if needs be,
but with another member if possible. More enjoyable and perhaps handy in case of an oopage of
some sort. I expect my MAC to behave in an exemplary manner, i.e. to get me there, enjoy the rally,
and get me within 1 mile of home before tossing something out the exhaust. I did find out recently
what drippy mess it makes to overfill the Primary case with a less then perfect felt wiper seal in place
over the clutch. 2 ½ ozs. of oil just didn't seem enough, but, there you go.
#143 I'm still on primary chains, but I've noticed basically three schools of thought on primary belts.
Original chaincase, with the newer narrow belt, which presumably means the mainshaft breather oil
wanders about inside the chaincase unless there are some holes somewhere behind. A home-made
belt cover, where it is hard to know just what is going on, or nothing at all. We raced a Venom with no
primary chaincase, just some foam strapped to the frame under the ESA to keep oil off the track. It
was a while ago and I don't remember clearly, but the quantities of oil coming out were not massive,
and we didn't have a generator drive. Could be it isn't a big problem. I had a Venom Club, and from
time to time, possibly connected with bore wear and engine speed, it spat out considerable quantities
of oil via the engine/oil tank breather. A friend, more thorough than I, believed on his similar Club it
was the oil frothing too much and thought he'd pinned it down to a certain make of oil- we're talking of
25 years ago. The only result was I checked engine oil, as a reflex, every time I stopped. The alloy
rear half of primary chaincase was a pin type. He'd beefed up the flange on the inner but did say that
for a sand casting, his inner was pretty thin. With a bit of imagination, it would be possible to fit the
outer half of the primary chaincase only with a belt drive, which would trap the mainshaft breather oil,
and look more "classic". 25 years or so ago, somebody in California I think made a complete alloy
primary chaincase but it was noticeable to say the least. Mechanically, probably a lot better
#147 25 years or so ago, somebody in California I think made a complete alloy primary chaincase but
it was noticeable to say the least. Mechanically, probably a lot better. Bruce FYI The patterns to said
item were in my possession up to a few years ago. I was unable to find a foundry to complete a set
(and was unwilling to try myself a la John Britten) so they went back to Olav Hassel. They were
originally made by Bob Strode of Washington State for a Venom Special road racer and included an
outboard swingarm trunnion support as part of the casting. The trunnion was an inch longer to fit the
case. Another friend had the finished bike until recently. I think Olav had one set made, but his latest
creations (a Metisse and a racing rigid MAC) had modified original items. Between the casting and
machine work it became a lot of effort to reduce the minor oil loss from the pressed steel case. Never
rode the Strode bike, so I can't offer an opinion re handling. ps Translation, please, Mr. McNair - by
"pin fixing" do you mean screw-type
#148 Yes, pin type is the same as screw type cases. Don't know why, but, there it is.
#149 I'm interested in the idea of a primary belt drive as most of my time is spent trying to keep the oil
in the chaincase or at least off the garage floor. One thing that has always worried me even in the
standard chaincase with the small amount of oil in it, is the lubrication of the clutch ball race assembly.
Having just replaced one it is not the cheapest item in the clutch
#150 Yes, lubrication is marginal as designed. The result of Britain's use of roundabouts instead of
stop lights? Many owners change the ball bearings for straight rollers; one can file the cage to suit.
This has been successful for many. The increased contact area seems to compensate for the rollers
skidding. For a more direct solution, I found a tip in an old FT that specified an oil slot, cut horizontally
in the "thrust cup" (C29/26) just above the ball race. I used an abrasive cutoff wheel in a Dremel tool.
The slot is about 1/16" wide by ½" long, cut from the clutch side, and slopes down toward the bearing
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when viewed in cross section. This has improved oiling so that I am still using the original ball race,
now with 30K miles on it. Thanks to Joe Keys. If/when I change to belt drive on the Venom I will
probably change to rollers (and keep the slot). The oil from the crankshaft breather should be enough
in the original primary case to reach the bearing. And of course I "never" sit at a stop with the clutch
in...or follow stop-and-go traffic up Pikes Peak...
#151 I was actually referring to the large clutch ballrace assembly C26AS that is an interference fit in
the chainwheel assembly although the same problem would also exist for the clutch thrust bearing if
there was no oil in the chaincase, as you point out. I have converted my clutch thrust bearing
assembly to rollers also.
#168 I just fitted a Watson belt drive kit onto my Venom Clubman. I use it within the original primary
chaincase. The reason for fitting it was not a clutch problem, it was only the habit of oil spreading on
the left side of the bike and accumulating in the flanged alloy rear rim after prolonged high speed
outings. I got bored of cleaning the bike from oil. Now I expected no oil loss as none is in the case.
But bad news. The engine breathes out enough oil, that the case slowly fills up with oil again which
finds its way out of the case after a certain milage. Question : How can a garter seal be fitted into the
drive side crank case ? It seems there is not enough meat in the case to give a good seating. I have a
"top hat" steel insert in the drive side case plus a parallel roller bearing conversion. The breather hole
in the crankshaft is filled with Araldite. The engine cases are converted to the VMT type breather
system. As I see it, the seal must run on the boss of the (machined) gearbox sprocket, on which the
pulley is bolted on. Is this a very thin seal ? Would the oil not breath also between sprocket and shaft
? Would scavenging be improved if that restricting "filter plug" is replaced by a normal plug ?
#176 This reply addresses several emails I received about the belt drive, garter seal and shielded
gearbox bearing and engine breathers. Hi Tom. Saw Steve Leonard in the Island in January at the
MMCC annual dinner and will pass on your good wishes when I go over in August for the Manx. I am
trying to persuade John Watson to join this website so that he can be contact anybody interested in
his belt drive. His email address is Jwatsonbraeside@b... The belt in his road going conversion is
unaffected by oil. There is no number for the shielded bearing as it's a modified original sleeve gear
bearing, although there is another on long term trial in a road going Velo. Unfortunately they are likely
to be pricey, around £85 last quote. But I have recently been given the names of two companies who
may also be able to make such a bearing at a more reasonable price. Cost likely to be dictated by
demand. I may also show them a chain wheel bearing and get it costed. The garter seal mod is not
too difficult to achieve, but I think is dependant on certain factors:- the "shoulder/boss" on the inside of
the front sprocket/pulley where it abuts the main bearing inner race needs to be sufficiently wide for
the seal to run on it, mine is approx 200thou and poses no problem. I think that depth was achieved
by machining the inner sprocket face to clear the reinforced "Walker" crankcase. The shoulder needs
machining to be perfectly concentric and smooth so it doesn't tear the seal lip. I then measured the
thickness of the alloy where the crank sticks through the case. My crankcase was about 9mm thick,
and as it isn't load bearing where the seal fits could stand to be reduced to accept the seal. I then
bought a seal which was 4mm x 35mm (diameter of the sprocket shoulder) x 42mm. The seal is a
NAK VR - 4 x 35 x 42. The drive side crankcase was then machined from the outer edge to a depth of
4mm to accept the seal, which can then be replaced without having to split the cases. This mod
should also be possible on cases which have been "top hatted." In answer to Johann Patek's
question about replacing the filter plug, I believe Veloce used a standard gearbox filler plug instead of
the filter plug in later engines, whether for cheapness or any particular reason I'm afraid I don't know.
I think the answer to an oil tight engine is sufficient/effective breathers in the crankcases. From the
various engines I've seen it doesn't have to be fitted under the mag, better in an accessible place like
the top of the crankcase over the "map of Africa" But it does need the internal drilling through the
crankcase between the flywheels and timing gears as on Thruxtons and later Venoms. I have also
blocked off the hole in the crankshaft and the fit of the sprocket on the main shaft doesn't seem to
matter as the engine is no longer excessively pressurized, at least not below the piston crown.!
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L #239 Has anyone tried to use a 525 O-ring chain on the final drive of a S/A Velo? It is only
about .020" wider overall than a standard 530, and the 18% reduction in roller width should be more
than offset by the modern chain's resistance to stretch. I'm getting 20 - 30,000 miles from the O-ring
chains on my more modern bikes. The ones on the Venom don't last but 6 - 8,000, and the sprockets
wear accordingly. This is not a good idea for a racer, as the o-ring chains suck up a bit more power,
but for a tourer it seems more reasonable.
#240 Decided to get a new final chain for my '56 MAC, getting ready for the Spring Opener. Is 428
size the proper size to use on this sweet old thing? Have heard a lot being discussed on chains, and
overload has set in.
#241 You will have to skim the sprockets down to 5/16" width to use 525 chain, otherwise there
should be no problem. Most modern racers use 520 chain regardless of capacity, I've been looking
after a 160BHP Yamaha R7 now in its 4th season's racing which runs 520 'O' ring chain and never
had one break yet, touch wood! The chain size is still imperial, given in eighths of an inch, hence 530
is equivalent to 5/8" x 3/8" i.e. the 5xx is for 5/8" and the x30 denotes 3/8". 525 is therefore 5/8" x
2.5/8" (or 5/16") and 520 is 5/8" x 2/8" (or 1/4"). There are exceptions such as 532 and 632 chains
available which were fitted as OE to such machines as the Kawasaki ZX10 and Suzuki Hayabusa, but
the xx2 here refers to roller diameter which is larger than the standard designation for these chains
and will not fit normal sprockets. The main thing to watch on a Velo is clearance behind the chain
which is tight especially to the primary chaincase and will not permit use of an 'O' ring 530 chain due
to the wider overall width of the chain. I would advise use of a 520 'O' ring chain and skimming 1/8" off
the back side of both gearbox and rear sprockets if you go down this route, you should have no
problems with stretch if the correct adjustment is applied
#242 See my posted reply re 'O' ring chains for info on chain sizing. 428 is one of the strange ones
which doesn't fall quite right in the general rule, but is equivalent to ½" x 5/16". I've been using a DID
primary chain on my Venom which is sold as an endless primary chain for speedway bikes and is
exactly right for the Velo.
#246 Big-bore race bikes are not a good example of my o-ring proposal, they can change chains and
sprockets every race if needed. They use the 520 size to reduce drag. Street riders need longevity, or
they change for the "pose" factor. A 33% reduction in bearing surface between chain and sprockets
seems like an awful lot. Chains are relatively cheap and available to me, rear drum/sprockets are not.
Plus I am basically lazy and prefer riding to wrenching any day. Guess I'll have to find out for myself -
but I think I'll thin the gearbox sprocket from the backside only. Also, one should use 428H instead of
plain 428, it's stronger, lasts longer, and fits fine in the primary or on MAC final drives. The H means
reinforced (thicker) side plates. . lengths to suit Japanese bikes. I do this and get two primary chains,
it works out cheaper. The joining link has to be 428H as a 428 will not fit due to the H chain been
slightly thicker.
#249 Re chains. On all my British bikes I have owned the past few years, Velo's and Goldies I have
always used on the primary drive DID 428H. The H denotes heavy duty. 428 is equivalent to
Reynolds part no 110046 and 530 is equivalent to 110056. I tried using a heavy duty 530 on my
Thruxton and found it very lightly touched the outer primary chain. If you go to a bike shop you can
buy 428H in long lengths to suit Japanese bikes. I do this and get two primary chains, it works out
cheaper. The joining link has to be 428H as a 428 will not fit due to the H chain been slightly thicker.
#251 My reference to race bikes was intended to demonstrate that the smaller width of chain was not
likely to reduce the strength or ability to transmit power, and yes, I agree that race bikes can change
chains every race if budget or sponsorship permits. On the other hand, underfunded teams such as
the one I support have to make things last as long as possible and we would expect to use no more
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than a couple of chains in a season of short circuit events, although I would always fit a new chain
before a TT race (different riders/team/bikes/environment). Gearing is changed for different circuits,
but mostly only the rear sprocket and then we generally use a range of only three or four teeth for all
the circuits in the UK. The front sprocket is the usual (very) hard steel type, but the rear is Dural, and
we are still using the same set of sprockets we started with in '99. The machine has done 3 full
seasons of British Superbikes and is currently leading the MRO National Powerbike championship so
is fairly hard worked. We use Regina 520 ORS, and I'm very careful about adjustment - make it too
tight and neither your chains nor your sprockets will last long. A bit of extra slack might mean it slaps
on the swing-arm occasionally but shouldn't do any other harm. If it's too tight it not only affects chain
wear but also increases stress on gearbox bearings and upsets suspension function. Given the
amount of oil that finds its way on to the chain from leaky primary chain cases on Velos I have my
doubts as to whether there would be any gains in running 'O' ring. The additional drag is unimportant
when you have 160BHP but is a significant performance loss when you only have 40 horses. 'O' rings
are great on modern machines which don't leak oil and the chain would get little lubrication
otherwise, but I find the standard Regina "Professional" grade 530 RS non 'O' ring chain to work well
and have seen little deterioration in 3000 miles so far on my Venom. I would also add that changing
the chain before wear reaches a point that the sprockets begin to suffer will extend the life of these
expensive items quite considerably. You're right about the 428H, Regina's stuff has 2.0mm thick side
plates as opposed to 1.8mm on their standard chain. As far as joining links are concerned you should
ONLY use links made by your chain's manufacturer for that specific chain, there are so many
differences between chains that only the right thing will do!.
#253 I agree with Pete C's comments about chains, I use a 520 on sprockets thinned down on the
inside and even with an alloy rear sprocket (the hub's machined to take Vincent sprockets), they don't
need adjusting even during practice and racing at the Manx Grand Prix. But where does he get 40
horses out of a road going Velo? Surely he doesn't believe the figures in the red book, next he'll be
quoting 100 mph for a standard Venom! Anyone want to peck at the corn I've scattered?
#252 I run a 530 O-ring. I moved the countershaft sprocket out about .050 so it clears the primary
cover. Obviously this mis-aligns it to the rear sprocket but it has not been a problem (put a straight
edge across your sprockets sometime, I bet you'll be surprised how far out they are). I make my own
front sprockets out of worn out Velo sprockets by turning off the teeth and welding on a new outside
from any donor sprocket, this gives the .050 offset. I tried shimming out the sprockets once but it
doesn't help the already fragile drive dogs. Regarding horsepower loss, I got answers ranging from nil
to 10 hp. Regina chain told me there is some power loss when the chain is cold but when it heats up
it's insignificant. Somebody once did a dyno test, sure wish I could find it. Many small displacement
dirt bikes use them.
#255 To the racers: Racing experience, while impressive, has nothing to do with the question. Longterm
durability is the issue, not strength. If I have to throw a new chain at it every few thousand miles,
what has been gained? Been there, done that. If you believe the chain manufacturer's literature, a
properly lubricated o-ring chain has no more drag than a standard one. Even 400cc commuter bikes
come with them. The o-rings serve to keep grit and dirt out as well as keeping lubricant in. When
someone reports 20,000 - 30,000 miles on a standard 530 drive chain, I'll buy one like it!
L #284 In getting the '56 MAC ready for the Spring Opener, I replaced the felt seal that is
positioned over the clutch inside the outer primary case half. Making sure the seal was as even and
as far down in its positioning ring as it would go, I had applied Seal-All adhesive to its positioning ring.
After the adhesive had dried, I soaked the seal in oil over night, but I noticed the seal was not
softened up much, and was pretty firm to begin with. I put all back together, cursing the rubber
seal/metal retaining ring set-up, but finally got it right. Upon operating the clutch lever after this, I saw
that the primary case "bulged" noticeably when the clutch was disengaged, lever pulled all the way in.
Obviously the felt seal was interacting with the clutch, reducing free movement. I decided to carefully
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un the bike a bit just to see, and except for there being almost immediate take-up of the clutch in low
gear from a standstill, shifting up and down while running seemed normal, no graunching or hard
changes. So, can anyone tell me if this is normal when initially running a new felt seal, and will some
running in reduce contact or? Thanks
#285 felt seal case-bulging is normal with a new one, at least they've always done it on mine for the
first few months. I've also opened my primary case at times to find a lot of wool fibers in there. Maybe
it quiets the chain!
#286 The felt seal thing; when heated up from hard riding, the clutch would drag when I went from
neutral to low gear, once to the point of stalling. I now am wondering if this is a direct effect of the seal
contacting the clutch combined with some swollen friction plate material, or if the clutch alone would
create this situation. I adjusted the clutch as close to perfect as I could, which is pretty good, so it
probably isn't a matter of adjustment being off. But if it is like a number of other older bikes I've had,
mostly dry clutch, the plates will swell after hard usage
L #793 I have a copy of the BMS Velocette Singles Service Series book which covers the
Venom. With the inner primary chaincase removed they refer to the bolt head at the top/front of the
engine plates. It says if you want a leaky chaincase (is there a choice) fit a standard bolt at this
location. This one must have a thin shallow head to provide essential clearance. If this is true does
anyone know where to get one or do I just need to grind a bit off mine!
#798 If it were me I'd just grind it off (but then again I'm not a purist). I've got various electrical "bits"
off mine at the moment, so have a good view of the bolt. Its head is about 7/32" thick giving about
1/16" clearance to the inner chaincase.
#810 Had a quick look at the book. It shows the offending bolt but if you look closer it is being used /
shown with the optional additional stiffening plate so I suppose that if you use one of those you need
to thin the bolt head down.
L #1041 Opening the primary case, I saw the following problem I never experienced : The
primary chain has seized links, some rollers are broken. The chainwheel is out of alignment, outside
2.5 or 3 mm. There is no sensible end play on the sleeve gear. I'm puzzled as there is no provision to
shim neither the drive pinion nor the clutch or the sleeve gear. Where could this trouble could come
from, and how to cure it ?
#1045 if everything in your clutch was fitted the right way, my suggestion is that the big threaded ring
that secures the main bearing loose and the whole clutch moved away from the gearbox because of
the force you put on it when operating the clutch. If the bearing sits relatively tight in the housing, you
won't feel any play. Anyway, if this is the case you should have encountered some clutch drag. Maybe
you adjusted it and some time later it occurred again and so on...
L #1051 Regarding primary chain alignment, they are usually out of line by about 4-5mm my
friend Herman Jassing from holland has encountered this problem and I have fallen foul of it as well.
the standard primary chain is a bit weak if you tend to give the bike a bit of stick. you can fully stretch
a chain in 1500-2000 miles if you ride a bit hard. I was told to fit a 428H DID primary chain which has
thicker side plates and is a heavy duty chain. it’s a tight fit to the primary case but they are ok. I fitted
one and ran the bike. I had to take the outer chaincase off and to my horror the chainwheel was eaten
away on one side very badly where the chain was trying to align its self and pulling into the chain
wheel because the sprockets were out of alignment. it hadn’t done it with a standard chain but the
heavy duty chain showed up the problem. the chainwheel is a fixed item so any adding shims has to
be done at the engine sprocket end. if the engine sprocket is too far out, you can always let it down
by using grinding paste and a mirror. member that a mirror is flat because it is ground and a pane of
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glass is not. it seems that all the bikes that were made were not too well aligned on the primary side.
Herman has checked a lot of velocettes and they all needed aligning on the primary side. I hope
someone can use this information. p.s. remember that if you do decide to fit a heavy duty primary
chain always rivet up the link as split links are a definite no no.
#1053 I mentioned about primary chain alignment and I said that you either had to shim or let down
the front engine sprocket. I was lying in bed when it dawned on me that I should have said shim or let
down the inner cush drive, as it is that will determine the alignment and not the sprocket. my mistake.
#1057 I have taken the bearing ring nut out, it was ok, and the bearing is snug fit in the case, so any
end play would have been noticed. Thanks for the idea, Holger. Billy, do you mean that's normal to
have 3 mm or so out of alignment, and is not why my "normal" chain has been destroyed ? The
outside of the chainwheel teeth is worn too (the chain wheel is outside alignment). So the only two
other possibilities I consider are lack of oil (there were very few in the case), or too tight a chain. It was
ok when I opened the chaincase recently, but I remember last year I found it over-tightened once. Just
in order to check the sleeve gear bearing, is there a way to take it apart without opening the gearbox ?
#1060 I have done quite a bit of primary chain (well belt in my case) alignment work. One thing I have
noticed is that if checking with a straightedge across the chain wheel the state of the trans in the
mounting plates has a significant effect on alignment measurements. This applies to rear chain as
well. The effect riding the bike has on the trans (notice how when you adjust the primary chain,
making sure to leave the jack screw pushing the trans forward, then go for a ride the primary chain
still tightens up as the trans gets pulled back on the drive side only) will change alignment. So you
might try moving the trans in the plates and see if there is any change. Also main bearing shimming
will of course change alignment by a small amount, as will clutch plate thickness.
#1062 It is also possible that the clutch chainwheel bearing is worn, loose or missing (yes, I've seen it
missing!). Also, of course, the sleeve gear nut not being fully tightened would cause misalignment.
#1063 Have you checked the mainshaft nut under the cap on the gearbox cover? That could allow the
clutch to slide over to the left, wearing the outside of the clutchwheel's teeth.
#1064 The final drive sprocket is mounted on the mainshaft, not the clutch.
#1067 When you checked your primary chain did you check in five or six different places on the chain.
Every primary chain I have checked has variable tension depending on the concentricity of the chain
wheel. If your unlucky it can vary between tight to flapping about. It's also interesting to check (with a
gloved hand) when everything is hot, I am surprised how tight it gets on expansion.
#1068 When you stripped the clutch to check on the sleeve gear bearing was the chainwheel still tight
and central on the large bearing? I think Paul Zell has the right idea when he refers to the clutch
plates and inserts wearing and misalignment taking place. Have you measured the inserts and the
steel plates and compared them with the thickness of new items? I have seen Velo clutches where it
is possible to rock the chainwheel even when the clutch has been adjusted perfectly, due to worn
inserts. A combination of the above and your own observations of little oil and tight chain could have
caused overheating leading to seized and broken rollers, culminating in the wear you noticed on the
chainwheel. As Geoff states the mainshaft nut in the box shouldn't affect the clutch, which should
still work and rotate even if the mainshaft is out of the gearbox, but don't try it too often as the
pressure exerted is taken by the unsupported clutch and bearing and may distort or crack the alloy of
the gearbox shell. you stated in your second reply that the bearing spacer was the original and the
gearbox bearing was still tight so I can't see what else could cause such misalignment other than the
above.
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#1069 I always check the chain tension in different places. For years, I always had it on the slack side.
But last time, I remember I tightened it more than usual, to the specified value (red book) ½ or 1" free
play cold, thinking it would get some more play when hot. This, added to dry case, could explain the
chain havoc. But this doesn't explain chainwheel misalignment. I checked all the clutch parts :
Chainwheel was true on the backplate, as well as on the sleeve gear. Thickness of all plates is right, a
bit less than new parts, a bit more than used ones. Some plates are not perfectly flat, but as far as the
clutch worked properly and didn't drag, I do not think this could cause a real thickness excess of the
assembly. Anyway, even without any friction and plain plate, i.e. assembled with backplate and
chainwheel alone, the later is still outside about 2 mm. The alignment was checked with a ruler on the
outer face of the engine sprocket (in different positions of the engine, and sprocket). The edge must
point at the outer face of the wheel teeth. It does at the middle of the tooth instead. I reckon this
measure must not be affected by the position of the box in the mounting plates, as far as the shell is
tight between them. But I can be wrong, and I'll try Paul's suggestion. Misalignment could be due to
wrong spacer length (Dai, do you know the right length ?). Maybe it has been like this for the last 35
years (never checked it before), and the oil + tension revealed the prob. This would mean such a
misalignment is acceptable.
#1070 The primary chain normally tightens when it get hot.
#1071 maybe your problem is due to warped gearbox mounting plates. During several decades of
hard work this might happen. At least my plates were warped when I stripped the bike although it was
fitted with the double plates at the drive side.
#1072 Both my spare parts list for MAC (spring frame model) list B35/3 sleeve gear distance piece for
the MAC. not B35/2 ? could this be the problem.
L #161 I raced on short circuits from 1990-95 with an alloy chainguard over the chain using only
chain lube, the clutch release bearing having been assembled with grease and I didn't have any
problems only renewing the grease occasionally. In 1997 I started racing in the Isle of Man and
reckon I do about 700 miles during practice and race week. I use a belt drive that John Watson and I
developed, which runs dry. I lightly oil the chainwheel bearing, but just used grease on the release
bearing and have not suffered any problems. Try a belt drive, it's so simple and John even makes
one that can run within the primary chaincase with or without oil. I also used a shielded sleeve gear
bearing to keep the oil inside the gearbox and the front pulley on the crank has a "garter" seal to keep
the oil in the engine
L #1383 Does anybody know from what year GTP's used a 3/8' pitch chain from the ½'' used on
earlier models. Also are there any differences in the chain cases?
#1384 The spares book says 3/8 used from gearbox number 6 - 1150, which is early 1936. The
spares catalogue says there is only one chaincase.
L #1825 My Velo owners guide goes into great detail on how to set the rear chain slack after
making a "special tool" and removing one shock assembly. What is the proper slack on a 66 Thruxton
with the bike sitting on the centre stand?
#1826 The amount of slack will depend to some extent on the size of gearbox sprocket, so the
simplest way to find out is to undo the bottom mounts of both suspension units and pull them back out
of the way. Then adjust the chain so that when the swinging arm is moved through its arc, the chain
has about ½ to 1 inch of free play at its tightest point. Refit the suspension units and measure the free
play. This is the amount you should set to in future when setting on the centre stand without removing
the units. To some there might appear to be excessive slack in the chain now, but I can assure you
that if the adjustment is not set in this way not only will your chain and sprocket life be shortened
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dramatically, but the suspension will not operate correctly either since its movement will be restricted
by an over tight chain. A slightly loose chain will do less damage than a tight one!
#1842 ...get someone to sit on the bike until the suspension units are at the requisite 11.5 inches.
L #1833 I have recently purchased one of the VOC "improved" chain case spacers with the
rubber 0 rings. However it is a much bigger diameter than the original spacer. It will actually fit over the
original spacer with room to spare. Do different Velo models have different sized chain spacers? or is
it designed to be this way?
#1841To my knowledge, there is only one size spacer on Velo primary chaincases. The diameter is
not important but the length is. The two O rings seal the oil in. Remember that inside the spacer,
there's another spacer that goes over the 5/16 bolt to clamp the chaincase washer to the crankcase.
L #2192 Two questions: 1) Is it actually possible to seal the chaincase so it doesn't leak?
2) My original manual describes all lubricants and schedules in detail, but makes no mention of the
chaincase or primary chain. Does this imply that it is adequately oiled by virtue of the crankcase vent?
#2193 I have a 1961 Venom - I keep oil in the chaincase and it doesn't leak at all . Various Velo
handbooks all indicate that the primary chaincase should have oil in it: The Book of the Velocette by
Leslie Heathcote, 1941 says " the primary chain is enclosed in an oil bath chain case... replenishment
through the inspection plug hole in the front of the case. About a quarter of a pint is generally
sufficient, although excessive oiling will not cause the clutch to slip" !! The 1966 edition ( by Ferrers
Leigh) also says that a quarter- pint of oil is required A Velo handbook of uncertain age ( no cover or
front pages - my guess is 1950's) says that the chaincase should be refilled with one eighth of a pint
of SAE 50 oil My 1953 Burgess "red book" is a bit confusing on the chaincase matter - on the one
hand it says that "The idea persists in the minds of some Velocette riders that too much oil in the
(primary chain) case will cause clutch slip. This is quite wrong, provided that the chaincase has always
bee kept properly supplied with oil and th clutch is properly adjusted" But the same red book also says
" The primary chaincases on Velocettes are not strictly of the 'oil bath' type, but provide sufficient
protection from dust and dirt to ensure that they are kept in good order. It is quite sufficient to squirt a
little engine oil over the chain, whilst at the same time moving it round slowly by means of the
kick-starter to spread the oil all along the chain" I guess that if you squirt the oil in often enough and
the case doesn't leak(!!) you could easily maintain about a quarter of a pint of oil in it. Take your pick -
all seem to agree that there should be oil in there, none of them give any tips on making sure it
doesn't run out!
#2194 1/8" of a pint (Imperial) 70cc of SAE 20/30 Castrol GTX is in the Haynes manual. My
chain-case is the screw type with the cork joint.
#2195 Rod Burris in "Velocette" makes reference to 71cc of oil but also comments on the chaincase's
notoriety for leaking oil - irrespective of type/sealing system!
#2199 I stuck the cork gasket to the inside chaincase with silicone sealant and then lightly smeared
grease on the other side of the gasket. Then applied an 1/8th bead of silicone to the outer chaincase
and assembled it. That way the silicone forms a seal which can be dismantled and is still oil tight.
L #2774 I am assembling a MkII KSS engine and gearbox from bits, into a Viper frame. I have
modified the engine plates for the gearbox and the shell is in position. I am dry assembling the clutch
and primary drive to see what's missing and check alignment to the rear wheel sprocket. On the
spares book for a Venom/Viper there are shown various shims M245-M245/4 to go between the
sprocket boss and the main bearing . There are none similar I can find in my KSS spares list. The
clearance between the sprocket face and the bearing housing on the crankcase is .028 measured
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with feeler gauges. Are they necessary and if so are they to ensure alignment of the clutch centre and
the engine sprocket.
