Single clutches

[Jordan]

I'm curious about the desire to have matching pairs of primary gears.
I understand that the crankshaft gear was available in various sizes so that one could be selected at engine assembly time that provided best fit, for quietness maybe?
But best fit to one crankcase wouldn't necessarily mean the gear pairs would also fit another engine with equal precision.
Should we accept that at this point in time, any usable gear pair should be acceptable?
So long as the error isn't "too tight".
Addit:
Standard involute gear tooth form copes with variable clearance.
Whatever the clearance, the teeth will roll over each other rather than slide.
There might be some backlash, but that's not usually fatal.

[IanHood]

I've no idea if matching gears are actually a thing but what I do know is that the 350/450 crank gear that Eldert just supplied to me (thanks Eldert), works perfectly with the NOS clutch basket I had in my spares pile. Given the often terrible (from the factory) factory clearances found on some bikes I can't imagine too much thought was given at the time to find good matching gears...

Ian

[blethermaskite]

I'm curious about this.....I was always led to believe that once a 'pair' of gears had 'run in' together introducing 'another' used gear in place of one of the original pair would promote unusual wear and or/ unacceptable running noise? I suspect introducing one new unused gear to a used gear in a pair would pretty much minimise this outcome, but still be a little noisier than a 'run in' (from new) pair.
I have on occasions swapped in a gear in a busted gearbox and seemingly got away with it, but a couple of times I ended up with significant 'whine'.......seemed to work OK but noticeably noisy. Might just be blowing in the wind on this!
Cheers George

[Duccout]

Hi George,

I think that a whine will result from mixing worn gears. Years ago I found that my 900 had a fault with the machining on the clutch body, so I bought a used assembly from eBay and because I did not want to disturb the electric start sprag clutch I left the crankshaft gear in place and replaced the clutch gear as there was plenty of backlash. The result was a lot of gear whine! When I rebuilt the engine of my 250 I discovered that a PO had lost the spacer under the clutch and replaced it with a large washer that was a long way from being flat, allowing the clutch to wobble about all over the place. I fitted the correct spacer but the gears really whined after that and I guess it was because they had worn to fit each other and when I replaced the spacer they had to get to know each other all over again!

Cheers,

Colin