The Knowledge - Velocette Owners Club

The Knowledge - Velocette Owners Club


The Knowledge

Being a compendium of eGroup discussions compiled from:


January 2002 - June 2005

Complied and Edited by:

2002 Les Carman

24 January, 2003

2003-2005.5 David S. Liebl

July 2005

Provided courtesy of the VOC and VOCNA

Table of Contents

A. Diagnosing Troubles

1. Hard Starting, Poor Running .................................................. 3

2. Poor Gearchange ......................................................... 25

3. Faulty Electrics ........................................................... 29

B. The Engine

1. Bottom End & Crankcase ................................................... 34

2. Cylinder & Piston ........................................................ 50

3. Cylinder Head & Valves .................................................... 59

4. Timing Gear & Pushrods ................................................... 81

5. Oiling System ............................................................ 96

6. Crankcase Breathing ..................................................... 122

7. Racing & High Performance ................................................ 131

C. The Electrics

1. Ignition & Timing ......................................................... 137

2. Sparking Plug ........................................................... 144

3. Battery, Dynamo & Magneto ................................................ 148

4. Lights & Horn ........................................................... 157

5. Electric Conversions ...................................................... 161

D. The Carburetor and Fuels

1. Carburetor.............................................................. 174

2. Fuels .................................................................. 189

E. The Drive Train

1. Primary Drive, Chainwheel and Clutch ........................................ 193

2. Gearbox ............................................................... 212

3. Final Drive, Chains & Cases................................................ 228

F. Running Gear

1. Steering Head, Forks & Shocks ............................................. 245

2. Brakes, Wheels and Tires .................................................. 260

G. The Frame and Ancillaries

1. Bodywork, Paint & Polish .................................................. 270

2. Cables & Controls & Instruments ............................................ 293

3. Exhaust Pipe & Silencer ................................................... 300

H. Manuals & Spares ............................................................ 305

I. Miscellaneous ................................................................ 312

[Editors Note: These contributions to and 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.


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


#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

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 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

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


#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

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


#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


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

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


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

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


The bike is a 99% standard Venom Clubman mk2, except for carbs and alternator (alton).

#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 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 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.

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 rebore


#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.

#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


#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: (the Group owner’s) and a treasure trove of Velo

info (including carbs settings). For guidance on checking the settings try: 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.

L # 4835 Just got my Velo from UK. Its got a good spark and fuel to the carb but won't even

make a pop. Followed the Velo startin drill from my books as well. The only thing I can think of at this

point is that when I got the bike all the cabling was disconnected. Is it possible that the exhaust valve

vacuum release is not properly hooked up? it seems unlikely because I seem to be getting

compression but I’m out of ideas at this point. And I am quite certain it did run before being shipped.

# 4837 After kicking was the sparkplug wet? One thing that works on my velo's is to give several

priming kicks with the decompressor pulled in. (this may be my imagination but...) Flood carbie well

(turn off petrol if you don't know bike as in this case for safety), do my primary kick thing as above, then

kick gently to compression, decomp, push kick starter slowly to bottom of movement, then give a good

kick. If valve and ignition timing is OK, Maggy has spark, and carb is wet and in good nick, it must go!

# 4838 I think that you need to experiment with old bikes until you find out what the particular

machines likes. For example, reading your note, my MAC will not fire if I flood the carb. Absolutely no

way. I close the air slide then follow the standard Velo starting procedure (ease over compression etc.)

and after one or two kicks it either fires or starts.

#4846 Tickle carb till finger wetted, close air lever 3/4 way, turn engine till compression felt, then with

kickstar at top, operate exhaust valve lifter, kick slowly to bottom of kickstart stroke, release valve lifter,

and kick manfully over compression, with throttle opened only the merest amount, avoiding the

tendency most people have of snatching open the throttle as you kick. Repeat this several thousand

times cursing loudly. My '47 MAC sidecar outfit refused to start after I added a lead substitute ( Redex)

but was fine again after drained out and refilled with standard lead free, which I have used ever since

leaded became unavailable. Some many years back, I was asked by Phil Bleasey (ex Fishtail editor) to

help him pick up a Venom he had bought from a chap who had done quite a good job of rebuilding the

bike, but eventually gave up on the machine as he had never managed to start it. Everthing seemed

OK till we realised that it was timed to exactly 38 before top dead, but on the exhaust stroke. 10

minutes later we were flat out on the by-pass! Good luck, you'll love it once you've got it going.

# 4836 Sometimes a good hill does the trick.

L # 4848 I recently took delivery of my 1960 Venom that has been expertly restored by Dave

Smith in Chicago, fitted with a 10.5:1 compression piston, squish head, and a new BTH magneto and

twin plugs. Because of the minimum RPM required to light off the BTH I was learning all sorts of new

words trying to get it started. I'd been aware of various "mobile starters", i.e. the Foxley, that use a

rubber tire powered by a gasoline engine which one positions against the rear tire. Definitely a two-man

operation and expensive also. I finally found a chap who makes a battery-powered starter that consists

of a pair of parallel rollers mounted in a fabricated steel structure, each of which is powered

independently by a Ford truck starter motor. A folding steel plate on each end allows the rear wheel to

be rolled onto the platform where it contacts both rollers. A foot switch supplies power to the starters

through a HD starter relay. In practice the bike is put into third gear, the front brake is applied, the

decompressor lever is pulled in, the unit is engaged, and when you release the decompressor lever the

bike is instantly running. You can then roll the bike off the starter and motor away. Not only is this

useful for starting the bike, but I've also used it to thoroughly purge the oiling system of the old oil when

changing oil. I've also learned that AMAL used to make a device they called the "Easy Start" for the


Monoblock carburetors, which replaces the slide stop screw. There is a little "toggle" in this device

which when actuated, raises the slide by .030", the ideal amount to provide excellent air velocity across

the idle jet and get the bike running quickly. Once it warms up a bit you can deactivate the toggle and

motor away. I certainly can't take credit for this idea, an acquaintance in England came up with this idea

and is making a couple of these for me for the AMAL Mk I Concentric fitted to the Venom and if there is

enough interest I suspect he will offer them generally for sale. Those interested in the roller starter can

contact: Mr. Art "Doc" Zimmerman Doc Z International Ltd. 24220 Bruce Road Bay Village, OH 44140

Phone: (440) 841-7112 email: docZ01@... Current price is probably around $600.00, which doesn't

include a battery or the battery cables, but this thing really works well and saves beating the kickstart

mechanism to death.

# 4851 George, If you need rollers to start a Venom, there's something wrong. A good BTH mag will

put out a super spark even at low revs; that's not the problem. A sump full of oil with close ratio (TT)

gears may be. Maybe the technique too?

# 4853 I have a '60 VM clubman with a Dave Smith supplied squish head, 10:1 ratio, BTH TT mag,

and a 1 1/4" TT carb, and have no trouble starting whatsoever. Check mag output and carburation, the

BTH should give a fat spark at almost no revs, with hand turning of the mag shaft, or a slow kickover.

But, if the idle circuit isn't right, even a docile beast like an MSS will be a difficult starter. Will it idle

slowly, once started?

# 4854 My '51 MAC was once hard to start for a while, but the problem eventually came to light when it

also began idling poorly or stopping completely when the throttle was closed. Tracked it down to the

idle- jet having a tiny bit of 'something' stuck in the hole-almost too small to see with the naked eye but

once removed everything was back to normal- ie 2 or 3 kicks at worst and usually a first-kick start even

after several weeks of storage.

#4859 My definition of “hard starting” is having to kick twice. If we do not fire up on the first kick a look

of surprise spreads across the face. Is it not more particle to have the thing set-up right and avoid the


# 4855 I used to think I could no longer run fast enough to start my bikes via bumping sons

showed me up! Actually the magneto may be the culprit....was it rebuilt? As an aside....a lot of us

AHRMA guys used starting rollers both powered and driven but IMHO they are a waste of bucks ($) if

all is properly tuned.

L # 4867 Can anyone clue me into how to get a Venom started again once it's hot? The Mag is

fine I have spark and I have fuel and compression. Starts like a champ cold. Runs great. But if I stop

and let it sit longer than 5 minutes I might just as well fine a pub and wait an hour.

# 4868 Gees. Most people look forward to a good excuse to sit in a pub for an hour. Seriously,

though... do you have a phenolic thermal insulating washer to isolate the carb? That helped me.

# 4873 I agree, but we need to help him solve the problem because there are times when the hapless

Velo rider is stuck with a beast that won't start and there's no pub within cooee. So, the procedure

according to JJ is as follows: 1. If spark, compression and fuel are confirmed, find a hill (or if flat ground

enlist the help of a bike pusher) and bump start. I despair to see Velo riders wearing out their right knee

joint (and less importantly, the kickstart ratchet) with a beast that clearly has no interest in firing and

continuing to run after that single shot we get, courtesy of that low geared kick starter. The second best

starter in my shed is Li'l Speedy, the '39 MAC racer - and it doesn't even have a kick starter! 2. Nearest

I can get to help the Venom problem specifically, is a problem we had with Kamahl, the Concentric

equipped Mk2 Clubman. When almost hot, it fires, then spits back and won't run. A timely hint from my

old mate Richard (who has the world's best and much ridden Mk2 Clubman) prevented me and PD'O

from setting fire to this bugger. A smidgin of choke to get started when almost hot solved the problem

completely. It doesn't appear to be related to jetting or float level (because I know Richard's would be


spot on - he's that type of bloke). It's just what experience and a period of getting to know you

determines is the answer for this specific "starting when almost hot" problem when running a

Concentric. Like yours, if you get to it in the first 5 minutes of stopping, just kick once and ride off. But

after that period ....... 3. By the way, the best starter is Old Faithful, GP equipped VMT457. Correct carb

settings and 30 years of "getting to know you" explain this behaviour. Not that you need 30 years - it

only took about 18 months for me to wake up to the need to get carb resleeved and float level spot on

in order to turn it into a pussycat with respect to starting.

# 4874 I had a hard starting problem when my Venom was warm and discovered that if I killed the

engine by letting out the clutch gently while in gear it started easier if I had to start it while still hot or

even just mostly warm. I think maybe it has something to do with the engine not sucking in several

chugs of gas with no spark. I know there are probably lots of reasons not to stop this way and that if the

bike is spot on (as mine has seemed to be lately) it should start regardless or engine temp, but it's a

tactic to be tried with a taciturn Velo.

# 4880 The position of the piston has a lot to do with it.

# 4876 Well now , there is one problem about setting off down hill with a reluctant starter - What do

you do at the bottom of the hill when the dear little thing has failed to start? In good order a Velo will

start easily. If you are involved in racing you will have noted that two or three steps and bump will see

the thing burst into life (one good thing against clutch starts!) So; no hills or rollers will rectify a machine

in poor nick, and that is what the problems are, be it mag or carburretion. Look after those knees!!

# 4872 First, Re. the little gadget that clamps on to the slide idle adjusment screw. Maybe my memory

is defective, but I can remember that the very first MSS that I rode prewar, brand new & belonging to a

very proud mate, had that little accessory, & so did other MSS's of the time, (those that I remember

anyhow !) Of course I only rode my 1930 KSS normally. Further to this, I have a 37 MSS, as original as

you could possibly expect, except for the caburettor that was used as a target for a child's hammer

attack, long before I found it sitting up in a mallee pole thatched cow barn. This fact, & the wet cow pat

carpet had ensured that the bottom had almost completely rusted off the rear stand, upon which it had

stood for many a year, after the sidecar had been taken away around 1948. - & it was still standing

believe it or not, some 20 years later ! The stand was repaired, & the carb. replaced from the spares

box. This bike still has that satin chromed throttle stop clamp, & also the sudden death throttle twistgrip

set up. The point is, I was always of the view that this easy starting gadget was standard on the MSS's

of those early years ? I have to say that the hard starting thread has given me many a chuckle to start

out the New Year, especially the starting rollers ! I am left wondering how the Hell we ever started our

bikes back in the pre historic times ? One thing I do remember was that it was a point of pride that your

Velocette started while your mates were wrestling & wiggling levers on their 'Other Makes ! One clue

has to be pointed out, -- the bikes had brand new magnetos ! - everything else was new also, so my

advice is to add to what has already been said many times, - have your magneto checked out by a

RELIABLE magneto man of good repute ! As to general hard starting , - especially when hot, common

sense , - assuming that all else is in good fettle, points the finger at over generous flooding, a sure way

to upset a Velo, - especialy a MSS, or Mk. 2 KSS in my experience, -- but I still have no real idea why

some Velos at odd times, can sense a gathering crowd, & absolutely refuse to fire, but I think we would

all agree that Veloce's unique kick start gearing has something to do with it. I do know that a big bloke

with Velo starting experience can kick a reluctant Velo into life, (probably first kick), when smaller

mortals have given up, but are not prepared to swallow their Velo pride, & ask for a push, - select a low

gear, - lift the decomp. lever, & the motor will spin over, clear out the rich mixture & burst into full song

immediately ! We Velo owners are a strange breed, but we have to accept that we ride a very spirited &

proud machine. Neglect to change it's worn shoes, forget to curry comb it's fine coat, & worst of all

forget to give it a bucket of oats now & then, -- & while it will tolerate this for a while, - it will eventually

decide enough ! I really feel for these new owners who have eventually found their first Velocette, & all

the baggage that can sometimes come with it. ---- Unfortunately Velocettes are particularly prone to the

after effects of an uncaring owner.


L # 4946 I'm having difficulties with my 1969 Clubman, specifically getting the darn thing to start.

I got the bike about two years ago, my first Velocette. After I learned the standard starting routine, I

could always seem to get the bike started... one or two kicks if it was hot, or 10 or 15 kicks when cold. I

never really figured out exactly where to set the spark retard lever, relative to the conditions, just fiddled

around with it until I got the thing going. Now, I've stupidly let the bike sit for I don't know how long...

probably since last August or so. I couldn't get it started for quite a while. So, I checked the plug, and

yes a little moist, and got some carbon off with a paper towel. Put the plug back in and it started first try.

Then three days later, it was cold and rainy... then the sun came out, an it tried it again. Wouldn't start.

Thinking I knew something, I took out the plug and wiped it clean. Put it back in, still wouldn't start.

Finally gave up exhausted after an hour or so. Since then I have not been able to start it... Yesterday it

fired off for a few seconds, but I was so surprized by the noise of a running motorcycle, I couldn't keep

it going. Then it wouldn't start again after that. So, my question is sort of "what do I do?" Or rather, what

is the sequence of things I should start checking out, so that I don't go and adjust something that

doesn't need adjusting, and make matters irretrievably worse?

# 4950 Are you using the same old fuel that has been in the tank all this time? I have had problems

with fuel going "off" if left more than a week or two.Try draining and using a drop fresh fuel and at least

its reatively easy to try first!

# 4951 Sounds like a sparks problem - and since you've found cleaning the plug helps, it might be

worth fitting a new one. From there it's worth going through the HT stuff - leads and plug cap, decent

rubber boots at each end of lead. If the bike runs OK ( you should be able to get 90+ out of a clubman)

when started the timing probably isn't far out. At the worst the mag may be weak - clean / new points,

correct gap, brushes, needs new capacitor, remagnetising, rewinding in that order of difficulty. But try

the plug first - it's cheap and easy regards.

# 4953 I once had an occasion on my MAC when the pilot mixture adjusting screw spring was too

weak which allowed the screw to work out on a trip. On attempting to restart, it wouldn`t. Checked the

spark which was OK along with all the usual roadside checks like fuel at the carb, compression there

etc. Eventually thought it may be mixure and found the pilot screw well out from the 1 1/2 turn starting

point. Adjusted to 1 1/2 turns out and he presto it was a runner again. Maybe worth a check.

