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Replacing lost bottom bracket to crankset

Old 08-15-21, 02:42 PM
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stormy_ll
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Replacing lost bottom bracket to crankset

Hello everyone,

I am currently doing up a bike and have appeared to have lost the bottom bracket. I have identified itís a British fit but have no idea about how to find the correct size for the crankset that I am trying to use it with (original to how I got it).

if anybody has any pointers on how to find a correctly sized BB I would be very grateful.

it appears to be unbranded, it says j5 21 made in France on the right side and A6 made in france on the left side.
Thereís a 48 big ring with 5 connection points and a smaller 38 ring. Happy to provide pictures if anybody needs.

Thank you!
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Old 08-15-21, 03:12 PM
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Somebody has suggested it is a strong light crank which seems to look pretty accurate based on google images but I cannot find an exact model or identification as to which BB will fit!
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Old 08-15-21, 07:50 PM
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Probably a Stronglight A6. You need a square taper bottom bracket.

See here for an orientation about square taper. I think you want an ISO taper (not a JIS). [ON EDIT: NOTE: CHECK THIS, possibly with an actual taper at a bikeshop or a coop - a lot of Stronglight cranks are listed as JIS (but older ones seem to be ISO. But check!\ And it will be a 118 or 120.5mm length. Keep in mind that if the crank arms were damaged, there's no fixing them: you need new crank arms.

See here for some older Stronglight dimensions

Last edited by WizardOfBoz; 08-17-21 at 08:37 PM.
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Old 08-17-21, 07:38 PM
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...you can fit a new spindle by trial and error, but you need to be in a place where there are a number of old spindles or sealed unit square taper BB inserts in differing lengths, to use as your trial fits. In the old days, all the smaller local shops had a box of takeoffs lying around to do this. I have a bike co-op nearby where I can access the things. Otherwise, you're kind of stuck ordering a 120mm spindle length BSA threaded sealed unit and hoping for the best. Once you fit it up dry, if the chain line is not to your liking, you can then measure how far in or out the chain wheels need to go, and order a better fitting one your second try.


Edit: I can't tell from your pictures, but that square taper socket needs to be clean and not boogered up from being ridden a little loose. So inspect it on both sides carefully, before you spend money on a new spindle.
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Old 09-01-21, 04:09 AM
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Stronglight is still in business and has a website. I'm new, so I can't post the URL - but if you Google "Stronglight Website" you should find it.

Have you considered contacting them to see if they can help ID the crank and confirm the required spindle length and interface type (JIS or ISO)?

Last edited by Hondo6; 09-01-21 at 09:34 AM. Reason: Correct typo.
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