#2779 The shims are available to align the chain if required. I have never used any on a Velo and
doubt that you will have to. However they are there if you find the build-up of tolerances means you
need them.
#2781 Call me a Doubting Thomas, if you will, - but you have the 'original' Viper gearbox SHELL (?) in
the frame & have modified the plates (?), but have you in fact checked the gearbox end plate assy. in
situ, against the KSS magneto chain case ? Unless miracles have occurred in the past 40 years, this
engine just does not fit, unless (1) you are using the earlier series rigid frame gearbox, or (2) you are
prepared to go without most if not all of the primary chain adjustment ? I have heard & seen it all in
this department, but I still stand by my original decision back in the 60's to cut the 2 bottom frame
tubes & lengthen them by some 3/4 inch to get enough room to allow it to fit & give you primary chain
adjustment. Result, original engine/gearbox plates match holes in Mk. 2 c/case, admitted with a slight
forward tilt of the engine that has never worried me. All the projected bits go into place no problem,
including the generator, which is pretty close to the front down tube, but works OK, all you have to do
is make up 2 new front engine plates, & modify the original primary chaincase, (details if you want
them ) . I cannot be sure, but I am prepared to claim that I was the first Velo freak to do this back in
the 60's, USING THE LATER SERIES BOX ! Sure, Ivan Rhodes,(bless his soul) had done it with his
lovely Mk. V111 engined special, around the same time, & others had followed suit with the Mk.2 KSS
engine & the earlier 'box. Cutting the frame tubes & inserting a couple of properly prepared (lathe)
fillers, then reassembling the plot with new front plates, then reaching for the arc welder, is no real
drama at all I can assure you ! My frame did in fact spring apart the required distance when I ran the
hack saw through the tubes ! I am in constant email touch with an 85 year old Velo rider/ enthusiast in
the UK, who is a retired bank manager & has little if any mechanical ability (& who isn't into the Velo
information stream). He has over the years acquired 2 such 'Specials' , one apparently with no primary
chain adjustment, with the service quirk of constant replacement of chains, & the other having
problems of the same order, but he has now had for some time a magnificent special built by
someone who really knew his stuff, & I suspect extended the bottom frame tubes the same as I did all
those years ago ! I know of one 'conversion' which I have never actually seen, where the offending
portion at the front of the gearbox cover, plus a quantity of the front nut/bush of the cross shaft was
just removed ! - possibly a part of the KSS mag. chaincase as well ! Would be interested to know if
you do in fact have a 'miracle' on your hands ?
#2782 There is one alternative you have not considered, using a prefix 11 box. With this gearbox the
right hand side can move behind the timing case, only for the left hand side to foul the swinging arm,
however you can remove about an eighth from the left hand nut / bush which gives you about 7/16 th
clearance in total. Tight, but it just about works on my KSS special. Fitting GTP close ratio sleeve gear
and corresponding fourth gear gives you Venom ratios. As this gear cluster can support the power
outputs of both David Holmes and Nigel Lines racers the MKII engine puts relatively little stress on it.
Of course you are stuck with the seven plate clutch.
#2783 I have checked and I have room to move the gearbox within the limits of the slots so that
forward it does not touch the mag and back to almost the frame downtube. The gearchange
approaches the downtube. The limit on back movement is the slot in the chaincase back for the small
shouldered screws. I have not tried a chain on yet. I could with this mod move the gearbox further
forward if I lengthen to adjuster slots. I have not put the gearchange levers etc on so cannot say that
all is well yet but it looks it. This is due to my particular choice of method, sounds like a bit of luck also!
I used the original series 5 box. I did not want to move the footrest brackets back as I was not keen to
try the recommended unbraze and slide option. I do not have the heating equipment or much
experience of brazing or welding. This also leaves the option to put a Viper engine and gearbox in. I
found the holes on the Viper plates just aligned with the two lugs on the rear downtube of the frame
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and the upper crankcase hole. I bought another pair of plates at an autojumble. Chris Wiggins gave
me a tracing of the rigid KSS/MSS gearbox plate and I traced on that the Viper plate with the 3 holes
corresponding. This showed that the gearbox was too low. I had the gearbox pivot hole, the forward
gearbox slot and the hole at the lower crankcase/footrest lug bolt filled and a piece welded in at the
bottom for the gearbox pivot. The Viper plate has a bigger hole forward for the Viper gearbox and is
not closed at the rear. I drilled and filed a new forward gearbox slot and gearbox pivot hole. The rear
slot with the adjuster corresponds. I replaced the through bolt between the footrest lugs with 3 items. 1
a piece of the end of the original 3/8 bolt shortened and threaded 1/4BSF to go into the timing side
plate. I use a nut on the outer end now in place of the bolt head. 2 a 1/4 BSF Allen bolt between the
plates through a sleeve (made by drilling out a piece of a 3/8 engine bolt) in the engine and 3 another
Allen bolt through the threaded end of a 3/8 bolt in the lug(CS head to miss the back of the
chaincase). The holes in the engine plates are close but the head of the timing side Allen bolt clears
the cut down 3/8 bolt. I will have to mod the spacer tube to go around the Allen head. The Allen bolts
are stronger than turned bolts or screws being cold forged and I happened to have a few from way
back. The only slight reservation I have is whether this combination will allow the bottom tubes to flex.
The KSS power is less than a Viper or Venom but there will be road stresses. Now the gearbox is in
place I see that the plates are out by a small amount at the frame. I can force the bolts in, probably
because the plates are open here and will flex, so I may file the little out of holes in the plates. I know
it sounds a bit convoluted but part of this bike obsession is solving problems. Thanks to all for the help
to date. I am sure to come back and will report back when I have succeeded.
L #3147 I've been assembling the proverbial basket case MAC, and understand that a spacer
tube is required between the two halves of the chaincase to prevent them from being squished. Is that
spacer all there is, or might there be another piece somewhere of which I'm not aware? There is a
listing in the parts book for another spacer, but no sign of it in the drawings. Any and all help
appreciated--a really good explanation of the spacers and their fitting is what I require.
#3148 Yup, Two spacers, the first to space out the cases themselves is a piece of tube which locates
around the flanges of the holes in the cases, the second is a sleeve which fits over the fixing bolt,
between the big washer and the crankcase boss.
L #3337 I'm confused by the reference to a felt seal used on the outside primary cover. I'm
aware of a cork gasket behind the inner between the gearbox, and the other around the pin joint, but
where does the felt fit? Is there any reference in the parts book? Mine is a '46 MAC, built from a
basket of bits, and I can see no remnants of felt on any of the chaincases I have--would this felt fit
around the lip provided by the clutch inspection cap? By the way, any idea how thick the cork gasket
should be?
#3340 The felt seal fits inside the outer primary chaincase adjacent to the outer clutch plate which it
seals against. A soft rubber (neoprene?) lip seal instead of the felt. Over the summer a friend lent me
his '54 MAC and had problems with a dragging clutch (even after going through the adjustment
procedure). When you pulled the clutch in you could see the outer primary chaincase flexing. I
purchased a new felt ring and 'shaved' it down a little and this seemed to resolve the problem. I'm not
sure what the part number is for a MAC felt ring (if there is any difference) but, the MSS / Venom part
nr is F309. If you can get your hands on a MSS / Venom Parts book the felt ring is shown on the
inside of the outer primary cover. I assume that your chaincase has been changed at sometime for the
later 'pin' / 'bolt up' type rather than the band type. I've just popped into the garage and measured up
a spare cork gasket (the one that fits between the two chaincase halves) and they're about 3mm (1/8")
thick. Both felt and cork seals are readily available here in the UK but, I'm sure you should be able to
get some a bit nearer to home.
L #3869 I'd welcome recommendations on a make of chain to use for the primary chain on my
1956 Venom restoration. And to complete the chain, does it need a riveted link or will a normal spring
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link be OK?
#3870 Regina do a standard primary chain for speedway bikes which is endless and ideal for the job -
but it does mean you have to fit the clutch/engine sprocket/chain assembly as a unit which can be a
bit of a fiddle! Available through any Regina chain or Pirelli/Metzeler tyre stockist in the UK.
#3871 I buy chain in bulk 10 foot lengths from bearing and industrial supply shops. It is much lower
cost than Reynolds or other "motorcycle" chains you'll find at your local brit-iron parts supplier.
Typically it is the brand US Tzuabki, or another brand name. I've heard that the chains with a brand
name tend to last longer than the generic ones. Still, these chains do stretch a bit. I can't say if they
last as long as Reynolds, since I never have spent the money to try Reynolds chains. A 10 foot chain
is enough for 2-3 primaries, or 1-2 final drive chains. The cost is typically about $20-30US, including
one master link. I buy from McMaster Carr, MSC, or Grainger in the US. You'll need to get a chain
breaker tool for about $15US to push out the pin to get the right length. Additional master links are
around $1-2US each. Here's a tip: safety wire you master link (spring like). I saw some race bikes
doing it years ago, and I have done it ever since. It is hard to describe how to do it, but you can
probably figure it out. I can send a photo if you like.
#3875 I have always used Reynold here in UK since 1955 without complaint. Always used split links
on primary and rear. On our low output machinery when doing say 12000 miles a year a rear would
last say 2 years and a primary four. This with good maintenance like thorough cleaning and boiling the
rear in a mix of tallow and graphite grease. Thank god for spray cans now.
#3874 I can't recall ever buying a chain of any description in my whole life that didn't come from an
industrial supplier, - as I see it from my entire working life in the engineering world, that is where the
best chain is available ! True, there are special applications, & prices over the counter, but it is a
simple matter (in honest terms), that what you pay for is what you gets ! In recent years I have bought
all my chain from a good friend who has a company that ' builds' all sorts of chains, (some of them
huge) using mostly plates, rollers, pins etc, that come from Japan in bulk, he swears that he uses only
the best quality materials available, & like my own experience, has no problem with the quality of
chains that are available other than 'Reynolds' etc. I of course spent most of my earlier life refusing to
use anything other than a British made chain, but common sense dictates that modern technology is
capable of producing high quality products in any (really) developed industrial country. Of course,
even the most expensive (non 'O' ring) chain will destroy itself in a short period of time if it is plain
neglected, under lubricated, &/or over stressed, - most Velo owners reading this will probably have
had the experience, at some point in their riding life. These days for the first time in my life , after
many years of shaft drives, I am being propelled by a modern O ring chain, & almost wear my eyes
out checking it for lubrication , for which I use the remains of a 4 gallon drum of industrial black 'Moly'
grease, applied with a handy wooden twig ! despite what you may think, this doesn't fly off all over the
place as some of the expensive chain lubes do, & it seems to stay where it is supposed to for a
surprisingly long time.
#4809 I just bought a Reynolds chain and the familiar "Made in England" was missing on the links.
Does this mean they are now made elsewhere? I just wondered what brand of chain would be
recommended by the more experienced riders. I know the slim profile works better with the Triumphs.
Also on the box Reynolds insists that all production bikes should have the riveted link. I have never
fitted this type but now im a little concerned.
#4810 I should imagine that such commodities as chains are made all over the world - wherever
labor's cheapest. As for the riveted link - they're probably right, but the only failure I ever had of the
familiar split link was on holiday in the IoMan - fortunately a friend had a spare in his pocket and I was
out of action for just 10 minutes! I always have a spare tucked about me now whenever I take the
Thruxton out...
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L #4202 Hello Has anyone worked out a way of determining the correct amount of chain slack in
the final drive chain without pre-loading the rear springs? In other words when the machine is off the
centre stand ( I don't have one) and the spring units adjusted to the mid point in the upper curved
slots. (I am just lazy - but also believe there must more than one way to do a job). The red book
suggests making a special jig with holes at 11 ½ inch centres and compressing the rear springs so
that the holes fit the bolts at both ends of the spring units so they are partly compressed.
#4203 I just sit on the bike and make sure it does not go too tight. You don't get this problem with a
rigid frame!
#4205 Don't get this problem with a rigid frame! Chain slack in the final drive chain without
pre-loading the rear springs? In other words when the machine is off the centre stand ( I don't have
one) and the spring units adjusted to the mid point in the upper curved slots. (I am just lazy - but also
believe there must more than one way to do a job). The red book suggests making a special jig with
holes at 11 ½ inch centres and compressing the rear springs so that the holes fit the bolts at both
ends of the spring units so they are partly compressed. Better still, I used to get my Mum to sit on the
bike while I adjusted the chain ;-)
#4223 What you are looking for is an additional amount of up/down slack to allow in the chain when
the Final Drive Shaft, Swinging Arm Pivot and Rear Wheel Spindle are not in the same line.
Theoretically, it should be possible to calculate a figure but it would vary with machine weight (full tank
of petrol? panniers fitted? clog irons in your toolbox), the degree of clappedness of your Woodheads'
springs and even the position of the spindle in the fork. There is no substitute for loading the rear
suspension then rolling the bike along until you find the tightest point. It would appear that all
sprockets are slightly eccentric and chains wear irregularly. Try using an old tie-down strap between
the R/H fork and the frame "arcuate slot" to pull the suspension down.
#4224 Set it up correctly at about 11 ½" remove the weight and measure the chain movement.
#4229 The book published by BMS based on Geoff Dodkin info and pictures says 11/4-11/2 inch at
centre of chain run with bike on stand and rear wheel clear of floor. Seems to agree with the 19
between centres method.
L #4794 How can I tell if my Venom primary chain is worn? Is it to do with the length compared
to a new one, or when gearbox adjustment reaches maximum? Can anyone tell me the length of a
new chain?
#4795 Take the slack out of the chain runs and then try to pull the chain off the back of the clutch
sprocket. If it comes away more than a little it's shot! Alternatively, lay the chain out straight and see
what slack there is between one direction - closed up - and the other - out tight. There should be less
than 2% wear. More than that and its time for a new one. Don't bother with the side play type test, that
just shows if the sprockets were out of line and have thus caused wear on the links sideways.
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F. Running Gear
F.1. Steering Head, Forks and Shocks -
L #134 I have a 1960 Venom road test that states the top speed is 95mph with 65mph lights.
But with the sidecar on this makes very little difference to us. Can anyone explain why the forks can
be removed with ease but are quite illegitimate to put back to obtain the correct pressure on the
shrouds to prevent them rattling. Or has anyone learnt the secret.
#136 There is probably some approved method to stop rattles. The hairy method a few of us use is to
run the bike, down a very quiet road with a few bumps but not too many, with the lower pinch bolts
out. Don't brake heavily, it could be interesting. Stop from time to time to see if that's done the trick,
and when it has, put the pinch bolts back. This is slightly suicidal and I refuse any legal liability, but it
generally works when bouncing up and down has failed
#138 By the way have you remembered to offset the forks springs to the nearside and include the
rubber washers between the shrouds and springs?.
#144 I start by putting the bottom yoke in the vice. I clean any paint off the inside of the inside of the
fork yoke and grease it. I then put a wedge in the slots of the lower fork yoke, and check the top
spring claw, F262, will fit easily. I leave the wedge during assembly. My tools include my version of
LET 796, and another device which I can't identify on the shelf, for holding the damper while screwing
the bottom nut.
L #229 This is a pretty specific request for info; does anyone know if there is a replacement
taper-roller steering head bearing for KTT's mk 1 and 8? I just pulled the forks from my mk 8 and the
cups are, understandably at 64 years, a little dimpled. As I'm also ready to put my mk 1 back
together, I thought it a good idea to change this out as well. Anyone have any experience here?
#230 There was an article in UK Fishtail 298 on using taper rollers in a MKII KSS that maybe of use
#232 May I suggest taking the original bearing races to your local bearing supplier. Try Yellow pages.
If you get the ID right and the OD can be cylindrically ground to fit. Might be worth a shot
L #278 I am ashamed to ask to the member, it’ a non-Velo thing. But I am interesting to know
what kind of none original Tele fork fit on the Velo swing arm frame? and how do they fit ? How
handling effected? I am thinking the machine for novice racing purpose as well as road ( 250cc). I
would prefer pre-63 folk and English one. ( timing cover said "MADE IN ENGLAND" is it?),no
alternation to the frame ( in case I will replace it back later) and more widely available than Velo fork
with rebound damping. once I heard that Roadholder would fit, but I realized there were several type
of Roadholders. I gave it up because not knowing what I was looking for.
#279 You could try a set of Metal Profile forks. These were British, available for many years without
any major changes and were commonly used as an aftermarket upgrade by racers of the period. You
might find some by scouring the autojumbles or spares advertisements.
L #294 I've two sets of suspension units, both incomplete, both slightly different. The most
salvageable have annular spring supports fixed(?) to the damper unit: the other set has an indent
approx halfway up the damper, presumably for collets. Anybody recognize this description? If so
please where can identification/spares be obtained?
#296 Woodhead Monroes measure 6.5 cm OD and have an annular ring at the bottom.
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L #300 Does any one know what pressure I should pump the air forks up to on my '48 MAC I
have been told it is virtually impossible to obtain seals for them here in U.K is this true.
#301Do not over pressure it. Just a few strokes of the hand pump until the forks are nearly fully
extended. Then with your weight on the saddle, release some air out of the Kilner valve until the edge
of the shroud coincides with a small dimple, or perhaps a little before if you want a bit more ground
clearance. The dimple was originally painted with a red dot.
L #359 My newly acquired Venom is less than stable at the back end, especially with a pillion
and there is smear of oil on the left shock absorber. The shocks are the early Woodhead-Monroe
type and I would like to retain the appearance. There is a web site for a place in the USA that will
rebuild these shocks using new parts and retaining the appearance but I don't want to send them that
far, not least because I'm enjoying riding the bike and don't want it laid up for both weeks of the
British summer! Hagon have Girling pattern shocks for Venoms available but they have no parts that
are compatible with the "long fat shroud" look of the W-Ms. Is there anywhere in the UK that can
repair or replace W-M shocks for Velos? Or should I bin them and fit Hagons? (The bike is mainly for
riding and isn't totally original anyway - VR cases etc.)
#363 You could try contacting Martin in the attached Q & A
www.velocetteowners.com/qanda/su001.htm
L #416 I've solved my immediate problem with the original leaky dampers by buying a new pair
of shocks from NJB - www.njbshocks.co.uk (reasonable at £78 + post). The bottom eyes of my
original shocks had 2 tapered rubber bushes, the NJB shocks come within a parallel bush and shim
washers to line them up. They have transformed the ride and are highly recommended - they look
identical to Girlings. Now I've got my old shocks off I can see that the dampers are way past simply
refilling. The tube has rusted where the bike was stood for years and the seal has gone. The options
seem to be somehow hard chrome the damper and replace the seal or get new damper units for the
old covers. I don't think I'll bother as I'm happy with the bike as it is now but I can't see how
drilling/refilling alone can be satisfactory..
#487 My 1948 MAC has Dowty air filled forks fitted, working fine till last weekend run of 110 miles,
they now lose pressure completely over 4 day period, anyone else had this problem and is it curable?
I have refilled each leg with clean oil and hope this may help, what grade oil is best straight 20 grade
recommended originally.
#524 I hope changing oil has rectified your Dowty. I had a pair that I was going to fit to my 1948 MAC.
I dragged them around three house moves in twenty years, leaking oil continuously! I looked to fit new
seals but these are now virtually impossible to get hold of. Carol who does all the UK Velo auto
jumbles had some seals for Dowty, but I don’t know if she has any left. Another alternative is that
Sammy Miller does/did spring conversion kits for Dowty www.sammymiller.co.uk if you get
desperate..
#528 Thanks for reply the oil change has made things worse, forks lose pressure in 10 hour period
now, are they likely to "collapse" suddenly whilst being ridden? Could you let me know how to contact
Carol to see if she has any seals, cheers Dave..
#537 The last number I had for Carol Kear was 01242 239432.
#684 I have managed to find a source of Dowty Fork Seals at a much lower price than other suppliers
charge, that is if you can find a supplier, I can get them through the hydraulics company I work for.
L #658 I dismantled the (girder) forks the other day - an interesting exercise! - but I can't seem
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to free the bottom of the spring from the forks, anybody know if it's screwed/clamped on or is it just
being held on by rust? Forks are marked "The Webb" if that helps!
#664 The bottom of the spring is screwed onto a flattened thread: tap it a few times, lubricate it and
then unscrew.....they can be tight.
L #879 Here's a question for the group... where can I get tapered tube for heavyweight Webb's
to replace my damaged ones. And how were they made originally, was it in one complete tube from
the top lug down or two? (i.e. four tubes per set or eight tubes per set).
#882 I believe that Percival and Webb of Dudley West Midlands are still going strong. I think they still
make girder forks and do overhauls and repairs. I think they are a offshoot of autocycle which is run
by Chris Williams.
#889 Try Ray Daniels 144 Station Road Stechford Birmingham B33 8BT Phone 0121 789 8900
L #1033 my 500 velo has a set of ajs or matchless front forks, which I think are the same, I just
wondered why? can any body tell me if there is any benefit to them.
#1034 You don't give a description of them, but later model Matchless forks were both compression
and rebound damped with a rebound spring that kept them from "topping out". The Thruxton and
Scrambler Velos had rebound damping, but for off road the Matchless forks were a better bet. Norton
(I'm in trouble now) put the Matchless forks on their P-11 desert racer instead of their Roadholders.
L #1076 One of my VM's gives a very slight 'fluttering' sensation from the front end on fast
sweeping bends. It is worse with flat bars, with clip-ons and weight further forward it is not so bad, but
still there. What could be causing it? Frame and forks are straight, s/arm is fine, r/shocks are new,
tires are good TT100's. S/head + wheel bearings are fine. Yokes are straight and forks straight in
them. I thought of these possibles: 1. Tyre pressures wrong 2. Im not going fast enough (quite
possible) 3. unequal damping from front forks - i.e. no oil in one (I’ve not checked this properly, but
one is leaking) 4. front wheel unbalanced (full width hub using TLS) (not checked yet) 5. front wheel
out of true (not checked yet, but using alloy rims so not impossible) Screwing the steering damper
down a bit further/or backing it off has little or no effect (on the flutter). Any advice welcome.
#1077 had the same problem on a high mileage bike a few years ago. Eventually I found I could make
the problem go away by putting a slight drag on the front brake while heeled over in a corner.
Disassembly of the forks revealed nothing "wrong" but I finally discovered that the bottom fork tube
bushing had worn the slider out to where holding the slider in a vise the top of the fork tube could
move back and forth over a quarter inch. New sliders fixed it. Hope this helps.
#1085 For what it's worth, here's my experience with Velo handling issues; Regarding the head
waggle at lower speeds; I'd definitely check the fork bushings. Slack or shagged head bearings can
give a similar feeling, but usually only at slow speeds. Unequal fork oil levels give more of a rocking
motion up front; setting your shocks to slightly different places on the 'arc' does the same at the rear,
as will slack or shagged swingarm bushes and completely worn out shocks. Combining all of the
above makes the whole plot feel seaborne, but the bike won't throw you even when completely worn
out in the chassis, it just takes more bottle to ride quickly - at least this is my experience. (This applies
to swingarm models; if you ask me, the rigid MSS/KSS mk2 shouldn't be trusted at the limit, the
geometry doesn't 'sing' as do earlier KTT/KSS models) All Velos will weave a little at over 100 mph;
not dangerous or scary, just one of those Velo traits we come to love. Except the mkVIII for some
reason; it feels very true at high speeds, which is odd given the geometry of the swingarm models is
basically the same. Could girders be more stable at high speeds? My rigid KTT mkIV weaves just like
a Thruxton at over the 'ton', but at that point it's the least of your worries! Brakes please! In light of all
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this, check your forks! Velos feel so much more secure when all is shipshape. And I can't recommend
Work Performance rear shocks highly enough; I've had them on my VMT for 5 years and now I only
notice the front fork's inadequacies.
L #1096 Simple perhaps, but so that I don't waste time & money ,what is the modern equivalent
please ,of the oils recommended for the front forks in the Service Manual.
#1097 I like Silkolene SAE 20 fork oil. It's sold at most motorcycle shops.
L #1342 As part of my complete Winter strip/rebuild I took the front forks to bits on my 1960
Venom, not that there was any problem it was just that all the parts were being resprayed so it
seemed a good opportunity. I replaced the pistons and the bushes in the fork damper tubes and also
the front fork tube bush and the fork slider tube bush and the oil seal. The fork tube/stanchions were
straight and did not appear to be particularly worn. I have just put the fork legs back into the steering
column assembly and the fork cross member and tightened everything up. With the bike on the centre
stand if I grasp the front wheel between my legs I can move the handlebars a couple of inches. I
removed one fork from the bike, removed the spring dust cover and also the headlamp cowl bracket. I
refitted the fork leg without the wheel. Although I could twist the slider tube against the spring there
did not appear to be play in any direction. I refitted the spring cover etc and refitted the fork leg.
Without the wheel I could twist the slider tube but there was no obvious movement. However once I
put the wheel in I was still able to twist the handlebars whilst gripping the wheel. I realize I must be
missing the obvious but frankly I do not know what it is.
#1363 Install the front fender brackets-all three of them making sure they're straight-and snug the
bolts fairly well. Check for your "twisting" action now. It should be significantly less. With the front
fender mounted the whole assembly should twist very little. Be sure the fork pinch bolts on the lower
steering head are tight, too.
#1366 I think you are spot on in your suggestions. I think there were two problems. One - I hadn't
appreciated how important the mudguard brackets were to the rigidity of the front forks and secondly
having cleaned the rust from the fork stanchions so that I could get the sleeve tubes off to remove the
springs, how important it was to get the bolts really tight on the lower steering head. Although I
thought mine were tight with the rust free stanchion it was allowing the sleeve tube to move when I
tried to twist it.
L #1374 Can anybody tell me / point me in the direction of a drawing / write up of how girder
forks are supposed to be assembled? The spindles / plates in mine (Webb) seemed to have an odd
combination of threaded / not threaded which did not make them easy to get apart! Also, what
material(s) are the spindles / bushes supposed to be made of?
#1376 The answer re girder fork assembly is rather long and depends on whether you have the right
bits to start with! The spindles should be a decent steel EN16T (not silver steel or mild steel) The
bushes are a bronze, not specific really but not too soft. The spindles are screwed into the link on one
side and the opposite end is unthreaded and shouldered. This allows the spindle to be screwed into
the link to adjust the length and hence end play. Between the link and the yoke or girder blade there is
a knurled hardened steel washer. This must be adjusted to allow one washer to revolve with no side
play. There is a lock nut outside of all the links. The threaded end is a lock nut which sets the spindle
length fast once the adjustment has been made. The other (on the smaller end) stops the link from
falling off! Follow the above and you can get forks which are a delight to ride with and the handling
can be nicer than tele forks (on the right surface)
#1377 How do I make a puller to get the bushes out (what's left of them - I strongly suspect the ones
in the bottom link are totally worn away?
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#1378 Richard, look at expanding type pullers made for pulling bearings from blind holes. Kukko,
Hazet, and Heyco, all three well known German automotive tool makers, build very nice examples. In
the USA, MAC Tools make several nice examples.
#1379 Tap a thread in the bushes, screw in a bolt and tap them out with a drift from the opposite end.
#1380 The new bushes should be pushed in and bored in line. As you will probably not be able to get
that done you will need an in line reamer or at least a reamer with a pilot to ensure that the finished
bores are in line with each other. There is one other method. This requires a lathe. The reamer is held
in the chuck and the fork member held with a centre in the tail stock. The reamer passes through one
bush and then reverse the fork member and ream the other bush. As the lathe has been used the
bores should be in line. Whichever method you use you will require some expertise and tooling.
#1381 I am thinking to buy the reamers. But I do not know how to use them. Big question of Hand
reamer makes hole really parallel? Reason is that someone previous owner reamed first gear bush
but did not do parallel. As sequence first gear on layshaft lost the almost one side of tooth. It can be
very expensive. My mistake was I bought the bushes, not having the reamer or any tool but used wet
and dry very carefully. At the end my engineers square said it not parallel!! So now I wasted £10 for
bushes. My next step was phone some velo related shops today. They are all busy and not really
interested in such one small job(I do not blame them.) My next step will be buy reamer( I do not know
which I should get adjustable, taper or so on and it seems to be more type from previous mails) I still
bit afraid of waste further £10 bushes and cost of reamer. I have micrometer ,engineer square and
patient to work on. If I get the reamer it will be all fine? how to use them?(is it fit on the tap holder?)
#1382 Hand reamers are among the most difficult cutting tools for a machinist to master. Accuracy
can be improved if the reamer can be held in a chuck and the part to be reamed is held in a lathe
chuck, machine vise, or on a flat table. Reamers are easily damaged if dropped, turned backwards,
forced, or harshly used. Adjustable reamers are best when one must ream numerous holes that vary
by a few thousandths and want only one reamer. Good quality reamers are expensive and one could
expect to pay $40.00 US dollars and up for a good quality hand expansion reamer for ½" holes. Spiral
reamers are easiest to use and easily produce straight holes with out chatter. Reamers in most all
cases must be flooded with cutting oil to work best. There are cheap adjustable steel blade reamers
that sell for $10.00 US dollars and up, but are not easily used by hand and will chatter and give a poor
finish in most cases. Only freshly sharpened reamers or new reamers should be used for brass
bushes.
