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Old 08-07-10, 08:27 PM   #1
mazdaspeed
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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?
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Old 08-07-10, 08:29 PM   #2
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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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Old 08-07-10, 08:52 PM   #3
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The crank is an old suntour one. Can't really call them up... lol
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Old 08-07-10, 09:35 PM   #4
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Sometimes you just guesstimate and swap out as needed.
http://www.sheldonbrown.com/chainline.html
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Old 08-07-10, 10:36 PM   #5
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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?
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Old 08-08-10, 06:10 AM   #6
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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.
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Old 08-09-10, 01:30 AM   #7
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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?
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Old 08-09-10, 06:00 PM   #8
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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?

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Old 08-09-10, 06:33 PM   #9
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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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