82/83mm BB compatability
09-05-14, 09:12 PM
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82/83mm BB compatability
Another simple (dumb) question, but BBs are not a specialty...
I'm trying to replace the BBs on my Burley tandem, the internet lists the BBs as 82x121mm (but I will double check any markings when I pull the units, especially as it seems like the front BB shell measures 73mm wide). I'm not finding any google listings for 82mm, but I am finding 83s. Since they are threaded into the shell, is this a big deal? Am I mistaken in thinking the 82x121mm refers to a 82mm shell width and not the diameter of the shell?
* Reprinted in the Tandem Bikes forum*
I'm trying to replace the BBs on my Burley tandem, the internet lists the BBs as 82x121mm (but I will double check any markings when I pull the units, especially as it seems like the front BB shell measures 73mm wide). I'm not finding any google listings for 82mm, but I am finding 83s. Since they are threaded into the shell, is this a big deal? Am I mistaken in thinking the 82x121mm refers to a 82mm shell width and not the diameter of the shell?
* Reprinted in the Tandem Bikes forum*
09-06-14, 01:20 AM
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In 82x121 the 82 is the width/length of the BB shell, measured across the bike, along the axle. Not the diameter. It's officiellt called width as opposed to length as the effect it has on the finished frame is width.
The 121 is the effective axle length. If it's an old square taper with threaded stumps sticking out, don't measure the stumps.
I wouldn't worry about being 1 mm off on BB shell width. At worst, if you're 1mm short you can use a spacer/washer to get the BB cup further out.
An 82 mm BB shell diameter would be huge. Maybe if you have an eccentric in there to adjust chain tension.
The 121 is the effective axle length. If it's an old square taper with threaded stumps sticking out, don't measure the stumps.
I wouldn't worry about being 1 mm off on BB shell width. At worst, if you're 1mm short you can use a spacer/washer to get the BB cup further out.
An 82 mm BB shell diameter would be huge. Maybe if you have an eccentric in there to adjust chain tension.
Last edited by dabac; 09-06-14 at 01:26 AM.
09-06-14, 12:07 PM
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Yeah, 82mm diameter sounded a little huge, but being blind the measurement process is, well, involved, and I just hadn't done it yet.
"A mm short" can be resolved with a spacer, but what about a mm long, as this is the situation I think I'm running into. If I read correctly (and chances are I didn't), the English thread is 29 TPI (aprox 1.14 threads/mm), so I'm guessing about half a thread too long per side isn't a concern???
"A mm short" can be resolved with a spacer, but what about a mm long, as this is the situation I think I'm running into. If I read correctly (and chances are I didn't), the English thread is 29 TPI (aprox 1.14 threads/mm), so I'm guessing about half a thread too long per side isn't a concern???