L #1652 Haynes velo manual says.."occasionally difficulty is encountered when attempting to
reposition the fully assembled fork legs in the steering head yokes. If the lower, split yoke cannot be
spread sufficiently to ease the passage of the stanchion before the clamp bolt is replaced, a rope
tourniquet can be used to good effect". Is there any other way than using a 10lb hammer and chisel
to widen the split yoke in order to get the split collar in place? Wouldn’t the tourniquet just compress
the springs?.....anyway funny the red book doesn’t help in this.....Any environmentally friendly
suggestions?
#1653 Re: the bottom fork yokes. The right way (I think) is to use a tapered wedge with a hammer -
not 10 lb its rather overkill - and ease the split clamp on the yoke just enough to allow the separate
stanchion clamp to slip into place; align the spring location to angle the fork slider & fork spring
correctly then remove the wedge and clamp up with the bolt. If this is done sympathetically its an easy
job, otherwise......
#1655 Well I tried to prise the lower yoke and managed to open the gap but it seems the yoke hole is
now slightly elongated and it is harder to get the split collar in. Do you wedge the yoke open while its
on the bike? I took it off and tried still no joy Have you ever tried the tourniquet? Have you ever tried to
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fit the collar first by knocking it in the yoke? Now I wonder how I ever got it off. Are there any other
tricks?
#1663 I also struggled with my forks recently, I managed to get the collar to fit most of the way into the
yoke when I cleaned the rust etc off both. I persuaded it to fit all the way by pushing the bike forward
and pulling the brake on as hard as possible. Another way is to lift the front end of the bike and drop it
rapidly. Harsh but does help as long as someone is holding the bike.
#1664 Thanks I was beginning to think there was no hope on this one. I even dreamed about the
darned thing. Only problem is im at the beginning stages of rebuilding the bike so only the bare frame
to work with. I guess if I heated it up and maybe froze the collar that might help, but then id lose the
paint.
#1753 When I overhauled my forks I cleaned all the surfaces with fine wet dry to as shiny a finish as I
could get and put a light oil covering and that made the sleeves at the top of the springs go into the
yokes ok I also used the rope Spanish windlass trick and a few thumps with a heavy hide ended
hammer to overcome the stick friction if you know what I mean. I also use the bumping technique to
ensure the forks were bottomed and the spindle aligned before tightening the forks bolts as per the
red book.
L #1731 I have reassembled the forks on a venom and topped them up with oil. There is a slight
oil leak past the large retaining nut which secures the damper assembly inside the bottom of the fork
leg. The BMS service series book says this is common and can be fixed by removing the nut with the
weight on the bike to keep the damper in position after draining the oil. They degrease the thread etc
and use 3M super weather strip adhesive, or a sealer used on Vauxhall Viva's (that dates it). Does
anyone know of a more modern sealant that I can find easily?
#1733 Bath silicon works a treat. I also make up top hat washers to accurately locate the 3/8 bsf
thread in the much larger hole.
L #1838 I have a Venom 57 which is currently fitted with Girling units of type TT Gas Shock.
These might be fine for racing, but is uncomfortable in regular road use. I am looking for a set of units
with a softer setting ideal for one-up on road. I know of a few alternatives: Hagon, NJB. Are there
more alternatives, and which is the one to choose ? Nice if someone with experience from testing
several alternatives could give me a recommendation. Any thoughts about ideal spring rating front and
rear?.
#1839 I would recommend that you use the standard spring rating for Velocette shocks and simply set
the top mount in the forward part of the mounting arc if you want a softer setting, or the rearward part
if you want a harder ride or are carrying a pillion. This is the reason for the Velo spring frame design
and is superior to other manufacturers' designs up to and including the present day. This is because
99% of other machines which have any form of adjustment on the suspension system use spring
preload adjustment to compensate for carrying heavier loads. This method does not change the
spring rate (which is what you really want) but basically alters the ride height by changing the amount
of load required to start compressing the spring(s). Ideally your machine should be set up so that
sitting under its own weight there should be a small amount of sag (about 8-10mm at the rear and
20-25mm at the front). This can be done on the rear on Velos with Girling, Hagon or Koni shocks by
adjusting the preload ramp cam to give the required amount of sag. When you then adjust the position
of the top mount in its arc, the resultant change in leverage ratio changes the effective spring rate
without having to change the spring, which would be the only way to achieve the same result on any
machine with fixed suspension mounts. If you have damping adjustment on your units (a luxury not
afforded to most Velo owners although some Koni units do have some internal adjustment) you
should not make the mistake of winding on too much damping. The trick is to have just enough to
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keep the machine under control - too much rebound will cause the units not to recover quickly enough
after hitting a bump and wind itself down over a series of bumps in quick succession with the effect
that the ride will feel hard due to the system working on a harder part of the spring and in some cases
the machine might develop a weave due to the resultant change in geometry. Too much compression
will transmit shocks straight through to the frame and will give the feeling of riding a road drill!
#1840 Many of us here in the US have had Works Performance shocks on our VM and VMT's for
years; the owner, Gilles Vaillancourt, is a Velo enthusiast, and has made what some consider the
perfect Velo shock. I think John Ray described them best, 'you just don't notice them when you're
riding' - high praise when you think how often you 'notice' your worn out Girlings! They have modern
internal specs, and I think he offers 'deception' shocks which have long covers like early Woodhead
units, but I've always used the open spring type which look appropriate on my VMT (yes, my '60
Clubman uses nos Woodheads, which are rapidly becoming noticeable).
L #1916 Are the original Velo clip-ons longer in bar length than generics available today; are
they different in any other way?
#1924 I don't think that the current ones will be any different in length , but watch out on the fork leg
diameter . I bought a pair of clip ons from Grove which were supposedly 'Thruxton type ' but were not
correct . the Velo clip on bars butt onto the tube which clamps onto the fork leg . the ones I obtained
were secured in front of the fork leg clamp . I kept them until I found a pair of second hand ones at an
Autojumble .
#1917 What is the exact bolt up configuration for the loops most forward bolt on both sides?
#1925 These blot into the fixing point inside the 'arcuate ' section of the frame . 5/16 bolts with
spacers to ensure they clear the shock absorber tops on adjustment . The offside mount is also the
mounting for the VMT oil tank.
L #2826 According to the various books I have all I need to do is slide the fork slider tube
assembly smartly along the tube to jar the seal and bush free. Does anyone have a trick or alternative
method? For further information if this helps. The forks tube is rusted and must be replaced. Judging
by that much of the other parts are due for replacement.
#2830 That's exactly how to do it! Clamp the slider by the spindle boss in a set of soft jaws to protect
it, screw out the spring from its location and remove it, then use the stanchion as a slide hammer to
remove the top bush and seal - easy!.
L #3133 I am currently re-building a 1970 Venom Clubman, the shock absorbers are well past
their best. Could anyone recommend a replacement? I have heard that NJBs are quite good? Any
advice would be gratefully received..
#3137 Last summer I had to replace my rear shock and have been quite happy with a pair of Hagon
Shocks.
#3140 Heard suggestions that Hagon aren't good long-term, but don't know exactly what long-term
means.
#3150 I fitted NJB's last year, because the Girlings failed MOT on damping, but only a few miles and
seem OK.
#3151 Heard our Australian friends reproduce the Konis, under a name which is more or less "Koni"
backwards.
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#3152 They sell all the KP they produce under the name "Castlemain"
L #3597 Vibration on my '66 Thruxton has broken the central stay on the front mud guard. The
break is thru the 5/16" bolt hole, where the stay is clamped between the slider and the triangular plate.
My first inclination is to fabricate a steel gusset and weld the damaged stay. I'd suspect I'm not alone
in this malady. Is there a "recommended" repair to reduce the likelihood of this stay promptly breaking
again?
#3601 I've had to make this repair a number of times, and the best repair that I've found is to cut the
stay on both sides of the wheel about 1 1/2" above the broken bolt hole and make up a lower portion
from 1/8" plate about 1 1/4" wide and long enough to reach an inch above the cut off stay, then drill
new mounting holes in the new plate. The vertical centerline of the new mounting plate will then be
well behind the centerline of the original stay, so I notch the new plate to match the cut end of the
stay, butt weld the joint and bevel cut the remaining square corner off of the new lower plate. After
painting, the mod is noticeable to only the discriminating eye and the stay will not break again. I tend
to use a lot of revs when I ride so have had a number of these breakages over the years and have
decided that the cause is due to the requirement that the engine balance is biased to a front to back
shaking which makes a pendulum out of ancillaries such as the fenders (mudguards), oil tanks, etc.,
leading to bracket cracking. The centre front stay is weakest at the top bolt hole, so that's where it
breaks. If you watch the rear extension of the rear mudguard (fender) of your Thruxton, you'll see
cracks developing near the rear mounting holes which will soon lead to the back portion of the fender
together with rear light and number plate dropping into the road. I was able to make a repair to mine,
using a portion of a larger section BSA fender of heavier material and slightly larger radius. I trimmed
it to fit inside the VMT fender and welded it in place, bridging the break by about 6" each direction.
After careful smoothing of the welded joints and repainting, people only saw it after I pointed it out and
it did not break again.
#3602 That centre stay isn't really a mudguard stay. It helps keep the two fork bottom sliders in the
act.
L #3864 Can anyone recommend a suitable material for the damper on Webb Girder forks.
#3865 There are readily available discs for M20 BSA's and the friction discs used on Harley WLA (and
similar models) rocker clutch pedals may be adaptable
#3868 For years I have used friction material tossed out by the clutch service mobs, It appears that in
a lot of cases a ring of material of a suitable size is cut from flat sheet, this leaves a whole lot of scrap
circles up to about 4 inches in diameter. It comes in various thicknesses, but the thinnest, while being
thicker than what was used originally can be adapted to do the job. I even 'Araldite' slabs together to
make up new friction drive cones for one of my ride on mowers . There are several different
compounds used. Try visiting a clutch repair specialist shop, & ask the shop foreman. All my steering
& fork dampers have this material installed.
L #3881 I am the proud owner of an MAC which is close to the same age as me, thanks to a
generous Christmas present from my wife. The MAC was first registered in January 1947, so it must
have been produced around the same time as me in August 1946. Like me, the MAC looks well worn,
but unlike me it should be amenable to refurbishment. If I held the front brake on and pushed the
handlebars back and for the fork spring looked unmoved, but the top spindles moved in their links. I
have now removed the girders and comparing the parts to a 1939 Spare Part List I appear to have
lightweight girders with the thicker bottom links, married to a 'Heavy Type' steering column. This
leaves me with three 7/16 spindles and one 3/8 at the top of the girders. I raided the Club's spare
parts store and found all the necessary new bushes and the three larger diameter spindles. I also
purchased a 3/8 diameter stainless steel rod of the correct length, threaded at both ends at last
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week's Kempton Park autojumble. The threads were advertised as 26 t.p.i. and match the threads on
the other spindles. This leaves me with at least three problems with which I would appreciate your
help. What is the best way to repair the threaded top link. Perhaps I could use helicoils, but I can't find
any advertised at 26 tpi is there an equivalent thread designation, e.g. BSF etc.? With the answer to
this question I can get a matching tap and extend the thread on my ss rod. I would also appreciate
advice on how best to remove the existing bushes; will I need to resort to a hacksaw blade? Any other
related 'watch its' or pearls of wisdom would also be appreciated.
#3882 While I have no personal experience in what I'm about to write, I've read extensively and the
following comments are derived from that written information: In the old Fishtails, it was stated
repeatedly that stainless steel has very poor shear strength and that the use of stainless in fork
spindles may lead to failure. You may want to visualize the result of shearing of that SS spindle that
you got at Kempton. There are different grades of stainless and the more easily machined (threaded)
grades are also the weakest.
#3883 Im not sure I follow but if you have a "bad" hole that is 26 tpi you can certainly rebore it to the
next larger size and retap Have a machinist turn a "knocker" to the appropriate od and id and press or
knock the old bushings out, Its very simple to make and can be of any material even aluminum.
#3885 1) Helicoils, try www.uni-thread.com/helicoil1.html 2) Removing bushes. Using a larger tap cut
a thread in the bush, screw in a bolt and drift the bush out from the other end. 3) Don't use the
stainless you bought for the spindles. The recommended material is EN16 steel. 4) You should "line
ream" the bush, not ream the bush from each side separately.
#3886 If I can add a few thoughts. The steel to use is EN16, another material to avoid is silver steel.
Taps & dies are available from Tracy Tools, Dartmouth. A steel bush oversized screwed into the links
and silver soldered or brazed in place will allow you to re-thread to the required size. As Dai said, a
line reamer or one with a pilot is essential. You can however do the job with a lathe and suitable
tailstock centre. Hold the reamer in the chuck. If the bushes are out of line you will have wasted a lot
of effort!
#3890 Girder fork links, I don't know if my method is the best, but it's certainly the simplest in my mind.
I wouldn't know how many sets of links that I have refurbished, - or how many new sets that I have
made, however, I just drill the old threads out cleanly, then fill up the hole with bronze gas welding &
retap. There is more to this sometimes, especially in the case of early Velocette two strokes, old plain
bolts sometimes having been used in drilled out links, in place of the original spindles! - if all the links
are in bad shape, (bent, twisted, offset, plain & threaded holes elongated), & of the same dimensions,
it is better to start, (after straightening!) with a link with the ruined smaller plain holes, - & just redrill
these & tap to the required size, to make a link with the larger diameter 26 TPI threads. This process
is repeated with the other plain hole link if needed, & you finish up with a couple of links with stuffed
threaded holes both ends, these are the ones that you fill with bronze & redrill to the original small
size. This may sound a bit confusing , but it's quite simple. Silver soldering a 'slug' of mild steel into
these holes is also a good way, as I prefer to do the drilling & the tapping of the new thread AFTER
the hole has been filled, rather than making up fiddly threaded inserts, the thread of which isn't
improved by the heat of silver soldering into place. There is also the problem in cases of bad linkage
damage of making sure that the new holes in the links are in fact of the same distance centres. The
GS rebuild, (& many others), has a complete set of links rebuilt by this method, & NOS spindles. One
perk of using the original links, rather than making new ones, is that you retain the makers stamp on
the side of the links if you are lucky ! As to the spindles, - obviously a No No to use silver steel or
stainless. As it happens I have a large quantity of high quality (probably original British spares) NOS
spindles, ex the stock of our old Velocette exponent Frank Mussett, I am lucky in that I can just go to
the shelf & select a new set, - but certain sizes & lengths are now depleted, & I have resorted to
shortening existing (longer) stock to do the job. I don't know if I have the size(s) needed, or if postage
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is viable, but given the size needed, I can check what I have left. I also have many NOS 'exotic'
spindles of the 20's & 30's that I cannot identify, possibly Rudge etc. maybe of use to some
enthusiast.
L #3908 Anyone know what taper-roller bearings are suitable for the head- races of a 1946 rigid
MAC, or failing that a source of good cup & cones as there are some very poor ones floating around
at present. My MOV has tapers, but were fitted by the previous owner, so apart from removing them I
cannot identify them.
#3910 You can use the same ones as for a Venom/MSS etc, but the o/d is slightly different so they
have to be wrapped in suitable shimstock for a tight fit. The lower inner or the stem needs modifying
slightly also.
Taper rollers or cups and cones are available from your friendly Lakebay Velo dealer!
www.veloed.tripod.com
#3913 Not quite a simple as that, because the base of Venom (etc.) cups are basically square,
whereas the rigid models are "cupped" on the outside as well as the inside.
#3914 That's true, but they can be packed out and fitted nonetheless.
#3915 Unless the Venom taper races are very much shallower, then the outer ring of the races will
have to be ground into a curved shape to fit the frame, so together with the Venom races being a
smaller diameter there is a lot of work that needs to be done to make these fit. I think I shall have to
dismantle my MOV and see how it was done.
L #4113 can anybody tell me what sort of oil to put in the struts of my 65 viper thanks
#4114 I'm using 10w/40 at the recommendation of Ed Gilkison. He also recommends 120cc per leg
check out http://velogb.tripod.com/page14.html
#4115 I had a look at that link and it may have given me a lead on why my primary chain eats my
chain case. thanks again
#4117 I, and many other Velo users I know use Silkoline 20W fork oil as it's designed as a fork
damping oil www.silkolene.com
L #4133 Why the scratch on double-damped Velo forks? I've ridden single-damped Venoms
hard, and the yabbada yabbada of the front end over less than perfect roads did nothing to inspire
confidence! I've put later style front ends on all my tele fork Velos since then. Now, girder forks can
tend to make one's wrists ache and teeth chatter, so all hydraulic forks seem like luxury by
comparison, even if heavier.
#4134 If you have the girder fork's dampers up too stiff you will have a rough ride. Let the forks 'float'
and the difference is amazing. This will not affect the roadholding either. By comparison, the double
damped forks are too stiff on compression and transfer road shocks far more. (at least on our roads!)
#4137 Having restored the dd-forks on my Venom I found the stopper plates for the damper piston
rings to be a very tight fit in the damper cylinder. During compression the oil has to pass through this
clearance and then through the gap (axial clearance) between the piston ring and the stopper plate. In
order to get a more defined flow area (resistance) I reduced the diameter of the stopper plate by about
1 mm. This should transfer the flow resistance to the axial gap alone. The gap was then adjusted to
0.25 mm (by guessing). The result is a somewhat softer compression damping but surely not ideal.
Rebound damping also feels insufficient. Has anybody experience of tuning the velocette double
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dampers (compression/rebound damping? What are the spring rate rates in front?
#4139 I had a Velo fork tube in one hand the other day and a damper out of a '70's Moto Guzzi in the
other. With a bit of trimming the Guzzi damper looked like it might fit, though Guzzi dampers are not
known for being all that good. They do make after-market dampers for the Guzzis, so with a bit of
research and effort one could have gas charged, adjustable, modern dampers in a Velo fork. That
said, the stock dd forks with 10w oil work fine for me. I will take note of Ingebrigt's observations next
time I have some apart.
L #4136 Greetings all, I need to replace a worn out set of gaiters on my '66 VMT. Knowing the
upper spring seat must be "twisted" on the stanchion to ensure the spring is clamped in the spring
seat, is there a way to install new gaiters without completely stripping the mudguard, stays etc. from
the bike?
#4138 The easiest way to fit gaiters is to remove wheel & guard, drop off the sliders and providing you
have short tubular shrouds fit the gaiters & all the rest. Without short tubes to hold the gaiters you will
have to strip the stanchions off too. Have fun - its really not that bad!
#4141 Surely he must have short tubes if he is replacing the gaiters. If it had the long shroud tubes he
wouldn't be able to fit the gaiters in the first place. Totally agree with you regarding the replacement
method. When refitting the top bush, I found it useful to use the old two piece split clamp headlamp
bracket(beloved of all old café racers) as a slide hammer to knock in the bush. Don' forget the oil seal
before fitting the bush.
L #4145 While we are on the subject of front forks I will ask a question again just in case
someone out there has the answer and missed my question last time around. What is the centre to
centre distance between the front fork tubes? I have measured various top and bottom yokes and
they are all different centres so I am looking to find a set which will make the fork tubes parallel. Hope
to get a distance this time
#4148 You could undo the top stanchion nuts, undo the damper rods ( retain with string for
reassembly) slacken off the bottom fork yoke bolts and draw the stanchions right out downwards...
probably have to undo the brake cable.
#4150 I'm not sure how I'd be able to reassemble and rotate the upper spring holders 15 to 20
degrees to lock the springs tightly in place. Am I missing something in the reassembly phase? I can
not think of any way to do this task except remove the mud guard and stays, orient the sliders to the
side and reassemble. I'd hoped to save a few steps and avoid the potential damage to the paint work.
#4151 Exactly; you cannot locate the spring carriers with the fork legs complete below!
#4170 Sorry to disappoint you but the distance that you are looking for is a variable; it's one of the
reasons for the front wheel spindle having that shifty little bush which is clamped in the L/H fork slider.
No doubt there is a Charles Udall drawing that shows this dimension but I would be interested to know
what the +/- tolerance is. I have fork yokes that have been bored so far off centre that the forging has
been built up with braze in order to keep the appearance of concentricity - by the original
manufacturer! The yokes were bored as a pair and must be kept as such. If your yokes are out of
parallel and there is no evidence of impact damage then it is possible that they are not an original
"matched pair". The forgings are soft as butter and it doesn't take much to knock them out of
alignment. By the same token, they can be easily re-aligned but you need to find the right bloke to do
it.
L #4406 So after spending a year or so rebuilding the venom and riding it around for 700 miles
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or so I managed to fall off it a couple of weeks ago. Looking at the bike the damage seems pretty
cosmetic although there are a couple of points I need a little advise on. 1. The gear change level got
bent. This is aluminum and I think it can be straightened. My question is should I use heat, and how
much? 2. I cant be sure on this because I cant lift the bike onto its center stand yet, but the front
wheel alignment does not look right. Is there a way of checking this apart from eyeballing it? If
something is bent does anyone have any advice re straightening the forks?
#4407 . I'd straighten the shift lever cold. Just take it off, clamp in a vise with protected jaws, and bend
it straight. I've straightened a lot of forks as follows: Disassemble the legs and place a stanchion on a
pair of alloy blocks that you have made from a chunk of metal about 2 ½" square by 1" thick, bored to
slightly larger diameter than the stanchion and cut in half so that you have a pair of vee blocks with
round cradles. Then place a third block on the bent area to receive the ram of a hydraulic press, and
press it straight. I use a dial gauge on a holder to find the high spot, mark it with felt pen, then press.
The stanchion will have pretty good memory, so you'll have to press it past straight and it'll spring
back. Take it slow, checking regularly, and you'll be able to get it within .002"-005" of straight if it
hasn't been kinked. When I'm trying to get the last bit of bend out of it, I mount the gauge right beside
the ram of the press, take note of the gauge reading, and increase the deflection .002" per attempt
until it is the best that I can get. Then I mount the lower triple clamp in the vise with the steering stem
horizontal between the jaws, and clamp the stanchions in place. I use the MK I eyeball to verify that
the stanchions are parallel in the horizontal plane and then slide the top triple clamp on to verify that
the stanchions are parallel in all planes. If not, I bend the lower triple clamp cold, using the clamped in
stanchions as levers until it's all parallel. Reassemble, and Bob's yer uncle!
#4410 A quick and easy way to check if the forks stanchions are bent is to simply undo the large top
nut and pull up the damper rod a little. If it is not coming up the centre of the stanchion, the fork leg is
bent. The damper rod is seldom bent, revolving it will soon show it is.
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F.2. Brakes Wheels and Tires -
L #44 Bob Jolly makes replica mk VIII magnesium hubs/brake plates/shoes (yes these are mag
too), in Australia, they cost about $800 us/ea, depending on exchange rate.
L #21 I found that a set of tires, Avon Speedmaster ribbed front, Roadrunner rear, lasted 3
thousand miles, period. .
L #83 Does anyone know the correct tyre pressures for Dunlop TT 100's when fitted to a
Venom?
#90 Avon Roadrunner AM20 90/90H19 front @ 22 psi, Avon Super Venom AM18 100/90V19 rear @
24/26 psi. An added benefit, they even make the bike look faster!!!
#653 1960 Venom clubman, I am using Dunlop K81 (TT 100) tyres front and rear. What are the
suggested tyre pressures?
#84 Modern tyre pressures need higher pressures than those figures published in 60's and 70's. I
have a table of pressures for tyres which I hope to publish on the technical site soon. However if my
memory serves me well, TT100's are 3.60 X 19 front, 4.10 X 19 rear. That gives pressures of 26 tpi
front, 28 tpi rear for a machine and rider of 580 pounds. This was confirmed by a leading UK supplier
of tyres who independently recommended 24 and 28 respectively. By the way I run Avon Venoms
and Super Venoms on my Venom at 22psi front 26 psi rear, and they handle perfectly.
L #172 I have recently acquired a Venom Clubman which has a very slightly buckled Front
wheel rim. In addition, the front brake is grabbing and sending a vibration through the forks which
feels like the wheel brake drum has become slightly oval. Please could anyone advise the best
course of action? Is it possible to skim the drake drum, and to straighten a slightly bent rim, or do I
need new components. Also if anyone has any contacts who have experience of such work, I would
be very grateful to receive your feedback. Finally, I am considering at the same time upgrading the
front brake to a twin leading shoe one. Again, any help in sourcing one would be useful.
#173 Is the rim actually dented or merely out of true? A bit of careful and patient spoke tuning will
correct the latter. If it is dented, it must be disassembled and straightened. Don't let some sharp talk
you out of it, as Dunlop alloy rims are very desirable items. Personally, I have had little luck skimming
Velo drums when not spoked to a rim. If you can find a lathe that will accept a complete wheel, it is
worth a try. True the rim first.
#174 Before you buy a TLS, make sure the drum is round and the linings well matched. Give the
original brake a fair trial. I changed my Venom over to a Dodkin/Velo TLS in 1988. It has never been
much more powerful than the original, and is utterly useless when backing down a ramp! Perhaps the
racers find it more fade resistant, but don't assume that it will let you do stoppies.
#175 Grove Classics sell the iron half of the front hub for a Venom/Viper approx £150, if you need to
replace it.
L #226 I have a Borrani WM2/1.85-19/36/Record RM-01-4354 Rim laced to a Venom full width
hub. Does anybody know if a replacement is available that matches or nearly matches this Borrani
#227 I am assuming you have a flanged Borrani aluminum rim. Currently I have three Velos that sport
alloy rims including Dunlops Akronts, UK made ali rims and have had Borranis in the past. Borranis
are recognized by those in the know as being the best. Even if you find a second hand Borrani you
need to ensure that the dimple pattern, spoke hole angle and diameters are suitable for lacing to a
Velo hub. Currently in the UK to my knowledge there are two replacement flanged alloy rims available.
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Unless you look at them closely they look similar to Borranis or Dunlops. However they are not as well
finished, so if you buy one check in the area of the weld for the quality of finished. Secondly one of
these rims has very crude looking dimples, so take care. Further details on the rims can be found via
the link below. www.central-wheel.co.uk/cwc/rims.html
L #463 For my 1952 MAC rigid documentation say front and rear tyre both 3.25 x 19. My front
tyre is Metzeler Perfect ME 11 - 3.25 x 19. My rear tyre is Avon Roadrunner 90/90 H 19 - 3.60 H 19. I
was informed that it could be difficult to get the rear tyre homologated in Germany. Is there any
information / documentation available about my rear tyre size being eligible?.
#471 From the German representation of Avon Tyres I got confirmation that the "old" tyre size
3.00/3.25 corresponds with the actual specification 3.60 (or 90/90 in Metric). So they have sent a
certificate to me saying that the tyre 3.60-19 is the right application for a Velocette MAC.
L #547 I was wondering what would be some appropriate tires for my Venom. I'm looking for
something a little more modern than what was originally used.
#548 You can't get any better than a good set of TT 100's they were good enough for the TT they will
give you everything you want with the venom.
#549 I'm a Dunlop fan for the moderns, but on the Velos there is nothing better than Avons,
Speedmaster II front and Roadrunner Universal on the back. They are made in the old molds but of
modern compounds. They wear out very quickly (

(WM1) x 36 holes? Was the rear rim (WM2) 19" x 40 holes?
#954 The rear brake drum and sprocket are one piece The top links are 3.25" between centres The
bottom links are 3.5" between centres The carbs in 29 would have been a brass Amal (pre mono
block type) The front rim is 21" WM1 36 holes The rear is 21" WM1 40 holes Which brake rod are you
referring to? - the rear is .25" with a BSF thread; the front isn't (I'll have to check if that's the one
you're after.) The rear brake drum has 1" linings for the KTT, as far as the width of the hub overall
goes I'll have to do a sketch.
L #1081 I have just laced a pair of alloy rims for my Clubman and am having a lot of trouble
getting rid of the few last high spots as I try to true them. Are alloy rims inherently more difficult to
true? How near enough is near enough in terms of run out? I'm somewhere between 1 - 2 mm, but
compared with the results I've had with steel rims they still look a bit wobbly to me.
#1082 In my experience (I have built a number of wheels, but not the VM one referred to) it is
generally more difficult to get alloy rims absolutely true - and the Dunlops are worse than the modern
Akronts GENERALLY, although I have had at least one Akront that had to be sent back as it really
was too bad. (I have never worked with Borranis). For road going machines I'd suggest a RADIAL run
out of about 2-3mm but no more is fine, so I would be happy with the 1-2mm you mention. It is usually
very difficult to completely get rid of the 'kick' where the rim is welded (i.e. rim is joined to make the
circle). I'd guess racers would want to achieve something a bit better than this, but that should be fine
for the road. So yes - I'd expect better results with steel rims but not to worry too much with what
you’ve achieved with the alloy ones.
