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Should every engine bearing be C3 or just the crank case and cams?
How about the bevel bearings?

Regards

I use all C3 fit bearings where the bearings are fitted in alloy (cases and cam bearings). All the bearings mounted in steel housings (clutch and bevels) I use standard fit.

Regards Nigel

That's interesting, Nigel.
Why the difference?

Hello Jordan

Originally I fitted them following advice from others back in the the late 80's early 90's. I find that standard fit bearings often go tight under their interference in the cases. Also having checked the alignment between the cases from one side to the other I think a little more clearance can't hurt. However the bearings that fit in the steel housings for the bevels and clutch don't have so much interference as they are not subject to any change of interference via heat expansion. It's not hard and fast and occasionally in the past I have used C4 fit as well, but not for some years. Whatever it's worked for me for 30 years....

Regards Nigel

Thanks Nigel.

I once saw a (not motorcycle) factory recommendation for bearing internal clearances when replacements were needed.
It said to use C3, even thought the original fitments had less clearance, but with no explanation as to why.
Maybe they thought a machine that had been used and then rebuilt could be less dimensionally perfect, and could do with the extra looseness.