# 4954 Thanks for the initial help. I appreciate it. I need to take the carb off anyway, because I've

noticed that the throttle sticks when it's wide open and the spring can't move it back down. And while

I'm at it, I'll drain out the old gasoline. When I checked for spark, it didn't really look that strong to me. I

don't really know what it ought to look like though, and it was a bright day. Again, thanks for the input,

and I'll be sure and report back after I check a few things out.

# 4958 Eric, a good mag should make a spark that will jump a 1/4 inch gap when turned by hand. My

Venom can sit for months with stale gas and still fire after a few kicks. Don't blame the condenser too

quickly for poor cold starting. Make sure the plug insulator is not cracked (try a fresh one) and that the

cap is in good shape. The plug gap should be 0.018". Take the ground brush out (gently, the spring is

hair thin) and check for oil on the slip ring, that would mean a bad seal. And make sure there you've

tickled the carb until your finger is wet to the first knuckle; when my Velos are being difficult lack of

sufficient fuel has been the problem 90% of the time.

# 4960 You didn't mention using the valvelifter/decompressor lever, I found my Viper starts a lot easier

with correct use of it. Also oil could have drained down into crankcase causing excess drag when

kicking over. Try a new plug and fill with fresh fuel,good luck and let us know how you get on.

# 4965 No, I didn't mention it. I think I'm doing the right thing. During my sessions of unsuccessfully

trying to start the bike, I like to have a contest to see who gives out first, my left forefinger, or my right

leg... Anyway, I've got two shiny new B8ES plugs, and reasonable weather predicted for the weekend,

so I'll report back. Just need to pick up a little fresh gasoline and something to clean up the carb.


# 4991 I promised to report back. It lives! I did the easy thing first and put in a new spark plug.

Replaced the tired looking N3C with a new B8ES. I won't lie and say it started first kick, but it almost

did. I didn't bother cleaning out the carb or replacing the old gasoline. I'll purge that out with my fresh

tank. Thanks for the helpful suggestions everyone! On my ride, I stopped at my neighbor's place. As my

primary chain case left a few drops on his driveway, he asked me if I knew why the British were never

famous for manufacturing stereos.... because they couldn't figure out a good way to make them leak oil.

# 4993 This is no consolation to you but I am having exactly the same problems with my 56 Venom. I

guess all these years of push-button starting from German and Italian (!) bikes has just lulled me into a

false sense of security. The Venom has punctured all that.... Regards Ian PS: My earlier problem with

the "choke" was solved when on removing the Carb I realized that I was operating the choke lever in

reverse i.e. when it was closed I thought it was open, and vice versa. No wonder it was difficult to start !

L # 4985 I have just replaced my GP carb (temporarily) with an Amal Mk1 1000 series 36mm with

all settings as per factory so I can enjoy a motor that idles. My bike is an early 1968 so no coil. The

motor has recently been rebuilt and is running on BP 98 octane premium unleaded here in Australia.

The problem I'm trying to solve occurs at any speed where the throttle position is constant the motor

hunts almost like a four cyl motor on three cyls with the forth firing occasionly. However the motor feels

very comfortable under acceleration and wants to rev. There is some pinging but I can remove this by

retarding slightly so not a problem. My mechanic has suggested that its a combination of the fuel being

set for injection motors rather than carburettors and the larger inlet valve in the Thruxton head causing

the problem?? All suggestions welcome.

# 4992 Try to boost the octan by 2%. I had severe problems when the engine was hot with too low

octane. What are the settings used by You for the GP - slide, needle end jets You use ( I have a early

1968 too running on the GP).

# 4999 I can confirm that I have the correct throttle needle, needle jet and discharge nozzle for a 4

stroke as per your email. I haven't tried drilling out the air correction passage and will sit on that one for

a while, as you say there is no going back once done. I'm starting to wonder if the velocity of fuel/air in

the inlet manifold is too slow under constant throttle and if I might solve the problem by fitting a venturi

inside the manifold to speed things up. As the problem goes away under throttle.

L # 5515 anybody have any advice ? My dad’s Venom is a 1st kick starter when hot and runs

beautifully,but trying to start it from cold is a nightmare! Recently rebored,new concentric carb and coil

ignition, my brother’s Venom set the same starts readily hot and cold! We have tried flood/not

flood-choke/no choke and every available combination! It rarely fires when kicked and then will

eventually just burst into life and then start fine for rest of day.It does seem to wet plug easily and

sometimes the front of oil tank is wet with fuel,

# 5521 Don't use too heavy a grade oil and check oil not draining down into crankcase causing excess

drag when kicking.

L # 5537 Here’s one for the experts. A Venom,well set up & running well but runs out of go at 70

mph. Check all settings, all to spec but still runs out of puff at 70.Valve timing checked & found to be

ok, still 70mph.Valve timing RETARDED one tooth, we now get 70 mph & engine still pulling!I have

even seen 90! Any theories?

# 5538 Hi, Have you checked valve timing with disc? You will be aware that the sleeve on which the

cams are formed has a taper interference fit into the cam wheel. Has this assembly been dismantled at

any time and reassembled incorrectly in relation to the timing mark?

#5539 With the cam an interference fit in the wheel, it can move and retard the timing. You need to set

the cam up with a degree disc and turn the cam in the wheel till you get the cam timing corresponding

to the marks on the wheel. It’s not a bad idea to weld the cam to the cam wheel when you have dialed it


in. With the cam timing right, these motors can fly.

# 5540 Please note my original text, all settings were to spec.The only way to time valves on a Velo is

with a deg disc, you can use the old valve rocking technique, but you need the disc to check the angle.

# 5541 I once had a very reluctant Viper. I found the petrol tap filters totally clogged. Cleaned them & it


# 5542 Fuel starvation was my bet, the obvious. Do the simple things first.

# 5549 Don`t forget the breather hole in the fuel tank cap. I have seen an occasion where when the

cap was turned to fasten it something inside the cap moved, or didn`t move, and covered the breather


# 5547 Did you change the ignition timing after moving the valve timing? You may have retarded the

valve timing and advanced (?) the ignition?

L # 5636 I have a few questions for Mac owners out there but I will start with what I have got so

you have the info. 1949 Mac m17 cam set to marks and confirmed to be good ( valve timing check

done) 276 pre monoblock carb ( new ) Advance set at 4* ( fully retarded, has BTH mag with ATD)

running 91oct. new valves and guides, new cam followers, fairly fresh bore ( @1000mi ) 18T sprocket I

suspect no exhaust baffle Now on to the symptoms Started with book specs for carb ( middle groove on

needle, 130main ) and was lean at WFO and at the top of the needle range ( white B7HS plug), put

needle up one notch and now get dark plug in low to middle range, still white at middle to top, kept

going up on the main jet with the same results only to get a VERY little color at a 160 main ( color was

around the base of plug and very bottom of electrode ( cap side)), suspecting float level I went WFO

and held down the tickler and did not get any adverse effect, even seemed to go better ( maybe

because I was hauling down the road with one hand wedged between the tank and motor). This lean

condition with such a large main jet vexes me, all I can think of is float level ( float is without leaks ). I

have a float needle from what I think is a velo 276 that sets a higher float level and I have installed it,

have yet to run it though. Could it be something that simple? When I look at a parts diagram from

hitchocks I see only two float needles ( top and bottom feed ) but I know that amal made different ones

( as evidenced by me having one with a higher float level). Has me scratching my head. as an aside I

was able to reach 60mph and a pitmans book I have states that as the max speed for the Mac but with

the white plug I think I will wait until I get the bike sorted before attempting to sustain a speed over 55

for any length of time, what kind of speed are you getting out of your Mac and how did you get there?

My goal with this bike is to be able to at least cruse at 55 for the portions of highway I am forced to take

to get to the B roads that I like to ride. Seems strange that I can easily hit 65 on my mostly stock Enfield

g350 and hold that speed for quite some time before worrying about the motor and this bike seems to

hummingbird out at 60, 55 seems to be pushing it right now. Sorry about the long post but this one has

me scratching my head.

# 5637 Not sure I can answer your questions. First, can you check that the new fuel level is the same

height as the top of the mainjet? If it was originally lower then that would weaken the mixture. Too high

and the carb will flood continuously (and it'll be richer). I have a 54MAC and use an NGK B6ES plug

with no problems. These are longer reach than an HS I think. My MAC will happily sit at 60mph with

plenty of go left. It has an M17-7 cam though. I have clocked it at 82mph before. An exciting (and

worrying) speed for an old 350. Yours is probably stopping at 60mph because its not getting enough

fuel. An old chestnut but you have checked the tank cap breather, haven't you?

# 5638 Look out! Regarding the plug question, NGK plugs with an "HS" designation are 1/2" reach -

i.e. thread length. Those designated "ES" are 3/4" reach. They are NOT interchangable. 1/2" plugs are

most commonly used on iron head engines, 3/4" on alloy heads, although I must admit to not knowing

which variation should be used on a MAC, whether iron or alloy. Easy enough to tell if you've got the

head off though!


# 5641 I think it is impossible to check the fuel height in a pre monoblock carb due to the way they are

put together, I am sure that the level will go up as there is more fuel in the float chamber which would

put more fuel into the mixing chamber so maybe it will be that, I will try the new float level soon. I think

the b6 is a hotter plug so that would tend to make the plug chop even worse and I am stuck with using

the shorter plug due to clearance. Your speed sn encouraging and I think you are correct about not

getting enough fuel, I have mains for that style carb going up to 210 but as it is was I think I could keep

going up in jet size without making much difference in the top mixture, If the new float level dose not

work I think I may try stuffing a concentric carb on it just to see if that makes a difference. fuel cap

seems clear ( can blow thru the breather ). again thank you.

# 5642 you are correct about the plug reach, in an iron mac the plug would stick into the chamber far

too much and could even cause clearance problems due to the location.

#5647 The iron MAC should be good for about 75 MPH. I have a '47 MAC with a sidecar attached. it

cruises happily all day at 55, and will do 65 at a push. It is geared down 2 teeth. Early MACs had 19

teeth on engine, and 22 on gearbox sprockets. This was later changed to 22 engine, and 19 on

gearbox. This made the clutch turn faster, and therefore less likely to slip. If you have 18 gearbox, and

19 engine you are undergeared and my just be running out of revs. With 22 engine, I have found one

tooth down an advantage, as they are slightly overgeared as standard. Without taking my carb apart to

check, i think it has 180 main jet. I get around 45-50 miles per (UK) gallon. It does tend to cook plugs if

pushed hard for long periods. Unlike Venoms and Vipers, the bigger cutaway on the piston goes to the

front (exhaust valve). I would check ignition timing fully advanced, at 36 - 38 BTDC, and also check

cam timing with timing disc, as the marks can be out, if sets mixed, or the cam has turned in its

gearwheel. If it falls between 2 teeth, err on the side of the cam timing being advanced. The MOV head

is identical except that the inlet port is smaller, I think 7/8 as against 15/16 ? The MAC was set up to

run on 76 octane fuel, if you feel brave enough, shortening the barrel by 1/8" will usefully improve

compression ratio.

#5650 I am wondering if the leanness you are seeing could be due to an air leak? Take a look at the

carb mounting points, did you use some sort of sealant there? I have checked for air leaks on other

motorbikes using a spray lubricant around the carb/manifold joints with engine running. This may not be

foolproof, but if you get a change in rpm , it is an indication of leakage. I'd agree with the other good

advice to double check ignition timing especially. I've seen people chase a lot of "carb problems" that

were actually ignition related.

# 5654 My personal preference is not to use sealants on intake port joints but to ensure that the faces

are flat and clean. Use a paper gasket between the heat insulator and the head, and between the carb

and insulator unless you have a later carb fitted with an "O" ring. Consider the conversion to "O" ring on

both sides of the insulator to be a worthwhile mod if you have the facilities to do it. Leaks at these joints

will manifest themselves as fast or uneven idle. When the throttle is opened by any degree the

influence of manifold air leaks is pretty well negated, certainly at wide open there will be no effect at all

(unless the carb is literally hanging off its studs!). From what you've said about your timing being

checked at full retard I think I would go along with Bob's suggestion of checking at full advance, this

being the critical factor as far as performance is concerned.

# 5668 Timing, gearing, and float are likely culprits. Timing---Make sure to check your timing at full

advance. You can jam a small stick of wood into the advance unit to do this. Timing at fully retarded

setting is only good for idling. If the advance unit is faulty, you won't know it by checking the retarded

timing position. Next thing is, is the advance unit sticking? Maybe the timing isn't advancing with

increased rpms.... That would be very bad. Gearing---I'll suggest counting the teeth on all 4 sprockets.

If one or more of them is not the standard size, your gearing can be way off. If they are incorrect, I can

show you how to calculate your final drive ratio. It is simple math. Float---Finally, you can check the

float level, but it's not easy. Try to remove the lid of the float chamber. You can then drop a stick down

from the top edge to measure the level. Transfer that line around to the main body of the carb, and see

if it is close. Alternatively, you can drill and tap a hole in the float chamber, and add a barb fitting and


clear fuel line. Fill the float chamber, and the fuel in the tubing will raise to the float level. You can move

the tubing to be near the carb body to check the height. You can cut new slots in the float needle. I

have a carb or two that came with home made cuts, above or below the factory locations. Just use a

small file and work your way around the needle slowly. Spark Plugs---Also, you may want to try a colder

plug. NGKs can be very sensitive. For a few bucks, it's worth a try on a sparker from the next heat

range. best of luck!

# 5652 As a lark, I have cams M17/3,5,6,7,8 you could try to see if there is any difference with cam

timing. Also, perhaps your 'baffle-less' cam has in fact a baffle but blocking the exit slightly? Have you

tried your mag OFF the bike to see how it sparks at higher revs? Just casting around for all the

possibles. Your MAC should be faster.

L # 6033 I have a 1956 venom, Have fitted new inlet and exhaust valves and guides, clearance

on the guides as per the book. Compression is excellent, no ring or bore wear. The pump seems to be

scavenging OK, the right amount of oil in the crank case after a run, no wet sumping after leaving for

any period of time, the bike goes really well one of the best I have ridden. However it uses large

amounts of oil! 200 miles to approx half litre. Any ideas would be welcome. It does not appear to smoke

from the exhaust, maybe just a little on over run I put this down to clearance on the exhaust guide (

three thou).

#6035 Unless the VM is leaking a bit (!) I suggest that the bore is worn. Or, the oil control ring is either

broken (I have had this happen) or not working. Is the combustion chamber/ piston crown very oily? Is

the exhaust black? 3 thou is not a lot of wear on a guide and should not cause this problem

# 6036 If the oil return pipe from the head to the push rod tube gets a bit of sealer stuck in a banjo bolt

the head will fill up with oil and over oil the guides. I may or may not have personal experience with this

:-). You mention smoke on the over run possibly from the exhaust guide. I have wondered about this

myself but never verified. Most blame smoke on the intake guide. Does oil in fact pull through an

exhaust guide on over run and does it burn (either in the combustion chamber or in the hot exhaust

port) and show up as blue smoke?

# 6038 The smoking on the overrun is more likely to be from the inlet guide than the exhaust, it's from

oil being pulled through the guide due to the increased vacuum in the inlet port when the throttle is

closed. If oil is getting down the exhaust guide it will be mainly due to sloppy guide clearance coupled

with excessive oil level in the head (due to your blocked rocker box drain!) and poor breathing allowing

case pressure to build up and force the oil through. I can also confirm that this does not only occur on

the overrun, but under power too, and is likely to cause very heavy smoking - it really doesn't take

much oil in the exhaust to create a massive smoke screen!

