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Thun Thompson BB

Old 04-21-15, 04:40 PM
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Kranken
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Thun Thompson BB

Hello .. so i've got this late 70' bike which has a thun thompson BB .. is there a way to convert it into a square taper one ??
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Old 04-21-15, 06:17 PM
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Possibly might be able to use a 3-piece adapter such as might be used on a Schwinn Ashtabula BB shell to allow a square-taper BB and crank. Depends on the dimensions/diameter of the shells. I've never done it but somebody in the mechanics forum might know
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Old 04-21-15, 07:42 PM
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Home / Bicycle Parts City Bike / Bottom Bracket / Bottom Bracket Complete / Thun Bottom Bracket Cotterless 127/40mm Thompson Press-Fit
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Old 04-21-15, 08:11 PM
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Better yet^ and seems to be made for the job!
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Old 04-22-15, 09:02 AM
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the fact is that i have a similar BB shell to this picture , so i don't know if the one JohnDThompson suggested will work (not my BB shell by the way ) .
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Old 04-22-15, 11:42 AM
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The ID of your shell (not something that looks like it) is what you need to know. AFAIK Thun Thompson shells are 40mm, and Schwinn (probably most other cruisers and BMX shells) are 2.02" so about 51mm. If your shell ID measures something between those (guessing 46mm if it's exactly like the pic shown and the shell wall is about 1mm thick) then you might be out of luck. If it's closer to 51mm you MIGHT get a machinist to turn down the adapter "cups" of a Schwinn-type conversion kit but that's a big "MAYBE" and would cost something additional to the $20 or so those kits usually run.
Good Luck...and try the Mechanics forum (but measure the shell first).

Last edited by unworthy1; 04-22-15 at 11:45 AM.
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