Shimano Octalink BB
03-06-21, 12:23 PM
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Shimano Octalink BB
Hi
Fitting used cranks from ebay, the replacements are 3 to 4mm further away from the chainline than the original (further out from the frame). The current BB is a Shimano Octalink 121mm. To fix the issue, I think I can use a 118mm BB, however, I'm not sure of the dimensions of an Octalink BB. Does the length of axle for the non-drive side from the BB body stay constant whether the length be 113, 118, 121 or 126mm? (ie the difference in axle length is reflected in the length of the drive side part of the axle). If not, to account for the 3 to 4mm difference, would I require a 113mm axle, to balance on both sides?
Looking at photos and common sense would assume the former case is true; but you know what the say about assumption.
TIA
Fitting used cranks from ebay, the replacements are 3 to 4mm further away from the chainline than the original (further out from the frame). The current BB is a Shimano Octalink 121mm. To fix the issue, I think I can use a 118mm BB, however, I'm not sure of the dimensions of an Octalink BB. Does the length of axle for the non-drive side from the BB body stay constant whether the length be 113, 118, 121 or 126mm? (ie the difference in axle length is reflected in the length of the drive side part of the axle). If not, to account for the 3 to 4mm difference, would I require a 113mm axle, to balance on both sides?
Looking at photos and common sense would assume the former case is true; but you know what the say about assumption.
TIA
03-06-21, 12:50 PM
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note the chainline diff. is only 1.5mm between 118 & 113.https://www.sheldonbrown.com/bbsize.html
03-06-21, 04:18 PM
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How wide is your bottom bracket shell?
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03-06-21, 07:53 PM
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Both “ends” of an bb axle are shortened when the sizing drops. To adjust “3-4”mm on the drive side I’d go narrower than a 118 (vs your 121). The only time you’d really want/need it dead on would be with a single speed or fixie...is that the situation you’ve got here? If so, typically the 109 length Octalink is used for fixed gear.
03-06-21, 09:28 PM
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Octalink interface comes in two forms, "v1" and "v2", and these are not interchangeable. See THIS post.
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