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I have an old Trek 520 Touring frame I want to update into a commuter/cyclocross bike using various old parts.

Currently there is a 120+/-mm Shimano UN71/2 bottom bracket installed. I put on a set of traditional road cranks and the non-drive side crank clips the frame.

My question is - if I track down a new (for me....) bottom bracket with a 122.5 or a 127.5 spindle, will it be long enough to avoid the clipping or should I stick with the current bottom bracket and track down some "flared" cranks?

Thanks for the shared wisdom.
 

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matching parts...

The BB spindle length must be matched to the crank to produce the correct chainline. The spindle taper must also match the crank. All shimano cranks take a JIS taper and Campy requires an ISO taper. Once that's done, the frame should not interfere with the crank. You're got the incorrect notion that the frame requires some sort of special crank.

If you have a double chainring road crank that you want to use, the big ring should be 47-48mm from the center of the seat tube to the tip of a tooth on the big ring. Measure from the side of the tube and add 1/2 the ST diameter to get this dimension. If the big ring is too close, then the spindle length should be increased by twice the amount of the discrepancy. Here's a link to some typical shimano square taper BBs.

http://www.nashbar.com/profile.cfm?...rand=&sku=8104&storetype=&estoreid=&pagename=

http://www.parktool.com/repair/byregion.asp?catid=59&imageField2.x=22&imageField2.y=14

http://www.sheldonbrown.com/chainline.html
 
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