B31/B33 Flywheels

[martinh10]

Can anyone tell me what the physical difference is between B31 and B33 flywheels? They have the same crank pin position (for an 88mm stroke) and presumably the same O/D but have different part numbers. I have three sets, two of which have casting numbers 66-610 (which I believe are B31) and one set without numbers which look pretty much the same. I assume the B33 items are a bit heavier and have some physical difference by which they can be identified.

[Ian C]

I've attached a pic of a flywheel from my M33, so does this work for comparison?

[martinh10]

Thanks Ian, that confirms that all mine are B31. I just wanted to be sure before I put the unmarked ones back in the engine.