bottom bracket replacement
05-03-07, 10:49 AM
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bottom bracket replacement
Hi all. I have an old Shogun 12 speed that I'm rebuilding and I want to replace the old cup and cone style BB with a newer cartridge type, square taper BB. The old one has 68mm English threading and measures 127mm from the ends of the square tapers. My LBS has a 68 x 122 UN54 in stock. That is the longest one he has. Will it work? Or should I go ahead and order a 68 x 127?
I realize this may bring the cranks slightly closer to the frame, possibly resulting in chainring/frame contact. I'm just unsure because I have never has any experience with these old cup and cone style BB's before.
I realize this may bring the cranks slightly closer to the frame, possibly resulting in chainring/frame contact. I'm just unsure because I have never has any experience with these old cup and cone style BB's before.
Last edited by Butterthebean; 05-03-07 at 10:58 AM.
05-03-07, 11:02 AM
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All I can suggest is try it and see. Will the LBs let you install the 122 mm bb in your frame and fit the crank arms loosly to see if it will work? You would have to just thread it in by hand and slide the arms on easily so that nothing gets scratched or dirty but it should let you know.
I had to do exactly that on an old Trek MTB with a pecular bb configuration and the dealer let me try a couple of alternatives to see which one worked.
I had to do exactly that on an old Trek MTB with a pecular bb configuration and the dealer let me try a couple of alternatives to see which one worked.
05-03-07, 02:32 PM
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I know my tripple chainring bike configurations aremore pickey with spindle length than my doubles. I would just bring in the crank to the shop and slide it on dry and see how close you will be getting to the bottom bracket shell.
05-03-07, 05:45 PM
#6
Mechanic/Tourist
It's not just a matter of the cranks hitting the frame. If they go in too far you change the chainline, which could affect shifting and your ability to adjust the inner travel of the front derailleur. Any good mechanic should be able to figure out the changes from the old bb and Shimano specs without mounting the equipment at all.
05-03-07, 09:50 PM
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Originally Posted by cny-bikeman
It's not just a matter of the cranks hitting the frame. If they go in too far you change the chainline, which could affect shifting and your ability to adjust the inner travel of the front derailleur. Any good mechanic should be able to figure out the changes from the old bb and Shimano specs without mounting the equipment at all.
Good point...maybe I need a new LBS.
Thanks guys for all the tips.
