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Is there a difference between Shimano BB71 or BB91?
NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.
I noticed a creak in the bottom bracket this morning, obviously due to too much wet sandy riding. The specs for my Reign state it has a Press Fit Bottom Bracket BB71. I cant find any shimano tech docs on a BB71. I can fnd tech docs on a BB91. Overseas I can find BB71 for sale but only BB91 in Aus. I am guessing a BB71 is in fact a BB91. Can anyone confirm if they are indeed the same or if they are different. I will need to order one as you cant just rip the cups out and regrease (I dont think) but have to replace the lot.
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BB91 is a higher spec than BB71 but essentially the same thing. A lot of OEM stuff is not offered by shimano as replacement/aftermarket parts. How old is bike/bb? You may find when you pull it out that the bearings still run freely and the cups just need removing, cleaning and greasing where they contact the frame. Where the BB cups are in contact with frame is more likely to be causing creaking than the bearings themselves, as this is often not greased properly during assembly. Also check your pedals are tight and crank bolts tight.
It got serviced last week for 1st bed in service. They checked all bolts, so they should be good but I will double check. Sounds like I will order the BB91. Shimano doesnt recommend to pull out the cups and put back in as they may be damaged via removal. The creak only turned up today, thus wasnt there from or before the service. I will order the BB then try to regrease before I replace and see how it goes. Thx.
Pretty extreme replacing the BB for a creak. I would be pulling the cranks off and greasing the interface between the spindle and brgs and the lh crank and spindle. Then I would be making sure the pinch bolts in the LH crank are torqued evenly. I would highly doubt you will be needing a new BB after 500km even if you were riding in the rain and sand. Even your chainring bolts can creak so pull them out and clean them and reinstall with a smidge of lube.
I've never fitted a press fit BB but I imagine you would need a press similar to the old BMX BB press to fit it. If you fit it crooked you could not only stuff the bearing cup but also there is the potential to ovalise the seat in the frame.
I'd be taking it back to the shop seeing it's only a new bike. Not worth the risk stretching the bottom bracket replacing the bearings which may, or may not, be the source of the creaking
I just ripped the crank out and repacked everything with grease and tightened all bolts. I didnt realise you could repack these without taking the bb out but you can. Also found that the bb is indeed a bb91 and not a bb71 as advertised by Giant on their website. It was low on grease and the crank bolts were not tight, so everything should be sorted now. Should be able to get another 500 kms now.
good stuff J,
now get back to work... you have had long enough away...