L #1338 Hi I have bought the rear brake drum(worn tooth) the reason ,I was told I could fit the
detachable sprocket. I am told the instruction of how to do this and it is seems to be reasonable as
cost of drum was £5.00. new was £60.00. the problem is I do not have the lathe and welder. my
school lathe is too small do anyone know who I ask to do this ? I am sure that who knows Velo know
exactly where sprocket have to be( I am bit confused because drum was from Venom but I want to put
the small ½" chain.)
#1340 , Re. 're-toothing' your rear brake drum/sprocket try John Hemming at 01547 530 759. He did
mine & it's a good concentric job. More than fifty quid though.
L #1294 I am rebuilding a very original '57 Venom and would like to fit modern - but original
looking tyres to preserve the period appearance. Could any of you advise me on a suitable choice and
supplier (in the UK)?
#1302 Avons are a very good choice, they are period ,were fitted original, are still made in the UK I
think and the rubber doesn’t crack like the Dunlops. Ribbed front.
#1303 See the following post on the VOC site www.velocetteowners.com/qanda/ty001.htm I will also
add that you could equally well fit an Avon Roadrunner rear and ribbed Speedmaster front. If you are
seriously riding your Venom, my advice would be to stay away from the block treaded Avon MkII SM
Regards.
L #1640 Can anyone offer any advice with this first-time wheel removal problem? I took the rear
wheel out yesterday to fit a new tube. My bike is a 1951 MAC and I noticed (when removing the
wheel) that the speedo drive outer housing had been turning with the wheel, leaving a very tight bend
in the cable immediately after the connection collar. With the wheel out of the bike, the speedo drive
unit pulled off and I checked it over. It seemed OK and the inner part was free to turn and was
well-greased with clean grease. There was a spacer which I guess pinches up the outer part when the
wheel spindle is tightened up, leaving the inner gear free to rotate, driven by two lugs. There were no
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earings or anything like that inside. When I put the wheel back in I was careful to make sure that the
Speedo drive was correctly installed and that the outer part wasn't free to turn with the wheel. After a
trial run, I see that's done it again, and the cable is being forced into an even more acute angle this
time. Can anyone give me any advice on how to solve the problem?
#1642 There Should be a spacer known as a clamping sleeve on the inside of the speedo drive. This
locates on the extension of the bearing spacer tube and its inner end butts up against the RH wheel
bearing. The speedo drive is clamped between the outer end of the sleeve and the distance piece
whose other end sits against the inside face of the swinging arm. When the spindle is tightened up
the whole thing should be solid and the speedo drive will not turn. It's not unusual for the clamping
sleeve to have dropped out and been lost when the wheel has been removed at some time but I
should warn you that the machine should most definitely NOT be ridden without it! There is one other
possible cause - that a FRONT wheel spindle has been used in the rear. This is longer than the rear
spindle and will bottom out in the stub axle before it clamps the plot together!
#1643 Thanks a lot you've confirmed something there. The speedo assembly did indeed fall off and a
piece dropped out, which is obviously the clamping sleeve you mention and I'm pleased to say that I
worked out what it must be and fitted it again when I replaced the wheel. You've also confirmed by
assumption that the whole assembly is held in place just by pressure. So maybe I (and the previous
owner) just didn't do it up tight enough. (probably unlikely.) I certainly couldn't move the outer speedo
drive by hand after I'd tightened up the spindle. I'll check the tightness of the spindle again and then
compare the lengths of the front and rear spindles.
L #1910 I'm rebuilding what was an incomplete '57 Viper. Is there a washer/ spacer between the
single leading brake plate and the RH fork tube? If so what thickness should it be? It looks like it
needs a spacer of about 2,5 mm. But I not sure and can't find anything in the books about the subject.
#1912 There should be no spacer between the brake plate and the fork lug. The wheel spindle
(W21/6) is inserted from the LH side, through the split sleeve distance piece (W64/2) and dust cover
assembly (MAS73), through the bearing spacer tube (W62/2)(inside the wheel hub), through the brake
plate distance piece (W52/3)(which normally stays firmly corroded in place in the brake plate itself),
through the RH fork lug and is secured with a thick washer (KS51/2)(about 1/8" thick) and the wheel
nut (W65/2) on the outside of the fork lug. Tighten the wheel nut first with the brake lever pulled in,
then with the pinch bolt on the LH fork lug loose, bounce the forks up and down a couple of times to
centralize the assembly, then finally tighten the pinch bolt.
L #1963 I am rebuilding the wheels on my viper, but am still undecided on chrome or aluminium
wheel rims. What are the advantages and disadvantages.
#1965 Ally looks pretty, is slightly lighter and won't rust. Steel is better in virtually every other respect.
#1971 also you should consider stainless steel, the boys at srm do that stuff and it is not much more
than British chrome.
#1977 An early Borrani rim on a MAC front hub saves 3 pounds, 13 vs. 16 without brake or axle. The
flanges trap oil and the alloy is harder to keep polished. Great for a Clubman, overkill for a tourer.
#1992 Strength, durability, repairability, resistance to buckling or damage from tyre levers, even
electrolytic corrosion from non alloy nipples although I am guessing now. It really is just my opinion,
and it depends whether you want to use the bike as regular transport or show it. I would have gone for
Borranis every time when I was 19, and TT100 and KR70 if I could have afforded them, but now I
would keep to steel for practical reasons. The concept of unspring weight which is often dredged up
when making a case for alloys has been proved to be bunkum if my information is correct, so it really
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is mainly a question of aesthetics, unless you want out and out performance and are prepared to take
a little more time on maintenance.
L #4918 I have a wheel which appears to have been laced with an incorrect rim. The spokes are
not lined up as they should be. The rim is a Dunlop which I was going to have rechromed until I
realized that it wasn’t correct. How do I recognize what the rim is. Are they stamped with an ID Ref. so
it can be seen what the rim is? I need the correct ID Ref. for a rim for a cotton reel rear.
#4919 No such thing as an ID for wheel rims as you describe. The difference is in the drilling. This
varies for spoke angles. I would recommend that a tame wheel builder would identify the drillings
wanted, then have the rim re-plated.
L #1987 I am looking to have my wheels rebuilt, stainless rims, spokes, and nipples. dose
anyone know a good shop here in the usa that can do that? most of the places that I have found
online are in the uk and they are hard to connect with.
#1988 Buchanan's www.buchananspokes.com/ don't list stainless rims on their web page, but when I
spoke with them several years ago they were not adverse to using customer supplied rims.
#1989 North East Wheel Building (John Smith) Ridgewood The Boundry Shinney Row Co. Durham
0191 385 4266
#2005 Ed Gilkison's. www.velogb.tripod. com
L #2212 Hi All, Does anyone have any recommendations regarding tyres for my clubmans
Venom? At present I have a 3.25/19 ribbed on the front and a 4.10/19 studded on the rear, according
to my Velo manual the rear should be a maximum of 3.50. Are there any modern compounds
available in the correct sizes?.
#2213 have Avon Venoms rear100/90/V19 and front 90/90H18 The bike had these on when it came
to me. . I was thinking more along the line of touring style tires as I shall not be racing it! Perhaps
Avon Speedmaster front and Avon SM2 rear (or Dunlop K70) Any comments from you more
experienced riders would also help.
#2215 The 4.10 section is fine for the rear of a VR or VM - it’s a replacement effectively for the 3.50.
#2219 See Q&A section of Velo Owners Club Site. I fitted the Roadrunner AM 20 Front and Super
Venom AM18 Rear as recommended there to my 56 Venom (Clubmanised) Best tyres I've ever had
on a Brit Bike.
#2227 For goodness sake leave the tyres on. In my experience all red blooded Velo riders can't help
but indulge in a bit of scratching when out touring, when road and weather conditions are right. When
you're sliding down the road watching your pride and joy grind away its extremities you'll regret not
having the best 19" road tyres money can buy. And at the moment the widespread consensus is that
the Avon AM18 / AM20 combination is the best for our Velos. I've had them on VMT457 for the past
couple of years and they really are very good. When I put my '69 Clubman on the road for the first
time last April, the pristine looking (but 20 years standing) tyres were hung high in the roof of the shed
as museum pieces and new Pirelli MT65's were fitted. These are also quite suitable for Velo use.
There's no way I would ride a bike of any make equipped with aged tyres on the road, whether riding
with purpose (which all Velos should be!) or just pottering.
L #2267 My venom has tire security bolts installed (to stop the tire slipping around the rim). Dave
Smith (Dave Smith Classic Motorcycles) tells me that Velocette never installed these on
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venom/thruxtons/etc What the forum's views on the need for these. I am planning to install the new
Avon tires as recommended on this message board. The bike has dunlop steel rims.
#2268 Cant imagine any Velo needing them. Power delivery is not that brutal
#2269 Security bolts are not needed on any Velo unless its used for trials with low tyre pressures.
They are truly not of any benefit!
#2270 My experience with my '49 MAC (in '49 - '55!) was that I needed security bolts with chromed
wheels but the painted rims held. Not originally fitted - I had to drill a hole. These would have been
Dunlop 3.50 x 19" (rear) Admittedly, this was mostly on corrugated, pot-holed gravel roads, and I used
to shove her along a bit.. Would modern tyres be any different? The roads certainly are.
#2271 As rubber has improved, it seems to grip the rims well in - in addition to the road! I have raced
with chrome wheels and alloy and never had any need to use security bolts. Different with a more
powerful machine perhaps but even a Manx was OK.
#2398 I had a rapid deflation on the freeway years ago, which required the use of three lanes to
prevent falling, due to the tyre beads falling into the center well of the rim. Since that time, I have
installed two rimlocks (balanced) on everything I ride. This summer, during the first morning of the US
Club rally, one of the members had a rapid deflation which put him in and out of the hospital due to
lack of rimlocks for the week of the rally. I saw him at an event a couple of months later, and his bike
sported rimlocks. Obviously, this won't happen to everyone, but why take the risk?
L #2325 Hello list. Who do you like for wheel rim replacement and rebuilding? (48MAC) I don't
mind buying rims from the UK but I hate to send the wheels that far for rebuilding. Anyone here in the
US?
#2326 Buchanan in California is supposedly among the best here in the States:
www.buchananspokes.com/
#2356 I believe that Ed Gilkenson's business, Velocette Repair Service, in Lakebay, Washington does
wheel building. I've dealt with him for years and he is one straight-up guy.
L #2912 My Viper (1955)is in need of a new wheel rim so thinking of fitting a twin leader brake
instead of the original, is it a simple matter of just swapping drums or do I need to do any mods to the
fork leg? Also can twin leader drums still be obtained new if so from where? Finally is it a worthwhile
conversion on a bike to be used just for touring?
#2913 Mike at Grove Classics( 01582 )873066 has remanufactured the Thruxton type TLS which is a
straight swap!!
#2914 If your Viper has a full width hub you need only to change the backing plate assembly. I did this
on my '67 Venom, thought the TLS would help coming down our big mountain passes, two-up. To tell
the truth, the original well-bedded SLS was its equal. It also works when backing up - unlike the TLS.
The soft linings on the TLS didn't last very long, either. But the TLS sure looks sexy!
#2915 Same drum, different backing plate. I've had both types and I think that the VM/VR brake is
adequate for everything except high performance use. If yours doesn't work well it may be time for
new linings and careful setup. These drums are not able to withstand kludgey lacing and will pull oval
by over-tightening of the spokes, giving a pulsing feel to the lever. This can be corrected by a minimal
turning of the drum in a fully trued wheel and oversized or shimmed linings to match.
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#2916 If I remember correctly you may also have to change to the Thruxton front fender stays of
which the right hand one is slightly cranked to clear the top cam arm. I concur with the fact that the
TLS brake only works when you are going forwards, making hill starts on steep inclines a case of
juggling feet! But I found the brake to be quite a bit better than the single leader if fitted with racing
quality linings (I originally used Ferodo AM4 material although this is no longer available - a brake
lining specialist should be able to advise a modern equivalent), machined to size to match the drum
and correctly assembled and adjusted.
#2919 As an alternative to new a stay you can simply use a ½ inch spacer
#2923 Grove Classic have them in their stock list - £299.00 + VAT + Postage I agree with Tom Ross,
a correctly set up sls with good linings is as good as the 2ls and I've raced on both. And the sls is
better in reverse. What else could you spend that £360 on for the bike?
#2929 You could try "floating" the brake shoes.
#2934 Don't forget that pre-unit Triumph rear shoes fit the Velo rear brake perfectly, and are already
"floating". The cheap, bonded import ones on the back of my Venom worked very well with no
bedding-in, and lasted 25k miles. The drum and sprocket were both done by then, but the shoes were
not (quite) worn out.
L #3042 Just got off the phone to the very helpful folks at the Avon tire company office in
Washington state as I was unable to find a new replacement tire for my 1970 Velo Thruxton. Both
front and rear rims are 19" WM2. This presents no problems in the front as a 90/90 AM 20
Roadrunner is available, however nothing for the back, without changing to a WM3 19" or WM3 18"
rim. Don't really want to switch rims on this bike, although I certainly will to keep riding it. Just
wondering if anyone else had come up against this problem and how they resolved it?
#3043 Some time ago the famous Geoff Dodkin recommended the following tires for my Thruxton, to
which I stuck with best results till today: Front : Avon 90/90 H 19 Roadrunner F2 (a ribbed racing
compound) Rear : Avon 4.10 H 19 Roadrunner Universal (use only road compound !) Although the
front is a soft racing compound it lasts on the road for appr. 6000 miles. As much as the rear, if you
choose road rubber. Once I tried even the rear in racing compound, but this got me only 1000 miles
out of it. You will be amazed how handling will be improved with the above tire combination.
#3044 I see two possibilities and while I was on the phone ordering a set for a '49 Ajay, I checked
stock on both possibilities. Both possibilities in stock!! Tires were ordered from my fav tyre supplier,
South West Moto Tires, 1-877-805-8473. With new Metzler tubes, freight free, cost was $186.
Ordered AM 20 front "Road Runner" 325-19 TL, fits 2.15 - 3.00 rims AM 18 rear "SuperVenom"
100/90-19 TL, fits 2.15 - 3.00 rims currently used on my '66 Thruxton running Dunlop WM2 alloy rims,
and in stock Speedmaster Rib, 3.50 - 19 TT fits 1.85 - 2.50 rims SM MK II, 400-19 TT, fits 2.15 - 3.00
rims.
L #4537 Can anyone help with the setting up of a new twin leading shoe assembly I purchased
from Grove Classic and which is currently performing at about 10% of the efficiency of the single
leading shoe standard set up I have just removed ! The brake is very spongy and lacks feel and bite
and is currently not safe for the road.
#4539 Quoting straight from the "Red Book" Re-Setting the Brake Shoes. The brake shoes are set
when the brake is assembled at the factory, but renewal of the brake shoes will necessitate re-setting.
To do this, remove the split pin and withdraw the clevis pin from the yoke end at the top of the
adjuster rod. Operate the front brake handlebar lever which will bring one brake shoe in firm contact
with the drum and retain the pressure on the lever by securing it to the handlebars by the use of a
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strong rubber band or other means. Slacken off the two lock nuts on the adjuster rod and apply firm
pressure to the top cam operating lever which will bring the second brake shoe in contact with the
drum: Hold the cam lever in this position and turn the adjuster rod to a position where the clevis pin
can be inserted through the cam lever and yoke end of the adjuster rod. Then re-fit the clevis split pin,
tighten up the lock nuts on the adjuster rod and release the pressure on the handlebar lever. Finally,
check the brake control cable and carry out any adjustment which may be necessary.
#4540 In a recent magazine article it was suggested that if you really want a 2LS to work at its
optimum performance it is essential that both brake arms on the back-plate are parallel, otherwise one
shoe will get more effort from the handlebar lever than the other one. Do this first then let the shoes
bed in. It may take a little time, but when you think about it the end result will be the best brake. If you
have had the drum skimmed you may need oversize linings.
#4541 First make sure that the outside diameter of the mounted brake shoes is close to the inside
diameter of the drum. When you apply the brake, the angle of the lever to the cable should be slightly
less than 90 degrees. This should correctly adjust the first (lower) shoe cam. Then the link to the
second (upper) shoe cam should be adjusted such that both shoes will meet the drum at the same
time. Then ride the bike a little, remove the backing plate, and inspect the wear pattern on each shoe
for drum contact. If you don't have full contact, the arc of the shoe does not match the arc of the drum
and must be corrected to achieve that condition. The drums are weak and can be distorted by
careless tightening of the spokes. The common repair for this is to 'turn' the drum which produces a
larger drum ID, which then requires thicker lining turned to fit.
L #4818 Currently, the chrome rims from my '39 Mk2 KTS are both WM3s, with 36 spokes at the
front and 40 at the rear. The state of the rims means that they both need replacing. My wheel
(re)builder suggested I rebuilt the front with WM2 (1/4" narrower apparently) to take a narrower tyre.
The spec' in Ivan Rhode's "Technical Excellence Exemplified" suggests the tyres should be 3.25 x 19"
(front) and 3.50 x 19" (rear). Should I have the front rebuilt with WM2 or stick with WM3? What was
the original size and what would handle best? Should I be fitting 3.25 x 19" (front) and 3.50 x 19"
(rear)? (the tyres were already removed when I took over the bike so I don't know what it last ran with)
#4820 3.25 front tyre should be on a WM2 rim 3.50 rear tyre on a WM3 rim these old British bikes
usually had this combination so your wheel builder sounds OK to me.
#4823 I believe the difference between the mkII KSS and KTS was the difference in wheel sizes, the
KSS was 21"/20" versus the 19" on the KTS. This is not news I'm sure. I did want to point out that over
the years your machine may have had modifications. My point is that the correct wheel/tyre
combination should fit nicely with the mudgaurds. Machines that have had the wheels converted to
smaller sizes generally don't look right visually with too much of a gap between the tyre and
mudgaurd.
#4826 I have original Veloce sales brochures from 1938 and 1939. In both years the following rim
widths are noted by Veloce: KTS WM3-19; KSS WM1-21 front, WM2-20 rear.
#4824 Some memory in the back of my head of something that I read long ago tells me that the KTS
came supplied with the unlikely WM 3 X 19" rims both ends. I can't quote the citation, but I remember
it as being authoritative.
#4825 Regards the KTS tire/rim query; I would stick with WM2 front and rear, as a WM3 rim is really
for 4" plus tire sizes, and isn't standard on a prewar bike anyway unless it was a real hauler, like an
Enfield KX or something American (which used small truck tires prewar, it would seem; there must
have been no corners here at the time). I've owned a few Broughs, and they all had WM2/19". Plus, in
terms of handling, you'll probably find the bike is more responsive the narrower the tires you put on,
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ut more comfortable the wider the tires, which is my general rule for early machines. So, as an
example, my '28 Sunbeam has 21"/2.75" front and 20"/3.00" rear wheels, and my mk1 KTT has
21/3.00" on both wheels, and each handles like a surgeon's knife. They will even go between the
Bott's dots on a road warning grid without a bump (do you have them in England?). These bikes are
used for high performance bend swinging. As a contrast, I use 19"/3.25 and /4" on my Venom, as it's
used for more long rallies. I have used 3.50" on the rear, which really made it corner more quickly, but
was generally more nervous feeling. I would recommend 3.25-50" for the front, and 3.50/4.00" for the
rear of your KTS.
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G. The Frame
G.1. Frame, Bodywork, Paint and Polish -
L #302 Finding it hard from archive photos to tell which alloy surfaces should be polished and
which left 'rough' on my '68 Clubman 500 rebuild. Timing chest cover is obvious but what about brake
plates and surfaces on other side of hubs? Gearbox cover on kickstart side? etc.
#304 Regarding which areas to polish on a Velo restore: timing cover valve inspection cover gearbox
outer cover brake plates hub backs Some people do a lot more, like crankcases and gearbox cases,
and some Velos came with unpolished timing covers and gearbox covers (the Specials, with
fiberglass engine covers), which sometimes show up on other bikes. Engine/gearbox cases were very
clean as cast, but not polished
#306 My '68 VMT came from the factory with fully polished engine and gearbox cases. It is totally
unrestored (some might say neglected) and the only remaining polished area was found behind the
primary case! The first (and only previous) owner was definitely not the polishing type, more of a
"working machine" sort. OTOH, my Veeline was completely "as cast". It had f/g covers that hid
everything up to the bottom of the fuel and oil tanks. The difference is very obvious, the castings are
quite rough. I polished the timing cover on the Veeline myself, not a Simichrome job, needed my
buffing wheels and plenty of compound. Still not sure if it was a good idea. I have read that the factory
left the engine and gearbox unpolished on Specials and Veelines to save the labor. Plus it cools
better. But most Velos came with polished cases. Not like a mirror, just bright. I applaud any attempt
to resist "overpolishing" your Velo, too many are overdone.
#307 I have owned both my Venom and MSS since 1973, they too were unrestored. Polished areas
were consistent on each set of castings covering the following Timing cover T/S crank case around
timing cover periphery, front edge of pump housing, front edge of filter bolt housing, front right hand
side of T/S crank case D/S crank case barrel flange, front and bottom of face of crankcase Gearbox
cover and sleeve gear cover Top inch or so of the shell where the serial number is, right the way
around to the concave front side of the shell. Front and rear break plate Front full width hub on the
near side 3 hole disc only on the rear FW hub I was also told by an ex Velo dealer.
#1036 I am always envious when I see Velocettes with polished timing covers and gearbox end
covers. My timing cover is smooth but their gearbox is a very rough casting. Has anyone any useful
advice on how to improve the gearbox appearance. I am not necessarily after a mirror finish but at
least an improvement on what it currently is.
#1037 It basically requires lots of elbow grease but have a look at www.englishcustompolishing.com it
has a wealth of info on the subject
L #352 For the colour schema Velocette had their own identification which gave the original
polychromatic Silver Grey of the 150 the no. 1. For to get this colour I recommend to contact L.E.
VELO SPARES Bullers End 43, Bradford Lane Walsall WS1 3LU.
#447 I have a Le Velocette mk1 I am trying to identify the greyish colour, that they are painted. Does
anyone know the exact colour and where I can get it
#452 According to Roy Bacon's book "Velocette Flat Twins" the colour schema for the Mk1 from
1949-50 is: Main frame pressing, top and bottom fork crown, front mudguard, front fork legs, front
fork lower shrouds and saddle bracket in silver grey. Polished alloy leg shields and wheel rims,
chrome plated fork stanchions and headlamp rim, dull chrome plated exhaust pipes. Black headlamp
shell, handlebars, headstock, radiator surround, rear engine pressing, rear fork footboards, cylinders,
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sump, hubs, generator, silencer box, number plates, battery strap, stand, rear brake pedal and
pannier frames. Also saddle top and pillion black and black footboard rubbers..
#468 Some of the MAC / MSS type single width hubs seem to come in a kind of metallic green'ish
colour. Does anyone know :- a ) what the color was ( is now ) b ) was it specific to some models c )
what models ( was it the Green bikes only ).
#469 Vipers were made in a colour called Willow Green between 1956 and 1960 – not sure of the
equivalent colour today.
L #655 Velocette MAC 1951 Today I began the process of neutralizing the rust in my tank and
applying a sealer. The first stage was to pour in a de-greasing agent and slosh it around. Then I had
to wash out the tank with clean water to remove all trace of the sudsy stuff. When I'd finished I noticed
that all the water has made the "velocette" tank-transfers wrinkle and start to lift. As it was a sudsy
water solution which caused the problem, I'm assuming that they were the slide-on type transfer and
I've got a couple of questions if anyone could advise me on how to go about replacing them when the
job's finished:- Any tips on the best way to remove the old transfer remains? The VOC parts list
includes " A132 - Tank Transfer (modern)" Is this the right one, and if so, is it a slide-on type? I was
thinking of applying the slide-on type transfer and then giving the whole tank a coat of spray laquer.
Does this sound like a good idea? I'd be grateful for any pointers.
#657 I have got the same problem the Velocette tank transfer has wrinkled its been like it since I have
the bike so have no idea what caused it, the rest of the tank is perfect, The problem is how to remove
it without damaging the enamel? I have two water slide transfer to replace them, I am told if you use a
drop of washing up liquid in the water, it reduces the surface tension so they can be positioned easily
without wrinkling, and gently pad dry with a tissue then leave for 24 hrs, before trying to use any sort
of fixing spay, I certainly would not try lacquering the whole tank, as any Paint sprayer, will tell you
need to remove all the silicones from the surface which is very difficult to do, without damaging the
enamel. I am not sure of the best way to fix the transfers, onto a polish surface so they are
permanent. Are there any experts out there to tell us the secret.?
#661 I've got an old Velo manual - unfortunately it's lost its front cover so I don't know the precise title
or year but it has the following section on "fixing transfers": "Transfers are printed on duplex paper
and the two sheets must be separated before transferring. Divide them by rubbing a corner of the
transfer. Apply a very thin and even coat of adhesive varnish to the face of the transfer and keep as
close as possible to the lines of the design. Allow the varnish to set until very tacky and then place in
position. Press down evenly and firmly and drive out all air bubbles by rubbing with a soft cloth rolled
into a ball, commence in the centre of the design and work out to the edges. Then with a damp - not
wet - sponge or washleather press down again taking care not to move the transfer. When you are
absolutely certain that every part of the transfer is in contact with the surface apply water freely with a
wet sponge. When the support/backing paper is well soaked lift it up starting at a corner and peel
and/or slide off. Press the transfer down again. Sponge with clean water to remove all traces of
material on the surface of the transfer - this is very important as unless properly done the transfer will
crack on drying. To remove all traces of adhesive varnish around the edges of the design use a wet
sponge to which has been added a drop of paraffin, quickly wipe off with a damp washleather. When
the transfer is dry - about 24 hours - varnish to add lustre. It must not be varnished directly it is
transferred."
#663 My 1952 red book manual for the MAC. chapter on transfer, is more or less the same as
Professor Lunt, quoted. except it says use the old fashioned goldsize, instead of varnish. but that was
50 years ago. The A132 tank transfer (modern) is now the replacement supplied from Veloce spares
ltd, which suggests it will be the modern water slide type, not the old duplex type transfer, So the
water slide type should be applied as I said in my earlier mailing. It is the way to spray fixed it after?
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to stand up to the all that spit & polish that we lavish on our pride & joys these days, I would make
sure it is not a cellulose base spray.
#666 I cannot say I have fully mastered applying transfers even after rebuilding a few bikes, but here's
my experience. Varnish transfers - when you get them right they are the best, but they are not easy to
apply. I have an oil tank with all the letters attached but if you look closely it looks like "alphabetti
spaghetti" . Follow the instructions posted by George. I have used Polyurethane varnish successfully,
but you must get the tackiness just right. Buy a spare transfer and try applying one on a can first!
Waterslide are easy to use but they can appear translucent rather than transparent. There is no need
to use washing up liquid as they float off easily, in fact it may cause problems with subsequent lacquer
adhesion. For both types of transfers I always rub the tank down carefully with something like 1000 to
1500 grade wet and dry to remove any high spots. Rub two pieces of wet and dry against each other
first to make it even finer. After doing this you can polish back with T cut if you want. You can lacquer
over the transfers, I have used two pack with no problems, but I suggest you buy a spare transfer to
see if there is any reactions first.
#997 I have heard the term 2 pack paint but here in Canada it is not a term we use. I assume it
means paint and hardener but really I don't know. Could anyone help me to understand this term and
to perhaps lead me to find the correct blue and silver colour for the 67 VMT. Paint codes useful in
North American would be good. Also what recommendations do you have for the type of paint to use,
and lastly what is the best method to deal with the tank transfers. It seems the 40 VMT's that came to
Canada were delivered with this colour scheme.
#1014 Martin Arscott sells self adhesive transfers at £5 a pair. Tel +(0)1442 862966 or mail
marscott@t... I have used both varnish and waterslide transfers. Varnish are very difficult to apply,
and waterslide leaves a slightly white finish. For your tank I would recommend two pack
www.austinseven.mcmail.com/paint.htm successfully as you can repolish it. I have painted four Velo
tanks with two pack, I recommend a clear lacquer over both the paint, transfers and lines - sorry I don't
have the correct paint codes
L #825 One of the previous postings suggests Car Plan Vauxhall Antique Gold as a good match
for petrol tank lining colour. It seems to be unavailable, at least round where I live. Any others
suggestions welcome.
#831 You might want to contact one of the specialist painters such as www.precision-mcpaintwork.co.uk
who do gold lining on petrol tanks and have the original templates. They are
extremely helpful and answer EMails.
