Problem installing M770 crank in new BB90 bearing- Mtbr.com
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  1. #1
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    Problem installing M770 crank in new BB90 bearing

    Hi

    I'm building up a Yeti ASR-5 frame with the components from my old hardtail. Everything has been fine, until I tried to install my old M770 XT crankset using a new Shimano BB90 XTR bottom bracket (the one with black bearing cups). The BB instructions say it fits M970 and M770 cranksets so it should be ok.

    The ID of the new bearings is 24mm, the same as the OD of the spindle, so the fit is quite snug. However, at the outermost (chainring) end of the spindle there's a flange 25mm diameter and 7mm deep, which stops the spindle going all the way through the BB. Consequently the chainrings sit about 7mm too far out and the spindle doesn't protrude far enough to fit the non-drive crank arm. I'm reluctant to bash with a mallet because getting a 25mm flange into a 24mm hole sounds like a recipe for damage.

    The BB on my old frame was also Shimano but, I think, XT version (silver cups) and has a bearing with a 25mm ID.

    Has anyone else come across this problem and found the solution?

    Thanks

    Jez

  2. #2
    BLAH BLAH
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    Do you have to many spacers on the bb cups?

    I use this bottom bracket with SLX cranks with no problem.
    Whats this line for?

  3. #3
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    It's a 73mm shell, so just one spacer on the drive side.

    The overall BB width inc bearings is 97mm. The length of the shaft (excluding the collar/flange) is 110mm, so I've only got 13mm of spindle protruding on the non-drive side.

    Was your SLX crank tight on the bearing, i.e. did it have to be knocked in with a mallet?

  4. #4
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    OK, time to 'fess up to being an idiot!

    The 25 x 7mm flange turned out to be the hard plastic outer cap from the old bearing. It was a tight fit on the crank spindle and had come off with the crank, rather than remaining in the bearing.

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