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  1. #1
    Senior Member mazdaspeed's Avatar
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    Process for determining bb spindle length?

    I want to replace the ofmega bottom bracket on my Bianchi with a shimano un54 and I am not sure what length is needed. The ofmega spindle is 121mm i think (double crank) but it has a longer and narrower taper than the jis shimano. I want to use a normal double crank. What do I need to measure or look up?

  2. #2
    Senior Member Retro Grouch's Avatar
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    The biggest variable is the crank. As a general rule crank vendors can recommend a BB spindle length.

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    Senior Member mazdaspeed's Avatar
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    The crank is an old suntour one. Can't really call them up... lol

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    Senior Member Torchy McFlux's Avatar
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    Sometimes you just guesstimate and swap out as needed.
    http://www.sheldonbrown.com/chainline.html

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    Senior Member mazdaspeed's Avatar
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    Could I just measure the spindle from a jis bb that used a similar crank and was on a frame with a bb housing that is the same width or close to it?

  6. #6
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by mazdaspeed View Post
    Could I just measure the spindle from a jis bb that used a similar crank and was on a frame with a bb housing that is the same width or close to it?
    Different square taper cranks have differrent offsets and, consequently require different BB spindle lengths. What I've done in the past is to test fit the crank on any BB that I happen to have on hand. Then I can make a judgement about whether I need a slightly longer or shorter BB spindle.

  7. #7
    Senior Member mazdaspeed's Avatar
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    Problem has been solved, I actually managed to find an italian threaded dura ace BB with a 113mm spindle, which is the exact requirement for the dura ace crankset I found... haha

    Now what to do about the extra 115mm UN54 I got for cheap?

  8. #8
    Senior Member Chombi's Avatar
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    Quote Originally Posted by mazdaspeed View Post
    Problem has been solved, I actually managed to find an italian threaded dura ace BB with a 113mm spindle, which is the exact requirement for the dura ace crankset I found... haha

    Now what to do about the extra 115mm UN54 I got for cheap?
    Yup The DA7400 crank on my classic 1985 bike was a 113mm spindle legnth, I guess 113mm was a standeard for DA double cranks?

    Chombi

  9. #9
    coprolite fietsbob's Avatar
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    Italian threaded frames are 70mm wide, loose ball BBs for Italian stuff had the inner races on the axle that 2mm wider..

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