# 6051 Make sure that the valve guides are tight in the head. I've had one that felt tight, but the hole in

the head was oval. When it heated up, the guide spun around in the head, and allowed oil to pour past

it. The oil is going someplace, is it leaking out? Maybe out the breather? Is the primary chaincase filled

with your missing litre of 50wt?

L # 6079 Hi Folks, A few questions from a bloke who remembers the good old 60s wanted a velo

when all he could afford then was a BSA! Just bought a 1959 Viper with a documented 30,000miles

and about 95% original. No known work on the engine. It starts ok and clears to a smoke free exhaust

in less than a minute. Oil seems to be circulting with a steady stream in the tank. It runs quite well on

the road but is perhaps a bit flat until the revs pick up. No trail of smoke. There is a rattle from the top of

the engine which might be the small end??? It's not there all the time. Any thoughts on what usually

rattles on a Viper? The thing that I am quite concerned about is that the engine oil level was low when I

first tried the bike. I filled it up to the higher level and took the bike for a 3 mile run. On stopping I notice

oil spewing out of the breather and this stopped after a couple of minutes of ticking over. I remember

Velocettes always used to have a long breather pipe and a few drips of oil would find there way to the

chain but this seems a big pool of oil. Any thoughts? I was also given with the bike a new alloy viper


arrel with liner. Is this an aftermarket bit or could you get vipers with alloy barrels? I expect I will have

to strip down the engine eventually but would like to have a few rides on the bike first. Are there any

recommendations for places to get work done like new valve seats/guides , rebushing the con rod etc

etc. All thoughts and comments gratefully received.

# 6081 You'll probably get some extra advice on the rattle, but your oil problem might be that some oil

has seeped past the non-return valve into the sump whilst the bike has been standing. When the oil

pump scavenges this oil and returns it to the tank it's added to the bit you've already topped the tank up

with and the tank is then over-full and blows out the breather. Try checking the oil level in the tank after

the pump has had a chance of clearing the cases. Some Velo's wet sump a little, some don't. If the bike

has stood a while before you fired it up this could be your problem. If wet sumping is a problem then the

ball in the non-return valve can be re-seated. The normal method would be to give the ball a slight tap

against its seat, but some prefer to machine the seat flat giving a 'knife edge' for the ball to seat

against. An alternative method, but definitley not for the forgetful is to put a quarter turn stop valve in

the oil feed line (I personally wouldn't trust myself to remember to turn it on). As you have noticed

Vipers are supposed to perform better if you keep the rev's up. This isn't from my experience, but from

other friends who own or who have previously owned them.

# 6087 Vipers had alloy barrels - with an adapter plate to the crankcase mouth- until about 1960. The

barrel is the alloy MAC one with a bigger bore. The oiling sounds like a bit of wet sumping - as the other

replies have suggested. The oil return on a VR should be in spurts; a continuous flow indicates too

much oil. I would guess that it 'spurts' when it has been running for a few minutes? The rattle could be

anything. Small or big end, bore/piston wear, wrong ignition timing.... etc. The VR is known to like

revving a bit. The top revs are 7200 and its not really a 'slogging' engine. However; my first Velo was a

VR that had the fuel tap filters clogged with gunge. When that was cleared it flew! As far as work goes it

depends on where you are (and of course what needs doing)

# 6090 Had another go on the bike and no oil pouring out of the breather at the end of the run so it

looks as if I have expelled all the surplus oil. Oil level is now just under the top mark on the oil tank

transfers. Top end rattle is still there and I think it is probably the small end as it is quite high pitched

and only there on revs just above minimum idling. Thanks for the info on the alloy barrel. My bike is a

1959 and is supposed to be original so it must have been on the change. The question will be whether

to fit the alloy barrel or rebore the existing caste iron one. I guess the change to caste iron was to even

out the temperatures around the barrel. I'll try and enjoy the bike a bit first but will definitely be stripping

the engine to have a look. I'll ask again about who to trust for things like rebore and rebushing later. But

although I'm near Reading and Henley On Thames I'd rather get the bits to the right people no matter

how far away they are.

# 6092 Another thought re the top-end rattle is wear on the rockers & their bearings in the rocker box.

The alloy barrel will give no trouble; if it's OK on bore size & not up to max. oversize it could be used. I

suggest Nick Peyton or Ralph Seymour's for bits & work - both reasonably close. Of course it may not

be too bad when you look inside.

# 6099 Check the end float on the cam shaft and idler gears. My Venom had rather excessive

clearance and was much, much quieter when this was corrected.

# 6101 Piston slap is quite common, you say it is noticeable just above tickover, this would also fit

piston slap especially on light load. .

# 6104 I think it's a bit too high pitched for piston slap and perhaps not regular enough. The only way

to find out for sure will be to strip it down. As soon as I get the manual I'll have a go at it. My curiosity

will get the better of me! The problem will be that I'll probably end up restoring everything.

# 6105 An "Old Dogs" trick is to use a screwdriver as a stethoscope. Jam the handle into your ear and

probe the running engine with the blade. You'll soon identify what area of the engine the noise is


coming from (top end, barrel, bottom end, timing chest etc.). It can be quite revealing. I wouldn't advise

getting too close to the HT lead!

L # 6179 My Venom makes an irritating intermittent squeak while riding. Of course, as these

things go, I can't reproduce it in the garage. While poking my head around while riding, I think it may be

coming from the Lucas Dynamo. Does anyone know if the bearings in the Dynamo require periodic

lubrication, some other form of attention, or is my Dynamo on the way out?

# 6186 Ah, the Intermittent Squeak! Shortly after buying my first Velo, it seemed certain that a mouse

had taken up residence in old and crumbling foam inside the seat of the Venom, as every time I took

the bike out for a ride it squealed in terror, especially when I wound on the throttle. I even went so far

as to take the cover off the pan to release the hapless vermin, but the foam had crumbled honestly

without rodent help. Anyway, after putting the bike on the stand and running her up and down the rev

range, it was clear that the squeak was coming from the cylinder head. How had the mouse survived in

there? Removing the head and annealing the copper head gasket got rid of the mouse for good.

# 6193 I'll try additional diagnostics when out on my morning ride this weekend. I know it is an engine

generated noise, as pulling in the clutch, letting revs drop to idle at speed stops the squeaking. This is

still a very new bike (612 miles from new so far), and was built quite casually it seems in 1970, so

anything is possible. By the way, how does the head gasket potentially make this noise?

# 6194 Loose head hold down nuts allows the head to lift when hot, creates leakage past head gasket

# 6195 I had a similar problem and the beauty with singles is you can give the head a little lap against

the barrel. Problem solved, tightened me nuts and me head's not loose either.

# 6188 While your noise could of course be one of any number of things, it might be worth checking for

something mysterious which gave me a bit of grief lately on my own VM .. . symptom was a weird

screechy sort of noise (almost like that sick rattle that accompanies a partial nip-up of the piston). The

cupped dust cap over the lef tside front wheel bearing is meant to be a press-fit onto the narrow

shoulder of the collar/spacer that sits on the end of the bearing spacer around the axle. In my case it

had become slightly loose (dunno how) such that it could move enough to longer be aligned axially with

the axle ~ & consequently the inner edge of the cup could pick up on the face of the ali hub underneath

it, & it would start or try to spin despite the efforts of the axles clamping effect to stop it .. . . so hence

the horrible screeching noise as it argued with the two opposing faces/forces . .. The solution was to

dismantle the assy &, after pressing the cup back onto the (far too) narrow shoulder in carefully

squared alignment, a couple of spots of TIG have hopefully secured it permanently. BTW, the collar it

sits on was extra tight on the hub/bearing spacer so I relieved that fit slightly while all was apart.

L # 6301 Has anyone any idea why an engine that has a strong tick over, accelerates well with a

good handful and has a good top speed should always cut out when the throttle is opened a fraction off

the throttle stop? The carb is on a standard setting with a good plug and ignition.

# 6303 blocked idle jet?

# 6304 Sounds a little weak - is the slide worn?

# 6307 Try raising your needle one or two notches! douglas.

# 6308 Try a bigger pilot jet. If it wont start anymore then the pilot jet is too rich, go back one size and

that is the right size. Pick up should then be clean and responsive.

# 6311 Go back and review the AMAL tuning instructions and study the pictures. Throttle openings up

to 1/8 = pilot circuit throttle 1/8 to 1/4 = cut-away 1/2 - 3/4 = needle position 3/4 to full = main. If the bike

starts fine and idles well, the problem is the transition between the pilot system and the slide cut-away.


The four metering circuits in the carb have a slight transition from one circuit to the next. I.E., the pilot

does not stop its control exactly at 1/8 throttle, it simply diminishes its effects as the cut-away begins to

take control. That being stated, you can make a small correction to the pilot mixture to help the

transition to the cut-away. Assuming an AMAL, Monobloc, Concentric, or Standard, with carb settings

including size of cut-away specified for your bike, alter the air screw 1/8 turn increments to see if the

condition can be corrected. Small patient changes are encouraged only after the bike is fully warmed.

L # 6349 I have just bought a Viper 1960 model one owner it looks as if all the right bits have

been looked after the only thing I am unsure about I get a bit of pinking under load and I am wondering

if this can be caused by the concentric. I have plenty of 376 carbs and wouldn’t mind going back to one

of those but I am unsure what to expect of the Viper it seems to want to be revved not as mellow as say

a MAC, also how can you tell a Venom top end from a Viper without stripping is it possible?

# 6352 First, make sure you are running a high enough octane rating fuel - Super Unleaded at least,

either Shell Optimax or BP Ultimate being my preferences, NOT Premium Unleaded under any

circumstances. LRP is a poor substitute and should be avoided. Have no worries about using Unleaded

in a Velo - the valve seats were almost made for it! A little bit of pinking is almost inevitable and could

be tuned out by richening up slightly in the throttle region in which it occurs, but I find usually that by

opening the throttle a little further it usually passes through the affected region. I really wouldn't worry

too much about the problem so long as it is only a bit of pinking (or audible knock, as it is commonly

known in automotive engineering parlance). Dropping a gear so the engine is revving a little harder with

less load is another way of getting past it - no engine likes being slogged in a low gear with high throttle

openings and I believe the Viper is no exception. A Venom has a 1.2" or 30mm (approximately) bore

inlet port - someone please correct me if I'm wrong, but I suspect the Viper port will be significantly

smaller, perhaps around 1" to match with a 376 carb..

#6355 I have just put a new concentric on my Viper as the old one was worn. It is a 26mm, has a 210

main jet, 25 pilot, 3 1/2 slide(although the book reckons a No.3) and the needle is in the central

position. I get no pinking at all, but admit I am running Super unleaded.

# 6358 The easiest way to spot a Viper is that the cylinder studs are fully exposed for five fins on a

Viper and only the last fine on a Venom.

# 6381 Thanks for all those kind souls who sent in their suggestions in answer to my bike's problem of

cutting out when I just opened the throttle a small amount. I tried them all, but it turned out to be broken

and perished O-rings on the throttle-stop and mixture screws, simple when you know how. The moral?

try the simple things first.


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 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 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.

L # 4989 The gear change peddle on my 1956 Venom type 12 box would not centre after every

gear selection resulting poor to no gear selection. Easing the rear cap bearing on the selector pivot

shaft (it runs across the top inside of the gearbox end cover) immediately restored free movement. I

fitted a thin fibre washer "shim" to keep the cap out the necessary amount and the box now works fine.

# 4990 During a rebuild of my Venom it was pointed out by someone wiser than me that the incorrect

shorter camshaft followers had been fitted.

L # 5144 Can anyone shed light on the problem of false neutrals, usually when going up the box.

The problem manifests as not getting the next gear, and usually staying in the presently selected gear.

The problem is cured by lightly tapping the gear lever in the opposite direction and then having another

go. All 'slap' has been taken out of the linkage and the "big bore" pipe replaced with one of smaller O.D.

(in case the pedal was bottoming out on the pipe before the next gear was selected). I have replaced

the ratcheting pawl, spring and cam plate central boss with new items; although there was no visible

difference between the new parts fitted and the parts removed.

# 5148 Sounds like your pedal is not returning fully to the centre position between gear changes. This

can be caused by a weak return spring or by something in the operating linkage being too tight. You

mention that all the slop has been taken out of the linkage, this might be your problem - you've

tightened things up just that bit too much! Otherwise, if the problem occurs only when going up through

the box it could be that the previous gear change isn't pushing the cam plate fully into gear. This could

be accounted for by insufficient clearance between pedal and exhaust at full depression (but you say

you've checked this) or by something fouling inside the box. I replaced the bent tin link inside my box

with a pair of rose joints, but these did need slight modification to ensure they didn't foul the case during

operation. Might be worth checking? If you've used rose joints you should be using the bronze bushed

type. The fibre or plastic bushed ones really aren't suitable for this application and also could be

causing your problem by having too much drag. Make sure all your joints are free and smooth running,

without any slack, for the best operation.

L # 5525 This morning I took my thruxton out for a run round, it being a nice day and an

opportunity to start running in the new Avon tyres I have fitted. All went very well until turning into the


oad where I live, I changed down into first gear and there it remains, it refuses to change up at all, I

cant even select neutral, engine running or stationary, only way I can move the bike is by pulling in the

clutch. I have tried rocking the bike backwards and forwards in gear and trying to select and upward

change of gear all to n o avail. Disconnecting the linkage I find that I can move the gearbox lever arm

backwards from the vertical but no movement forward of the vertical. It feels absolutely solid trying to

move the lever forward and I have no wish to use force or damage anything. Can any of you guys out

there help?

# 5526 Although you'll probably get better advice to follow - so hold on a bit, but if it were me I'd have

to strip the box to examine the internals - linkages, strike plates, pawls, camplate, selector forks etc.

Although you may free it off without stripping the box, there's something in there not quite right and it's

a bit of a pain if it sticks again (or worse) when you're out on a run. I know it's a real pain to have to do

this at this time of year, but It's not a bad job. The box can be stripped whilst still in the frame, it can't be

to difficult as I've managed to strip and re-build the box before now.

L # 5628 I thought that one could only get slip and drag from a lack of free play on the clutch

cable: i.e. with the operating mechanism "partially operating" the clutch (through no cable free play) and

the spring carrier wound up tighter to compensate. I however, have a clutch slipping under the modest

acceleration of a running in Thruxton and yet dragging so much that it stalls on engaging first - one has

to set off down a hill and keep moving. I have free play in the cable when measured as it exits the top

of the box. Notching up the spring pressure to cure the slipping will surely make the drag worse - even

when I take the extra cable play that will result. I am a little stumped. The bike has only done 90 miles

in this incarnation and has just come back from Goodman Engineering with "one of those new clutches

c/w 20 spring carrier". Will it improve with a bit of bedding in or am I missing something? Kind regards

in anticipation.

# 5630 Suspect you may need to adjust the clutch TO THE BOOK several time to clear this as

everything is so new.

# 5640 Did you check that the plates were not buckled? If you fitted new friction plates with insert

(rather than the bonded type) then it will tend to drag until they wear in. The slightest drag will make

first gear hard to engage, a good blip of the throttle does help by making the clutch spin and "free up" a

bit then a good press on the0 gear lever. The "slipping" clutch makes the plain plates heat up and

distort making the drag even worst so you should adjust the clutch to stop the slip. Think about bonded

plates and chainwheel with the new slotted plain plates if your problem continues, they are not too

expensive and I found themn well worth it to get a clutch that works nicely.


