The Knowledge - Velocette Owners Club

steady fitted and tightened Engine bolts tight and holes not worn. Check your petrol and oil tanks are
tight (I spent days worrying about excessive vibration, only to find I had not tightened the petrol and oil
tank bolt) Check ignition and cam timing. Check the carbs is set up OK
#571 Don't forget the most important part needed for a ton-up Velo, as used on the 24 hour record bike
- a good racing fairing! Worth at least 10 mph, given proper gearing.
#572 regarding vfr 232 a 1960 venom clubman which was a very fast bike. it was fitted with a 12r box. I
was reading one of the posts regarding max rpm and top speed with a 19 tooth sprocket,
which was about 100 mph. I know for a fact that vfr 232 was cable of a bit more than that. it used to
show 105 on the straight with me lying prone. the question I have is, was there three top gears. one
for mss one for venom and one for tt close gears. 26 teeth seems to ring a bell. if a bike was fitted with
a higher top gear, it surely must give it more top end. my bike was always good for 90 in third. I still
have the bike, although it hasn't run for some time, but if someone wanted a go on it to prove its
output, I wouldn’t be against it. did a tt close box have a higher top gear than a standard 12 box ?
#573 Top gear ratio is all in the sprockets, not the internal ratios of the gearbox, as I've never heard of
an internal top gear ratio other than 1:1 in a Velo. The options on sleeve gear and (I think) first gear
are what differentiates the suffix R from the standard series 12 box. A close ratio sleeve gear in any
box will leave top gear at the ratio determined by the final drive sprocket (or custom combinations of
any of the other sprockets for that matter) but it will bring all of the intermediate gears closer to top - for
instance a 17 tooth sleeve gear (in place of the standard 16 tooth) in my MAC racer left me with 1:1 top
but overall drive ratios of all the other gears were higher by the equivalent of almost two gearbox
sprocket teeth, when compared with the overall ratios available with the standard sleeve gear. So if
you'd like to run a 19 tooth sprocket for your ton and a bit Venom, but have first, second and third the
same as if you had a 21 tooth sprocket, then go close ratio sleeve gear, which for series 12 gearboxes
means an 18 tooth sleeve gear as the standard sleeve gear in the series 12's is a 17 toother to start
with. For sidecar use go 16 tooth sleeve gear - it will have the opposite effect, and was used in the wide
ratio series 14 boxes. And of course whenever you change sleevegear the layshaft pinion needs to be
changed accordingly (from 16/28 to 17/27 to 18/26 and so on). Read the chapter on gearboxes in
Burris - it’s a good explanation for those wondering how the hell to calculate these things called gear
ratios.
#575 thanks for the info regarding sleeve gears, mine has a 18 tooth fitted, it is a genuine 12r box.
these boxes make a world of difference for performance on a venom, but are a pig to use in traffic. they
are definitely for the open road. regarding fitting a thruxton cyl head to venom, if you don’t shorten the
barrel by 90 thou it will be as flat as a pancake. I considered trying to buy the venom cyl head patterns
and having my own head made. thruxton valve angles are at 39 degrees whereas venoms are at 45
degrees. if I had some venom head blanks I could have the valves at 39 degrees and keep the stock
venom valve sizes. a thruxton inlet valve at 2 inches is a bit on the heavy side, and a venom inlet
valve at 1 inch and three quarters is a better bet for higher rpms. any feedback on this is welcomed.
when fitting a thruxton barrel to venom head and tightening up the valve to piston clearances, these
bikes transform into a fast bike. dialing in the cam is a must for performance as is accurate ignition
timing, it needs to be set at 38 degrees, and on the money. I seem to remember that Taylor Gue of
Stroud in the sixties made a venom very fast and that when they were doing a road test of a thruxton in
motorcycle sport in 1966, they also tested his bike to compare it with the thruxton and found it to be a
faster bike. dig out your old copies and have a look.
L #945 The Velo tech website (thanks again Dai) has the formula for C.R. vs. compression plate
thickness. Plates normally come in 0.030" and 0.010" thickness, I'm running 0.050" under my Venom's
similar barrel (it came with these plates from the factory). It never pinks now, even on our watery U/L
premium, as long as the fuel mixture is adequately rich. Plates are available from the Usual Suspects -
oops I mean Sources, check the List archives. As a Velo rider, you will soon be on a first name basis
with them. And I strongly recommend that you join the VOC and VOCNA; the VOC's Spares Service is
excellent. See the VOC website for links. I assume you have an Omega piston, I have had some
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