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Thread: Bb91?

  1. #1
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    Bb91?

    Hi there,

    I'm the happy owner of a 2009 Epic Marathon Carbon. It currently has a XT crank-set. The bottom bracket is designated Shimano BB-91, OS, press-in bearing. Now, I'm considering upgrading to XTR, but how does it work? Do I simply buy a standard XTR crank-set and keep on using the press-in bearings in my frame, or do I need some special XTR version build for BB91?

    Thanks,
    sebbesen

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    Quote Originally Posted by sebbesen
    Hi there,

    I'm the happy owner of a 2009 Epic Marathon Carbon. It currently has a XT crank-set. The bottom bracket is designated Shimano BB-91, OS, press-in bearing. Now, I'm considering upgrading to XTR, but how does it work? Do I simply buy a standard XTR crank-set and keep on using the press-in bearings in my frame, or do I need some special XTR version build for BB91?

    Thanks,
    sebbesen
    You got it When you buy your new XTR Crank, all you have to do is uninstall the XT cranks and slide the XTR into the existing BB-91 cups. This will leave you with a left over XTR external cup BB, which makes it convenient to sell the old cranks, with a standard BB.

  3. #3
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    Excellent Thanks!

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    I just ordered a S-Works carbon 29er ht ss frameset and it has the Custom BB-91 OS press in. I'm hoping to use my XTR970 crankset with it. Anyone know the width? Is it 73mm or does OS mean wider?

  5. #5
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    Make sure you remove & reinstall 9 & 10 from your XT crank.
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  6. #6
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    Quote Originally Posted by amillmtb
    You got it When you buy your new XTR Crank, all you have to do is uninstall the XT cranks and slide the XTR into the existing BB-91 cups. This will leave you with a left over XTR external cup BB, which makes it convenient to sell the old cranks, with a standard BB.
    If you're replacing the crank, replace the bearings. Ask the LBS for a set of BB91 bearings. It's not really a home mechanic job as you need a tool from Shimano to pressout the old bearings and press in the new ones.

    I believe that Shimano only makes 1 grade of BB91 bearing.

  7. #7
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    Quote Originally Posted by skiwi
    If you're replacing the crank, replace the bearings. Ask the LBS for a set of BB91 bearings. It's not really a home mechanic job as you need a tool from Shimano to pressout the old bearings and press in the new ones.

    I believe that Shimano only makes 1 grade of BB91 bearing.
    If the bike is new (when this was originally posted it was) that wouldn't matter. Even if it was old, he would have to get new BB-91 bearings which would still leave him with an external cup XTR BB, just like I said. Also, unless its a ceramic upgrade, I would never buy just bearings, it not that much cheaper than buying the whole cup assembly.

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    I have a 2010 Stumpjumper Carbon Expert 29er HT with the FC-M762 cranks and the BB-91 OS. I was told by the dealer and Specialized support that the XTR cranks were not compatible. Only the XT hollowtech II, Race Face and the Specialized cranks were compatible with the press-in bearings. This seems unfounded based on the above thread and experiences on this forum. Did something change from the 2009 model listed above?

    I was interested in using the www.SRM.de powercranks that are based on the FSA Afterburner or FSA K-Force Lite cranks, which I thought shared the geometry of the Shimano Hollowtech II. If anyone knows if the FSA are compatible I'd appreciate the help.

    Thanks,
    John

  9. #9
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    Quote Originally Posted by jsnafziger
    I have a 2010 Stumpjumper Carbon Expert 29er HT with the FC-M762 cranks and the BB-91 OS. I was told by the dealer and Specialized support that the XTR cranks were not compatible. Only the XT hollowtech II, Race Face and the Specialized cranks were compatible with the press-in bearings. This seems unfounded based on the above thread and experiences on this forum. Did something change from the 2009 model listed above?
    The XTR is a Hollowtech II crank. I have XTR on my Epic. You must use the BB91 bearings from Shimano, not the XTR bearings. Just as you would with an XT. As I stated above it pays to replace the BB91 bearings whenever you replace the crank. They wear just as fast as the Hollowtech II ones do.

  10. #10
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    The XTR970 cranks installed no problem with the BB91 on the S-Works Carbon HT SS.

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    will the new sram x9 2 x 10 cranks fit the bb91. all i see they offer is bb30. is this the same or different?

  12. #12
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    Here's a compatibility chart that someone else posted here...

    Cheers!
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  13. #13
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    thanks that helps

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    Can the BB91 cups, once they're pressed out of the frame, be repacked just like outboard assemblies?
    http://htfuaaron.blogspot.com
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  15. #15
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    I've got an issue with my 2010 carbon expert HT. The chainline is off to the right some much that the there is no way I can go big big and the chain almost rolls off the middle in the big on the back. I've had a hollowtech II XT cranks and a New 10 speed Xt crank on it with custom 40/30 rings. I need the cranks about 1 cm inboard. Anybody seen this?

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