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

L #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



#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.

#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 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.

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, I am only

measuring 0.52v+ at the field and output terminals with the engine above tick over 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 probability: 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 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 with

respect to ground. There should be a sudden increase from near zero to 6volts or more as revs go up

to say 1500-2000. Don’t 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.

# 4834 I would suspect you have a 'dry' joint somewhere. John

L # 6325 Hello, for the last couple of weeks, my electrical circuit has been going crazy. I've

blown two rear bulbs, and a couple of fuses isolating the battery, and every time that happens the

engine labours massively: I guess either the alternator loads up the engine or the electronic ignition

(Rita-type?) system doesn't like having the battery out of the circuit. Anyway: I've gone over the whole

system and there's no shorts anywhere, so I checked the voltage, and it's reading almost 17v at high

revs. This means the regulator's failed, yes? So, expecting it does, I've been searching the interweb for

help identifying this regulator, and I've drawn a complete blank: My velo has a belt-driven alternator

(unbranded, unidentifiable), and a regulator mounted under the seat with 'repco' cast into the aluminum

casing. The contents are sunk into epoxy, on the underside and it's secured, off the rear mudguard, by

two bolts (one at either end). The casing has shallow heat fins on it. There are three spade

connections: AC, Output, and AC (that order). There are also two insulated nut and thread fittings on

the top which are continuous with the AC connections. I've seen pictures of Lucas, Podtronics, JG,

V-Reg II, and Boyer Powerbox regulators, and it aint none of them! The previous owner fitted this

system, so I don't know what it is. Ideally, I'd like to replace it, like for like, so as to spare the rear

mudguard from my drill-bit. However, I wonder if it would be acceptable to merely fit a zener diode

between the output of this device and the bike? The rectifier in this unit obviously works well enough.

Any suggestions appreciated.

# 6329 I missed the reference to the blown battery fuse. Sometimes an older battery will short out cells

from sulphide accumulation, I would still try a new one before blaming the regulator. Also some Yuasas

had a documented problem with bad internal welds, an intermittent contact could also produce current

spikes that would blow the fuse. That said, my old Ducati 350 (now there's an electrical system that

made Lucas look mil-spec) ended up with a home made rectifier - two diodes in a half wave

configuration, and a zener from a H---a 450 twin. It worked.

# 6330 I'm already on that track! I bought a new battery, but that failed totally, at speed! (with engine

braking problems thrown in, so it wasn't drivable) Just went from full charge to zero in a second: must

have been a contact breaking inside... Luckily a seven year old kid sold me a yb9 there and then. I

don't even want to know why he had one of those... this was in east london. I'll cary a large capacitor

about from now on, to get me home! Would that let you start a bike with no battery? Few swings to

charge it... So I exchanged the failed one, and the replacement is sitting in the hallway charging right

now, and will go on tomorrow evening. You reckon 17v is acceptable in the charging circuit with a fully

charged battery at high revs, then? I'm no electrical engineer, but I reckon a 20a 12v fuse can take

240w. So at 17V, this is 14A...Yes, I don't think my circuit's putting this out (ammeter goes up to about

+9 at really high revs, although I don't rev it that hard very often. I guess it's within the realms of the

possible...), although it's always a good few miles into a ride the fuse gives out (like 40-50), so it might

be a cumulative load/melt type problem. Also, I'm a little worried this might have had something to do

with the battrery failing: too high a charging voltage? I don't know. I'll put the new battery in, test the

voltages up to max revs, and if this is okay (17V?), I'll go over the harness again, trust the regulator,

and assume the blown battery fuses must be due to a short somewhere. Damned if I know where,


# 6333 I would not be happy with 17volts, 14.5-15V would be more acceptable. If you are getting up to

17volts then maybe you should look towards the Zener, if you have a high output alternator you are

normaly expected to use two Zeners in parrallel to keep the voltage to more acceptable limits. Just my


# 6389 Quite agree - 17v will boil the battery a treat - and blow your bulbs when the battery is dry. The

zener approach is terribly wasteful - even if you're using no power you're dumping 120 or 150 watts in


the zeners as heat - and using 1/4 horsepower for the privilege.

# 6390 I now have an external zener in addition to the one integrated into my regulator, and

everything's a lot happier. 15V in the charging circuit, and the zener's not too hot. Whilst some people

might tune their engines to get that extra 1/4 hp, and bolt anything on in order to get it, I'm pretty happy

with a working, reliable bike. The only bits that can't break are them wot aren't there! Besides, I can't

believe this drains more power than a V-belt, dynamo, and mechanical regulator.

L # 5025 After trying to get the band chaincase on Dad's 53 MAC to seal and painting a couple

of parts, we put everything back together, once the clutch was adjusted correctly it fired up well and

everything is working properly except the charging. The generator was not apart except the end cap

was changed for a better one. The D and F wires were hooked up in their correct positions, but there’s

no charge. Is there any way to check the voltage coming out of the generator with a multimeter? Or

does anyone have any other suggestions?

# 5027 Have you tried polarizing the dynamo? Long piece of wire. One end on the live battery terminal,

touch the other end to the dynamo body (you should see sparks). Just a quick touch. You can check

the charging by taking the D and F connections out of the end plate. Insert two wires and connect the

other ends together and attach to one side of a voltmeter. Earth the other side to the bike frame or

battery and start the bike. If you are charging you will see a voltage. An analogue voltmeter is better

than digital one for this test.

# 5036 Are you sure? ( "Have you tried polarising the dynamo? Long piece of wire. One end on the live

battery terminal, touch the other end to the dynamo body (you should see sparks). Just a quick touch.")

I agree you certainly will see sparks, you will be shorting out the battery! You would be better off

"flashing it" on the F tag, thereby energizing the field coil and restoring the residual magnetism in the



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 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


#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.

#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. Iif 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.

#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 #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 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!


#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?

#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


#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


#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 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.

#1048 Remember the MSS in question is an Iron MSS, different frame, stroke etc. all affecting the

balance factor, so 55% may be OK.

#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 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 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?


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.



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 ?


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 #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

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

38 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

bearings 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


#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?

#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

#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

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.

#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,

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 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 !

#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,

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!

#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 #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

"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

L # 6353 I am in the process of rebuilding an old MOV engine, and needed to replace the main

bearings (Both roller bearings). I removed the inner races by teasing out the rollers, lifting off the cage,

and slotting a large open ended spanner over the roller channel, placing a fulcrum in the form of a 3/8

stud under the spanner as close to the bearing as possible, and whacking the spanner. Both came

straight off a lot quicker and easier than grinding through them as the last time I did this operation. ( I


know, - this is no help with a Venom!) Then I was faced with removing the outer races, and like the

Venom, they are a bugger, as you can't get to them to encourage them on there way. I have seen

engines that have had holes drilled so a small pin punch can be employed. I put the cases on to cook

to a point where they spit back at you when you spit on them, and went for the gardening gloves to hold

the case while I whacked them on a plank of wood. A couple of hefty whacks and nothing had moved.

Thinking that they go in so easy when the case is hot and the bearing is cold, what it needs is the

bearing cooling to get it out, so I took an old face flannel, soaked it, folded and rolled it up to about the

inner diameter of the race, held the case bearing side down, and plunged the rolled flannel up into the

bearing. Both of them fell straight out much to my amazement. I guess this would also work for the

steering races, and would not need a welding set that the 'ring of weld' method needs..

# 6356 I have seen the whacking the crankcase on the piece of wood trick done before but it resulted

in breaking off a piece of the mating lip around the crankcase, so be careful.

# 6367 I've read of a similar trick in an old workbook. The book suggested heating the crankcase, then

touching the bearing race with a large piece of dry ice. As it is very very cold, it will chill the race.

# 6370 When I replaced the main bearings in the Thruxton, I made up a dolly from a large bar of

aluminum. I machined a taper, not quite the depth of the bearing, then a lip just wide enough to catch

its outer edge. I used aluminum, thinking it would be kinder where it came into contact with the bearing.

It turned out to be too kind. Being over cautious with the oxy, the cases were not quite hot enough and

a tap with the hammer was absorbed by the dolly rather than transferring it to the bearing. Next time

round, I propose to use 60mm solid steel and will make it in such a way that it can be used for removal

and insertion. If the taper is “just right” after being in the freezer all night, and the case is heated to a

more accurate temperature than blow lamp or oxy will allow (kitchen oven at say 150ºC) then as

observed, the bearing should just fall out when the cold dolly is applied to the inverted bearing. A minor

amount of machining will see the same dolly used to insert the new bearing, with both bearing cup and

dolly in the freezer overnight. With luck it should just slip in like a you know what, and be easily held

hard against the inverted hot crankcase till the bearing grabs. I had earlier replaced the steering head

bearings in the swing-arm frame with so little drama that I quite forget how it was done. There is no

internal radius in the headstock, so the new bearings go straight in. The tapered rollers were over the

counter bearings from an automotive trailer kit, cheap and easy to come by. The rigid MAC frame still

awaits conversion to tapered rollers. As Geoff has implied, this is also relatively easy and has

apparently stood the rigors of racing. However, I won’t be happy unless I see the bottom of the bearing

hard up against the headstock, and the internal radius here remains an irritant.

L # VOCNA 3 Have any of you had experience with the thicker heavier flywheels used in

Venoms from 1956 to about 1958. If so, disregarding balance factor, can you detect a difference in

engine running smoothness and throttle response compared to the later thinner and smaller O.D.

flywheels used up to end of production?

# VOCNA 4 I can tell you from experience that if you mix up earlier and later flywheels, there is a real

problem! Someone, no names please, built up the crank on my '61 Viper with thick and thin wheels on

each side, and even though the crank was set up/balanced perfectly, there was vibration above 4000

rpm which I just couldn't trace. It wasn't until the crank was out for rebalancing that John Prideaux

noticed that one was 1/8" thicker than the other. But they were the same o.d., so perhaps it was just

factory variance. I would say its difficult to detect any difference attributable to flywheel changes. The

smoothest Venom I've ever ridden was a '69 Special. Snappiness of response? Hard to compare, but

general engineering principles apply. My mk IV KTT has a few pounds taken off the flywheel, and by

comparison all early KTT's are slow to rev. Its my understanding that larger flywheels were used early

on to help with a reliable tickover and smooth low and mid-range running. Lighter flywheels were used

later when higher revs and snappy acceleration were valued over plonking, and as the Venom was

tuned further for racing.


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 Again, I have not had personal experience here, but they come

well recommended. And they have not caused their riders any Summer Ride mishaps, 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 AL-engine 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 98octane

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 MSS-piston

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

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 D-shaped

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 there a filter of any kind that can prevent the oil pump from getting 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 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



#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 ( 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

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.

L #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!

#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

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


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 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 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!

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 ie. The front. Am I



# 4829 Correct, split to the front.

L # 6041 I Have just purcased what looks to be an original, plus .020 oversized piston for my

iorn barrel 1937 MSS 500. This piston (81.5mm)from the Goodman Co. has the conventional ring set

up with two compression rings and an oil control ring on the top but also has a fourth ring near the

bottom of the skirt. The piston is very solid with no expansion slots at all. I have been told that iron

barreled MSS bikes had a lot of seizure trouble with "stock" pistons and were sometimes fitted with up

to .012 thou clearance to prevent seizing up though this seems like way too much. The book says

maximum wear on the cylinder is .008. My question is how much clearance ought I allow for when

reboring the cylinder?

# 6056 As standard the bore is 3.189" with clearances of: Top land .0178" to .0185 Top skirt .0092 to

.0105 Bottom skirt .0052 to .0065 but if you’re worried you can go up a thou or so on this without any

worry. I leave off the orphan ring on the bottom of the piston, but it's your choice.


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 demispherical

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


#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


#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!

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 ?

#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


#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 I have an engine simulation program, which I have just 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


#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.

#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


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 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.

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


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 rocker

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


#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.

#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, metalsprayed,

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 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."

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


#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 but 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 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 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


#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 (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,

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 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


#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 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 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.

#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


#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 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 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 "Tempilaq" 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. [editor’s note:]

L # 4832 I am currently looking at replacing the valves and guides in my KSS engine number

7360. It appears that there was an increased head diameter for the inlet valve after engine number KSS

8972. My existing inlet valve measures 1 1/2" across the head. Is this the early or later dia? The

exhaust is also 1 1/2" dia. Should I use valves and guides to suit the KTT, as I have been

recommended to, without valve seals? Has anyone experience here? The oil feed to the rockers is to

the later standard without the feed pipe and with the feed groves in the camshaft bushing, so some

work has been done at some time in the past. If I go to, or already have the later valve dia. what should

the carb. size be. The head now measures 1" bore. I have been advised to have the cams reprofiled to

17/8 form to gain a bit of extra power as the engine is going into a spring frame with the attendent extra


# 4930 In March 63 Veloce issued a document titled ""Engine modifications and settings for a MKII

KSS when used for racing" Essentially they recommended cr 7.8:1 for 75 Octane petrol, 9:1 for petrol

benzol valve sizes as per later KSS which are the same size as KTT For the road a K17/8 (confirmed

by Peter Miles) Inlet port 1 3/32" (as KTT) Ignition 30 degrees with contact breaker 0.015" Tappet

clearance 12 though inlet, 25 thou exhaust Hope that helps - there's some other information on piston


diameters, ring clearance that probably is of little importance for a road bike.

# 4913 I think the Big inlet was introduced in 1939 along with the suction filter crank cases , you can

tell if you have a big valve head because the inlet is visibly bigger than the exhaust ( 1.68 " vs 1.5625" (

1 9/16 " ) ) the small valve head has valves about the same size in and ex . Part number for the big inlet

valve is K2/16 and the earler valve K2/14 . exhaust valve is K2/15 Inlet and exhaust valves and guides

are available from the VOC spares Co.

L # 5397 Apparently on MACs there are two covers on the rocker box held in place with four

screws on each? A question that arose at the club tonight is what is the thread size for the screws?

# 5398 Just looked, but my MAC has only one cover held on with a lot of 2BA bolts. Have I been

short-changed? Why have I only one cover? Now I really won't sleep tonight worrying.

# 5399

# 5400 The older iron MAC cylinder head has 2 covers on a vertical joint, which clamp round the valve

spring covers. Off the top of my head, I think these are held on with 4 1/4" whitworth bolts. Later ally

MACs the cover is held down with lots of 2BA screws.

# 5402 Must be talking about the earlier iron models. My 54 swingarm MAC had a one piece rocker

box held down with 8? BA screws.

# 5405 Thanks for the notes. The MAC in question is a '46 Iron head. There were two opinions the

other night (i) the screws were 1/4" whit and the other (ii) 2BA. I will add your comments next week

when the article appears at club night.

L # 5875 As part of the cylinder head holdown stud upgrade from 5/16" to 3/8" I was given four

skinny o-rings for cylinder stud to head seal and told I should chamfer the head before installing them.

Any particular angle or depth for the chamfer? Are these seals effective? Anyone need a set of 5/16"

crankcase & cylinder head studs?

# 5878 You can use a standard 90% countersink tool,(do not use a large Drill instead) to get an even

depth I found it best buy one fitted with a handle. It is easier to use a hand held one rather than one in a

hand drill. A drill press however would also be OK as you can adjust the depth accurately. I accept

what the previous answer said but I preferred my chamfers to be a small amount bigger than the O

rings. How skinny is skinny? the O rings I use are 68 thou thick, best not to use ones much thinner.

