The Knowledge - Velocette Owners Club

wanting to measure everything up before I pull the motor down for an inspection and clean ( Ignition
timing , valve timing , the clearances etc ) . How would I go about 'retarding ' the valve timing Paul , is it
a simple matter of putting the top drive one tooth out of current alignment ? It could be possible that the
timing is out as there is no scribe mark on the top bevel to align with that on the cam drive gear
,alignment is marked with paint dots . Having said that what marks there are and scribe lines are all in
the correct position at TDC. When I had my KSS racer I simply stripped it put it back as the Velo KSS
tuning sheets , put a new K17/8 cam on and ran it ( untouched and without fault ) till I sold it . So
playing about with the valve timing is something I am not familiar with . Maybe I will have to wait and
measure the valve to piston gaps then if it looks OK, wait again and see how it runs ? I'd like to find out
who built it and may be able to get some info via 'Fishtail', It does look to my eye as though the bike
was built by someone who knew what he was doing .
L #2164 I am fitting a thicker spacer / insulator between the head and the carbs on my Venom. I
will need to replace the studs with longer studs or bolts. Question: What size and pitch thread is in the
head ?
#2176 5/16 BSF, 22tpi.
L #2298 I have a 1951 rigid MAC and as there was a slight oil-leak from the head gasket I
changed it, but there's still a slight leak. I find oil between the cylinder fins and on the magneto just
behind the cylinder. The gasket was a copper ring. Should I have heated it up or anything before fitting
it?
#2299 Is it an iron head? If so there shouldn't be a gasket. If it's an alloy head then you should have
annealed the gasket by heating it to cherry red and then quenching it in cold water to make it soft
before fitting it.
#2300 There are no oilways running through the head gasket face on a Velo so the oil leak cannot be
attributable to a leaky gasket. More likely that you have the usual leak down the cylinder studs. To cure
this, countersink the stud holes in the top face of the head and fit a suitable "O" ring under the washer.
For additional oiltightness use a new Nyloc nut on each head stud.
#2301 I have a '35 MAC which has a copper gasket too - to anneal a copper gasket, heat it red hot and
then quench it in cold water. This should enable it to be reused nicely.
#2302 thanks for your advice too. There is oil running down the cylinder bolts, as you say. I noticed
when I last had the head off that one of these bolts is not quite straight, not by much, but it's almost
certainly making a difference.
#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.
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