Shimano bottom bracket for Press-Fit applications.This item allows youTo mountShimano Hollowtech II mountain bike cranksetsTo select MTB frames which use Press-Fit bottom brackets. Manufacturers part number ISMBB9141A Please noteThatThis item will not work unless your frame is specifically builtToThe BB91 standard
Strengths: The replacement of this BB requires no special tools and was extremely simple.
Weaknesses: As this style of BB has no threads or adjustments the only way to stop creaking noises is to lubricate everything, and this will not fix the problem. Once the plastic has allowed the bearing to move the plastic deforms and will need to be replaced.
I am reviewing the factory fitted BB-71 - essentially the same part as listed. As I discovered you can not purchase a BB-71 after-market only the BB-91. The part basically is the same dimensions as an external BB, however the bearings run on PLASTIC. In a mtb application it does not take long for dirt/mud/water to penetrate the housing and cause the bearings to make excessive noise and adversley affect the performance of the bearings.
I searched all the forums to see others experiencing similar issues. I tried cleaning and lubing everything however the noises continued.
In pure frustration I sought an after-market CNC aluminium part that seems to have fixed the problem. Why couldn't Shimano come up with this solution?
I will avoid buying a new frame that has a press fit BB in future!
In summary think long and hard before you purchase a MTB with a BB-71/BB-91 bottom bracket.