They should also be a tight fit on the studs. Use nylock nuts as they also help to prevent oil migration

down the studs..

# 5880 Your O rings should be fine.

# 5881 The proper tool is available from Mike at Grove classics. It makes the job easy!

L # 5982 The guy who is willing to refurbish my 1936 MSS 500 head by reusing the old

valves/guides and adding a sleeve to the guides,is concerned because he says both valves ARE

magnetic. I am assuming his concern is that someone used an inferior/improper valve in the past or

perhaps fitted an intake valve in the exhaust side sometime in the past. (He does a lot of porting/head

work but I doubt if he is familiar with the old Velos...) I am only looking to keep the top of the engine

somewhat oil tight as the guides are going to leak (air/oil) in their present state. Bear in mind this is a

1936 machine that will be putting down local roads and I am not terribly concerned about a small

reduction in performance by NOT replacing valves, seats, guides, etc. So the question is it

normal for this exhaust valve to be non magnetic? And is it ok to keep using it? I always use high

quality fuel in all my old bikes.


# 5973 Originally it would have had a magnetic exhaust valve. However if you are going to the expense

of rebuilding the engine I would recommend new valves, even if it is just due to the fact that a ground

exhaust valve will sit even deeper in the no doubt pocked seat. Not such a performance issue on the

exhaust side, but certainly will be on the inlet.

# 5984 The original valve material is magnetic for both IN & EX. If you get new valves from the VOC the

EX will be higher spec than original. The material Veloce used was EN52 for both - and that is quite OK

for road use - the exhaust will suffer on unleaded fuel though but probably not enough to worry you. If

you intend to thrash it, get a better one. I would not sleeve cast iron valve guides though - get new.

Does your head man know what he's doing?

# 5930 I would be more concerned about the guy doing your head rather than the valve itself!

Providing the exhaust valve is not bi metallic, i.e. different materials for head and stem (check with a

magnet) it should be OK. It's probably 21/4N rather than Nimonic (although it could be a Venom valve

that is fitted as - while their head size is identical the length is not). Your inlet is probably EN52. If you

want to learn more visit the G & S Valves web site. Odds on your valve originated in their factory, as the

VOC, Grove, Dodkins, Uncle Tom Cobly and all source their valves from G & S. The reason for the difference between the inlet

and exhaust valve and guide is that the stem diameters differ 3/8" for the exhaust 5/16" for the inlet,

plus there's also some minor detail differences in the guides. Everyone at some time should experience

the pure pleasure of replacing valve guides in iron heads. Just a big hammer and suitable drift -

guaranteed results each time with none of the stress of: Is the head the right temperature? Will it pick

up? Have I put it in too far / not far enough? By the way if your valve seats are pocketed in an iron

head, you can replace them with inserts. While the recess has to be machined accurately, its another

big hammer and drift job. Regards Dai Hello all, I have a question about valves for my 1937 MSS 500.

The guy who is redoing the valves on my cylider head said he is concerned because the exhast valve is

non magnetic. He says both valves are the same size... I notice my parts book says the intake is a

M2/4 and Exhaust is a M2/5 also I noticed the guides both have different part numbers... If they are the

same why the different numbers?

L # 6023 Hi guys. I thought that I would send a quick note to let you know how things are

progressing on my mkI KSS. Remember, the cam and skids wore out very quickly on it's first ride. I've

borrowed and bought some spares, and loosly assembled the bits on the workbench last night. When I

placed the cambox onto the head, I realized that the inlet tappet is not centered on the inlet valve. The

tappet is only hitting it halfway. I looked closer at the valve to see if it was bent, but it seems straight. It

appears that the tappet must have been putting a sideload onto the valve. That rocker broke at the

tappet, so the stresses must have been severe. The end of the valve has mushroomed quite a bit, and

now I cannot remove the valve from the guide without cutting the valve end off. So.... I'll try to fit my

cambox onto another head if possible, to see if they cambox or head is at fault. Does anybody have

any other ideas of what could have lead to this? Maybe the valve guide is in the head crooked, and

now the valve end is too far away from the tappets?

# 6025 The early Mk1s had a camshaft that had a much larger base circle diameter than later models,

the rocker skid inserts were correspondingly shorter than later models. If the cams and skids don't

match, the rocker will strike the valve at the wrong angle, and is possibly what your problem is. I am no

expert, and cannot tell you when the change occurred, or what the skid lengths or base diameters are,

perhaps someone else out there can oblige! I ended up adding oil jets aimed at the cams to cure the

rapid wear on my KTP, the head now is no longer in danger of going rusty!

# 6027 Has the inlet valve been pocketed into the head through too much seat grinding? It’s a common

problem with old K bits. If not is the valve the right length? A miss-match of bits eg followers, rockers,

cam will give problems with contact areas and angles on the rocker movement. Have you got the skids

& tappets sorted out? I now have some to measure if required.

L # 6182 I have just bought a 1967 Venom and have taken the head off to check there was no


damage to valves as one of the tappets was tight. At first sight the valves look OK but I am wondering

whether to replace the valves anyway to use unleaded petrol. I have receipts that show new valves

were last fitted by Geoff Dodkin in 1987 but it has not done many miles since these were fitted. Is it fair

to assume that these valves would not run on unleaded? Do you have to do any other adjustments for

unleaded? I would welcome any comments and suggestions.

# 6183 I've run extended miles (100K on a commando, over 50K on a Royal Enfield, etc) and about

5000 miles on a Velo, all with standard valves with no problems or excessive wear. Don't worry, be


# 6184 No need to change anything. Just set your clearances and check every 3000 miles or so. If

they gradually close up then you are getting valve seat recession and will have to consider having the

seats replaced with a more suitable material. But in fact the original bronze seats are normally quite

suitable for running unleaded and I doubt if you will experience problems. Do use Super Unleaded

(97/98 RON) though, or the audible knock will be horrendous!


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 #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,

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 #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"


#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


#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?

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.

#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 #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 by 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 in the frozen North!

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


#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.

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?

#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)


#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


#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.

#3452 There is no doubt in my mind the VMT followers differ from each other, seen enough of them

and read the material you mentioned, but have you come across timing spec unique for VMT? If I

remember correctly the exhaust has a longer distance resulting in later events and more overlap. Could

be the end result is only a few degree and not worth publishing spec for. Be nice to know.

#3455 First off, there are the early follower configuration with the 3/8" radius to the skid (think of the

skid as the circumference of a roller that is 3/4" in diameter, but just doesn't roll), and the later

configuration used on the 1954-1971 engines ground to a 1 1/4" diameter (I think, without looking it up),

both styles using the same part number for inlet and exhaust. These should have no markings etched

on them. The later, larger radius followers (MAS 118) were designed to create more rapid valve lift in

order to increase the time that the valve is open, also unmarked. Then arrived the VMT lifters, ground

to 1 3/8" radius (again, I think that's the spec) to further increase the open time of the valve (duration)

with the center of the inlet 'roller' moved toward the pivot shaft (retarded) in the order of 5-10 degrees

(again, no one seems to know how much) and the Exhaust 'roller' moved away from the pivot shaft

(advanced) to a similar(?) measurement. These VMT followers are (should be) marked 'IN' (MAS

118/3) and 'EX' (MAS 118/2) with an etching pencil. The purpose of the changes is to increase the

open time (duration) for the valves in order to develop more performance (generally at higher engine

speed) with a given camshaft. The two different followers for VMT are designed to also increase the

'overlap' period when both valves are off of their seats. This allows a higher specific horsepower to be

developed by exhaust tuning, although within a narrower power band. The increased overlap and

duration created by the VMT followers causes the M17/8 cam to give the engine a different valve timing

spec. than is given the VM engine, but the 'Red Book' fails to address this timing spec and I've not seen

a VMT spec published anywhere else. Perhaps a VMT owner who has checked the timing of his engine

could contribute his findings to the list. Should you want to try the VMT followers, a good starting point

would be to set up the engine with MAS 118 VM followers and a degree wheel to the factory spec and

them substitute the VMT followers and recheck the valve timing. Perhaps I'll do that with an engine that

I'm now assembling and report it to the list. Bear in mind that engine performance for specific purposes

may be enhanced by using other than standard valve timing, but that's what custom cam grinds are all

about. If you're working on a street engine, mixing and matching with different cams such as M17/ 5,

M17/6, M17/7 and M17/8 and the various styles of followers could produce some interesting results, but

check carefully to prevent valve to valve or valve to piston contact when doing so.

#3456 Sorry. error in the posting above. VMT followers are: Inlet advanced and exhaust retarded from

VM, opposite from the below stated info.

#3480 If you look at the Cam file I loaded in the files section of the site you can see the implications of

using various cams and various followers:

#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 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 needed recording. Message #3503,in

conjunction with the information in message #3480 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 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* 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.

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


#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


L # 5306 Can anyone tell me how I can take the atd unit apart? It’s a lucas type and Ill like to

change the fibre gear, but I don’t understand how the weights and other revolving bits are fitted to the

central shaft.

# 5308 Get John Hales to fit a steel gear in place of the fibre gear - fit and forget! John Hales +44

(0)1509 813 507

# 5313 John Hales is your man. Excellent job, good value for the workmanship, a nice bloke to speak

to, and lighter than the original fibre - but be prepared to wait months.

# 5315 Well yes, thank you.. But I like to do me own repairs! It's a hobby after all. I did renew my velos

big-end, surely this cant be more difficult than a crankshaft overhaul?? Its only an atd unit!

# 5317 To get to the gear take a look at the back side and you will see a steel ring about 3/16" thick.

This is a press fit on the center shaft and holds the whole thing together. Press it off carefully and you

will be able to get to the gear. Then it is just a matter of removing the four rivets going through the gear.

# 5319 I'd still recommend you get hold of one of John Hales' gears, even if you're going to fit it

yourself. They really are nicely made and as someone else pointed out, lighter than the fibre one as

well as being a damn sight more robust.


# 5321 Actually I have got a steel gear from Grove Classics. I thought Ill give that a try. The fibre gear

has lost 4 teeth.

# 5324 I don't believe the Grove gear is the correct one - I went down that route before I got JH to do

mine. John's gear is a beautifully made really well lightened piece of work. As I remember, Mike

Fotherby's one is actually either a plain steel gear or a manual ignition one, definitely not a replacement

for the fibre gear. As it happens my engine is dismantled at the moment. I'll take a couple of pics and

post them on the site for all to see. I'm sure the difference will be immediately apparent.

L # 6216 Has anyone on this list experience the failure of a cam spindle in a VM or VMT. If so,

were you able to determine the failure mechanism, what went wrong?

# 6229 I had a problem 2 years ago with a MAC when I was doing my runs out to all the VOC centres

in UK. ( Cam spindle setup is the same) Presumably I had failed to properly tighten the nut on the end

of the spindle on the outrigger plate. By the time I reached Scotland, there was a lot of valve gear

clatter, and on checking, found that this nut had come loose. the now unsupported spindle had worked

loose in the crankcase and had migrated inwards, allowing the nut to drop into the timing chest to play

with the cogs where 2 adjacent teeth on the camshaft were knocked off. The timing was still OK, as the

angled teeth had not come away from mesh before the tooth after the gap came into mesh. The now

wobbly fit spindle was pulled back through the outrigger plate with long pointy pliers, and the nut

locktighted on. The bike ran fine on the trip to see the some racing at East Fortune, and the run home.

Once home, I locktighted the spindle into the crankcase as well, replaced the cam, and have had no

further trouble (touch wood). Use 'em and abuse 'em !!

L # 6337 I am putting the cylinder head back onto my 1967 Venom (engine no 6420). It has the

one piece push rod cover tube ie no gland nut in the middle). My manuals and spare parts lists only

show the type with the gland so I need some help please! When I dismantled the head, there we no

gaskets fitted on either the top or bottom of the push rod tubes- only the two O rings. Is this correct?

Does the seal just rely on the O rings? If it does, do you assemble the o rings with oil/ grease or does it

need any gasket cement?

# 6346 No gaskets required, the O-rings will do the job of sealing the joints on their own far better than

the gaskets ever did! A little smear of grease to aid assembly is all that's needed, no gasket cement

required, although you could use a very thin smear of silicon sealant in place of the grease for a belt

and braces approach but this will mean a bit more difficulty when it comes to dismantling things again

in the future..

# 6359 My venom has a shim over the O-ring before putting on the rocker box or the lower plate cover

on. I believe this was how Veloce assembled them.

# 6366 The spares list makes no mention of any shims, could it be possible this was an early version

of the one piece pushrod conversion, or something someone has added in order to utilise an undersize

O-ring? I cannot see any necessity for any shim in this position, if the recess is machined to the correct

depth the ring should seal without any additional help.

# 6371 Yes could be someone has changed it, my Venom is a 1970, one of the last made (in the last

batch of 20). In theory it should be better without the shims but I use them because they were there and

I don't suffer leaks.

L # VOCNA 163 I have found a source for new and rebuilt Velocette camshafts. Gary Robinson,

on the Isle of Wight, can supply these parts. He has been rebuilding Vincent and Velo cams for 30-40

years. He can build new cams from scratch, using EN19 steel, or build up the lobes on a worn cam with

stellite and then grind it to the correct profile. He can supply cams with the following part numbers: K17

K17/2 K17/5 K17/8 K17/10 K17/11 M17/3 M17/7 M17/8 Here is his contact information: Gary Robinson

(calling from USA): 01144 1983 760 765 Cranmoore Ave Cranmoore Isle of Wight UK PO41OXS .


Paul Zell recommended Gary Robinson to me, as did Ivan Rhodes. cheers pete

# VOCNA 165 Does anyone out there have any experience with the built up lobes? Particularly those

built up with stellite? Any chipping or cracking?

# VOCNA 168 My racer had a stellite built up core with a polydyne grind and wore extremely well

even with the elevated revs of 7500 to 8000 I was running at. I detected no visible wear after 5 years of

racing. I have worked with satellite in years past and the key is not to overbuild. The layer thickness is

somewhat dependant on the grade of satellite but a general rule of thumb is not to exceed a .020 -

.030 build up. Too bad he doesn’t list a polydyne grind for a Velo as I am interested in getting a couple


# VOCNA 176 I'm delighted to learn that stellite faced cams may be available. I have had a scuffing

problem with the piston skirts and cam lobes in my race and customer high performance engines. The

skirt problem was resolved with liberal assembly oil and 50 weight high contact pressure oil. The cams,

though improved, still have a problem. Stellite cams may be the answer. Thank you for your insights

from you experience. Years ago in my tool room engineering days we used stellite in forming dies in

high wear areas. In those cases the thicker the stellite the better to resist cracking and chipping. Of

course we used inserts as compared to a welded on surface. Apparently the coated cam lobe is rigid

enough to prevent cracking. The question of the polydyne cam came up several months back. I tried to

research it with varying degrees of success. The best answer I got was from Dave Holder, the receiver

of Velocette when they folded. He said that the Thruxton cam followers with the M17/8 cam gave the

equivalent valve events. This was accomplished by changing the cam follower pad radius and its center

distance from the pivot. He gave me the dimensions and I can forward them to you if you like.

# VOCNA 178 Gary does custom cam profiles too. He may also have other Velo profiles listed other

than those that I quickly wrote down during our phone conversation. Call him and ask, he may have a

polydyne master profile. If not, you could loan him one of yours to make a new master from.... He told

me how he has done all the cams for the "Hogslayer" Vincent 500 sprinter (drag racer). He would

modify an old cam profile with grinding, then build it up with fiberglass. Then put it into the motor to

check the timing specs. If it seemed good, he would use that master to grind a new cam profile. Test it

at the track, then modify it again. He did this over and over for years, the bike now runs very fast, I think

he said an 11 second quarter mile. Pretty damn quick for a 500cc motor!

