Hi Mates
Just rebored my Venom Clubman c/ alloy cylinder , using a 020" Aerco piston bought in the UK, spot on .004" clearance but it still has a noise like piston slap, it had it before with .008" wear ( big end etc were ok), it's a noise you can alter with power etc, noisy on over run ie not on power/ pulling but when you bring the throttle back , any thoughts on the matter?
All the best
barry

My son, Brian, had this on his Norton. It turned out to be the rotor outer was pulling loose of of it's center. The knocking was most pronounced at idle. HTH

A similar rattle that you describing can be caused by the big end cage they tend to wear abainst the crank pin, this can sometimes be detected by side to side movement on the conrod, they will run to enternity like this but it may not make for a pleasant ride.

check the side play on the cam gear and idler . You can get a noise almost like a worn big end from excessive play . It should be ideally about .002".
I also run a venom but with an iron cylinder and it does have piston slap which does diminish as the bike warms up.
Does your noise change as the bike warms up.?
The alfin type cylinders can be subject to quite a bit of distortion and even separation of the iron from the aluminium jacket. You may have to have a really good look at that.

Several possible things it could be I guess, -but I agree with Rob to check the meshing of the camdrive idler pinion. This can be adjusted to give nice neat meshing in the geartrain.
I believe it makes a clacking noise when there's too much clearance between the pinions, and it would come and go with engine revs/load I would think.
These gears should always, if possible, be changed as 'sets' because they 'bed-in' as a set. Have any of your timing gears been changed?

I had something similar when the idler shaft hole in the crankcase wore oval. Didn't want to strip a good running bike, so I used some miracle Locktite stuff. Still nice and quiet 5 years later.

Ed from NJ

Hi Jools, just to clarify I am not talking about mesh of the gears. I am referring to linear movement of the idler and/or cam on their shafts. The helical gears will cause the gears to hammer back and forward on their shafts. if there is excessive clearance.

Hi Mates
Getting back to the engine noise , stripped the engine down again, the big-end Had .003" up and down wear ( not all the time though I had to move it about to get it) anyway , stripped the flywheel and put in a new big end,on assembling the fly wheels, (Radialy) one disc is spot on but the other is about ,002" ( in the vicinity of the crankpin ie not 90 to it)
Axial run out is about .005" , hoping that would be OK ( near enough?) not sure where to apply pressure to recifiey if not, any comments would be welcome
Barry

ideally ,after assembly, you should aim for no more than .001/.0015 T.I.R.of the shafts at or near the main bearing locations.
If you get some discrepancy when clocking up the od of the flywheels it is less important.
When the OD of the individual flywheels were machined there is a good probability that they may not be Concentric with each other.
After flywheel discs were machined,Velocette mounted the shafts to each flywheel then balanced those individual assemblies prior to fitting the big end .