#835 I use 0.25 inch gold tape from car accessory shops, applied before the two pack lacquer - I think
it looks excellent. You need to use a hairdryer to soften the tape to make it bend round corners. It's
not an easy job
L #997 I have heard the term 2 pack paint but here in Canada it is not a term we use. I assume it
means paint and hardner but really I don't know. Could anyone help me to understand this term and to
perhaps lead me to find the correct blue and silver colour for the 67 VMT. Paint codes useful in North
American would be good. Also what recommendations do you have for the type of paint to use, and
lastly what is the best method to deal with the tank transfers. It seems the 40 VMT's that came to
Canada were delivered with this colour scheme. Thanks, Michael
#1014 Martin Arscott sells self adhesive transfers at GBP5 a pair. Tel +(0)1442 862966 or mail
marscott@t... I have used both varnish and waterslide transfers. Varnish are very difficult to apply,
and waterslide leaves a slightly white finish. For your tank I would recommend two pack (see
www.austinseven.mcmail.com/paint.htm )successfully as you can repolish it. I have painted four Velo
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tanks with two pack, I recommend a clear lacquer over both the paint, transfers and lines - sorry I don't
have the correct paint codes
L #999 I've spent a while this evening trying to remove the closing/fastening screw from the
toolbox lid so I can deal with a bit of rust. I thought at first that the washer at the base of the thread
might be a circlip, it doesn't seem to be. Then I thought that the knurled portion might be screwed onto
the threaded portion, it isn't (unless it is extremely tight). The parts list/exploded drawing I have calls it
an assembly so isn't any help. I really can't see how it is assembled.
#1000 The knob assembly comprises 5 items, and is assembled in the lid. There is the knurled knob,
the stud, two plain washers and a double coil spring washer. The latter three are placed on the
reduced diameter outer end of the stud, one plain inside the lid and the other washers outside the lid,
and the knob is either screwed on, or pressed on, and locked. It is not intended to come apart!
L #1098 Greetings, I'm seeking a colour code or year/make/model info on an automobile for the
proper colour for a 1967 Thruxton. Can anyone on this group help me identify the colour?
#1100 I've already got the silver parts done, but need to complete the blue. I really amazed at how
difficult it has been to locate a colour code or even year/make/automobile model information to get the
colour right. I've been working on this task on and off for about two years. The closest I've come is the
colour was called Oxford blue when used on Rover autos some time in the late fifties / early sixties.
Pursuing this thru Land Rover disclosed a current Oxford blue, but is has a fair degree of pearl added,
and I suspect the formulation for Oxford blue has changed to a more modern appearance. Another
colleague told me that the 1964 Triumph auto used the same blue, and/or British Leyland used the
colour in the mid sixties. I located a PPG brand paint supplier who had an online paint code selector
and found two possible candidates under British Motors for 64-67 as BU-45 Midnight Blue, or Bu-29
Alaskan Blue. The Triumph is #13126 Royal Blue. Alas, since I'm looking at a paint sample that was
scanned into a computer on their end and viewing the scan on my monitor, I'm not sure what colour
I'm really looking at. I'd sure like to "crack this code"!!
#1101 I think you should find that Grove Classic M/C's (UK 01582 873066) or R.F. Seymour Ltd (UK
01844 212277) can help. There were some original colour swatches around - I think either or both of
these Companies will have some (Goodman Engineering also, although not sure if they are still in
business)
#1103 I checked with a fellow VOC member who has built two or three Thruxtons, he states the colour
is Ford "Anchor Blue" www.fordanglia.com/paint.htm for the frame and originally Ford "Silver Fox"
which changed later to "Sirocco Silver". You need to use the 65 -68 colour swatch. Apparently it was
Reg Orpin who created the original colours and he uses off the shelf Ford colours. He also said that
BL "Oxford Blue" was not the colour. BTW, Seymour's cannot confirm what colour the tank and frame
is. While I cannon vouch for the accuracy of the information I hope this helps.
#1106 I have a bike with the original blue still on the parts. I had it scanned but it didn’t come up with
a clear reading as the surface of the paint was scuffed and not clear. The painter took the piece and
matched it by experimenting with a few mixes It was a ppg brand of paint. What I ended up with was a
sample and I cant fault the match. He came up with this code: DCCNCP CONCEPT MIXED
PAINT.....DU508 URETHANE HARD-PT AND DT87001 REDUCER. It definitely is an oxford blue that
with the eye you cannot find a difference. He suggested the urethane as it is a one coat finish that is
superior to other finishes. I was wondering if there was a match to this so that we would all be on the
right track. I also would like to know if you are going to do the blue, silver ,and black just as the
original. I asked the painter just for a nice Mercedes silver and it came back tinged slightly taupe. Also
what did you do for the transfers and the gold do you have a clear over them
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#1107 I've used PPG as my paint supplier for many years and DCC is certainly my paint system of
choice. When used with the DU508 hardener it makes a great durable finish. It has been my
experience in the past, that whenever I had a custom color mixed, the PPG supplier gave me the
formula as a gummed label that was stuck on the lid. Did you by chance get the formulation and if so,
can you relay it to me? The info David Gibbison so kindly, and greatly appreciated, relayed to me
turned into a dead end for me at two PPG paint suppliers. Neither could identify the Ford Anglia
"Anchor Blue" code BJ. I must remain persistent. It is one of my best traits!!
#1109 Have just remembered - I got some help from Ray Thurston in the UK some years back on
VMT colours also my notes say 'Rover Night Watch Blue' and 'Ford Silver Fox Metallic' I have since
sold that VMT - but I do recall this gave quite a good match to the original (very thin) finish I have on
the unrestored VMT I’ve kept.
#1112 I got a lead from a colleague here in Washington state, Ed Gilkison, suggested I contact John
G., who emailed me several codes he found most acceptable when he restored his Velo. To quote
John" Dick, I actually found the original can of paint that I bought in 1980. It is a Sherwin Williams
"DARK BLUE #904 Mercedes Benz. The other can I have which is a newer match is R-M Mercedes
Code 904/Midnight Blue 7577. The silver I used was Honda Accord(car) Blade Silver. You want silver
with a flat fine metal flake not too metallic. You be the judge.
L #1102 Should my 1948 MAC have chrome or painted wheel rims?
#1104 My 1947 Mac had chrome wheels (rigid, Dowtys, iron) Looking at a photograph of her now
(sigh!)
L #1134 Just finishing assembling VM1959. Came to refit petrol tank and am a bit confused
about the purpose of the petrol tank strap (A276/2). It obviously fits between the 2 studs under the
tank but I'm not quite sure why. It almost comes up against the frame front downtube but doesn't
seem to perform any function apart from joining together the two sides of the tank, which doesn't
really seem necessary. Am I missing something obvious?
#1135 Ian Indeed you may be missing something quite important. The tank strap stops the two sides
of the tank flexing. If they do then the tank will surely split at the rear and petrol will issue forth. This
only happens when the bike is ridden of course! Veloce normally had a very good reason for such
details!
L #1699 Can any of you Venom historical buffs give me an idea of what the true original shape
of the '57 Venom dual seat should be? Having just powder coated the seat pan , I am about to have it
re-covered and want to replicate the original profile, but when I look the archive pictures on the VOC
site, I notice that no two seem to be the same. Some seem almost dead straight, whereas mine has a
deep "pan" under the pilot, and all seem to have uniform deep cushioning, whereas mine tapers to no
more than 2" at the front. Some have two curved stitch-lines on the side, others only one. The old
cover, carefully removed, appears to be original, but I have a sneaking suspicion that a previous
owner may have trimmed down (up) the seat-pan flange. Any advice - or directions to a definitive
picture would be gratefully received. On the same subject, can anybody recommend (from
experience) a good upholsterer in the south of England?
#1700 I think the flat seat came in 1958. The closest pic I have is a 56, but I don’t think there were
any changes for '57. The shot of the '56 I have is of a Viper, from side on unfortunately, but it does
appear the seat narrows markedly at the nose, where it mounts to the frame. There is a slight 'curve'
toward the frame rails at the front, but a gap is clearly visible - it is certainly not a flat seat. The seat is
flat-ish for the pillion, then follows the mudguard to the centre of the arcuate slot, then curves upwards
to its nose (hence the gap to the frame rails). There are two separate 'curved' stitches, the first starts
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in the centre of the seat (on the top) and curves forward such that if one extrapolated the curve it
would more or less follow the rear line of the oil tank. The second appears to start at the rear of the
seat and curve forward to a point virtually at the maximum radius of the rear mudguard. I will try and
scan it in for you if the general consensus is that it is the right one. Phew - a picture paints a thousand
words - how true that is !
#1701 Just found the self same picture I described earlier in Steve Wilsons British Motor Cycles Vol
6, p 225
Wilsons text appears to confirm no changes for '57, flat seat in '58. But I'd bet there are one or two of
this group who will know for sure.
#1702 Don’t mess about, send your seat to Leightons in Birmingham. they will do a top class job at a
reasonable cost. you just don’t get better www.rk-leighton.co.uk/ I can vouch for the quality of their
work.
#1710 When I recently re-upholstered my '57 Venom seat. I salvaged the cover and made a new
foam inner piece. I tried several means of fixing the cover to the metal seat base. I eventually used
Velcro strip to fasten the seat cover. This worked well. I acquired some continuous, 25mm wide Velcro
tape which had double sided tape on both faces. This went all around in the inside edge of the seat
shell. This stuck well to the recently painted inside face of the seat shell, The other piece of Velcro
had to be Evo-Sticked to the cloth side of the PVC seat cover. The hardest job was tailoring the foam
block to the right shape. I did not have a pattern to work to. I used a high density reconstituted block
foam which was faced with a 10mm thick flexible foam to ensure any lumpiness of the reconstituted
foam would not show through. I used a combination of tools (saw, bread knife, surform, etc) to
sculpture the block foam to the right shape- the seat shell has a lump in it for the mudguard and the
pillion part is a little higher than the front part. It took quite a time of trial and error to get it right. I did
not glue the block foam to the seat shell and this will help if I need to re-do it soon. I do not think it will
move. It looks good. Perhaps next time I will get it done professionally.
#1714 To sculpt foam when upholstering seats etc. use an electric carving knife. Borrow one from
wife or available at car boot sale near you for around £2.00 PS. Buy two if you can cos they tend to
fall off the workbench and smash or be stood upon when wrestling with seat covers!
L #2019 When refitting the petrol tank today I sheared one of the studs which are used to fasten
the stiffening bar across the front of the tank. In my defense, when I look at it, it has been sheared
sometime in the past and a new stud brazed onto the part still in the tank. It’s the brazing which has
failed today. Is the stud brazed into the tank or is it screwed into a threaded boss which is brazed into
the tank? In other words can I screw out what's left of the stud, make another and screw it in? If the
stud itself is brazed in the tank my current thoughts are to (very carefully) drill into it and tap it say
3mm (it’s a 1/4 BSF stud) then make a stepped stud, threaded 3mm at one end and 6mm at the other
and screw it into the 3mm tapped hole with Loctite. The stiffening bar could then be fitted as normal. I
want to avoid brazing if possible.
#2023 Firstly, I assume you are talking about the 3½ gal tank with round badges and knee grips. The
stud for the strap is threaded ¼" BSF, but has a 3/8" dia boss to locate the strap, and a larger flange
above that. It is (or was originally) welded (not brazed) to the tank. It is not a separate, plain stud
screwed into anything! I'd recommend cutting the old stub off completely, and turning up a new piece
to be welded in its place. Welding is better than brazing, as brazing can cause local hardening and
subsequent cracking of the sheet metal.
#2024. The Velo tank is the one with badges and the studs look exactly as described, so it looks like
welding a new one on is the answer. Tomorrow or Thursday will be the first chance I get so if anyone
has any other suggestions before then, I'd be grateful.
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#2025 Easier than welding, but not as permanent, if you make the new stud with a large area base
(tank end), maybe you could solder it in position, or even 'glue' it with Araldite.
L #2113 So I have partially dismantled the Venom that's been in hibernation for 25 years, and its
going quite well everything looks good, except for minor scratching to the piston (bore is ok). 25 year
old engine oil actually looked pretty good, which is more than can be said for the chaincase oil which
I'd rather not talk about. The questions I have are related to how to finish the bits and pieces I note in
many books there are references to "matt chrome plating" to be used instead of the original cadmium
plating on part such as kick start. What exactly is "matt chrome" and how does the plating process
differ from the regular polished chrome finish. The other question is painting cycle parts like primary
covers, oil tank and headlight cowl. I was thinking of powder coat, but now I am having second
thoughts. Which parts should be enameled/cellulose and which pieces powder coated? Any
recommendations? Anybody know of a good powder coat shop in the Bay area?
#2114 Many items were dull/matt/satin chrome in the first place and not cad plated. eg Kick start, steel
gear levers, brake levers, rear brake spindle steady plate, steel rearset brake pedal etc. etc. The
difference lies in preparation of the material. After polishing or other prep and before plating the part is
gently sand blasted. The chrome is not polished after plating. The details will doubtless vary
depending on your plater, but that's how it was explained, and done, for me. Painting should be just
that. Veloce dipped their bits in a production facility paint machine. That’s why the original finish is so
smooth and thin. Stove enamel can be applied to give the same (ish) finish. Often its too thickly
applied. Same with powder coat which is after all a plastic skin spread over the part. My opinion is that
it all depends on your requirements. Powder coat for a well used machine eg trials Stove for a tough
good finish. Do it your self for the right effect. This can be sprayed acrylic even brushed if you're really
good at it. We have a paint shop near me that sprays; not stove. The finish is excellent. This will not
be as tough as stove though. I would avoid powder coating as the parts look as if they are dipped in or
made from treacle - that's just my personal preference !
#2115 I have tried to achieve a "Dull Chrome" finish. I have tried the bead blasting and then plating
but it does not look right. The closest I can get is "Satin Chrome" where the component is rough
polished or brushed - but it's still not right. I have access to the original factory specification for VM/VR
if anyone really wants to know what the finish on a particular component was. Regarding painting, I
have tried the following and here's my experience for what it's worth: Cellulose - easily applied cheap,
you can cut it back to polish it, but it chips badly; Two pack - great finish, you can polish, it will chip,
but not too badly; Powder coating - cheap, does not chip but scratches badly and you cannot polish
the scratches out. However it is ideal for centre stands, side stands and rear cotton reel hubs. Do not
use it on iron front hubs as it burns if you brake hard! Ask the coater to phosphate the component
before coating, for added rust protection; Stove enamel - my only experience of this is a bent MSS
front mudguard with original enamel on it. Even beating the enamel with a hammer had little effect on
it. Finally I have seen black powder coating used as a base coat for two pack black.
#2131 Decided to put my 2 bits worth in, I have been involved in enamelling surfaces for close to 70
years, had a panel shop around the time from cellulose to 'Dulon' etc. when it came to restoring
motorcycles, I soon discovered a few shortcomings, in conventional finishes, as many people have,
but after consideration & noting how well original finishes had survived on old British bikes, common
sense found me getting a small specialist (?) stove enameller to do a couple of Velo cotton reels,
(hubs) for me, & an excellent job he did too, & I happily laced up my wheels & admired the result.
Unfortunately at a later date I used kerosine to clean up oil deposit & the paint just went sticky & the
resultant work involved saw me deciding to do my own stove enamelling, & I have done so ever since
! Number one lesson, if you stove enamel, make sure that it's baked properly! I use an old convection
heating type clothes dryer, with the circulating fan removed, & the electric element restrung in a box
around 5 times the original size, this has to be done to prevent circulation of fine dust by the fan, & the
larger element box is necessary to prevent sagging of the element when it becomes red hot. Also
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throw away the wooden 'hanger' bars, & replace with steel rods. The outside of the cabinet is clad with
insulating 'bats' & outer thin gal. steel sheet. If you want to enamel a modern frame, there is a good
chance that it won't fit in a clothes drying cabinet, so you will have to construct something bigger !
Stove enamel is cheap in the long run, & you use far less of it, & it's so much easier to use once you
get the hang of it. I spray in the open air, picking a good wind free day, but a light breeze is helpful in
getting rid of the over spray. I thin the paint well down & spray with lowest pressure possible, just
'drifting' the paint on, this is possible with stove enamel. One of the reasons that I spray in the open is
for the good natural light, black can easily lead you into missing spots. I always give a couple of coats
to frames upside down, before turning right side up & finishing all over. The paint will tack dry quickly
in the sunshine, & can be well checked before going into the oven. My oven will not take the
temperature up to what is recommended, but just over boiling water temp in fact say 120-130, but I
bake for longer, possibly half hour or more after the temp. gets to max. & then allow temp to drop
again. A wonderful advantage is that the enamel never dries up in the gun, & in fact I have left it for
months on end ! The best part is that once the parts have been fully prepared, it's just spray & into the
oven, & start assembling the bits as soon as the parts are cool enough to handle ! I have one
confession to make, I do the Henry Ford bit, - any colour, as long as it's black ! any colour work is
done in 'Dulon' or what ever it's called these days . Once you have used stove, you will never go back
! & a comment on powdercoat. if moisture happens to get in through a bad spot or a chipped area &
it's not noticed a horrible disaster follows, maybe the process has been improved in this respect, but I
have seen slabs of powder coat come off after moisture has somehow penetrated the surface.
(possibly over baking ?)
L #2126 Folks, I need to repaint the fuel tank on my Thruxton. How do I go about removing the
chrome filler cap assembly? It is not obvious to my eyes. All help appreciated.
#2127 The cap is held on by a pin, approximately 5/32 diameter, that doubles as the hinge pin. The
ends are lightly peened over. I used a pin punch and drifted the pin out without difficulty. Try drifting
one way or the other and you will readily see which direction is easiest. 30 second task. Upon
assembly, I used a drop of Loctite 242 on one end of the pin and did not attempt to peen the end. No
problem in thousands of miles. Put a smear of thick grease on the blued steel spring that holds the
cap in the up position so the cap will not bind on the fresh painted filler neck.
#2181 If you use a roll pin in place of the original plain pin (if indeed this is how your cap was originally
fitted) then there is no need for any further security. In fact if you purchase a new cap the chances are
that it will come packaged with a roll pin. This may need to be slightly squeezed at one end to aid
insertion but can then be tapped into place with a small hammer and punch and removed in the same
way. There is no need to peen over the ends after insertion.
L #2153 Any suggestions on cleaning a fuel tank? I just bought a bike that hasn't run in two+
years. The tank still has some old smelly fuel in it as well as surface rust inside. I'd thought about
ditching the old fuel first (2-3 quarts), flushing thoroughly with soap and water, rinsing with carburator
cleaner, followed by phosphoric acid to kill any residual rust, and then rinsing again with soap and
water, flushing with water and blow drying.
#2156 Be carefull. I would allow the tank to dry in little more than sunlight. Metel is porous and residue
petrol gas will continue to evaporate for a long time after even the best of cleaning. Explosive vapour
can collect until what we offshore workers call "The lower explosive limit" is reached and then ignited
by a heater in a blow drier or a static spark at the tip of an air line. I did my tank by water flushing and
shaking gravel in it, then flushing again. I then used a propriety two part sealer that formed a glass
fibre skin inside.
#2159 I've had excellent results using a two-part treatment sold by Yamaha, it is an enchant (probably
phosphoric acid) followed by a neutralizer. It leaves a clean steel surface that resists rust. The part
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number for the Yamaha Fuel Tank Rust Remover is ACC-FUELT-CD- KT. It works on British steel as
well as Japanese. If the tank is not leaking or severely rusted I would stay away from coatings.
Exposure to modern alcohol-laden fuels can deteriorate them.
#2160 I'm with Tom on this one; tank sealers are only a stopgap until you get the thing welded up
properly. The alcohol in modern fuels seems to make the layer of plastic brittle eventually and they
come off in big flakes, blocking the fuel flow. It may be that companies have adjusted for this now in
their products, but still, get the thing fixed properly if its leaking. And if its not, I've used a phosphoric
acid etch to remove rust inside a tank, and it worked quite well. Careful where it spills though, as my
concrete garage floor has a reminder where my Brough tank sat, and leaked, with the acid wash. It did
such a good job cleaning my tank out that I discovered that one under-tank mounting stud went
straight into the petrol, held only by a little chewing gum, or old epoxy, or possibly even soap.
#2322 A month or so ago I posted a question regarding fuel tank cleaning. I had a solid tank that had
sat since 1972. The fuel, to say the least was nasty and the interior was rusty. I tried a variety of
chemicals, mineral spirits, ospho (phosphoric acid), acetone, and soap and water to clean it. I was
successful getting rid of the fuel and fuel smell but the rust remained so I got some rocks and dumped
them in the tank with some soap and water thinking I could shake the tank and knock the rust off --
HA! Physically impossible so I set the problem aside and thought. The solution? Our clothes dryer. I
got some more rocks, soap, and water. Plugged the holes and wrapped the tank in plastic trash bags.
I then wrapped the tank in blankets and stuffed it in the dryer with pillows, etc. to keep it from moving.
I set the dryer on Air Dry so there would be no heat and sat back and waited. My wife thought I had
lost my mind. After an hour I pulled it out and found one half of the interior looking absolutely new
while the other half was still rusty. It seems when the rocks fall they miss half the tank's interior. I
turned the tank 180 degrees so as to rotate it the opposite direction and jammed it in for another hour
followed by turning it 90 degrees and then another 180 degrees. After four hours the interior of the
tank is nearly perfect and the wife had her dryer back. She still thinks me mad and is probably right.
Oh, a six pack of beer also helps.
L #2382 For a triangular type tool box, is there some sort of trick to removing the knob. It doesn’t
seem to want to unscrew. I was planning to do remove it before sending the tool box off to be painted.
#2390 John, assuming the cover has been removed from the box, notice a small circlip in on the
inside of the cover has been snapped into a groove on the knob's shank. Remove the circlip.
#2564 I am still building my mac (no 2) and even though she isn’t well advanced the time has come
round to start thinking about mudguards, the original guards where worse than u/s so I am looking for
a pair of originals, is their anyone out there that can help or advise on alternatives, (without going
down the fibre glass route)as I am starting to get a bit concerned, and I want the bike to look as
original as possible.
#2570 As far as I know fender (guard blanks) are still available ex Armours UK , while these blanks
are not exactly to the Velo pattern, I have used them several times over the years, making up the
chain 'valance' for the rear section, & the tailpiece joint. For the earlier models at least, you need to
buy 2 fronts, & 1 rear blank, the second front is necessary to make up the tailpiece on the rear, & get
the full length of guard. For Oz restorers there are 2 sources of new blanks here, one in Victoria & 1 in
South Aust., names supplied on request. Re Mark's inquiry other tinware, I still have some stocks of
rear chainguards for all models, & early 'D' toolboxes & No/Plate brackets etc.
#2571 I would give Renovation Spares a call on 01527 543796. They do a lot of pattern mudguards in
steel plus a lot of blanks. They might well have exactly what you are looking for. If not, and you can
find or borrow an original, they will make you a replica.
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L #2653 I'm after a 'smallish' fly screen to fit onto the Venom (something similar to a Manx
Norton screen, but to accommodate the headlamp as well). Can anyone recommend one that will fit a
Venom with minimal alteration. The headlamp on my machine does not have the 'cowl' arrangement,
but is fixed via brackets off the fork stanchions.
#2655 A fly screen can be easily made out of clear (or tinted) thin plexiglass available at hardware
stores or the Big Box home repair conglomerates. A 2sq. ft. piece should be good for 3 or 4 of 'em
and if you get thin enough plex you can make the first cuts with sheet metal shears. The curve to fit
over the headlight may need smoothing with a Dremel and a flat grinding disk. Without the headlight
cowl it will be easy to make a couple of brackets that come off the headlight mount bolts. With the
right bend they can give the screen a nice aerodynamic curve. One inch strap stock will work nicely.
#2658 Brian, for just the screen try www.meadspeed.com
L #2697 I have a Craven carrier and some Craven panniers to fit to my Viper, carrier fitted ok but
how do the panniers fit to the carrier? I assume some sort of fitting kit is used, has any one any
experience with the Craven equipment?
#2698 All of the Craven equipment I've ever seen, and the set of mid 60's Golden Arrows use the
same type of mounts. The panniers have a three point mounting arrangement. On the back side,
approximately 2 inches below the top surface, are two cylindrical rubber blocks approximately 3/4 inch
in diameter, 1 inch long with a 1/4 inch hole in the axis of the cylinder. The cylinder is held to the
pannier with a sheet metal band. The axis of the holes in the rubber blocks is in the vertical plane.
These blocks are the "hangers" for the panniers. On the pannier FRAME, are two "L" shaped "hooks"
which engage the rubber blocks. One lifts the pannier to the frames and "hangs" the panniers on the L
shaped hooks. On the back side of the pannier at the bottom, is a sheet metal bracket with the
"female" portion of a Dzus fastener. If you are not familiar with this fastener, you should search the net
and find a picture as they are clever and rather difficult to describe. The pannier frame has the "Male"
portion of the Dzus fastener mounted in a sheet metal bracket. As Craven equipment was all made to
be universal, after about 100 hours of screwing around and getting the 200 plus pieces that made up
the mounts and panniers all aligned and mounted snuggly, the pannier was secured at the top by the
two hooks and at the bottom by the Dzus fastener. To remove the pannier, you twisted the Dzus
fastener 1/4 turn, pulled the pannier away from the Dzus fastener and lifted the pannier skyward to
pull it off the L shaped hooks.
L #2709 How does one get the push/pull petrol taps to stop leaking? Got new corks to fit, do I fit
them dry, soaked in oil, or boiled in water after assembly? All methods have been suggested but
which works.
#2710 When I installed mine I soaked them in petrol after assembly, they only leak now if the bike has
sat for a while, but they stop fairly quickly after opening.
#2711 The best idea would be to fit a better tap; not a sliding type at all. The sliding type are always a
pain in the arse.
#2716 I gave up on the old taps years ago for day to day use ! Most of my Velos have them still, in
fact I have a big jar full of dozens of the old tap's component parts, so that if it becomes necessary, I
can conjure up any of the various assemblies. But ! if you want a trouble free petrol tap, swallow
your pride & find one of the earlier rice water 'gates' fitted to trail bikes & such. They are equipped with
a small bowl filter with an 'O' ring seal, & can easily be adapted to the petrol tank outlet, & of course,
you have a reserve position as well ! I have had one on my KSS 'Special' since about 1970. While the
'loose' fitting nut is undoubtedly metric, I found that it screwed right on to the 1953 MAC tank fitting,
but I seem to recall that I may have had to use a small brass ferrule in between - maybe I was lucky !
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The worst that can happen is that you may have to sort out an adapter fitting, one thing for sure, I
have never had a leaking petrol tap since
#2717 If you are insistent on using the old style taps there is a solution I found that worked for me.
There is a grease that is used on aviation fuel valves that in insoluble in petrol A smear of this in the
valve and on the cork did the trick.
#2722 Dow Corning High Vacuum silicon grease is also insoluble in petrol and works well. It's readily
available.
#2723 cork-neoprene works for me.
L #2821 After stripping down to bare metal I am at the point where I need to decide on Powder
Coating or Stove Enamelling for my current project. Any input/advice/experience would be helpful in
the decision making process. After many discussions I am erring towards Stove - and if anyone can
recommend a decent supplier, ideally somewhere in the Greater Midlands UK, that would help too.
#2846 I would go with Powder Coating ( cos I can't paint worth a dam ) but...If you have problems
finding Stove Enameling talk to some of the specialist Bicycle ( pedal type ) builders they do some
great Stoving. Ellis Briggs in Otley ( ? ) used to do a great job but not sure about the Colonials.
#2823 Well I'm here for the stove enameling !, I tried stove enameling around 1937 for the first time,
when I worked for a Co. who painted 'Wayne' petrol pump panels, the home set up was done with a
lung powered insect spray, & the baking was done by hanging the parts in a 44 gallon drum with an
ancient electric 'Beehive' heater in the bottom of the drum. It was a grand success ! Move on to the
60's & I was into restoring Velos, & when it came time to paint I decided to try again, but this time with
slightly better equipment. Having had a panel shop for some 8 years at one point, I had an air
compressor , paint guns & all the gear I needed, but was sick of the work & cost associated with
preparation to ensure a good finish. The fact is that most, if not all, the old motorcycle factories used
stoving on their frames & cycle parts at one point, so why not restore them that way. Advantages, I
don't use prime coats on frames or cycle parts, just get the metal smooth & clean & get a few good
coats on, & into the oven. But tanks & guards & sometimes tool boxes & things get a prime coat of
Auto 3D which can be baked & rubbed down, I don't bake at the full recommended Temp. My oven
goes up a bit over boiling water temp. & I leave the parts in a bit longer, you can use a filler, I use
panel beate's 'bog' but it must not be any real thickness, & you have to keep the baking temp down
even lower. You can have some bad experiences using fillers ! The paint never hardens in the spray
gun, you can hang it on a hook half empty, & come back weeks later & start painting straight off
again, although I usually spray things like brake pedals & stands on an old pot of paint, not that there
is anything wrong with the paint, but if there is the odd spit or blob from the nozzle it doesn't show.
