The Knowledge - Velocette Owners Club

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
housing?
#4617 First make certain that the nut will spin onto the shaft with no resistance, then use a socket to
drive the gear onto the taper. Then bring the nut and washer up to the gear rather gently to exert some
pressure on the gear. Tap the socket (that is large enough to fit over the nut) to further drive the gear
onto the taper, repeat, repeat, repeat. Or... make a puller for the shaft consisting of a substantial cross
bar drilled and tapped in it's center to accept the shaft thread, with two more holes drilled at 180
degrees and tapped to accept bolts that will press the gear onto the taper. If you're pulling the gear up
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