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Dura-Ace 7900 non-drive side crank hangs over the axle. Normal?

2K views 5 replies 4 participants last post by  cxwrench 
#1 ·
I’ve built my own bikes for years, but this is the first time I’ve used a crankset that doesn’t require a cartridge-type bottom bracket, so this too is unfamiliar territory for me.

I installed a Dura-Ace 7900 bottom bracket (English type) and Dura-Ace FC-7900 crankset. In installing the non-drive side crank, I noticed that there’s about 2mm of the crank's splines showing past the axle, almost as if the axle is 2mm short. The drive-side crank is pushed in all the way.

As far as I know, these cranks are compatible with both 68 and 70mm bottom brackets shells. I didn’t measure mine, but I assumed it’s 68mm since the threads are English type. (The frame is a Ridley Noah RS.)

Is it normal to have some of 2mm of crank not supported by the axle? Or have I screwed the pooch somewhere?
 
#3 ·
The gap's needed so you can adjust bearing pre-load with the cap. You can see the gap clearly on the sectional drawing below.

Just for information: the stopper plate (if pushed up) keeps the crank from falling off should the crank bolts fail and the cap come off.
 
#5 ·
I see what you’re saying, but something doesn’t make sense...

I understand that the cap will preload the bottom bracket bearings, but I still don’t understand why there needs to be 2mm of crank splines extending beyond the axle. When I tighten the cap, there’s no way the crank is going to be pushed onto the axle any further. Thus, in order to “preload” the bearings, a mere fraction of a millimeter would be sufficient space.

In addition, this brings up another question: assuming my bottom bracket shell is 68mm, there would be a whopping 4mm of crank spline extending beyond the axle if using a bike with a 70mm shell. Was this intended by Shimano? Or did they goof?
 
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