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  1. #1
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    moving from 73mm to 68mm BB, options

    I'm taking the broken decrepit full suspension and trying to put use as many parts from it on my hard tail. How do I use the rear shock on a hard tail?

    Anyways, I have a 73mm BB (FSA mega exo) laying around with the crankset that was used. The new frame is 68mm BSA.

    Now I know I can run my 73mm BB with spacers for something designed for a 68mm but do i want to do this? If I can do this and go ahead with it won't I need a new crankset to make up for the spindle length or with the spacers on the BB am i effectively creating a 73mm spot for my crank to sit?

    I'd rather be able to use everything I have and buy new bearings for the BB to make everything almost new.

    Options? Thanks.

    After more google and mtbr it seems as if all i do need are just a few 2.5mm spacers, i will be running 1x9, does this affect anything as far as crank placement?
    Last edited by illegalsmile; 07-27-2011 at 04:00 PM.

  2. #2
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    Looks like I figured it out... According to FSA and their manual for ALL mega exo BBs all I need to do is run 1 spacer on the left and 2 on the right. Easy enough.

    Having never changed the whole bottom bracket... should I run loctite on the a few threads? My crank spindle will fit the same correct? I just wonder because if they're 2.5mm then that's 7.5mm which would make it 75.5mm?!? I'm confused...

  3. #3
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by illegalsmile View Post
    Looks like I figured it out... According to FSA and their manual for ALL mega exo BBs all I need to do is run 1 spacer on the left and 2 on the right. Easy enough.

    Having never changed the whole bottom bracket... should I run loctite on the a few threads? My crank spindle will fit the same correct? I just wonder because if they're 2.5mm then that's 7.5mm which would make it 75.5mm?!? I'm confused...
    ummm...the spacers you add for the 68mm BB shell effectively make the shell 73mm wide.

    The crank spindle length remains exactly the same and fits exactly the same.

    IIRC the BB uses one spacer with a 73mm shell.
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  4. #4
    Fat-tired Roadie
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    The deal with having two spacers on the right is that one of them can be removed in order to mount an E-type front derailleur. You should have been using it all along, unless you use such a derailleur or have a bash guard that mounts the same way.

    I wouldn't loc-tite the bottom bracket. You really don't even need that much torque, at least compared to other bottom brackets.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  5. #5
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    Park Tools has a great summary and installation instructions here that covers the most popular external bearing BB systems.

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