# VOCNA 166 Any estimate on costs?

# VOCNA 179 My rebuilt k17/5 cam cost 70 pounds, plus I'm sending him the k17/2 worn out lobes to

use for a future customer.... It sounds like a bargain to me. Megacycle said to call them back in a month

or two. They were too busy to take on any work, it was tough to get them to stay on the phone long

enough to talk about the cam. Their cost was about $250, plus $500 to make a new master.

# VOCNA 181 I contacted my friend John Watson in England who prepares Velos for short track and

MGP racing. He is well acquainted with Gary and says he does a fine job. Only problem is Gary is very

busy and we should plan on at least a 6 month wait. It appears Gary is a good source. I want to get a

couple special cams made more lift. I tried Megacycle last year and they too costly, too long of delivery,

and not really interested. Gary may be able to provide just what I need at a reasonable price. Mirek,

can you wait 6 months?

# VOCNA 167 Got Robinson cams and followers in my KTT and Egli Vincent. Both stellited cores and

all doing well. Gary has a superb reputation in the Vincent world for hard wearing cams and followers.

Prices are cheaper than you will find anywhere else.

# VOCNA 170 I have many original KTT cams from mk1 - 8, and none are stellited. Repro cams seem

to be. The used stellited cams in general are in much better shape than the used originals.


# VOCNA 171 Yes they are. Stellite #1 (the hardest available) built up, no brazed on pads. He

switched (when I don't know) from softer and different grades for cam and followers to straight #1 on

both by recommendation from Stellite corp. He has done Vincent cams/followers for years. Vincents

are notoriously hard on them, poor oiling, small base circle, etc.. I've never heard anything bad from

the Vincent guys (also notoriously hard), only good. Gary talks quite candidly and mentioned the

failures he has seen have attributable to some peculiarity or problem with the specific engine. My Egli is

new so I'll be keeping an eye on them but can't comment personally. My original KTT cam went flat

toute suite after I got it. Rob Drury recommended Gary as he had done some KTT cams for him with

no trouble and already knowing his rep I went for it. I checked mine religiously after every ride for

about six good rides and they looked just perfect every time. BTW I have not had any trouble with

stock M series Velo cams or followers, they seem to last very well. All that oil flying around the timing

chest must be good for something!

# VOCNA 172 A comment on the m-cams. I had mine go flat by virtue of neglecting to measure the

distance of the protruding valve guide from the head, as you know there is no shoulder, thus the cam

was trying to push the guide into the head with the spring collar of course this constitutes operator error

and has nothing what ever to do with hard face quality but I thought a reminder of stem hieght might be

an apropriate note

# VOCNA 175 Good point! I rebuild 6 to 8 cylinder heads a year and it is not un common to find the

guides have moved into the head in the direction of the valve head. But, one head had the exhaust

guide moving in the direction of the spring retainer. Why? Go figure! Anyway as you say good idea to

check the valve guide height.

L # VOCNA 267 Why on earth would one trade a fiber gear mag drive for an alloy item anyway?

What's wrong with steel? I know its heavier, but I have a heavily drilled item on my clubman which can't

be much more than the alloy. I was under the impression that it was a Good Thing not to lighten the

timing gears too much, as their mass dampened some of the shock from the power pulses.

# VOCNA 262 Aluminum alloy gears should be ok, if they are sized for the job, and made from a good

alloy. Berg sells thousands of part numbers, from 2024 aluminum with T4 heat treatment. If you want

damping, cast iron is a good material. But gears made from cast iron ~may~ shed teeth easily. Same

for gears made of plastics or composite materials. I don't know if Veloce sized the gears properly for

materials other than steel, and for the loads from various cam proiles and strong magnets in the

magnetos. Paul, you may find that reducing the mass of the timing gears is much the same as reducing

the mass of the crank, or the rockers, pushrods etc. Reducing mass of any of these will allow the

engine to rev easier. The reciprocating parts (rockers, tappets, etc) give you the best performance

results, as they changing direction, and thus acceleration, very often. Of course, these parts are under

high stress too, due to these accelerations, so we must be careful. I would think that changing the

weight of the timing gears would affect the balance factor of the engine, just as changing the weight of

the flywheels does. (to a smaller degree though, with their light mass compared to the flywheels). Me?

I'll stick with a steel magneto gear, undrilled

# VOCNA 264 I've never bothered reducing the mass of the timing gears. First of all they are only

spinning at half crank speed. Their weight and diameter in comparison to the flywheels is small and

they are round and symmetrical so should not have an effect on balance. They don't have any real

influence on valve springs like the reciprocating mass. I know some guys do it for every last potential

gain, more power to 'em. I only bought the alloy gears because at the time (5 years ago) I was told that

was all that was available for fiber gear replacement. There are definitely steel replacements out there.

Don't know what it takes to drive a mag power wise. Wouldn't the magnetic field be something like

valve springs, whereby they take power to open but add power on closing? Or perhaps the spark

reduces the magnetic influence.

# VOCNA 266 I don't know either, but as a magneto is a generator, converting mechanical power to

electrical power at something rather less than 100% efficiency, the power transmitted through the drive


gear must be more than the wattage produced - a few thousand volts times a few milliamps! I think it

will absorb rather less power than a regular dynamo producing the same wattage, and considerably

less than a dynamo or alternator powering daytime lights. The two main causes of premature fibre gear

failure are 1. slack in the magneto bearings and 2. the fact the the same teeth gets the load

on every revolution, both from the magnetic flux, and from the operation of the contact breaker. Both

these causes are preventable by diligent maintenance: 1. by reshiming the bearings as necessary and

2. by periodically repositioning the atd on the magneto spindle. OK, we know neither task is easy. In

fact it's rather less trouble to wait till it fails and replace the whole thing. But if that routine is followed

one will get trouble free service for tens of thousands of miles.

# VOCNA 308 Other then striping the teeth off caused by loads in excess of the shear strength of the

material the gear tooth is made of there are generally just two types of gear tooth failure. One is when

the load, or torque, on the gear is uniform and not high enough to shear the teeth off but the contact

pressure on the tooth surface exceeds the fatigue strength of the material. In this case "spalling" occurs

caused by sub-surface fatigue of the tooth resulting in small chunks of metal coming off the surface.

(This is very common with Velocette transmission gears.) Eventually the tooth surface erodes to the

point not enough thickness remains to take the load and the tooth sheers off. The other is when cyclic

overloads, or hammering, occur that are large enough to bend the tooth. Depending on the amount of

overload the tooth bends back and forth 100s or 1,000s or 1,000,000s of times until the tooth fatigues

at it's root, or base, and breaks off. Spalling can occur in cyclic load failures too. However, the failed

tooth of a cyclic load failure is usually near full thickness where as the uniform load failure tooth is

usually eroded thinner. When we think of vibration in or Velos we usually think only of reciprocating

balance factor. However, there is another vibration caused by the power pulses of the engine called

"torsional vibration". Simply put torsional vibration is caused by the flywheel speeding up every time the

engine fires and then slows down until the next fire when it speeds up again, all in the same direction of

rotation. All piston engine exhibit torsional vibration. The more pistons the smoother, or more constant

the velocity of the flywheel rotation. Single cylinder engines are the worst. This is one of the reasons

why our Velos have round flywheels in addition reciprocating balance correction and cushion drives on

the crank shaft. For four stroke engine the torsional "impulse" occurs in the second order, or every

other revolution. At 4,000 rpm the flywheels accelerate and decelerate 2,000 times a minute. In

automotive work an un-flywheeled V-8 engine crank shaft commonly instantaneously accelerates 6 to 8

degrees ahead of it's continuos rpm at each cylinder firing then slows back to it's continuos rpm before

the next firing. I have no idea how many degrees the crank shaft accelerates in our velos. But, given

the large bore, high compression, and low mass of the flywheels I'm sure it is a lot. Where is all this

breeze going? Here goes: Our engines exhibit torsional vibration, the gears have mass, and the device

on the end of the gear train has mass and in some cases a load or resistance to turning. Since all the

gears in the timing chest are positively locked to the crank shaft by their teeth they are accelerated and

decelerated at the same rate as the crankshaft torsion vibration. Since the gears have mass and

maybe a rotating weight at the end of the gear train the load on the gear teeth is a function of the mass

times acceleration. In rotating machinery kinetic theory the toque to accelerate, or decelerate, a

flywheel possessing polar moment of inertia approaches infinity as the time for velocity change

approaches zero. So the gear teeth can "feel" high cyclic loads due to engine torsional vibration simply

because of their own mass, weight, even though there is a low load at the end of the gear train. In the

case of our aluminum gear a way to tell if tooth fatigue occurred is the look at the broken surface of the

tooth under a magnifying glass. If the failed surface looks grainy or crystalline it is likely a fatigue failure

from tooth bending has occurred. Never use aluminum or fiber gears in a motorcycle!


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 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 #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 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.

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 They deliver

free for orders over £30 in UK mainland. or you could try Silkolene who also do a straight 40 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 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 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 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

#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



#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.

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.

#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.

#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.

#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


#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!

#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


#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 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.

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 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 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 !

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.

L #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:


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 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 (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.

#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 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 ball 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 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


#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


#4299 Always bolt the two halves of the crank case together and heat as a unit. To prevent differential


#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 - 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.

L # 5014 I hope someone can help me with a problem with the oil pump housing on my late model

iron head MSS. The bike came to me in large lumps and very oily. On cleaning up and closer

inspection a number of problems have become apparent the fist of which is the oil pump housing.

Someone has been ham fisted and damaged (and I think also cracked) the oil pump housing on the

timing side crankcase and I need to find an engineer who can repair this for me.Anyone got any

suggestions of a competent person in the UK?

# 5015 This sounds like the sort of problem which can only be solved by replacement of the cases.

You can be sure that if the oil pump housing is cracked it will need to be welded, which will involve

notching out the crack, thorough cleaning and very careful welding to make sure of proper penetration.

There WILL be distortion and a certain amount of porosity no matter how well the job is done, and the

pump bore will have to be machined out which will result in an oversize bore, requiring an oversize

pump to be sourced. All with no guarantee of success I fear.

# 5017 As luck would have it I do have an over size pump marked OS .4 So maybe I have a chance.

Know any one who could do the machining? I know an ace welder to do that side of it.

# 5016 Nick Payton, the Velo Guru in South London, can remachine and sleeve the timing side

crankcase. Let me know if you need his phone number/address. He has just done it for my Thruxton.

# 5018 Well, I would agree that if anyone can do it, Nick Payton can - 0208 540 2118 will find him.

# 5019 I agree as well. Nick did this excellent job on my Venom some years ago. This is now one of

the driest area of the engine : ) But the case was not cracked, only scored.

L # 5343 Does anyone know what oil filter is used on the club conversion, I can't believe it is not

used on other applications. It would be helpful so as not to have to rely on them being in stock when


# 5344 I believe it to have been fitted to a Duccati if this is any help.


# 5449 I finally managed to get into the garage and have a look at the spare cartridge I bought when I

did the oil filter conversion . Unfortunately there are no makers marks on the cartridge of any kind (

dimensions 1 5/8 dia x2 5/8 long across the plastic end caps with a 7/8 hole . ) Single layer paper

element construction on punched stainless steel mesh support . Construction looks very simple and

straight forward . Somewhere in the recesses of my mind I seem to think I once read in Fishtail that

Citroen did a cartridge the same size.

L # 5775 When I disassembled my broken KSS (worn cam/skids) I saw that the lower end of the

oil drain from the cambox, into the crankcase, was broken. The soldered joint had failed, either during

my 100 mile ride, or previously. How much trouble could this have caused? There was plenty of oil in

the tank... That oil line should allow the cambox oil to drain, a broken line couldn't drain too fast, could

it? The cambox should still be filled with oil up to the height of the camshaft ball bearing? --for iron KSS

engines-- Jeff Clew's book "KSS" recommends joining the cam box drain oil lines, the front two.

Eliminating the feed to the engine shock absorber, and instead feeding that oil into the crankcase. This

is claimed to help stop oil leaks. But I do not see how that can be true. Any ideas? Ivan Rhode's book

suggests taking the feed to the shock absorber and feeding it instead to the exhaust valve guide... But

then we must oil the shock absorber with an oil can from time to time. I'm inclined to leave the oil lines

as Velocette built them. Does anybody have other suggestions?

# 5776 Pete, The broken oil drain could not have affected the cam box & rockers. The joining of the

two pipes and connection to the flap valve helps to drain the cam box and prevent (some of) the oil

leaks. The copper pipe should be hard soldered (silver solder) into the copper union, not soft solder. If

you are using castor oil in the engine without a chaincase, there is no need to worry where the oil goes.

However, R with a chaincase means you should drain the cambox into the crankcase; veg. oil on a

clutch is a real pain!

L # 5919 Hi Group I have just acquired a 1935 GTP in reasonable condition but it requires the

oiling pump arrangement set up from scratch. Any advise on how to do this please. Also the gear lever

does not return to centre between changes. Before I go ripping the box apart any thing else to look for?

# 5922 When adjusting the oil supply do it gradually and put some miles on the bike before making the

next adjustment as it gives time to burn off the effects of over oiling in the silencers. Otherwise you may

end up thinking that you need to reduce the oil supply even more and end up starving the engine of oil.

PS good luck with the Miller dynamo and coil ignition!

L # 5985 I am attempting to sleeve the oil pump housing on a '66 Venom. Can any one tell me

what the correct interference fit is between the oil pump and the crankcase?

# 5988 Have just measured a crankcase bore at 1.687" dia. and an oil pump at 1.689" dia. They have

not been together before but soon will be. This 0.002" interference is in line with a maximum BS 'keying

fit' for this size (A 1954 standard gives Hole +0 to +1.4 thou and Shaft -0.4 to +0.6 thou.). Should think

that an interference of between 0.001" and 0.002" would be satisfactory but this is not from direct

experience of this particular issue. Other group members will have specific experience and will surely

point out if this is not right.

# 5990 I have not done this myself but would agree that 2thou should be about right in theory. One

thing I would be concerned about is what do you intend to sleeve it with? If you fit a steel sleeve I feel

you should consider sleeving the pump rather than the crankcase. If you don’t you may find it difficult to

get the expansion you need when warming the cases to fit the pump. You may well need to bore the

cases first of course if they are damaged. Maybe someone else will be able to add their first hand

experience to this thread.

