FC-6550 crank on BBR60 bottom bracket. Left-side arm has a ~1mm gap between the arm and bearing race. It was installed in the correct order – the fixing bolt, which is an aftermarket aluminum one with knurled edge is as tight as can turn by fingers. Then the little locking safety plate thing was pushed in and engaged. Then the pinch bolts tightened to specified torque.
Then noticed the ~1mm gap. My 1.5mm hex/allen wrench will not fit it so am guessing it's about 1mm, no more. My first time fitting a hollowtech.
Is this considered good or should there be no gap and the crank up flush to the bearing race?
Thank you.
by HospitalBrilliant265
3 Comments
Those crankarms gently press against the bearing. Something is off with the bb width spacing. A 2mm spacer might do the trick.
There is always a small gap like this on my cranks. There is a bit of a seal on the crank arm to ensure it only makes contact with the inside of the bearing and not the outer cup. The gap is needed so under load it doesn’t flex and catch the edge of the cup. The drive side probably has the same gap but it’s harder to see.
What width is your bottom bracket shell supposed to be, and what is it actually? The SM-BBR60 requires a bottom backet shell of 68-70mm in width.
If your BB shell width is below nominal, this will happen. The Hollowtech NDS-arm-to-axle interface is built with ~2mm of tolerance, but it looks like you’re beyond that. Your solution would be to either use appropriate BB spacers, or axle spacers.