The Knowledge - Velocette Owners Club

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 velos....is there a filter of any kind that can prevent the oil pump from getting ruined.....it 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
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