crankset swap question- Mtbr.com
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  1. #1
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    crankset swap question

    went to swap the crankset from one bike to another and it seems like the length of the spindle is off.

    From 2012 Carve 29 SL
    To 2010 Superfly SS carbon

    crankset is stock SRAM s1250 from the Carve. both bikes use generic gxp/mega exo style bb's.

    when I tighten the crankset bolt all the way to spec I still have 1/2 a cm play between the crankset and the BB.

    What's the deal? Is this something to do with the difference between a 73mm and 68mm crank? I tried to look up numbers for this on both bikes but was fairly unsuccessful.

  2. #2
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    Is one BB shell 73mm and the other 68mm? If so, then you'll need to add 2 x 2.5mm spacers.

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    Thanks Andy. I think that's the issue. I think I have something laying around that might work for spacers.

  4. #4
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    Quote Originally Posted by Andy R View Post
    Is one BB shell 73mm and the other 68mm? If so, then you'll need to add 2 x 2.5mm spacers.
    This. sounds like you just need to add spacers between the frame and the bottom bracket bearings. The manufacturer's website should have a download sheet that tells you how many spacers should be on the drive side and non-drive side based on the bottom bracket width. If you want a different chain line, adjust the spacer's location as you see fit. If you don't have the spacers, just order a new bottom bracket bearing set. It'll come with spacers, and you'll have a new set of bearings if/when your current ones wear out.
    "a hundred travel books isn't worth one real trip"

  5. #5
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    Quote Originally Posted by khardrunner14 View Post
    Thanks Andy. I think that's the issue. I think I have something laying around that might work for spacers.
    Freehub spacers will work, if you have any the right thickness. Otherwise, what watts888 said.

  6. #6
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    Quote Originally Posted by khardrunner14 View Post
    ... both bikes use generic gxp/mega exo style bb's.
    Does the new bike have a mega exo bb in it? If so...it's not going to work.

    GXP and mega exo are not the same thing and are not compatible. Unless you have a spacer to make the 22mm section of the spindle 24mm, and then a spindle spacer kit to reduce any play.

    GXP
    - SRAM specific
    - Spindle is stepped from 24mm on the drive side to 22mm on the non-drive side
    - play is reduced because non drive side bearing is actually sandwiched between the shoulder of the spindle and the non-drive crank arm

    Mega Exo
    - FSA
    - 24mm straight across the whole spindle
    - reducing play relies on having the correct amount of spacers so that pressure is applied to both drive and non-drive bearings

  7. #7
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    eness215 I figured that out today as I could not figure out why there was so much play.

    I just removed the gxp BB from the old bike, used it instead of the MegaExo, then added some spacers (2 2.5mm spacers, one each side). It seems fine now except I cannot torque the crankset bolt really tight. The crankset binds if I do that. I can torque the 8mm down pretty good, then I have to back it off into the removal 10mm section. I cannot leave the 8mm torqued down.

  8. #8
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    DO NOT RIDE YOUR BIKE WITHOUT FIXING YOUR CRANK FIRST.

    you should measure the width of the new bike's BB (without cups). If it is 73, then you don't need any spacers at all between the bb cups and frame. If it is 68, then you just add one 2.5mm spacer on each side.

    Because of the way that the non drive bearing is sandwiched between the shoulder on the spindle and the non-drive crank arm, there will be some gap between the drive side bearing and the drive side crank arm. That is normal. I know it looks funny because you think it should be touching, but that's not the case.

  9. #9
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    73mm apparently. Thanks for the advice.

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