This uses up the pot, & then I mix a fresh pot of paint after giving the pot a bit of a swill with thinners,
& spraying that through, you can then get on with a frame or mudguards. The only time I give the gun
a full clean, is when I start on a fresh gallon of paint, which is quite often months or even more than a
year ! I can hear the howls of the purists now ! The fact is, stoving enamel is very easy to use, & is
very forgiving ! The big plus is, that after time in the oven, in my case an old converted vertical
convection clothes dryer, the parts can be taken out, & as soon as cool enough to handle, you can
start assembling things. Any dryer has to have the fan removed, otherwise everything is covered in
dust particles & I have insulated my dryer with insulating 'batts' & a second outer sheet metal skin. If
the dryer has open strung elements, removing the fan allows the heat to concentrate, & the elements
will sag & touch, so the element box has to be enlarged, with the length of the sides at least doubled,
with a few necessary alterations. There is of course more, but as far as I am concerned, auto enamels
are for the birds, & I have never even considered messing about with 2 PAK. & I have seen some
disasters with powder coat further down the track. From one who has been doing it regularly for 40
years, & will be painting the GS wheel hubs ,rims & spokes tomorrow ! - just a light coat to make sure
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that all is covered, then assembly of the spokes, true the wheel, then several good light final coats.
L #2827 I'd like to refinish the chipped and aged paint on a cast iron engine barrel. I'd
considered the old fashioned way, but I understand HMS Mayflower no longer has a spring sailing
from Plymouth, in the new world, home to England. What more modern methods are available in the
colonies?
#2843 I had mine bead blasted and stove enameled 2 years ago and all it takes is a quick wipe to
remove the oil and it looks as good as new. It was suggested that it might not allow it to cool properly
but I have had no problems.
#2852 I sandblasted and used an aerosol of heat resisting paint on the KSS. I stuffed paper into the
bore each end as a precaution when blasting. Can't say how good it is as engine not run yet. It is
Sperex VHT and claims to protect up to 700C. Instruction say cure at 121C for 15 min then at 315C
for 1 hour . I cooked in the fan oven at 150 for an hour and reckon any further curing can be in
service. The finish is a matt black which should help heat transfer. The product is sold by Simoniz in
UK and is a trademark of PJH brands of USA. Mike
#2855 What hasn't been mentioned so far is that when Veloce started using cast iron barrels (initially
on the VR/VM Clubmans) they, rather sneakily, painted them silver. Was it to disguise the fact that the
barrels were no longer "Alfin" - who knows? Anyway, my 1959 VM has always had a silver painted
barrel so when the time came for a rebore I used that Sperex VHT aerosol stuff but in silver.
Surprisingly it reached right to the roots of the finning. Not having a low-bake oven I "baked" it whilst
running in. Then I got carried away and sprayed the blue/rust exhaust pipes on my Harris "Matchless"
G80. These glow red hot when the engine is running at a fast tickover if the bike is not moving. Only
the two inches nearest the exhaust port has peeled in over 3 months winter use.
L #2849 Among other pieces I was about to send off my forks to the painter/powder coater. I
didn't know about temperatures used in powder coating, or for that matter, in stoving: so, apart from
scraping off some of the expensively applied coat after getting them back, what's the answer please?
#2851 Powder coating temps will weaken or melt the solder on forks. Otherwise it is fine to use
elsewhere and I have found that the quality of finish has dramatically improved over the years.
#2853 Powder coating is also a good way to keep it looking good and shiny as well as being tough. I
did mine, but of course you must block the holes with tin can lids and a long bolt. Don’t worry about
threads as they tap out very nicely. Powder coating is efficient as it goes in to all the little places and
the part can be installed straight-away.
L #2856 The full width hubs on my 65 viper were painted black {dulux} and the front hub has 6
no. 1 inch go faster holes drilled. I know the drum has to be painted but what about the rest? do I paint
like the drum or do I polish like the engine any ideas or suggestion greatly received
#2857 Paint the iron brake drum section and clean/polish the alloy bit - just like Veloce did! The iron
bit was a thin aluminum type paint; no thick stoving please.
#2891 I asked Ian Barnard (he of the "Best in Show" VM at Stanford Hall) about full-width front hubs
and his reply was: "I understand that Velocette originally electroplated the drum (so say Seymour's)??
Mortimers (Blunham, Beds.) have a paint called Astra Silver that is the closest I could get, I did try 2
others that were crap. I think it is stove enamel. Thin silver aluminum paint will peel off in less than a
year. The choice is yours, it ain't exactly in a place that is easy to re-do and I'd rather have something
a bit thicker if it stays on!" Now, if Veloce plated the iron part of the hub it would almost certainly have
been with cadmium. Here in the UK cadmium plating is only permitted for museum display use,
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apparently. Unpolished cad plating is best matched to vapour blasted unpolished alloy. The problem is
keeping it looking as good as it does when first assembled. Recognizing that the alloy would require
the occasional buff with Autosol, or whatever, Ian chose the pre-polished route - hence the choice of
the Astra Silver enamel. We do not know if this is a Vauxhall colour or not. Mortimer's number is
01767-640551.
#2892 We understand that the Brake-side of the full-width hub was Cadmium plated. Cadmium is a
poison and is now frowned on. Dull chrome is the next best. Just ensure the plater "masks" the brake
face and bearing housings.
#2895 I have checked the original factory specifications - it wasn't plated, the finish was described as
"aluminum enamel". A clue if not the total answer.
#2906 Could I lacquer my ally hubs to protect the finish after having them bead blasted or suggestions
on other options
#2943 I have had them bead blasted already and a couple of people have suggested having them
twin packed ally colour ?? I have polished the brake plates to a nice shiny finish but I don’t know what
the hubs looked like when they were new as im way to young!!!! so any more advice gratefully
accepted
#2945 I assume you have the composite full width hubs. The left hand side aluminum, the right hand
side brake drum cast iron. If so the left hand side is polished, leaving the radial ribbed area as cast.
The right hand side is silver enamel or twin pack.
#2946 Polish the outside of the alloy (left) half, paint the iron (right) side with a flat (matte) silver.
Assemble the two halves, and paint the entire ribbed center again. This hides the fact that they are
dissimilar metals. Twin pack is good, it sticks better. But I have used plain brushing enamel with good
results. A rust-resistant primer is a good idea on the iron. Apply very thin coats. If you don't stir the
enamel and decant some of the solvent off, it will look more like as-cast alloy.
#2953 Dull chrome makes them look alike.
#2947 You can leave the rear (all alloy) hub as-is. It will soon be covered in oil anyway! The one on
my Venom was never polished. But you can polish the thin alloy cover that goes over the wheel nuts.
L #2902 can someone tell me what finish should be on the oil pipes up to the rocker box as mine
have been polished down to the copper is it just silver paint?
#2904 Bright chrome.
#2905 I've had several unmolested engines, all of which had the feed pipe plated with cadmium and
the drain pipe to the pushrod tube plated with bright chrome.
#2908 The rocker feed, ball valves feed and return elbows are all described in the factory
specifications as being "dull chrome" I have unsuccessfully searched for a plater that can "dull
chrome" for many years.
#2910 I think that you are right about the feed pipe, as mine are not discolored as I would expect
cadmium to be, but the drain pipes are definitely bright chrome on all my engines, which are US
imports.
#2917 I might be inclined to disagree here. On my machine the rocker box drain pipe is bright chrome,
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ut the feed pipe is satin chrome. I believe this is the original finish. The machine is a Venom which
was first registered in '62 but left the factory in '60.
L #3497 Anybody know the thread size for the screws, that attach the round velo tank badge to
petrol tank?
#3537 According to my measurements it is 5BA.
L #3708 Has anybody purchased a seat from R.K.Leighton, I need a new one for my MAC
(1955). I saw one sold on Ebay for £123.00 recently and from the photo's it was difficult to tell the
actual quality. Leightons have quoted £106.00 inc vat for one including the shipping. which by
comparison seems quite reasonable. I’d just like some idea of the quality.
#3710 I have a Leightons seat on my 1954 MAC (although I decided not to go for the split level
version). Quality is good. They are well made. Mine has been on there three years now and still looks
good. The brackets did need a little adjustment though.
#3720 You say you didn't go with the split level seat on your MAC, which one did you use, as for the
brackets do they come with the seat when supplied by Leightons. The ones on my MAC are a home
made affair and are not good....being 6` 1`` a split level seat is not good as I seem to be half on the
tank and half off it not good when braking.
#3712 I have bought from them on several occasions and always had good service. They used to
make the seats for Veloce originally.
#3721 Presuming we're talking about RS frames, there are three sets of seat fixations. First is 3.5
gallon tank on 3.5 gallon frame, second is 3.5 gallon tank on a 4.25 gallon frame (about 1960) and
third was 4.25 gallon tank on 4.25 gallon frame. The rear fitting stays about the same, but the front
one changes position.
#3722 Mine is the 3.5 gallon tank on the 3.5 gallon frame the front lug is above the down tube. It’s a
standard 1955 spinger MAC....I'm not fully versed in the velo jargon so not Sure what a RS frame is
forgive my ignorance.
#3723 RS frames are the rear sprung push rod engined items. i.e. MAC, MSS, VR, VM, VMT but not
KTT.
#4416 I noted a subscriber asking about new Velo seats some time ago. I'm not aware of whether he
found what he was looking for, but I recently ordered a new seat cover from R.K.Leighton,
Birmingham 0121 333 3130 www.rk-leighton.co.uk and have been delighted with the very high quality
and perfect fit. The firm also supplies new Velo seats complete.
L #3887 Is there a way to remove the tool box knob/spring/washer//male threads from the tool
box cover? Also, the cover has been chrome plated....did some bikes come that way or is this a
'custom' addition?
#3888 The stud is a tight press fit in the chromed knob. It is normally supplied already assembled to
the toolbox lid and is not meant to be dissembled, but it is possible with care and a suitable press. I
don't think any models left the factory with chromium plated tool boxes, but they may well have been
supplied like that through USA dealers, who will have had them plated locally. It could of course be an
owner modification.
#3891 It is not generally known that the washer that prevents the knob from falling out of the lid, did in
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fact originally have a threaded internal diameter that matches the thread on the screw, or did have
once !!! original assembly was easy, the washer was just screwed on, until it fell on to the 'waisted'
diameter of the screw against the knob, when a sharp tap on the end of the screw easily burred the
start/end of the thread on the washer, (or screw), it was then virtually impossible for the threaded
washer to accidentally pick up the start of the thread & unscrew & fall off when the box was opened . I
realize that all this happened long ago, & I have come across knobs with a small hole drilled through
the screw & a split pin inserted, as well as other cute mods. The fact is that it took many miles of the
washer rattling around on the waisted screw, before it finally wore the hole in the washer large enough
so that the washer fell off the thread at a time when the box was opened. I have made dozens of 'D'
boxes, exactly to the original design & use this method still. In your case, the chrome lid is of course a
'happy' mod. & the knob can be removed by the careful use of a hand held 4 inch grinder , but a
simpler way where damage to paint etc. isn't a problem, is the judicious use of an oxy cutting torch to
easily slice the side off the washer & enables it to be removed, then a new washer, (I use a rather
thicker one ) can be threaded & used when you are ready to reassemble, after what one would
assume to be the removal (?) of the chrome, & a new paint job !
#3893 I appreciate the detail. This knob has a fancy flat spiral compression spring behind it that I think
did its job and prevented the assembly from vibration damage...or the box wasn't on a bike long -
#3911 There's no reason why you cannot do as suggested, but I think it is wrong about the original
washer being threaded. It is listed as a standard plain washer SL6/32. For initial assembly, this plain
washer is first placed on the plain end of the stud KA253, which is then inserted through the toolbox
lid. Then the Thackeray washer SL57/21 (we have them in stock, by the way) is slipped on the outside
of the lid, and finally the knob KA251 is pressed on.
#3894 I have to admit that I forgot about the spring washer, but it, like lots of other bits have gone
missing in a lot of cases over the years, & I don't include one in my 'boxes' (where would you buy one
anyway ?). The washer is in fact what is known as a 'thackray' (?) washer, quite common in early
Velo's, (& other bikes) as an anti- vibration device, the hand gear lever pivots was a common spot.
L #4356 Any suggestions about how to stop rear mudguard stays breaking on a Venom? The
RHS one has broken just behind the middle fixing (by the suspension). I've had this before and
bought new ones but this time I've brazed it together, repainted and refitted it. This time I've put rubber
washers on all the fixings. Any other ideas? (Other than revving less!)
#4357 Does the venom have tubular stays?, I broke one on my mac last year and fixed it by turning
down some tubing to an interference fit with the stay and putting the two pieces together, then tig
welding the break, then wrapping a piece of med gauge sheet metal around that and tiging up the
seam and ends, then sanding down and filling etc, then paint. the repair is barely noticeable ( small
bulge in the stay ) and has held up fine for several months. this is on a rigid frame mac.
#4358 Does your Venom have the centre stay fitted? i.e. the one over the top of the mudguard - part
number MAS60. Without this the whole plot will flex unduly causing premature fracture of the rear
stays.
#4359 I am surprised to note the breaking of the stay on a rigid MAC, the rigid framed models were
not prone to breakage in my experience. However noting the repair method used, - internal tubing, -
outer sleeve etc. Experience in my earlier years soon learned me that the moment you start welding
broken tubular stays, (& a lot of other things for that matter,) using any form of welding etc. the basic
strength of the parent metal is impaired to the point where eventually it may certainly break again
close to the original break, usually at the point where the internal insert, or the outer sleeve,
(whichever is the furthest from the weld) ends. I have to add that this does not necessarily apply in the
case of a well done frame tube repair, simply because the frame is a normally rigid non flexing assy.
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whereas fender stays do come in for a certain amount of fatigue strain. The rigid M series stays were
pretty much bullet proof, only breaking from accidental damage to the major assemblies, or bending &
rebending damaged areas over the years. I have made dozens of new stays to replace lost ones in
basket cases, & it isn't difficult to make new stays to replace the broken ones. Modern steel tubing is
easy to obtain in 16 gauge wall which seems adequate, & any bending required of this tubing is easily
accomplished cold by pulling around a convenient curved surface, in fact in my younger days a lot of
this forming was done by simply pulling the tubing around my knee ! (maybe that contributed to their
failure !) Do not use heat for this type of small tubing ! Over the years I have turned up forming
'spools' for small Dia. tubing, & these are just used in the bench vise, & the tubing pulled around by
hand with a larger neat fitting piece of straight tube over the part being pulled & kept in as close to the
spool as possible, & being moved away as bending progresses. The flattened ends are easily done,
most Velo. 'flats' being just that ! but if you want to do the professional looking rounded edge of the
'flat' This can be done by using the back of the 'jaw' in an open ended spanner of 5/8th inch minimum
width, although some years ago when I progressed from a heavy duty bench vise to a hydraulic press,
I took the trouble to make up a simple die plates to press these ends on smaller tubes. These dies
had nicely rounded edges on the working surfaces, rather than the sharp edge of spanner jaws. While
on the subject, I have a 100 % (?) cure for the spring frame front guard mount breakages, & also for
those rear guards with 'valances' that fracture at the top as a result of those pesky tailpiece flutters at
low RPM, (like sitting waiting for the lights to change ).
#4373 The first thing obviously is to get some more strength into the bottom of the vertical stay, the 2
bolt holes in the original stay really pushing the boundaries. I have heard of a more substantial piece
of steel being welded to the bottom of the broken stay, but I always have serious doubts about welds
in those circumstances, so I use a piece of machine steel, key steel or similar, a little thicker & a little
wider, it doesn't take much, admitted it's a pig of a job to get the bend right, up at the top of the loop in
the heavier & tougher material, so that the pristine fender surface isn't damaged, but it can be done, I
spent a lot of time linishing the contour on the top surface to match the fender, although I have since
considered using this part of the old stay & locating 2 good welds just below the edge of the guard to
two new separate bits as described above. There is little if any stress at this point. The rebuild on my
bike took place after an idiot (on his way to church !) had driven through a stop sign & done a 'U' turn
across my bows ! so the original guard, & already broken & repaired stays were well beyond repair, (&
the 19 inch rim & spokes also !) The fork tubes & clamps straightened OK. I was already considering
going to a 21 inch tire up front, I was riding it solo in those days, so that's what I did, & with the idea of
lowering weight & stress on the vertical stay, I replaced the front guard with a sportier looking
narrower steel item from ' Wassell' of the UK. - (are they still in business ?, if not Armours ?) I soon
found that there was a lack of real space at full fork compression, so the guard was put right down on
to the tire. At this point I decided that I may as well go all lightweight, so the lower rear stay was bent
from 3/8 inch OD 16 gauge tubing right around the rear of the fender, with 2 small lugs & two 1/4 inch
bolts. Attachment to the fork lug at the lower bolt, - I think I had to fiddle the tubing here to get enough
'meat' to go around the bolt. The front stay is formed in one piece, from 3/8 x1/8th. flat secured to the
inside front of the guard by two 3/16 th. bolts. It is SMALL ! I had to forge the end of the flat a little, to
get it out to take a 1/4 inch HT bolt safely at the fork attachment. There are NO gussets anywhere !
The unfortunate fact is that the entire forces of the guard trying to move back & forth is taken by the
single vertical stay, & the 2 bolts. The rear & top front stay, just going along for the ride taking no real
radial movement strain. If you have a Velo with the 'valanced' rear fender, it will almost certainly have
fractured the side valance pieces from 'tail piece shudder'. I started off by inserting wires in the edges,
& doing a 'perfect' repair job, but it soon broke again, so a bit of observation with the motor idling
showed that the problem was one of the valances flexing in & out sideways, - stop that & it should be
OK ! I never even repaired the fractured valances ! I bent up 2 short lengths of substantial section, ( 1
1/4 x 3/16th inch as I recall) flat steel that anchored on the inside of the top shocker bolt, & laid
perfectly flat down the outsides of the valances, this involves a bit of time & effort to get it perfect, but
once done, drill a 1/4 inch hole through the valance to correspond with a hole in the lower part of the
strap, a LARGE diameter flat washer on the inside of the guard, & despite the fact that the split is still
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in the valance, but almost impossible to see as the strap covers it on the outside & the large flat
washer on the inside. The fender has never shaken since, & nothing has ever broken.
#4360 No I don't have the centre stay MAS60 fitted. My rear mudguard assembly isn't like the one
shown in illustration H on Page 37 of my parts book. This illustration shows the centre stay but shows
a two piece mudguard with stays parts 56 and 57 which fasten at one end to the frame and the other
to the mudguard. My rear mudguard is one-piece with long curved stays which bolt at the front end to
the frame just in front of the suspension units and again at the rear of the suspension units before
curving down and attaching near the back of the mudguard. A difficult thing to describe but if you look
at Steve Bland's bike in members machines on the owners club site
www.velocetteowners.com/membersmachines/blandsteve/blandsteve.htm you'll see what my stays
are like.
#4361 You need MAS60. If not, the mudguard will bounce up & down and then - the stays break! In
the photos of Steve Bland's machine this bridging stay is hidden by the seat - its there though I'm
sure.
L #4635 The front tank mounts on mine consist of a rubber bushing with a tube through that has
a thick-washer type end on the outside (all one piece). Is this correct? Does the rear frame rubber fit
between the u shaped area at the rear of the tank? Does it need to be trimmed?
#4636 The front tank mounts are the same for all 'RS' frames from '53-'71, a moulded rubber grommet
flanged on the inside to prevent the steel tank from making contact with the frame. The mounting bolt
is a shouldered 3/8 Whitworth which can be screwed into the female threads in the frame only until
the shoulder makes contact with the frame, so that it does not crush the rubber grommet. The bolts
and grommets are also the same for all RS frames. My VMT had a molded rubber block to support the
rear of the tank, which dropped onto and was supported by the block without any effort. If yours has
the GP carbie, you may want to have the back of the tank free so that you can raise it in order to tickle
the float chamber, pivoting it around the front mounting bolts.
#4637 The front mounts appear correct and the answer to the rear mount is yes it is correct and no it
doesn't need. Further to my reply, I should amend that to read that particular front mount is correct for
use with a fairing.
#4639 Who knows the part number of the U shape rear rubber block ? My VM has a Thruxton tank,
but I don't have the VMT spares list.
#4646 Regarding the tank front mounting, you will need to remove the fairing bush and fit the normal
shouldered bolt and washer as described by Frank in his reply. Otherwise use an ordinary bolt through
the fairing bush, but it will look much better with the shouldered bolt set up. Yes, I also glued the rear
rubber to the frame and the tank rubber may need shaving down slightly to fit within the saddle at the
rear of the tank. I have never seen a supplement showing the tank mount/fittings.
#4648 I have a parts list of Aug 1971 It gives the Petrol tank fixing bolt buffer FK151/4 for Venoms,
Vipers and variants etc 2 off and for the Mk2 Clubman and Thruxton Petrol tank rubber A353 one off.
When I had my 3 ½ gal tank modified for a KSS engine in RS frame the distance between the rear
ears increased, so to avoid stress on the tank I have fitted a rubber washer here.
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G.2. Cables, Controls and Instruments -
L #39 The Scitsu electronic tacho www.scitsu.co.uk/
L #737 Velo. VM6333E had been abandoned in swampy Louisiana after the speedo cable had
done its magic on yanking the handlebars to full right lock - it didn't take a forensic scientist to figure
out the cause of its loss of favor with the original owner.
#739 I'm intrigued by this common reference to the speedo cable somehow becoming wrapped
around some other component. There's even a part in the VSL list which seems to be designed to
prevent this occurrence. I haven't run my being-rebuilt bike yet, but I can't visualize how this situation
would arise. Are we talking rear wheel drive, single sided hub or what? I'd be grateful if someone
could describe in simple terms the cause & the remedy of this problem,
#740 This can only occur on machines with QD rear hubs, and rear wheel driven speedo (which is just
about all of them unfortunately). The cable runs past the hub on the way to the speedo that is usually
mounted off centre on the handlebars, right? One day, one of the cap nuts from the QD hub works
itself loose, right. Some time later, just as you're peaking out in third gear exiting a sweeping right
hand bend, the nut decides to exit the sleeve in the hub, right? Instead of whizzing out and
disappearing without consequence, as the tube it resides in is in the top arc of its travel or the bottom
arc of its travel, instead it decides to poke its head out just as it passes the speedo cable, right? It
jams and as the cap nut attempts to coil the cable outer around the rear axle, there is an immense
and unplanned tension in the whole speedo cable, such force being transmitted right up to the point
where the cable is anchored, i.e. on the back of your offset handlebar mounted speedometer, right?
Now simple high school physics comes into play - turning moment = force x length of lever arm.
Basically the whole plot takes an unexpected turn to the left or right (depending on which side the
speedo is mounted). Hence the sad tales of these hapless riders, such as the former owner of the
PD'O Endurance in Louisiana. The solutions? A dab of loctite in each cap nut on assembly, and/or A
push in plastic or rubber plug in the open end of the 3 tubes in the rear hub, and/or Mount your
speedo directly over the centreline of the steering head (not very practical), and/or Leave your speedo
cable and your brake levers at home and attain some legendary cornering speeds!!
#742 Actually the problem only exists for full width hubs, the older "cotton reel" hubs don't trap the cap
nuts ("acorn nuts" here in the US) so they are not a problem.
#744 Re Speedo cable causing problems, I mounted a holding clamp matching that for the tacho
cable on the other side of the under tank strap. This I made tight on the cable and only tight enough
on the tank for the strap to perform its original function. Theory was that if the cable started to pull, the
clamp would twist and give a few seconds vital warning that something was not quite right. Obvious
solution is to never leave home without first checking your nuts.
L #959 I've got to the fitting of the speedo. It's a Smiths 3" Chronometric & looks in v. good
order apart from the alloy spigot which carries the thread for the speedo cable. This has been crossthreaded
at some stage and may not retain the cable nut(I haven't got a cable yet). Does anyone
have any good dodges to avoid an expensive solution, or at least know what thread is used on this
item?
#982 I noticed some of the newer cables are a very tight fit so you might find they will work for you
when you try your new cable.
#984 An unholy but effective dodge is to hacksaw through the cable nut end, across the threaded
section, in an "X" fashion and fit a small hose clamp over this part. You then slip the cable nut over
the alloy spigot threads and tighten the hose clamp until it engages what's left of the threads. You
then can carefully run it up snug and finish tightening up the hose clamp to lock it in place. Properly
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placed, the clamp screw will not even be visible.
#1001 Every screw in your smiths speedometer and the gearbox on the back of a Shadow clock is
Metric.
#1002 You are correct in saying that the screws on the Smiths Chronometric instruments are metric,
and also that the two screws that hold the mechanism into the case are an unusual thread, but the
size you give is incorrect. These are in fact M5 x 0.75, not 4.8mm diameter. I have tried without
success to source these from every possible supplier, including the current owners of the Smiths
rights - Speedograph Richfield in Nottingham. Beware of ordering these screws from SR - they will
supply plain ordinary 2BA screws and charge an unbelievably extortionate price for the privilege of
supplying the wrong items! I can only report them as being one of the most unhelpful companies I
have ever had the misfortune to deal with! The good news for those who want to manufacture their
own screws is that taps and dies are listed as available on the Unithread web site www.unithread.com
At £11.70 each for taps and BGP14.00 for dies they are quite expensive, but that's the
price you pay for oddities. The correct thread for the cable connection is M12 x 1.0, not ½" BSC x 26
TPI, hence your sloppiness, . Apparently this is because the original Smiths instrument company
started life in Germany before coming to the UK between the wars, so is not quite as British as most
people believe!
#1012 , I have just checked with Johnson's the thread is M12 X 1.0 at the speedo end, on the rear
drive end it is ½ BSC X 26 tpi -endcab
L #1004 You are correct in saying that the screws on the Smiths Chronometric instruments are
metric, and also that the two screws that hold the mechanism into the case are an unusual thread, but
the size you give is incorrect. These are in fact M5 x 0.75, not 4.8mm diameter. I have tried without
success to source these from every possible supplier. The good news for those who want to
manufacture their own screws is that taps and dies are listed as available on the Unithread web site
(www.uni-thread.com). At £11.70 each for taps and £14.00 for dies they are quite expensive, but
that's the price you pay for oddities. The correct thread for the cable connection is M12 x 1.0, not ½"
BSC x 26 TPI, hence your sloppiness.
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H. Manuals & Spares
L #31 By the way, I am wanting to obtain the Haynes manual for the Velo Singles to add to my
growing library, but no luck.
#50 Yes, the Haynes is out of print. I have an original copy of the Service Manual for the 1953
SwingArm MAC which should probably cover 99% of the 1956 models main service needs. Also
picked up an original copy of the owners manual which is a LOT more in depth then the ones we get
these days.
#51 There are several sources for out of print Velo manuals. As Bruce mentioned, ebay is a good
one and Velo manuals crop surprisingly often. To skip all the browsing through Harley parts, I usually
shorten a search to 'velocette', or 'motorcycle manual'. There's also www.Bookfinder.com where I've
found literally hundreds of difficult to locate titles on motorcycles. If you log on, it's pretty selfexplanatory,
and there's none of the waiting as on ebay, but be careful, you may get hooked. Also,
there's ARTCO, that's www.autoliterature.co.uk
#57 I have both the Haynes manual and the Main-Smith one. I find the alternative pics the most useful
parts, as their tech stuff is mostly the same as in the red book.
L #43 The compendium of tech articles which Dai Gibbison referred to was put together by Tom
Ross.
L #54 I copied the list you provided through the VOC of all the technical reports from past
Fishtails. Is it possible to get copies of any of these, and if so, how?
#55 The only way you can get copies of these individual articles is through the VOC UK club librarian.
His details are in the back of Fishtail
L #323 The Red Book is essential. I only use the Haynes manual in conjunction with the Red
Book because of the photographs. The other manual I refer to frequently is the BMS Service Series
book. It has lots of useful tips.
#330 Okay, so I'm green .After all this is my first attempt;,but what is the Red Book & where is it
available?
#332 Generally, when people on this side of the pond speak of the Red Book they mean the Service
Manual published by the factory. The Burgess book is another good source of information, but the
emphasis is on the older (pre-'53) machines
#333 I've found that ebay is actually a good source of manuals, even if one went to an insane price
recently. I've bought manuals for just about everything there, or found connections to people who
have them; sometimes it just takes diligence. If you send an email to a vendor (those are the people
with 300 plus beside their name!) asking them for something specific, you might get lucky. Currently
the price average for a 'red book' or Haynes manual is about $40us. Often these are advertised in the
Fishtail or VMCC newsletter, or even Old Bike Mart. Seek and ye shall find. Also, for those literate
souls with a computer, www.Bookfinder.com may be useful; just type in 'velocette' under the book
title, and you may be surprised at what you come up with.
#334 The “Red Book” refers to the original service manuals issued by Velocette for the MSS, Viper,
Venom and Thruxton models. They differed slightly over the years, the final ones being the best (and
the easiest to obtain) publication number F484/11R dated march 1971. The “Red Book” Paul refers to
written by Burgess covers M, K , GTP and LE is not as comprehensive as model specific books, but is
234

worth buying if you see one. For earlier Velos service manuals are brown, buff and pink! You can buy
photocopy reprints of any of the service manuals from either the Velocette Owners Club or Bruce
Main Smith publications www.brucemainsmith.com Personally I prefer to buy original second hand
copies, which are often available from the booksellers at auto, jumbles, normally retailing at £ 12.
When I next go to an auto jumble I will provide details of the sellers. Finally, I believe that the Red
Book is the best and despite having built four Velos I always read the relevant section in the Red
Book before starting work on any job no matter how small.
