Read any legible specs off old BB, and pick a BB shell width/spindle length that is closest to match. Otherwise you need to measure these two dimensions.

I'm guessing you need a 68x110-115.

You may also need specific BB tool(s) that may cost as much/more than the BB itself, in which case it is simpler and perhaps cheaper to have the LBS do the job for you.

http://www.chainreactioncycles.com/u...t/rp-prod71369