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Discussion Starter · #1 ·
I am piecing together a motor with new cases and bearings (long story) and I was wondering about the necessity of the measuring and shimming of the float on the crank and the gears. With a CNC machined case is this process still necessary? I do it with older British bikes but I would have thought that with such a modern engine this process was no longer necessary. Thoughts?
 

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In a word, yes. CNC or not if you are that deep it only makes sense to check. The newer bikes run a lot of preload on the crank [for noise reduction I suspect] and it can be hard on the main bearings. The generally accepted preload on the crank is around .1mm [.004"] and the trans shafts approx. .2mm. Pay attention to the shift drum too, I've found a few pretty loose. Do it once, do it right.
 

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CNC does not mean always perfectly correct. I've seen plenty of perfectly incorrectly made CNC'd bits. So, I say refer to wdietz186's last sentence.
 

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absolutely. you always shim every time they're apart.

0.15 - 0.20 preload on the mains, 0 - 0.1mm end float on the two gear shafts, 0.3 - 0.4mm end float on the shift drum is what i'd do.
 

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Also keep in mind that you are probably changing from a paper gasket to sealer so factory clearances change, so just throwing it together and hoping it is close can get dicey. I shim every case that comes apart also because you do not want to have to go back in later because something is wrong. My Factory 1997 m750 would not shift into top gear when you got it hot due to bad shimming from the factory. Trust nothing but your self and check everything.

The pre-loaded angular contact main bearings are more for case growth from heat as the cases heat up the cases expand and holding the balls tight in the races keeps things true. If you run too little the bearings can fail from damaging the balls/races, too much (as Ducati did in the early 2000's) and you can at best lose horse power and at worse break cases.

There are many motors that do not shim lower ends so it is possible but some of those engines have more issues and can be less precise as shimming allows.
 

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Discussion Starter · #6 ·
Thanks gents. It's going to be a rainy weekend here so I'll have at.
 
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