#335 Thanks for your replies re. 'Red Book'.I've got the Service Manual - I just didn't understand the
terminology - the cover of my copy is white.
#486 Don Mitchell Tel: 0116 277 7669 has some original copies of the red book called "Service
Manual for Viper, Venom, MSS, Clubman, Scrambler Models and Thruxton supplement" Publication
number 484/12R probably issued in about 1972. 124 pages. About £12. This is very similar to the
photocopied (larger size) reprint issued by Veloce Spares under part number VSL102 at £7.70.
[Editors Note: see also, www.mercianmanuals.co.uk, www.elk-promotions.co.uk ]
L #490 There is "VELOCETTE MOTOR CYCLES, a practical guide covering models from 1933"
by R. W. Burgess, edited by C. A. Pearson Ltd., my photocopy is from the 3rd edition from 1956.
Another "Red Book" in the same format is "The Book of the Velocette (Covers the LE and Valiant
"twins" and the Single-Cylinder models up to 1958)" written by Ferrers Leigh, edited by Sir Isaac
Pitman & Sons Ltd., mine is the 2nd edition from 1959.
L #553 3. does anybody know the ISBN No. for Ivan Rhodes book Technical Excellence
Exemplified I am told it is out of print now ?
#555 The ISBN is 0-85045-717-3. Yes, it is out of print. It frequently turns up on a search for
"velocette" on eBay
L #15 Got a few Velo bits from Grove Classic Motorcycles in England, pretty fast service.
#370 By the way, while Ken Gardner has retired and sold his business to Mike Fotherby (who
appears to be doing a great job) Ken has retained stocks of Velo two stroke parts mainly for his own
restorations, his number is 01608 684904. Please respect his retirement and only use him in
emergencies!.
#642 I have been trying to contact Goodman Engineering, Evesham, regarding their verification
service for several days - telephone is out of order and e-mails are returned "unknown address" - any
information about them please??
#643 Simon Goodman sold his business to Grove Classic Motorcycles about three months ago. Mike
Fotherby's number is 01582 873066.
L #32 I have been in touch with Ed Gilkison and Geoff Blanthorn, and Dave Smith of Dave
Smith Classic Motorcycles, and they are all good fellows to deal with, whether for available parts or
good advice
L #160 Sorry for the delay in getting back to you. Below you are the telephone numbers of UK
suppliers of reconditioned mags, I have not used them so I can make no recommendations. Some
may only provide exchanges. Dave Lindsley +44 (0) 1706 365838 FTW +44 (0) 114233 6269
Independent ignition supplies +44 (0) 1237 475986 Dynamos only P Dunn +44 (0) 1782 856839
L #273 If you want to update with a practical solution for everyday use with a modern carbs I
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would suggest contacting Allen at: Unit B9, Moorbridge Road, Bingham, Notts Tel 01949 836733 Fax
01949 836734 they have Mikuni alternatives with suitable base setup and a good supply of spares
should they be needed.
L #279 Rebuilding the Lucas magneto? I have sent off the armature to Independent Ignition
Supply in Devon(?) They seem like competent folks, and their prices are quite fair. Sent my magneto
to him which he extensively overhauled. I was impressed with the service and how helpful he was.
Mine has been running perfectly for the last year. I would give him a call and discuss your concerns.
His number is below. Tel +44 (0)1706 365838
L #408 (suspension unit rubbers) If you can provide a pattern or drawing, Hill’s Rubber Company
in the UK should be able to make them for you or grind down the VSL ones. They are not normally
very expensive; telephone number is 44 (0) 1189 580535.
#409 I think this is a spare that is still available. Contact Seymours' (01 844 212 277) or other dealers.
L #472 Anybody know of a good machine shop (preferably around Glasgow / Edinburgh)? I
have got the engine in my U stripped, and now need to get a new bottom end bush made
#474 You could try Owen’s Velocette drawing office for original copies of the drawings of the bushes if
you want a machine shop to make them up. (Also remember to check the wear on the shaft)
www.owensvelos.co.uk
#475 have a look at the Scottish bit on the VOC web site. There are a couple of people listed there
who might be able to help you.
L #478 Paul of Grangemouth Ship Repair uses Smith Electrical (Don't worry about the name)
Contact Eddie Williamson Tel: 01 324 888 020.
L #485 Here are some useful suppliers for Velocettes - Control cables: Johnson's Cables Tel:
01844 237479 - Wheels Essex Wheels Tel: 01787 460230 - Speedos: Jim ??? Tel: 01604 861930 -
Tyres and tubes: John Lovick Tel: 01760 722886 - Number plates: P Mellor Tel: 01484 653559 -
Chrome plating: S B Products Tel: 01733 266138 - Brake relining: Terrac Engineering Tel: 01604
647655 - Magneto and dynamo repairs: Dave Lindsley Tel: 01706 365838 - Spares: Grove Classics:
Tel: 01582 873066 - Spares: Veloce Spares Ltd. Fax: 0116 275 2703 - Painting: Lewis and Templeton
Tel: 024 7660 4663 - Transfers: Robert Derrick Tel: 01454 260596 - Service manuals and other
books: Don Mitchell Tel: 0116 277 7669 - Sprockets: Sprockets Unlimited Tel: 01386 831341.
L #520 Martyn Bratby can be found at:- No1 The Coachouse Works Limepit Lane Huntington
Cannock Staffs WS12 4PA Tel 01543 572583 He does Velocette clutch plate inserts and replacement
clutch friction plates (also a vast array of springs and reconditions carburrettors).
L #728 Does anyone know of a good supplier of s/s tube offcuts in lengths suitable to make my
own tiddly mudguard stays-1/2" & 3/4" o/d ?
#730 Mail Order Metals in Nottingham Tel 0115 9748211 Fax 0115 9745469 Email steve@m... Web
site www.mailordermetals.co.uk can supply the S/S tube
L #796 The best source of the unique parts is the USA is Olav Hassell, he is most
knowledgeable and an avid scrounger / source of Scrambler parts.
#815 Olav, I've found him very knowledgeable and willing to 'work' at sourcing parts for you and he's
in virtually the only place where Scrambler spares can be found.
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L #809 Re parts source in the USA; Ed Gilkison has quite a lot of stuff, but can be very slow in
delivery. If he doesn't have it, often he will refer you to another who might.
L #830 Dave Smith is at 815 254 3998 He used to be the exclusive dealer for Goodman's here
in the US, and is a valuable resource for spares.
L #1725 As I arrived at work this morning noticed a missing nut on my horn - 1961 Venom,
Altette horn - does anyone know where I can get a replacement - slightly tapered domeheaded,
chrome nuts that are fitted round the peripheral chrome ring of the Altette.
#1727 From Taff the Horn - 01792 23 37 63
L #1782 Does anybody know if the route holders that clip onto the handle bars are still in
production, and if so where I could buy one.
#1783 Try www.oldbikeshop.com
L #1843 Can someone please help my poor failing brain - and remind me what the thread form is
re: the four little tappet cover screws on a VM/VR/VMT
#1844 3/16 Whit. Same as timing cover.
#1857 3/16 Whitworth can be replaced with 10-24 UNC, the minor mismatch is not a big deal on such
a small size. I found exact duplicates of these "cheesehead" screws in stainless that way. The same
thread is used on alloy MAC rocker cover. And thread replacement kits (Heli- coil) are available in
10-24 for that broken off screw.
L #1902 hello there, could anyone please tell me what the thread forms are for the rockerbox
bolts and also the oil drainpipe bolts and also the carbs flange bolts.
#1904 Rocker box bolts and carbs flange studs are 5/16" BSF, the oil drainpipe and all other banjo
bolts are 1/8" BSP.
L #3428 Does anyone know where you can readily get Hylomar aerograde from?
#3434 Try, Hylomar Ltd, Cale Lane, Wigan, England, WN2 1JT. Tel: +44 (0) 1942 617000 Fax: +44
(0) 1942 617001. Medium is adequate for general shop use.
L #3937 Hello all, Anyone know if there is a dealer of pre-AMAL carbs bits in the UK?
Specifically I'm looking for a float for a B&B carbs. If not, maybe I'll have to try Founders Day.
#3938 Have you tried www.amalcarburettors.co.uk
#3939 I've found the website but it seems that they deal in AMAL parts (and I've seen the Surrey
Cycles caravan at autojumbles - they have a lot of AMAL parts). I'm looking for older carbs bits than
AMAL.
#3941 Have you tried Martyn Bratby? Although he mainly deals in pre-concentric Amals I know that he
sometimes has other bits and pieces (he sold an old B&B for a mate of mine) or he might know
someone. I haven't got his number at hand, but you may find it in an Old Bike Mart. Failing that I'm
sure someone in the group will have his number.
#3958 My old float is a cylindrical float with an indentation top and bottom and a tube through the
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middle top to bottom. Don't know if its common B&B design but the float chamber needle isn't
attached to the float but is attached to a mechanism in the float chamber top. The float rises on the
fuel and pushes a couple of bob weights upwards and the pivoting action causes the float chamber
needle to sink and restrict the fuel flow. Sound familiar? The indentation on the top (and bottom so the
float can be used either way up) is to allow the mechanism full travel. Anyway, if this sounds like one
of your floats I'd be very interested to hear from you.
L #4312 Does anyone know a source for tank knee pads:- 1956 MSS Scrambler? It’s the small
tank with the cut-outs for the fork upper stanchions.
#4315 Try Mike at Grove Classics (01582) 873066
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I. Miscellaneous
L #29 the Velo OC Thruxton Registrar would be glad for anybody to sent him the numbers of
their Thruxton, whether or not the owner is a VOC member. His name is Ray Thurston.
#910 Is there a list of the 1008 genuine thruxtons worldwide.
#920 Ray Thurston of the Woburn Centre keeps a Thruxton Register.
#1031 I have the VOCNA copy (thanks Dennis Q.) of invoices for Velocettes received by Lou
Branch, the US distributor, from 1950 to 1960. Any member with a machine from this source and time
period is welcome to ask for a copy, scramblers were particularly popular.
L # 169 Background: I have inherited a Velocette from my late Grandfather. It is a 249cc 2stroke,
dating from 1929, reg no EN 4251 (light two-fifty, or Model U, maybe looking at the pictures
etc on the velocette owners club website). Owned by my Grandfather since about 1938, and ridden
extensively around the Lake District between than and when it was last ridden (when it was involved
in an accident) in around 1953. I believe that it is essentially complete, although it obviously needs a
full restoration! The bike is currently in the Lakes, waiting for me to move it to Scotland so I can start
the (what will no doubt be long and protracted!) restoration! Question: I believe that the reg number
was registered with DVLA in the early 80's when they went computerized, so I am interested in
becoming the registered keeper, but we cannot find any documents amongst my Grandad's effects. I
have got the from the PO, but it has a space for chassis number, so anybody got any idea where I
might find this, to save me hours groveling round with an inspection lamp? I'd be interested in getting
in contact with anybody out there who has tackled the restoration, or keeps up, a similar machine, so
I can depress myself with the task ahead.
#355 The Model U I have inherited has now arrived at my house, and I have had a chance to
examine it in detail for the first time. AFAIK it was last used around 1953 when involved in an
accident - but some work has since been done by my Grandad - the tank for one has been taken off
and cleaned. I am trying to understand the controls it should have (getting ahead of myself? - I think
so - the engine is stuck (piston in bore) - I have filled the cylinder with diesel, just waiting for it to do its
thing). The bike has been modified in use (I'll post some photos when the film is developed), and is
fitted with a twist grip - is this original? What is the small thumb lever on the LH handlebar for -
should this be connected to the decompressor on the engine (and what is that for anyway?). The bike
is also fitted with a type FD Maglita - but the lighting function has been disconnected - a groove has
been machined into the flywheel to take a v-belt, and we found a battery support bolted onto the
frame, so assume that at some time it has been fitted with a dynamo. Has anybody got any info on
the Maglita? Thanks in advance.... My plan is to get the bike back up together for 2004 when it will be
75 years old, so this will no doubt be the first of many pleas for info! Amazingly BOTH tyres hold air,
and the rear - which looks as if it was almost new when it was taken off the road - has obviously been
kept in the dark as it still looks serviceable - the bike will rarely - if ever - be ridden on the road (for
one thing I don't have the necessary full bike licence - yet!).
#358 There was even a super-sports variant, the USS, produced in 1929 only, which was good for
nearer 60mph. Mine was registered in July 1929 according to DVLA (fortunately the appropriate
things were done in the early 80's and I was able to get a new V5 without any trouble). What were the
differences for the USS? As regards the controls, I have seen them with both lever and twistgrip
throttles. Dismantled the twistgrip last night - it is indeed the internal scroll type. Not sure it is original
as it is fitted with a distinctly homemade looking shim on the bar. Reversed clutch and brake levers,
Front brake is set up on the right - is this normal or reversed? magneto lever on the left, Can see no
evidence of a cable entry to the Mag, but then most of it is covered with about 1/4" of oily dirt- which
has fortunately kept the worst of the rust at bay. I don't know that all the two-strokes had
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decompressors (the early 20's models didn't), but if yours has one it's for stopping/slowing the
machine, not for starting. Definitely got one above the LH exhaust port, but no cable connected. I
hope this helps, best of luck, Pd'O Yep, always keen to learn/understand more - I am a long way off
worrying about getting the controls right though!
#171 Richard While I don’t have a model U, I do have a GTP that is similar in a lot of ways - the next
generation so to speak. The issues I foresee MAY be the following. They are mainly limited to
sourcing parts that are beyond refurbishment. If the steering races are worn, these are impossible to
get hold of. Similarly cups and cones for the wheels are difficult. I also believe it has a three speed
box and parts for these are difficult to get hold of. The engine is simple as with the GTP just phosphor
bronze bushes for main bearings. Frame number should be found on the lug at the junction of the
seat tube and top rail on the off side of the bike. If not look around near the bottom of the down tube
again on the off side.
L #422 Where is the number usually stamped on a head? I just want to make sure what I am
looking at is Venom and not MSS. Any other quick visible or measurable differences.
#426 The MSS and Venom head is identical apart from the inlet size. MSS inlet is 1 1/16 inch, Early
Venom is 1 1/8 inch, most Venoms are 1 3/16 inch. The early MSS also had 5/16 inch cylinder bolt
holes.
L #581 I bought a 1951 MAC recently, because my brother in law has a 1952 one. Now we
notice that his engine is about 2 inches "shorter" than mine. What I mean is - the push-rod tube is
shorter, i.e. no top section, and the cylinder is shorter to match, with much more of the rocker-cover
visible than on my engine. The engine runs fine, but I was wondering if this shorter engine is a
standard one, as we have never seen another and every picture we've looked at has the same size
as my 1951. (Picture of the "short" engine is in the "pictures" section under "Keith Brettell."
#585 My 1953 MAC is like yours, the rockerbox is right up under the tank and it has a two sections to
the pushrod tube but it is an alloy engine and the first of the swinging arm frame macs click on the
club Velocette site & history scroll down to 1913 & click the catalogue link scroll down to 1954 Click
on mac.
#586 also click on 1949 catalogue mac on velocette club site it’s a rigid frame one
#588 Just took a look at the short MAC. I've never seen one like that before. I was thinking that maybe
it might be a MAC/MOV hybrid as the MOV barrel was a bit shorter than the MAC but I can't see it
being 2 inches shorter. Maybe it’s a short-stroke special?
#591 The "short engined MAC" is mine, for anyone who's interested I've added a couple of close-up
Pics on the Photos section in the Keith Brettell Folder.
#618 Re Short MAC , In fishtail 184 Ivan Rhodes describes how in 1973 he acquired a box of bits
including an unusual short M type engine fitted to an RE frame , He re-built it into a 53 MAC frame in
1980 to be what the MOV might have become . He describes , engine number NOM 3184 , with
short 6 fin barrel, NSU conrod , what appears to be a Viper head ,53 MAC gearbox, light flywheels
,17/6 racing cam . Maybe you have something similar inspired by the F/T piece.
L #404 I have managed to put a dent in the chrome petrol tank of my 1960 Venom. It is about
2cm across and 2-3 mm deep. Does anyone know anybody who can repair this without having to get
it beaten out rechromed and repainted. The depression (apart from mine) is about 10cm from the
filler cap. I have heard of people repairing car panels that have minor damage without needing to
respray but not a chrome petrol tank.
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L #453 Can I use Araldite "Rapid" to plug a leak in a petrol tank?
#455 Many years ago I used Araldite to repair seeping welds underneath a Gold Star petrol tank that
had being repaired and welded by a tank repair specialist and had no problems. I got the weeping
area hot with a fan heater so as the Araldite ran into the weeping area as well as on top of it. It worked
for me.
#457 As Araldite is epoxy, as far as I know, it is supposed to be petrol resistant
#462 Thanks for your reply. I went ahead and used Araldite Rapid (a large blob, reinforced with a
small piece of cloth) before I'd read your message. Bottom line is... it worked! That's 3 days with no
sign of a recurrence of the leak. Speaking to a chemist I gather there's apparently no reason why
Araldite should dissolve in gasoline. I guess the only problem may be lack of adhesion of the resin to
the metal surfaces over time. Still - this was a cheap temporary repair that lasted a 250 mile ride on a
sunny day and longer. I left a polymerised "blob" of Araldite immersed in petrol in a jam jar overnight
as a control after effecting the repair and there's no sign of deterioration of the polymer. So - this
was a "cheap fix". Time will tell.
#470 I also used Araldite to repair a T90 cylinder head same place and also Araldited a TR6 clutch
together, we also use it where I work to repair steering units for the Challenger tank.
L #616 Can anyone tell me which numbers (engine, gearbox, frame) should match? My 1951
MAC has matching engine and gearbox numbers but they don't match the frame number.
#632 I have never known all the numbers to match, as Velocette built engines, frames etc and put
them into the stores for assembly later. The only way to confirm this is to check them on the original
factory records held by Ivan Rhodes.
#633 I can confirm that it is rare for any two numbers to match. The gearbox number would be
stamped with a prefix which I assume Tom is ignoring. Depending on the model there are generally a
different number of digits in engine, frame and gearbox numbers. Then there are various alphabetic
prefixes and suffixes. I would guesstimate that 50% of machines no longer sport the original set of
numbers. I keep a selective record of the machine details returned by VOC members, some 5000 plus
machine entries to date. Within the bounds of confidentiality, I will be happy to interrogate them on
request.
#634 This is getting even more puzzling then, because my bike has engine number with the prefix
"MAC" and gearbox with the prefix "9-" both followed by the same 5-digit number. (The frame number
is different.)
L #715 I'm about to buy a 1958 Venom. I want to restore it to what it originally looked like
(without being obsessive about it). I'd like paint, transfers, mudguards, seat etc to be right but I'll use
stainless fasteners etc. Advice welcome on how to find out original spec as looking through various
websites I can find lots of 1958 Venoms which look quite different from each other. I'd also like advice
on which workshop manual(s) are best.
#716 Best thing to do is get all the manuals and info and decide which picture of a 58 you like best
then buy or build or adjust the bike to suit you. Parts can always be added or replaced. I think overall it
is good to buy the bike already running and fixed up as there is a lot of problems in a rebuild that are
frustrating. I have done this to a 59 and it turned out to be a great bike, but one I had done by
someone else was horrible. With the Velos you get a lot of flexibility as to what the bike "should look
like".
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#719 I would concur with the what everyone else says regarding rebuilding your Venom. Attached is a
link to 1958 road test of a Venom in Clubman trim, which you may want to use as a starting point.
www.netbikes.com.au/roadtests/venom.htm Even the official Velo catalogue for 1958 was incorrect
www.velocetteowners.com/photogallery/catalogues/58venom.htm as that year the tank had badges
rather than transfers. Contact Mortons Motorcycle Media who can provide you with photocopies of the
road test for that year www.croesus-consultants.co.uk/v-tec/articles.htm
#731 you might want to get a good record first of everything that this motor does or doesn’t do 10
miles wouldn’t be enough to find that out, especially with a bike your not familiar with. I have done a
few, they’re easy to take apart not so easy to put back properly Detailed notes on the workings and
the dismantling always help including photos. Also what is the known history that may help too.
L #769 Would anyone happen to know the approximate weight of a MAC. (If anyone has specific
data to hand, mine is a tele/rigid).
#773 according to MOTOR CYCLING, July 26, 1951, weight is 330 lb (dry weight?) for the rigid MAC
with Velo front fork.
#777 I just weighed ZUMAC, our 1950 iron rigid MAC w/teles. It's complete and running, but no toolkit
and has about a gallon of fuel in the tank. 150 front, 164 rear, so Walter's number is "wet". Oh, and
there's no pillion seat, you can see this bike in the Pics section.
L #998 What seem simple jobs never are they? I've spent a while this evening trying to remove
the closing/fastening screw from the toolbox lid so I can deal with a bit of rust.
#1000 The knob assembly comprises 5 items, and is assembled in the lid. There is the knurled knob,
the stud, two plain washers and a double coil spring washer. The latter three are placed on the
reduced diameter outer end of the stud, one plain inside the lid and the other washers outside the lid,
and the knob is either screwed on, or pressed on, and locked. It is not intended to come apart!
L #1719 Here is an extract from the Owners Handbook you may find useful:
RUNNING IN A NEW ENGINE. A new machine must be driven with restraint, and must not be worked
hard until all working parts have settled down and are thoroughly free. The engine will not give its full
performance until this has been achieved and the process of causing it to settle down and free off is
termed running in." During this period hard pulling (" slogging at low speed on large throttle openings
must be avoided and no attempt must be made to drive at constant high speed. The throttle should
therefore be opened only a small amount, and changes to lower gears made in good time, so that the
engine may run lightly loaded. It is not advisable to drive at a set low maximum speed or to keep to a
regular speed, and provided that the speed increases on only a little throttle, as it will often do on
running downhill, there is no need to hold the machine back. After about one hundred miles use the
machine should be accelerated for short sharp bursts of speed. The speed and duration of these
short canters should be increased as the mileage increases and it will be found that the machine will
usually be run in after about a thousand miles.
STARTING THE ENGINE -Turn on the fuel, using for preference the right-hand side tap. Flood the
carburettor sparingly by depressing the " tickler " on the float chamber top or by leaning the machine
at a steep angle to the right for about ten seconds. Do not flood the carburetor excessively. To flood
so that fuel overflows from it is quite unnecessary and is wasteful. Do Not Flood at All When
Restarting a Hot Engine. Close the air lever three-quarters of its travel (leaving the air valve a quarter
open) and set the throttle so that the throttle valve is not more than I-in. open. Further opening will
reduce the depression on the pilot system and make the mixture too weak to give an easy start. Raise
the exhaust valve lifter lever on the handlebar and whilst holding it up depress the kickstart slowly.
After a small movement the ratchet will engage the ratchet gear on the layshaft and the crankshaft will
be rotated on further depression of the kickstart. Release the kickstart when it reaches the bottom
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and repeat the movement several times quickly to draw combustible mixture into the cylinder and free
the engine.
THE STARTING "DRILL"- After this, release the exhaust valve lever and' depress the kickstart slowly.
As the kickstart moves down resistance will be felt due to the compression of air and fuel vapour in
the cylinder. Upon feeling this raise the exhaust valve lifter and move the kickstart very slowly to the
bottom of its travel. This must be done slowly to avoid spinning the flywheels further than is needed
and we stress the point as being important. Bring back the kickstart to the top, and after engaging the
ratchets by making the first movement slowly, thrust it smartly downwards without this time touching
the exhaust valve lifter. It will be found that the crankshaft will turn several times and the engine
should start. Keep the hand off the twist grip when starting as the action of pushing down the kickstart
tends to jerk the hand and open the throttle involuntarily, causing weakening of the mixture and
making starting difficult. If the engine does not start at once, depress the kickstart again against
compression, ease the piston over compression slowly, using the exhaust valve lifter as already
described, release the kickstart and valve lifter and try again. Although as described this method of
starting may seem lengthy and complicated, a little practice will soon enable it to be performed
automatically. Be sure never to kick sharply before engaging the ratchets properly otherwise the crank
may slip and cause damage to the ratchet teeth. It will be noticed that as the kickstart crank moves
downwards it moves across the face of the disengaging ramp formed on the bearing housing, and the
ratchet moves inwards under pressure from the internal engaging spring. Careful and deliberate
movements in conjunction with the correct throttle opening will give better and quicker results than
continued rapid kicking. Release the kickstart immediately the engine starts. The ratchets make a little
noise just before disengaging when the engine is running, and this has occasionally caused enquiry. It
is quite normal and can be disregarded. After a few moments' running, open the air valve gradually,
otherwise the engine will begin to fire irregularly, usually missing about every other beat (eight
stroking) and black smoke will come from the exhaust. After starting a new engine, or if the main oil
feed pipe has been disturbed, the oil circulation must be checked. All normal running is done with the
air valve full open. Do not close it when re-starting a hot or warm engine.
OBSTINACY IN STARTING.- During cold or damp weather the engine may fail to start because the
high tension cable is wet and dirty or the outside insulation of the sparking plug coated with mud. This
provides a path for the high tension current from the magneto to leak to earth and diminishes the
intensity of the spark at the plug points. Clean the affected parts with a dry rag. Excessive flooding of
the carburettor in a cold engine, normal flooding when hot, or leaving the machine leaning over to the
right with the fuel turned on, can all make the mixture too rich to fire readily and will prevent starting.
Rectify by opening the throttle and air controls fully and rotating the engine several times as quickly as
possible with the kick starter to clear the over-rich mixture from the cylinder. In an extreme case of
over-flooding the fuel should be turned off until after the engine has started. After clearing as
described, close the twist grip, and, leaving the, air control full open, make another attempt to start. If
unsuccessful, take out the sparking plug, and clean the internal insulation and firing points thoroughly.
They may be wet with unvaporized fuel. Check the point gap and if necessary reset to OW to .023'
and rotate the engine several times to clear the combustion chamber before replacing the plug.
Provided that the trouble is not of a more serious nature necessitating workshop attention the engine
should start.
MOVING OFF- Allow an engine which has been started from cold to run a few moments before
running it up to high speed. A fast idling speed is best, and will allow the oil time to reach all parts. It
used to be the rule to run an engine very slowly to warm it up, but nowadays it is considered better to
drive off without any lengthy preliminary warming up. Obviously a machine just started from cold
should not be opened up to high speed right away even if the engine has been run in.
L #2030 I am planning to resurrect my Venom, after approximately 25 years of sitting in various
garages I have owned. As becomes my advancing years I was planning to rebuild it in a more
standard Venom form than the clubman style it is currently in. The question is what to do about the
engine and gearbox. At first I was thinking of a professional rebuilt but it's pricy and also takes a long
time. As an alternative I was thinking of checking what the head and piston looks like and check out
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the state of the big end. (All this was good when I stopped riding it) I was thinking I would check out
the engine first before moving on to the electrics, clutch esthetics etc. I am planning to have the mag
rebuilt, and clearly oil/fuel/carb/pipes etc need to be cleaned and/or replaced. I would like to avoid a
bottom end rebuild if possible. Is there anything I could do to flush the engine Are there specific
problems that I need to be aware of or things I should do before proceeding along this "incremental
restoration" route?
#2033 It seems an "as necessary" approach could work here. Has it had oil in it all this time and will it
kick over? If so, then set the valves and check for compression. If that turns out well move to the
sparkplug {probably get a new one}, and if that's working go to the oil tank and change the filter, along
with new fluids all round. The carb will require a dunking in a can of carb cleaner and reassembly. The
fuel tank and lines would also need cleaning. At this point the thing could start. If it does the tyres and
chains should be looked at for serviceability. Battery, lights,cables, etc. Easy first ride - gearbox
noises, wheel bearings, steering head bearings... Check it out slowly and change fluids often. Maybe
all this is too much to hope for, but it'd be more fun to ride for a while than to just tear it apart and
throw money at it.
L #2170 As part of the continuing re-build I took the rear damper units off the 1963 Venom, and
discovered there is about 12 thou of side play on the swing arm trunnions. Otherwise they feel fine.
Now I have owned the machine since 1970 and the previous owner since 1967, and since neither he
nor I ever touched them, it maybe they havent been moved since they came out of the factory. So the
question is what should I do. I could 1. just tighten the thing up (need to be creative re the tool
required) 2. take it apart and put new felt washers in (is this still the state of the art?) 3. just forget it If I
move anything I am worried about getting the whole thing lined up properly without the mystical,
special alignment tool Input anyone?
#2171 It depends if you are purely talking about end play or if there is play in the bushes. If end play,
set bike up on centre stand with rear wheel on the ground and slacken one trunnion clamp and tap the
swinging arm with a rubber hammer or similar to take up play. The relationship between the two
swinging arms will remain the same. If there is play in the bushes these and a new trunnion if
necessary can be obtained from Grove Classic Motorcycles (great service). I undertook this work over
the winter on my Viper, and it was not as difficult as the service manual makes out. Use a local
precision engineering firm to ream out the bushes to size once fitted into the frame The finished
sizes/clearance can be found on the Velo Ownere Club Web Site under technical info. Setting the
swinging arms up in parallel needed a little bit of ingenuity and a metre spirit level. The swinging arms
were clamped together using long threaded rod and a 2 large brass plumbers nuts of a diameter wide
enough to clear the trunnion and 2 suitably sized steel washers.
