The Knowledge - Velocette Owners Club

#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
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