# 5989 Richard My recent practical experience suggest that you are spot on with your advice. Last

year, Norm Trigg and I measured a range of Velo cases and pumps in our possession and concluded

that there was a tolerance on sizing as summarized below by Norm. " I have measured 20 pumps and


the bores in 20 crankcases. Measuring the bores is not easy. On some old engines the bores are

tapered a bit (I guess due to being pushed in and out) and even on new cases the bores are not

perfectly round ( I guess due to the uneven thickness of material around the bore). So I took the

maximum in each case. I found the following: Average diameter of bore in new cases 1.686" (maximum

variation + and -.0005"). Average diameter of the later pumps with the larger feed gears 1.689"

(maximum variation + and -.005") Therefore interference is .003". Average diameter of early pumps

with the smaller feed gears 1.688" (maximum variation + and -.0005" having excluded one pump at

1.686"). Interference of these pumps in new cases would be .002". However things become interesting

when we look at the measurements for used crankcases. The average diameter of bores in used MSS

cases was 1.688" (variation was +and -.002") So late pumps could have an interference ranging from

.003" to a clearance of .001" and early pumps would range from an interference .002" to a clearance of

.002" The average diameter of bores in used MAC cases was also 1.688"(variation was +.002", -.0025",

excluding one case at 1.6892"). So some late pumps would have an interference of .0035" while others

would be loose by .001" , early pumps would be .0025 interference and .002"clearance. It appears that

over the years the bores will be enlarged or scored and I have pump bodies that have been copper

coated or chrome plated to increase their diameter to try and overcome the problem." Back to my own

experience, I chose a pump with a 0.0015" interference fit to replace a damaged one in my MAC racer,

and fitted it with engine in situ after about 10 minutes gentle heating. A few weeks later I had to refit a

pump in another case on the bench (a much better way to do it compared to in situ) which was 0.0035"

interference fit and that was a real challenge, requiring several rounds of cooling the pump and heating

the cases to get it in. Therefore from our experience we'd conclude that 0.0015" to 0.002" interference

fit is the best practical target for Velo oil pumps.

L # 6185 I am just stripping down an iron head mac engine for spares and have noticed an oil

feed from the base of the rocker box oil feed pipe to behind the barrel where it is screwed in to the

crankcase never seen one like this, just curious to know its purpose. should anyone be remotely

interested I can send a photo thanks.

# 6254 It was introduced in 1938 to reduce piston slap only to be deleted late in the 40's. It doesn't

appear make any difference either way if you have it or don't.

# 6255 Do you have any documentation on the subject? Vincents squirt oil to the back (thrust) side of

the piston as did some Manx and some other Velos (iron MSS for one) do it via internal passages. I

have added it to a couple alloy Velo engines in the hopes of increasing lubrication and cooling the

piston, not for piston slap. Hard to deduce any benefit. Outdated, perhaps questionable. Many Vincent

owners plug off the cylinder feed with no problems.

# 6263 It was common in the early days to fit the front cylinder of V twin engines with an oil line. The

rear cylinder was sprayed with oil as the big end swung around through the oil in the bottom of the

sump. But the front pot always went dry. I've seen the oil lines on several different engines, at the rear

of the front cylinder.

# 6272 Information is limited, but what there originates from Bob Burgess and can be found in "Always

in the Picture" (pg79) and the Pearson Velocette book (pg17). The engine numbers of the start of the

modifications can be found in some versions of the spare parts list, and modification ceased sometime

in 1951.

# 6273 Just to add to the subject my 39 and 48 ironhead MSS engines has these also.

# 6264 As far as years they used it ( Velocette) my Iron head MAC has one and it is a 49, maybe it

went out in the 50's.

L # 6190 The problem is that my friend has almost stripped the thread on the banjo joint on the

oil pump return. At present we have managed to bolt up very gently with the ally washers and note that

the recommended torque is only 10lbsft which seems low. I presume there is very little pressure on this


joint. He is still rebuilding the gearbox so we have not yet recommissioned the engine and oiling

system. If we have to repair the joint is there any recommended way to do this. Is the thread 3/8ths

BSCycle i.e. 26tpi ? He has obtained a 7/16ths Banjo Bolt but of course this would need a larger banjo,

are these available or would he have to make one or mod the existing unit?

# 6197 Helicoil the damaged thread, but carefully! The thread is 1/8" BSP. Helicoil kits or the cheaper

but equally as good Recoil kits are available from such suppliers as - just make

sure that you use an insert that is not so long that it obscures the oil passage, and all swarf and the

tang off the insert is cleaned out before running the banjo bolt into the hole.

L # 6228 I have a friend who runs his BSA A10 on Valvolene 5-50W fully synthetic oil. Having

read articles on the superior protection of fully synthetic oils and of course witnessing it in modern cars

which travel round the clock without major wear to their engines on extended oil change intervals often

of 12 to 15000 miles, I'm keen to introduce it to my Venom. Can there be any reason that such a

viscosity of fully sythetic oil could not be used? The Velo oil pump is well designed and pumps copious

quantities, the major bearings are all roller and the amount of oil that appears to circulate around all the

other components provides high levels of saturation. There is a very interesting article in under the tech section entitled "The oil truth" that gives a very strong argument for

using synthetic oil that's worth reading. My own car, a Mondeo, runs on 5-30W semi synthetic with

12,500 miles oil change intervals. Whilst in Canada last year I hired a Ford Taunus (very like a

European Mondeo) and noted on the engine filler cap that the recommended oil was 0-30W ! Are we

missing out on this new technology by sticking to the oils specified when our bikes were sold 40 to 70

years ago. Surely Velocette, along with all other makers, specified the best oils available at the time,

but I cannot believe they are the best anymore.

# 6230 I am no Tribologist but all mentioned have plain bearings with the loads fairly evenly spread.

Roller and Ball bearings have Line or Point contact and therefore more extreme pressures. This can

break through the oil film on the modern oils. The older “straight” oils do not suffer from this affect. We

use a SAE 50 in the Venom and we have the extra effect of the sidecar.

# 6231 It may be sheer coincidence, but at the beginning of last years Summer Rally, I changed my

VMT to synthetic 20-50w oil. After 1k miles, the big end went in a big way; the rollers look as though

mice have been at them. And I was actually riding at a pretty sedate pace, for me, over those miles.

BUT, I know several other VOCNA members who swear by their synthetic, so what's a fellow to think?

# 6232 Paul, As I understand it, air cooled engines should use straight grade oil - not multigrade.

Going to synthetic oil doesn't really help as it's still too thin! I found problems with Castrol multi grade

oils many years ago and changing to straight 40 or 50 solved it.

# 6234 I use "Morrisons Best" 20W50 multigrade oil at £4 or £5 per gallon in my MAC with no

problems. I do change the oil every 1000 miles though.

# 6237 I understand that it is o.k. to use these modern oils i.e. full/semi synthetic/ multigrades etc. with

their detergents or whatever if your engine is clean inside, so if you've recently done a rebuild and use

these oils straightaway you're o.k. but if your engine has only had the old straight 40/50 etc. engine oil

in it is most likely coated with "gunge" the modern oils will shift thus causing damage when pumped

around the system.

# 6242 Tom and others If interested in Penrite's take on oil issues then follow this link.

6ae425e Bulletin V3 deals with castor oil versus modern oils in old engines while Bulletin V6 talks

about the pros and cons of using full synthetic oils in old engines. Bottom line is Penrite would

recommend a high quality mineral oil rather than synthetic in old engines. There's even a very short

bulletin on Harley transmissions.


# 6249 There was an interesting article some years back in Fishtail, where an owner replicated the M

series oil system (MAC/MOV). He used 20W at room temperature oil to replicate 40 W at operating

temperature. At 1080 pump RPM, which represents some 6000 RPM the delivery was 1.07 pints per

minute at 18 psi. Using paraffin at the same engine speed to replicate low viscosity the delivery was 1.0

pints per minute at zero psi. The Velo oil delivery system needs to be looked at as a system, in which

oil is an integral component of the system. Each "jet" in the system must have been carefully calibrated

based on a specific oil viscosity. Stick with it (as pointed out in an earlier post) how many of us are

going to ride enough miles, fast enough to wear out an engine! The VOC sell magnetic drain plugs that

I have used in all my bikes in both the oil tank and sump for a number of years. The sump picks up

more detritus than the oil tank. Most of which appears to be fine cast iron with a few silvery bits.

# 6293 Thanks for all your comments and feedback guys, but I'm none the wiser as comments have

ranged from encouraging to dire warnings. But hey- that's what chat rooms are about ! I was puzzled,

about the comment on a thin viscosity oil breaking down due to point loadings within roller bearings

whilst 50 weight oil was able to withstand these loadings. Doesn't a modern vehicle running 5W/30W

synthetic oil with overhead camshaft have higher point loadings between the camshaft and the

buckets/followers/valve stems and operates at far higher revolutions than the big caged roller bearings

of a slow reving old Velo ? I was not able to follow the logic from a contributor about the comparison

test done on an oil pump operating with 20 weight oil and then paraffin. I don't know the viscosity of

paraffin but I do know that it pours like water and that the 5W/30W synthetic oil used in my car for the

last 70,000 miles is thin when cold, but it certainly does not pour anything like water, or paraffin - not

very scientific I know, but you get my drift. The contributor who ran his big end within 1,000 miles of

switching to synthetic worried me. Can I ask what was the state of the main bearings and camshaft and

followers upon strip down ? and was the engine well worn already or were major components still within

normal wear tolerances prior to the big end failure ? I feel there must be someone out there in this

world wide Velo Web who can give a definitive answer to this oily question.

# 6294 Responding to the query; after the 'thousand mile synthetic oil big-end test', the mains and

cams/followers were fine. Just the big end rollers were damaged, although with all that steel running

around the oilways I imagine some other wear was accomplished, and I replaced the lot with parts

which looked better. Mind you, the 'rapid' wear after changing to synthetic may have been coincidence,

as in the course of the 15 years since the big end was last replaced, about 40k miles had gone under

its wheels. Plus, there was a stretch of a few years where it seemed important to duplicate the

Velocette 24-hour record whenever possible, albeit for shorter periods. In that regard, the bike and its

owner have held up remarkably well.

L # 6243 After looking at the sorry filtration system I have on my 1937 Velo MSS, I have decided

to place a very thin and very strong magnet on the bottom outside of my oil tank. The magnets I have

are from computer hard drives. My reasoning is the metal debris will collect on the inside of the tank

near the magnet area and prior to changing oil, one can remove the magnet and let the shavings (few I

hope) mix with the dirty escaping hot oil.

# 6244 Sounds like a good idear, but would not the tank and particles become magnetized and tend to

"stick" inside the tank? How about fixing a magnet to a probe mounted on the tank filler cap where it

can be remove to wipe off the debris?

# 6246 I use 3/16 diameter high strength magnets from Radio Shack in the brass drain plugs for oil

tank and sump. Just drill a hole in the plug and press them in. Always some swarf on removal.

L # VOCNA 205 I am getting near the point where I will have to check/set up the oil pressure in

the KSS. I know this is done through the access on the top bevel drive cover, which is tapped 1/8"

BSP. I understand the oil pressure should be 8-10 psi. To do that anywhere near accurately the oil

pressure gauge should be scaled around 1-30 psi. Most car pressure gauges are 0-80 or 0-100 psi,

and are not accurate enough to measure 8-10 psi. So any suggestions? Where do I find an oil


pressure gauge that reads in 1 lb increments to 20 or 30 psi? I have some extra bolts threaded 1/8"

BSP, so I should be able to make up an adaptor ok.

# VOCNA 206 I have a fuel pressure gauge on mine (a cool old Moon Equip. one), 0-15 lb. seems to

work fine.

# VOCNA 207 I wonder what the application is (was) with a 0-15 scale, I doubt it is an automotive

gauge. That is the sort of thing I am looking for, but I googled Moon Equip. and the only have 0-80 and

0-100 gauges now and there is nothing on eBay.

# VOCNA 208 Back in the good ole days, when cars had carburetors and you could tell what was

what once you opened the hood, 6-8 pounds was normal fuel pressure as I recall.

# VOCNA 209 I do not know much about these gauges and was focusing on oil pressure gauges - I

assume adapting a fuel pressure gauge is not hard - I guess I will find out. Do they have a capillary

tube like a "good ole" oil pressure gauge? I am not sure I want to go the route of a sender unit that

converts pressure into an electrical signal.

# VOCNA 210 Mine has the same compression fitting affair as a mechanical oil pressure gauge.

While we're on the subject, I also have a gauge on a push rod Velo but it's next to useless. The

peculiar thing is that on start up it will have upwards of 10 psi, then within 4-5 minutes (way before the

oil gets hot) it will drop to 1-2. Not that they need a bunch of pressure, I just have never understood the

reason for the big drop. The things it feeds, crank, cam, followers and rockers all have fixed size

orifices. Tried it on a couple engines with same result.

# VOCNA 221 What you describe is very common. It is one of the reasons why a cold automatic

transmission has such a harsh shift for the first few accelerations but diminishes before the engine and

trans warms up. It is caused by three things: pump leakage, viscosity of the oil, and a little to the

amount (mass) of the oil to be pumped. Mostly it is the viscosity of the oil. Our Velos are old engines

with rather large clearances compared to modern engines so we have to use high viscosity oil. Oil

viscosity is not linear to temperature. Most viscosities are given at 100 degrees C. Viscosity increases

rapidly below 50 degrees C and usually triples around 20 degrees C (room temperature). Hopefully it is

apparent that the oil viscosity is high when the engine is started which causes the high pressure. As the

oil warms it reaches a much lower viscosity long before the engine reaches operating temperature. The

Velo oiling system is a flood system not a pressure system. Even so 1-2 psi is too low. With o-rings

between the timing cover gear oil jets a new pump will deliver 5 - 6 psi a pump with normal wear will

deliver 3-4 psi. Pump wear occurs mostly on the gear and body faces. A new pump has .001" to .0015"

gear end play. If more than .003" clearance is present the pump should be rebuilt or replaced. You can

check the pressure side of the pump gear end play be pulling on the worm gear shaft in the timing


# VOCNA 213 You're right in your understanding that the 0-15 or 0-30 PSI gauge is likely to be more

accurate than those with bigger numbers on the dial. A Bourden Gauge is operated by a flat tube coiled

up in the casing, with the central, closed end of the tube connected to the spindle through a gear

reduction. As fluid (or gas) is admitted into the open (threaded) end of the gauge, the tube is

pressurized, causing it to uncoil, or attempt to straighten, thereby rotating the spindle with it's attached


# VOCNA 216 Lots of cheap gauges are available. McMaster Carr has them on their website: Do a quick search for pressure gauges. The catalog page 512 has a tutorial on

gauge types. Page 513 has several gauges with 0-15 psi ranges for $8-$9US each. They have 1/8NPT

fittings. Page 515 has some 0-15psi gauges with metal frames for $7.24 and $13. Grainger has similiar

items. Page 1198 has liquid filled 15 psi gauges for $16. part # 4ZG16 is 15 psi for

$8.55 You can also try MSC. You may need to open an account with some of these guys to order from

them, but it will be worth the hassle.


# VOCNA 217 I'm curious if you're going to fit one of these guages to your KSS! I think it would show

quickly if your cam wear issue is oil or hardness related.

# VOCNA 218 That is assuming that the oil actually moves in adequate quantity from the bevel housing

where the guage is reading the pressure, to the cam chest where the oil is doing it's thing. As I recall,

the RH cam bushing is the restriction that causes the pressure to build and it must allow the oil to pass

into the cam chamber. Perhaps a flow test from the drainback lines would give indication of oil


# VOCNA 219 These are identical to the gauge that is in the Ariel. Cheap and effective. The only

problem is that the bike vibrates the needle so much that I can't get a good reading, much like an

ammeter. Frank is correct of course, knowing the oil pressure inside the top bevel chamber will not tell

me if the cam is being lubricated, only that there is back pressure behind the cam bushing.

Coincidentally, Paul and I were speaking about this after our ride on Saturday. I'll be checking for oil

flow from the cambox drains.... I'll use the oil pressure gauge to verify that sufficient pressure is built up

in the cambox, as dictated by Veloce. But again, this is only telling half the story. I don't plan to leave

the gauge in place, only use it for testing. Who knows, maybe I'll come up with a good location for the

gauge, and leave it there for a few test rides. One chap in the UK recommended using clear plastic

tubing for the cambox drain lines, then I can SEE the oil flow.