#2187 There should be NO endplay on the swinging arm assembly. Two special washers are pulled
together using a length of studding through the "pin".
L #2234 I am beginning the restoration of my old bike and would appreciate people's advice on
various points. Please bear in mind that I am aiming for a working bike, am not intending to ever show
or sell the machine. I am not too troubled by the concept of originality as the bike was a bitsa when I
obtained it in 1975 and was even less original when it was stolen from me in 1979. I have decided to
have most of the larger cycle parts powder coated by a local firm (RPA). I know that I cannot have the
fork sliders baked because of soft soldered lugs, are there any other parts that I should omit from this
treatment? The bottom half of the engine seems sound and I am tempted not to split the crankcases
before building the engine. If I do split, am I correct to assume that I will not have to worry about main
bearing pre-load as long as I don't alter anything? One rocker and pushrod is missing and the
remaining pushrod is bent. There is a slight 'lip' on the inlet valve. I think the bike was probably
over-revved at some point and suffered a dropped valve. The unfortunate person who briefly 'owned'
the bike rebored the cylinder. What are the actual sizes of the various over bored cylinders or am I
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etter taking the barrel to someone who has a stock of pistons and matching it up that way?
#2235 I wouldn't use powder coat on anything with a 'fit'. eg fork yokes, swinging arms. Nor on fuel &
oil tanks. Frame, possibly engine plates, chainguards, battery platform, brake pedal. As regards the
bottom end. How do you know what's fallen in there? Safest to strip & assemble properly. VM pistons
were available in +.020", .040",.060" as 20thou is .5mm you can measure the bore size easily, even
with a cheap ruler! Find out what size you have, find a reborer who will accurately measure the barrel
and then decide if its useable or if you need to bore again. A new barrel & piston may be available
(not sure) Be as thorough as you can and you will get a good machine that will last. Cut the corners
and its trouble all the way!
#2236 I cant overstress enough that you should send your bottom end of your motor away and have it
overhauled and modified. nick payton is the man for you, he used to work for geoff dodkin and his
work is first class. my mate was a bit like you, he had a venom that was off the road for years. he put
it back on the road and it ran well. 500 miles later the crank axle started to pull through and it took out
the crankcase bearing ring. the bottom end was parceled up and sent to nick payton who had a batch
of drive side crankcases made and he machined it to his existing timing side half. if you send off your
lower end before it does that, you will save the cost of a crankcase half. the crank axle is a part that
may never pull through although there are more cases as the motors progress with age. having a
shock absorber spring wound up on it 24/7 and for years on end usually does the trick, mr payton has
the flywheel machined and a tophat mainshaft fitted and pinned and after that it is good for the life of
the motor. another very sensible and worthwhile mod is having the later breather added, which is easy
to do when the motor is split. also having a one piece pushrod tube fitted is a very very good and
sensible mod, which does require crankcase machining but again easier with the crankcase apart. he
can also check out your oil pump and bushings on the timing gears. one other thing I would do is to
check and see if your cyl head has been rose cut around the cylhead studs to accept a o ring. if not,
have it done and also if you do decide to have a one piece pushrod tube fitted, you will have to have a
machine job done on the cyl head to accept an o ring. I hope you can use this info, and please heed
my warning as the crank axle does come out and I can send you photos to prove it.
#2237 The Velo Owners Club UK sell an Engine strip and rebuild video (and a gearbox one too I
seem to remember) - the example engine used is a Viper. You will pick up a lot of good tips from this,
esp it demystifies the bottom end worries - i.e. once you’ve seen it done by an expert you will see how
relatively straightforward it is. I'd concur with Peter - take it all the way down, check that bottom end
properly and rebuild it well - it will reward you in the long run. The VM engine is such a good motor
when its right. Personal choice but I wouldn’t use powder coating if starting from scratch (although my
VM frame is powder coated - previous owner - and is looking good still) - for the reasons Peter
suggests - and also it can cause problems if water gets under it (although I hope you are going to
paint that grotty oil tank with something !)
#2240 New (iron) barrels for VMT and VM are available from Mike Fotherby. Pistons - Mike was due a
batch of Hepolites last week - I’ve not checked yet to see if they’ve arrived. Im still looking into get a
small batch of forged pistons made by Arias, think cost might be prohibitive though. No sign of the
Omega ones still.
#2248 Seymours of Thame also carry spares, but the VOC scheme is a must really - as well as being
a great Club, excellent magazine etc. Not sure who the barrels are made by - but they look pretty
good (ask Mike and he'll probably tell you) Let me know if you are interested in forged VM piston - I
need to get a minimum of 4 made before Arias will take on the work. But at such a small batch size it
looks like these will be £150+ when you add on the VAT and postage - ouch. the Hepolites are cast
not forged, and I believe will cost around £110 from Grove - but Grove will give you an exact figure of
course.
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#2252 I have just measured the barrel and it is bang on 86mm. It looks like it has been honed rather
than rebored or even just roughed up with emery. I had not done a huge mileage since a new barrel
so I am not really surprised. There is a bit of a ridge that has not cleaned up near the bottom of the
barrel and no wear ridge at the top. There is a tiny chip at the very top near the inlet valve position
which holds with my dropped valve theory. I have two of the rings and they both give a massive gap
so hopefully they wore rather than the barrel while I was using the bike. I can't wait to try a standard
piston now. To tell the truth, uncertainty about bore size has been a big procrastination factor so thank
goodness for the internet.
L #2350 This week I have collected my Mac that I bought a couple of weeks ago. Some of you
will remember my earlier posts. Today, I drove it for the first time. Very nice bike with surprisingly good
brakes (both half with hubs). I noticed some things that I want to change. 1) The seat is quite high. It
feels that I am sitting on top of the bike. The seat is original looking but it is a replica with a fibreglass
pan. There are also mountings for a saddle on he frame. Are there different seats available? 2) The
speedo is a bit slow. I know that it is not a fast bike!!! It is a 120mph chronometric type No.
S467/123/N. Is this correct? I think that it reads approx 20% to slow. 3) Are original type handlebars
available? The presently fitted bars are to far pulled back. That gives even more the feeling that I am
sitting on top of the bike.
#2351 My 54 MAC has an 85mph chronometric speedo. I'm reasonably sure that is standard fitment
for a MAC. There ain't many need a 120mph one. As for handlebars, I bought a pair that I liked at an
autojumble. There is a vast variety of 7/8" bars out there at a reasonable cost. Just find a set that you
like.
#2361 For a short period of time MACs were listed as being fitted with 120mph speeds (SC3308/00)
previously they were fitted with a 85 mph S433/1/L. However on latter speedos the key number is a
four figure number which follows the code if its anywhere near 1600 it should be OK. The speedo you
have is similar the speedo fitted to early Venoms the only difference being the last letter, so it should
read OK. The other thing to check is that you have the correct hub drive should read BG5303/10 or 11
(or 52283/6) - look on the little brass end cap for the number. Finally regarding handle bars, the
problem you experience are probably to do with the standard footrests. Having experienced, clip ons,
ace bars, standard bars, rearsets and standard footrests. In my opinion standard bars with rear sets
are the most comfortable for riding. The best bars I have found are Laverda Jota adjustable bars that I
have fitted to my Venom, you can adjust them wherever you need them to be. Often I adjust them
before setting out, depending if I am going on a fast ride or a potter. What other opinions are there on
bars/footrest combinations?
L #2548 Can anyone suggest someone who can straighten or repair a 1967 Velo 500 frame,
here in the states?
#2551 Contact the Frame Man at GT Enterprises in northern California. I've used his services on
several occasions and his work and labor rates are excellent. www.snowcrest.net/gte/index.html
L #2941 Hi Just a few basic questions for my first assembly. 1) Is Wellseal a good gasket
cement for the crankcase halves? Or is there another recommendation? 2) There was a 30 thou
spacer under the barrel is it a good idea to put another 30 thou spacer to counter the poor gas we
have or is it better to adjust the timing to suit. Hear in Canada we have a rating of 89 for so called
premium. 3) With regard to this spacer should there be a paper gasket below and above it?.....if I
have 2 spacers is that 3 gaskets? Is there another option rather than the messy appearing gaskets?
#2951 When assembling my VMT 334, with 3 shims, I used Hylomar Aero Grade between each of the
three metal shims and zero paper gaskets. Hylomar was also used between crankcase halves. In
almost 7,000 miles last year, this bike has remained dry, save for an early weep at the upper two
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piece push rod tube/head mating. This joint was remade with Three Bond gasket goo and has not
weeped since. I'd not add any additional spacers.
#2948 1 When I put my shiny black barrel and shiny polished head back on do I need new studs and
nuts(the four long ones).
#2949 No - if youre nuts are in good nick you don't need new ones
#2952 You can squeeze the nuts in a vice or tap them with a hammer. This will compress the Nylon
and give a better "second-hand" lock. As a matter of principle we always use new cylinder holding
down nuts. And always fit new O-Ring seals under the washers.
L #3167 Hi All, I have an interest in purchasing a basket case 1966 MSS. Can anyone tell me
what the differences would be from a Venom? Basically all that is there is an engine and frame. What
kind of wheels, g\box, fenders,tank etc would it have had?
#3168 There are a lot of differences between a 66 VM and MSS. Mainly in terms of hubs, (half width),
mudguards (what is a fender - around a fireplace?) black enameled steel with valances, mudguard
stays. The engine is nearly the same and it may have a lower compression ratio and M17/7 cam. Gear
ratios could be 14/ prefix or 12/ - depending on buyer's spec. None of the 'clubman' spec parts are
appropriate. I suggest you find a few photos and have a look.
#3169...also the MSS 1 1/16" port and carb.
#3170 Different cylinder head, piston, cams, carb, barrel length, for the motor (but by '66 more and
more bits were the same). Probably a wide ratio prefix 14 box and some different bits of tinware. Hubs
& brakes were the same as Venom by then. However basics are the same. Engine should be MSS
13xxx and frame RS 18xxx or 19xxx. You can build it pretty much as you like, depending how much
you want to spend. Don't forget that by that date, the MSS was the rarest of the singles- 48 MSS, 53
Viper, 157 Venom and 224 Thruxton, according to Ivan Rhodes' book, made in 1966. Not a lot. The
MSS is not a motorway bike, more a machine for the twisty back roads.
L #3318 Hello All, I'm fighting for months against an oil seepage on my 1957 Venom : starting
from cold, after 5 to 10 minutes, running or idling, oil begins to leak from the lower rear timing cover
screw, the one close to the oil pump. I try several remedies : surfacing the cover, mounting the screw
with various washers (copper, aluminium, Dowty), different gasket thickness, various sealing
compounds, loctited screw...It doesn't change anything. Some clues : the oil pump bore has been
sleeved; the paper gasket shows a good contact in this area between the case and cover; there is a
steel insert (not helicoil) in the tapped hole, loctited. I think oil leaks as soon as the oil fills the chest to
the level of this screw, but can't understand which way it takes. Has someone experience this already
? Any idea will be very welcome.
#3319 Is the screw too long and not tightening up the cover? Is it the cover or the case? Tried fitting
another cover? Is there a hairline crack somewhere?
L #3505 Hi, is there a preferred method to place the engine back in the frame? Must the G\box
and engine be installed together? From which side is it better to work from?
#3509 I have found it best to install with the gearbox attached and from the nearside (primary). It is
awkward but possible to do with the engine fully assembled if you don't mind knocking chunks out of
the frame paintwork (bitter experience !). It goes in better and is a lot lighter without the head and
barrel assembled.
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L #3613 Hello all, I have a 1960Venom with the alfin barrel and have just had pointed out to me
that I appear to have a Viper swept back pipe . The working outside diameter is 1.5" but the pipe has
an o.d of 1.75" where it joins the fishtail silencer and is 2.00" where it fits over the exhaust port stub. Is
this correct. If not, then where can I obtain the correct pipe(with sweepback). Is the small bore
affecting my low and midrange torque? Would this contribute to difficult starting?
#3615 I think Veloce reduced the diameter of their swept back exhaust pipes from 1.75 to 1.5 at some
point - I'm not sure exactly when - to improve mid range performance. It wouldn't affect starting at all.
#3616 Were there sweptback pipes and narrow bores in 1960? I can't remember. If you have
rearsets, you need the "higher" exhaust system.
#3617 My own take on this is that Veloce used Viper exhaust pipes for the Venom. About the norm!
The small bore pipe gives a power step which the large bore does not. I would use a large bore any
day, but if you happen to have a small one, use it!
#3618 I have found that the Viper head has a reduced diameter exhaust stub, about 1.5". Unless
someone has welded a larger section to the end of the pipe to go over the larger Venom exhaust
stub, what you have is therefore a Venom pipe. I had a small diameter sweptback on my Venom some
years ago. It went fine on it.
#3619 To clarify; the VR head stub is smaller than a VM. The small bore VM pipe is the same bend as
the VR but of course has a VM sized end fitting. Hence Veloce got two sorts of pipe bends at one go.
Only the stub fittings are different. There is a difference in performance between the small & large
bore pipe. The smaller one gives a bit more bottom end torque. However, overall the larger bore on a
500 lets it run out freer. Not of interest unless you use the twistgrip correctly!
L #4399 Greetings A couple of weeks back I bought a proverbial 'pig in a poke', a 1946 MAC
engine from the Kempton Park autojumble. All the major lumps look to be intact, but I will need to
helicoil a couple of threads in the crankcases. Can someone please tell me the correct thread form?
Just out of interest one of the cam lobes and its follower were worn to a frazzle. The oil passage from
the pump through the timing side crankcase, was blocked. By one means and another I cleared a
spring and a ball bearing out of this passage. This suggests the presence of an oil pressure valve, but
none of the oil circulation diagrams I have seen show such a valve. The other curiosity was that the
steel base plate to the oil pump was cracked; the pump itself looks OK.
#4400 The thread for the drain plug is 5/16" X 26 TPI in CEI form, The thread for the primary case
holding bolt and the dynamo clamp bolt is 5/16" X 22 TPI in Whitworth form, the thread for the upper
rear crankcase bolt and pushrod tower hold down is 1/4" X 20 TPI in Whitworth form. The "Oil
Pressure Valve" appears to be a bodge from a Demented Previous Owner as is the cracked oil pump
plate which is made of cast iron. These plates are often cracked by use of the four holding screws to
pull the pump into place in insufficiently warmed crankcase.
#4402 I may be mistaken but I think you will find the drain plug thread to be 1/8" BSP 28 tpi. The
threads in the timing cover and pump holding screws are 3/16" BSW. Exactly what threads are
stripped? As there are a number of other 5/16" and 3/8" W in the crankcase.
L #4482 My 1967 VMT had many nuts lock-wired together. They were all removed . Now it is
time to bolt everything back together again. Does anyone have any instructions or comments to share
about this subject?
#4483 Lockwiring is a possible indication that the machine may have been raced at some time, but
not necessarily so. Some owners may simply have preferred not to risk losing parts due to fasteners
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loosening under vibration. Racing regulations decree that filler and drain plugs MUST be lockwired,
but any further wiring is at the competitor's discretion. The correct method of wiring is to wire against
the direction that the fastener will loosen, i.e. if two RH threaded nuts are wired together the wire
should follow a Z pattern from one nut to the other. If a single fastener is wired, use the same principle
to wire to a solid anchor. The cut ends of twisted lockwire are SHARP! - ALWAYS turn back the cut
end of the wire on itself - the scrutineer will not be best pleased if he lacerates his hands on your
lockwire!
L #4565 Hi velo fans, new member signing in, can anyone tell me if all venom rear engine plates
including the additional stiffener are the same. I am interested to know as I have acquired a set which
I intend to use as a pattern in order to produce stainless replacements for my standard 1968 ones
(mk2 clubman). Without pulling the engine out I cannot check/ compare the sets, which is currently
inconvenient (I hope to get a couple more rides in before a winter strip down). Alternatively are engine
plate drawings available, this could be handy as I need to produce a cad file so that plates can laser
cut ideally. Finally has anyone thoughts on whether stainless plates will be stiff enough in 5mm
(standard size??), especially as velo saw fit to add the stiffener?
#4568 I thought you would have had 10 answers on this already. I have a half dozen or so swing arm
MSS, VM, VMT frames and engines and all the engine plates are the same. Aluminum alloy plates
have been made (I have a set but never tried them) but can't vouch for their integrity or that of
stainless.
#4569 All steel alloys (including most that are "stainless") have very similar stiffness, but they do vary
in strength. These are different properties. Strength is important when one considers threaded holes.
Aluminum typically has about 40% of steel's stiffness, but I've seen it used successfully for the front
plates
#4570 The Venom/VR/MSS are the same, but Velocettes listed different plates for the later Thruxton.
Don't ask why, maybe it was a change from Cycle to BSF for the oil tank bolts. However, make sure
you have Venom plates, the swinging arm MAC plates look the same -but don't fit, I know as I got an
odd one mixed in when I rebuilt my MSS. Confusion reigned for a few minutes when trying to fit it to
the engine.
#4571 VMT rear plates have the additional fixing holes for the cover plate over the top of gearbox,
otherwise just the same.
L #4579 Just a small thing, but as an apprentice motor mechanic years ago I was shown how to
bring copper up to red heat & quench to soften it. It is only in recent years that I have been told that
the quenching isn't necessary, - all the quenching does is clean the metal to a new brightness ! I have
checked this out & it seems to be correct ! but it does make one feel better to see the cleaned metal !
Another tip here, if you are working on an 'older' bike, & want to bend up a copper pipe with tight
bends & maybe a neat couple of 'coils' & don't have any of the (claimed) bending devices, or the
expensive low temperature alloy filler, just work out the length of pipe needed, soften it then press it
straight (by hand), on a flat surface, pinch off one end to seal it, flare the other end a bit to make it
easier to fill the pipe with molten lead. Run a torch up & down the pipe to make sure that it is filled. I
use spanner sockets to get the size needed for the bend or coil, just wind the pipe around the chosen
socket till you have it right, then out with the heating torch again & heat the pipe to run the lead out
again. ( a bit of a chore sometimes) It pays to rattle SMALL ball bearings up & down the pipe after you
are sure it has been emptied to remove any of the junk that lead is prone to leave behind, & then
wash out with petrol or similar . Note, lead is very soft, using solder etc. may run you into trouble on
small bends. Very small intricate bends can be made this way without hassle. On this subject, - don't
try the above softening method on brass of any description, the effect is to harden it & make it
exceptionally brittle, but it can be softened it would appear by heating it & allowing it to cool very
249

slowly, such as immersing it in hot sand & allowing to cool, I'll accept correction to this if I am wrong, I
have never claimed to be a metallurgy expert !
#4581 Hi All, Just adding my twopenny worth to this subject. The technical bit (ref. Engineering
Workshop Data - Caxton 1947). Annealing Copper Correct annealing temperature is from 200oC -
600oC according to level of impurities and level of cold work done to the metal. For most commercial
coppers 500oC is satisfactory. The mode of cooling, with copper, is immaterial; either water quenching
or air quenching is applicable but water quenching serves to remove dirt and scale. Annealing Brass
Ordinary copper-zinc are annealed by heating for about 15 to 20 minutes, at 600oC and allowed to
cool either in air or by water quenching. The practical bit (what it says in 'Model Boilers and
Boilermaking' by K N Harris 1972 and what I do) Nine times out of ten when you find instructions for
annealing copper and brass you will be told: " Heat it to redness and immediately plunge into cold
water." The last part of this injunction is completely superfluous, the only purpose it serves is to save
time. Harris goes on about air cooling to avoid distortion, but that's probably only relevant to
complicated shapes not motorcycle bits - I always water quench to clean the item and save time. To
achieve the right temperature with both copper and brass do not heat beyond just visible redness,
visible in subdued light, not in bright light or sunlight. For brass the 'heating for 15 to 20 minutes' is the
stuff of dreams (bad ones probably!) only for those with temperature controlled furnaces. It's more
important not to overheat brass and damage it's 'grain structure'. The practical form of heating is a gas
flame - a propane torch or for small items such as copper washers the kitchen hob is great (if you use
it without being caught!). 'Ordinary brass' (suitable for tubes) is typically 60% copper 40% zinc. In the
annealed condition both copper and 'ordinary brass' are noticeably soft and easy to bend at room
temperature (called cold working). After a modest amount of work they become noticeably harder to
work (called work hardening). It's important to stop bending or working the material as soon as work
hardening is detected. You then anneal the item and you can work the item some more. For complex
items this cycle has to be repeated many times
#4583 While I am well aware of the deterioration of brass alloys in seawater (& other mediums), & the
presence of steel, & the fact that it can lead to total destruction of the article, the culprit being
electrolytic action, I have often wondered how this sort of thing takes place over many years with
sheet brass items, I can only assume that it is a form of mild electrolysis taking place very slowly, by
virtue of the air &/or presence of other suitable elements of metal, & moisture in the atmosphere, this
over a very long period of time ?? This is most apparent in some OLD brass articles, & while the
original hardness caused in say sheet brass , while it was being spun or worked, remains forever I
guess, - unless softening is attempted, & I am pretty sure that this would be disastrous on articles
getting on to 100 years old ? This was most apparent recently when Mark Gibson presented me with
an acetylene gas generator as a repair 'challenge' This article was at least 90 years old I should think,
& the water tank part of it was full of the typical 'splits' in the metal that is apparent in old worked brass
articles, - especially something that has been work hardened by 'spinning'. In this case though, one
side of the tank pretty much fell apart in little bits of brass 'honeycomb' the moment I started to smooth
the dents, & the reason was certainly that the brass was nothing more than frail 'zinc removed' sheet,
typical of electrolysis damage. This plus other experience with old brass, leads me to accept that the
electrolytic process can destroy brass over the years, simply through the action of changing
temperatures, - the local presence of suitable metal, (stored in a steel container ?) & the action of
moisture in the air ? this of course only being apparent in very old articles. Maybe Richard can
comment on this ? As for the repair challenge, it was carried out successfully, but only after light
gauge sheet copper (easily available) was patched on the inside of the destroyed part of the tank after
smoothing & cleaning, & another 'patch' cut to bring the lost section back to the original contour, & the
whole thing sweat soldered back together, with clamps & such holding everything into place. Pic
available if you are interested)
#4584 You've got me delving back into the dim past with this. We are now entering the realm of
theory with a bit of guesswork. Like you I'm familiar with electrolytic corrosion. The problem you outline
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with old sheet brass items is somewhat different. The reference is 'Engineering Metallurgy Part 1' by R
A Higgins 1964 - this has been a useful book over the years. The subject is 'Cold -working' brasses.
The most ductile brass is high purity 70% copper, 30% zinc. (Even small levels of impurity lead to a
marked loss in ductility). It's commonly referred to as 'Cartridge Brass' or 'Deep drawing' brass and
this would be ideal for making items such as acetylene generators. For info only, such brasses are
rather sensitive to annealing temperatures and it's easy to 'burn' the alloy. (This trade term should not
be confused with oxidation. It is used to signify overheating, the result of which is rapid grain growth
that on subsequent working/pressing shows up as an 'orange peel' effect on the material surface).
The problem that I suspect you have experienced however is due to the fact that hard-drawn brasses
are subject to 'season cracking'. Higgins says 'In such brasses, any corrosion which takes place is
usual intercrystalline, so that cracks will ultimately arise, as internal stresses are relieved, by fracture
at the relatively weak grain boundaries. This effect can often be seen in old brass electric-light
switch-covers, particularly when they have been subjected to corrosion in a damp atmosphere.
Season cracking can be avoided by giving the component a low temperature, stress relief anneal at
about 250oC., after fabrication'. In addition, somewhere in the back of my mind, I'm aware that
acetylene gas has some pretty corrosive effects on certain metals but hopefully someone can remind
us.
#4585 The process you refer to in brass is known as 'de-zincification' and commonly wrecks water
taps & valves in hard water areas. The zinc is removed by electrolytic action leaving holed brass which
is also weaker. In water installations it was the case that a sacrificial anode was provided. Better
alloys are the choice today - unless you happen to have cheap taps!
#4586 Thanks chaps, it seems that I was basically correct, & the fact remains that any brass,
especially that of high zinc content is prone to this problem in the presence of certain factors. A lot of
years is probably a big factor ! The fact is that we as 'ooman beens' can only experience these
happenings over a short space of time in the big picture, & very few of us have the opportunity to
actually note what really happens to metals of all kinds eventually. One would expect that in the case
of brass, in the end after long periods of time, all that would remain is some form of copper residue, as
we have been taught that copper is one of the things that never really gives up ! I had one experience
with marine propellers where extremely expensive props were hooked to 2 Rolls Royce marine
engines & fitted to a 70 foot steel boat, which was built privately in a yard close to me, & I had
mentioned to the builder that he would need to buy & fit decent sacrificial zinc anodes to the back of
the hull. He was Dutch & had previously built timber boats, & intimated that if you fitted 'decent' props,
as he had done, the zinc was unnecessary ! The boat was launched into the sea, & some Summer
cruising enjoyed, the boat lay in port through the Winter, only occasionally being used as a week end
bar. The next Summer, the boat had lost it's turn of speed, & soon could barely pull itself away from
it's moorings & the Rolls engines were racing. An underwater inspection revealed little more than the
hubs of the props & 'nubs' of the blades ! Nothing to do with Velo's ? but it appears that certain (if not
all) EP oils can have the same effect on Velo gear box bearings eventually. I have to admit that in
ignorance of this fact, I have been using EP 90 in all my gearboxes for years ! - so we live & learn
L #4612 It seems you can never get a bike in absolutely original condition and hence the
restoration always involves discovering what was botched and how to rectify it properly. I have a late
67 VMT and I have a few questions about the exhaust. The front pipe is a later type with the pipe
being a smaller diameter it is affixed to the front footrest. I wanted to know the parts involved and the
order of assembly of this stud. Is it a square stud with a nut and washer on the inside, then an oil-line
bracket, then through the frame to a spacer, then the exhaust bracket then the washer and nut? If
there is a spacer how long is it and of what shape. Now to the rear silencer from the inside of the
frame out is it nut, washer, through frame to front footrest bracket, then silencer bracket, ( which if
these two is first) then rear footrest? If this is correct how much clearance should there be between
the frame and the top of the silencer. Mine is about the thickness of a piece of paper. And if it is not
the correct order how do you get the clearance needed for the silencer. I have another question about
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the older than pre- mid 67 silencer for the VMT, thats the one with the tube instead of the triangle
bracket on the top of the fishtail. What exactly does the rear footrest and stud look like that holds this
silencer on?
#4613 I do not know the late 67, but I have a early 68. The front tube there is 2" in dia, and is
mounted to the frame in front of the footrest.
#4622 have this problem with every new exhaust pipe I get (I've had my VMT 30+ years) as they're all
slightly different. I turn up the spacer after measurement from a bit of ½" galvanized iron water pipe. It
gets so filthy down there from bits of road and oil that nobody'll ever know.... There's a tradeoff - too
short and the pipe fouls the engine , too long and it fouls the kickstart. But it's not thou accuracy
required. Or perhaps you're after concours?
#4631 I read with interest (and sympathy) the problems seemingly encountered with exhaust systems
generally, as I have had considerable trouble fitting up my 68 mk2 clubman system. Firstly the original
fishtail was rotten and not being too impressed with the modern manufactured replacements available,
I sourced an original in good condition and had it fully refurbished including chroming. This was fairly
costly and few platers are keen to undertake this work as it tends to contaminate their baths,
fortunately I knew someone, etc, it was still cheaper than the new abortion. Secondly I had a stainless
pipe commisioned at JT tubes in Creekmoor (Poole Dorset), this again was forced upon me as off the
shelf ones were bloody awfull, the custom made one was not a perfect fit initially and I would advise
anyone going down this road to have it tacked, fitted on the bike and checked before final welding up.
The problem was exacerbated by the proximity of the kick start (cotter), gear change (linkage type
rear sets) and alignment- of the silencer (plus all fixing bracketry!)- as you all know. After optimising
the geometry to avoid all these elements and still keep as near as possible to the original, I ended up
with an excellent result, providing you like the bronzey look along the entire length of the pipe, which I
do, especially as you can clean off burnt oil and boot rubber easily (aggressively), run the motor and
restore the colour perfectly every time, A further complication was due to the replacement of the rear
suspension units with velo pattern JB's, these are longer, as are Hagons that I acquired at a jumble,
than the original Girlings by up to ½". This caused no end of trouble, as contact between the rear
wheel spindle nut and the silencer became a distinct possibility, necessitating setting the silencer
further out (1/8 - 1/4") by rotating the pipe on the cylinder stub, increasing the spacer thickness for the
pipe mounting bracket and fitting a spacing washer for the silencer mounting (pillion footrest mount),
hay ho, so it goes on, just as well I was intending to make new mounts in stainless (longer threads so
that I can use Nyloc's!!!)
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