what bottom brkt for a monocog?- Mtbr.com
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  1. #1
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    what bottom brkt for a monocog?

    Just picked up a 08 MC off craigslist with BB7's. I have an extra set of ISIS cranks laying around so I'd like to ditch the square tapered stock ones.

    Which BB shell size and length do I need.

    Thanks

  2. #2
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    Get your tape measure out. I'm assuming you're using the stock wheels. They have a cassette. Measure from the center of the cog from the center between your dropouts, or measure to the dropout. If you measured from the center, you want to produce a chainline with your cranks that matches this. Install the cranks on a BB that you have and measure the chainline. Center of frame to center of chainring. Compare this to what you measured in the rear. Take the difference and multiple by two. This is your BB length +/- what you had. If you measured to the dropout, you want to get a total chainline. 67.5mm. Subtract your rear cog to dropout measurement to determine what your front chainline should be. Since it is a cassette and ISIS BB lengths are limited, get as close as you can and then move the cog in the rear by swapping spacers to get it perfect. A perfect chainline is bliss and minimizes chain drop and wear.

    SEARCH FOR CHAINLINE

    Monocogs are 68mm. Two seconds on Google would tell you that.

  3. #3
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    we tried a 68mm x 113 truvativ BB and it didn't fit, so I'd figure someone on here would know since it seems to be a popular bike.......

  4. #4
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    please define not fitting. because that is a 68 mm shell and 113 is around the size u want for a single speed. thanx

  5. #5
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    The left cup would to thread in all the way. Was about 2 to 3mm gap

  6. #6
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    ok so first what truvativ bottombracket is it?? the truvative bottom brackets usually come with a little black spacer (almost looks like a really thin head set spacer) wich should take up that extra space.

  7. #7
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    Quote Originally Posted by jsigone
    we tried a 68mm x 113 truvativ BB and it didn't fit, so I'd figure someone on here would know since it seems to be a popular bike.......
    You installed it wrong.

    Every crank produces a different chainline. You have to do this one on your own unless you can find someone with the exact same combination of parts as you.

  8. #8
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    Original BB is 68 x 110 square taper.

    I just installed a 68 x 113 octalink to replace it and spaced the rear sprocket accordingly to maintain a good chainline.

  9. #9
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    my buddy had a giga x pipe truvativ laying around we tried. I'll call him to see if he has that spacer.

  10. #10
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    ok so that spacer will go on the drive side and on the non there should be a rubber o ring that goes on just like the spacer. oh and on the left cup see if i say's cup will not bottom out on frame if so and you cant find the spacers then it should be ok.

  11. #11
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    Quote Originally Posted by jsigone
    The left cup would to thread in all the way. Was about 2 to 3mm gap
    Yeah mine did that too. With an old UN72.
    Wanted: broken Titec 2 bolt seatpost, any size

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