# VOCNA 220 Thanks for the dope on the oil gauges - I have several options now and things are

sorting out. Is it possible to fit an oil line up to spray directly on the cam like the early Mk 2s? I really

don't know why Velo discontinued this oil line (in '37 I think), which runs from the top bevel box to a

small nozzle somewhere on top of the head, and sprays oil directly onto the cam face. Dave Poole

sent me some nice drawings and accompanying text showing how to retrofit this to late Mk 2s, but I

have no idea how much work it would be to fit on a Mk 1. I have the drawing digitally, and providing

Dave is OK with it (I can ask him), I could forward them on to anyone who is interested. My latest

roadblock appeared last week when I went to re-fit the oil tank and found someone had lined it with

some kind of sealer and it was cracking and flaking off. I figured this might not be good for lubrication

(that restrictive RH cam bearing being a case in point). So I proceeded to track down a good stripper

(something Gwen did not understand at first), and went to work on it on the weekend. Inevitably, the

reason for the stripper presented itself - pinholes in the top of the froth tower (weird how that could

happen on an oil tank). So tonight I pulled out the torch and solder and had a go cleaning it up and

soldering the pin holes. It seems to have worked and was holding liquid well, and I even got a lick of

paint back on it before coming up to check email. I am almost back to where I was 10 days ago - a

typical rebuild!!

# VOCNA 222 After all the technical stuff is bandied about I thought I might throw in my 2 cents worth.

Just remember that 2 cents doesn t buy much these days but here goes. How many KSS owners do

you think bothered to buy a gauge to measure the oil pressure at the upper bevel drive? Not many me

thinks and I am one of them. I m surprised that Veloce would actually give a specific value to something

like the oil pressure when in general they never bother to spec something so elemental as the cylinder

stud nut torques. Statements like tighten until a gas tight seal is achieved do tend to be a bit vague at

times. In keeping with the Veloce spirit of ambiguous specification I have measured my upper bevel box

oil pressure by loosening the plug about 2 turns while the engine is running. By the time I get to 2 turns

copious amounts of oil are oozing out the plug threads such that the whole timing side is covered in oil.

This necessitates at rapid shutting down of the engine because the process of tightening the bolt while

running will result in an oil slick of Exxon Valdez proportions. My theory is that the pressure sufficient to

push the oil up at least 6 threads in that quantity is more than adequate to push through to the cam.

With 8,000 miles on the engine and no detectable cam wear this theory seems to have a bit of validity.

If I were to only see a small weep I would be very concerned as I would estimate the pressure to be in

the 1-2 psi range. This sophisticated pressure measuring tool is to be found at any store offering a

selection of adjustable wrenches, vice grips and cold chisels.

# VOCNA 230 I must admit that after removing the rockers and looking at the head, it seems that the


cams rotate through a generous cavity below the camshaft that would be full of oil, and this must fling

around the inside pretty well. Dave Poole noted that when he put a 17/11 cam in (from a Mk 8), he had

to mill out the inside of the head a bit, suggesting tolerances are close, and adding to the likelihood that

oil would get picked up by the cam lobe through every rotation of the shaft. Given this, I am surprised

at the suggestions that the oil feed is insufficient and contributes to early cam failure on the KSS. I am

going to do the oil feed conversion on mine next year just because it's cool and I want to mess about

with it. My curiosity is too great not to hook up gauge and see what is happening up there.

# VOCNA 233 I had my KTT cam go flat soon after I got it. Not quite sure why. Surely the more

aggressive cam profiles and spring pressures contribute. I had Gary Robinson stellite the cam and

followers back to /11 profile with 5/8 radius followers. Noticeable change, a bit soggier in the mid range

but a good wallop on top. Most of the long time cammy racers I queried still swear by bean oil. Not

wanting to deal with the hassle, I'm using Redline synthetic and so far no wear issues. I check the cam

feed jet (a bit different set up than KSS) for blockage on occasion and have kept the pressure gauge

installed, doesn't hurt anything and at least tells me I have pressure to the jet. Bevel drive set up is not

something I want to do on a regular basis.

# VOCNA 234 Bean oil is good! While at the Manx Grand Prix last summer I met an ex-Ralph

Seymore mechanic now retired and living on the Isle of Man. He took pity on me and took me under his

wing. One of my problems was cam, cam follower, and piston skirt scuffing. I was given a gallon of 50

weight Castro (not Castrol) oil. Castro is an organic oil heavy with caster bean oil. Anyway my scuffing

went away. Two problems though; One is being organic it separates and spoils if not run on a regular

basis. I left it in my engine until February and it smelled terrible when I flushed it out. Other problem is it

absolutely incompatible with Mineral oil and will form globs if mixed together. This year I've also been

using Red Line 50 weight synthetic racing oil with no wear problems so far. I was also told for push rod

engines, in addition to o-ringing the pump body and timing cover to oil jet interface, to open up the cam

feed jet oil holes with a .010" larger diameter drill and extend the rocker oil groove the full length of the


# VOCNA 235 Were these considered racing mods? How does one put an o-ring around the oil pump -

that's a new one for me. I have rings on my timing jets, that's easy enough. The only reason I don't use

bean oil on my mkIV KTT is convenience, really. I use the thing quite a bit, and it pumps out copious oil

from the top end... and bean oil can't be found at the local gas station. On the summer rally, I'd have to

carry a case of bean oil, and although it smells great, its expensive. These are all now sounding like

really lame excuses... who's supplying it in the US, anyway? Also, when I switched the KTT OFF bean

oil, I used Redline Conversion liquid to flush the engine; I understand that Castrol won't glob up if there

is a little mineral oil, but your Castro has me worried.

# VOCNA 243 I didn't think of it until you asked, but, I believe the enlarged cam oil jet holes and

elongated rocker bearing oil groove are intended for racing. The O-ring mods simply improve the

efficiency of the oiling system. The oil pump O-ring mod is actually a rather old dodge. It is intended to

reduce or eliminate the cross port or external body leakage of the pump in its' bore. Experiences and

opinions vary, but, basically, many think there is a short circuit between the pressure and scavenge

ports of the pump. I am of the opinion that there are losses between the ports. Particularly if the pump

has been removed from the crankcase a few times resulting in the bore being out of round and/or

scored. The most common modification is to put a 1/16" dia. O-ring between the pressure and

scavenge ports. Some add two more O-rings on the outside of the pump ports. I have added the O-ring

between the ports on a few engines that had low oil pressure and observed an increased pressure by

about 2 PSI. I don't know who supplies Castro in the U.S. I tend to think the Red Line 50W is a more

practical alternative. Read Line states in their catalog "Even though Red Line Race Oils are straight

grades, their low temperature properties make them exceptional multigrades". The catalog goes on to

list the oil as "SAE 50 (15W50)". What all that means I don't know.

# VOCNA 239 Someone else may elaborate but the oil pump o-ring mod is very common, done it

myself a couple of times (I'm sure you'll find it in Tom Ross's compilation). Just turn grooves around


the pump circumference, I put one between the pressure and scavenge side and another at the other

end of the pressure side to seal potential leakage and sucking air into the pressure side. My KTT had

bean oil when I got it. I flushed it with conversion oil to avoid teardown (mine was Blendzall, didn't

know Redline made it). Problem was the stuff cleans so well it dislodged years of swarf which ended

up plugging the oil system. I ended up tearing it down anyway. Alan Goldwater (writes Alan's Wrench

for NOC) sold me on the Redline oil. He did a heap of testing with heat sensors, lab analysis, etc. and

found it to be the best, Mobil 1 also very good but Redline comes in straight 50w. Before you say it, I

know some of you performs his yearly oil change outside the McDonald's on day one of the rally using

oil from the French fry vat and seem to get away with it.

L # VOCNA 318 On the standard Velo anti sump system, the column of oil under the ball valve

must remain in place because if it were to 'leak down', it would have to be replaced by air. Since there

is no way to supply air, it cannot leak down. That column of oil must be in place before running the

engine, as the oil pump cannot pump air efficiently enough to open the ball valve against it's supporting

spring. Using a weaker spring is not required, as if the supply line is properly filled with oil, the pump

will open the valve due to efficient 'suction'. In reality, there is no such thing as 'suction', but simply

pressure differential (above and below the ball). Above the ball you have atmospheric pressure plus the

weight of the vertical column of oil described as the area of the cross section of the supply line

muliplied by the height of the oil measured from the surface in the tank to the supply orafice to the

pump gears (assuming no air bubbles). When the pump begins to move that column of oil, the entire

weight of the column is moved by the pump, aided by the atmospheric pressure. The ball absolutely

cannot remain on it's seat, as there is no way for any air to enter the vertical oil column and the oil

cannot be either compressed or expanded as it behaves as a 'fluid solid'

# VOCNA 380 The check valve is a great idea, but I'd put it down by the oil pump, not on the underside

of the oil tank. With the check valve up at the tank, the oil pump may be forced to suck 6 inches of pipe

air to pull the valve open. Mirek says his will do that, so that's good. But some say you must fill the

pipe with oil. Which is it? Putting the check valve down on the motor, right next to the pump,

decreases the amount of air that the pump may have to suck to open the valve. Also if the bike wet

sumps without any valve, and you then install a check valve at the oil tank, wouldn't the oil in the pipe

(between the check valve and the motor) just wet sump too? Or does surface tension keep the oil in

the pipe? It must, otherwise the pipe would be full of air after a few days.

# VOCNA 385 I hadn't thought about the need for air to get in to allow the oil to leak down.

# VOCNA 382 It is right that the pipe must be filled with oil - I always prime the pipe with oil before start

up. I did my test by sucking on the end of the pipe which, for reasons of personal taste, was devoid of

oil at the time. The oil that is in the pipe between the valve an the oil pump should not leak through to

the cases as there is no way air can get in to allow the oil to flow (this is, for some reason hard to

explain). It is the same principal as a pipette - fill a tube or pipe with a liquid an put you finger over the

top - the oil will not drain out unless you lift your finger off and let air in to displace the oil. As I

mentioned in an earlier note on this - it is really important not to have any air leaks in the oil supply line,

regardless of whether you have a check valve or not. If you have an oil leak the oil pump will be

sucking some air in as the engine runs (probably sucking more air at higher RPM as the pump will be

turning faster). The check valve may work as well at the engine end of the supply pipe, but would be

harder to fit given the way the pipe winds up into the tight space between the gearbox and the engine

cases. The VM check valve was originally fitted near vertical on the bottom of the oil tank and so was

designed by Britain's finest engineers to work this way - how could you doubt them? Seriously, I have

no idea if anything but a more or less vertical mounting affects the operation of the valve - would the

ball still seat OK if the valve is on its side?


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.

#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 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!

#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.

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

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 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 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



#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


#1248 A few aftermarket companies make one way breathers, especially for Harleys. Try

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 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 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


#4092 You don't take the measurements from any point to any point, they are just the length of the


#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.

#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


ack 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.!


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 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 .

L # 5619 The breather system on my Thruxton is linked up by two pieces of 0.5" bore plastic

tubing of as I understand it "critical" lengths. At a recent local VMCC meet I was asked what these

"critical" lengths were. I have measured mine which have been on the bike since before my ownership

and they seem to work OK with the dimensions of timing chest rear(below mag) to oil tank = 22" and oil

tank to atmosphere (and/or rear tyre!!) = 28" but is this correct? Does anyone know the "Correct"

lengths for these pipes please. I would not like to pass on duff information.

# 5620 The hose lengths are given in the parts book. P/No FA138 - Engine to oil tank - 21.375", P/No

FA141 - Oil tank to wheel - 27.5". Pete C.

# 5621 I have seen these lengths quoted before but how do you measure plastic pipe to .005 and

where exactly do you measure from? The "inside" ends of the stubs to which the pipe is attached or the

"outside" ends?

# 5622 ! 0.375" = 3/8", 0.500" = 1/2". Measurement to the nearest 1/8" is probably close enough. The

pipe is measured end to end of the plastic pipe.

L # 6063 Does the air breather hose from the crank housing connect to lower or upper

connection on the oil tank? (or does it not matter)?

# 6064 It connects to the top and there are many on the site that will quote that it has to be exactly

21.375" long.

# 6065 On the Venom it connects to the connection at the top of the oil-tank with the vent pipe

connected to the froth tower. Remember the correct lengths.

L # 6265 Adding a check valve, one way valve, or PCV valve has a big advantage. The venom

engine displaces 500cc within the cylinder. Put the engine on top dead center (TDC) rotate the crank

180 degrees and 500cc of air/fuel mixture will fill the cylinder. At the same time 500cc have been

displaced below the piston and have been compressed into the internal spaces inside the engine

cases. The higher air pressure, from the piston dropping, raise the crankcase pressure above

atmospheric pressure, assuming 14.7 PSI (1 BAR) at sea level, and this air pressure escapes the

engine thru the crank case breather. Rotate the crank an additional 180 degrees and the rising piston

displaces 500cc of air inside the crank case and creates a partial vacuum. If the crank case breather is

working properly, it prohibits the ingress of air and the crank case remains below atmospheric pressure

until the piston again drops to bottom dead center (BDC). If there is little to no blow-by around the


piston or up the valve guides, AND there are no air leaks, the engine will remain below atmospheric

pressure for all but a few degrees of the crank shaft near BDC. The vast majority of the crank angle will

create a partial vacuum, helping to reduce oil leaks, air pumping, and the loss of power from the added

work load. Obviously, the engine will need to rotate rapidly a few complete cycles to pump out the air in

the rank case via the small copper tube on the crank case breather. However, in only a few seconds

this will occur and the engine will essentially remain below atmospheric pressure inside the crank case.

Having a crank case breather keep the air out, the engine will show far fewer oil leaks, and the best

part, there will be no loss of energy by having to pump air in and out of the crank case. Less air

churning around, less oil being blown out into the primary chain case or the breather. There are

numerous one way valves available at any decent auto parts house. Ask to look thru their assortment of

PCV valves, or use a check valve like used on most autos in the brake servo hose. These are generally

about 1/2 inch spiggoted check valves and fit very nicely in the vent line going up to the tank. Cost is

under ten bucks US. Almost all modern engine employ a breather. Ride oil weep free.

# 6267 Wasn't Percy Goodman clever to devise a timed breather on the early K engines? This allows

the down going piston to breath out and restricts it's inhaling. Same device is still there on the Mk VIII -

and no other breather is required. Not bad for a 1925 design is it? For those poor souls who are

ignorant of the ways of a 'K', this timed breather is a cast on section that overlaps the drilling in the

drive side mainshaft and effectively blanks off the hole as the piston rises. No additional pipes, valves,

reed valves or other wot-nots.

# 6271 You have made some interesting points, however a lot depends on the design of the engine

&/or modifications, & the placement of the NRV, there is a case for claiming that in some cases, the

addition of an NRV can make the underside of the piston an excellent device for pumping oil out of the

internals & on to the road unless some sort of baffle chamber is fitted to separate & drain surplus oil

back into the system. However, -- my old mate Les Diener had a terse saying for this sort of thing, & he

had designed & tried timed breathers as well as various NRV's. And you are dead right about the

simple KSS design, --- maybe that is why I never worried about engine breathing in all my years of

riding Velocettes daily, -- they were all KSS's ! - apart from Les Diener's MOV which I rode at odd times

during the WW2 years, - mainly for petrol economy, ( my cammy had a sidecar attached & was

registered, -- but only for the petrol ration that it was entitled to ! ) it wasn't until the late 70's that I finally

got around to riding a MSS & it never seemed to need a breather!


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.

#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 rock