crankshaft compatibility

Hi, could somebody please tell me if all 750 crankshafts are compatible. I have a 1969 assembly stamped 06 0732, which has seen better days. If I can find a crankshaft from an earlier, or later model 750 will I be able to fit it, even if the part #s are different, cheers, David

fireflake said:

Hi, could somebody please tell me if all 750 crankshafts are compatible. I have a 1969 assembly stamped 06 0732, which has seen better days. If I can find a crankshaft from an earlier, or later model 750 will I be able to fit it, even if the part #s are different, cheers, David

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Yes, They are interchangeable.

Even an 850 crank can be used if it is re-balanced. [Except MK3 -850]. Jim

Like Jim said, they are all interchangeable, but there are some small differences. The earlier ( pre 1971?) Commando crankshafts with the ball bearing main on the timing side had a slightly smaller diameter on the timing side shaft than the later ones fitted with roller bearings on both. The difference was pretty small, on the order of .0003" - .0005" in diameter. The earlier crankshafts were also slightly wider between main bearings than the later ones. Norton said it was OK to fit the later roller bearing on the early timing side, so the different crankshafts are still interchangeable, but if switching to a later crank with dual roller bearings, you will want to check the end float, and shim the bearings if necessary, something that's not required with the ball bearing main. Norton recommended an end float of .010" -.024" in their first service note on crankshaft bearings, and .010" - .020" in a later one. If fitting a ball bearing to the timing side of a later crank, you might want to go to a looser fit bearing like a C3, instead of the original C2 fit, to avoid binding in the bearing with the larger diameter shaft.

Ken

Many thanks for your advice and knowledge, very much appreciated, David