Bottom Bracket Help Please

brett1980

I have just purchased a second hand xtr crankset M-952 and need to change my bottom bracket to a octalink from square. My barrell size is 68mm but am unsure of my overall spindle length. Do I just need the same as what is exixting or do different cranks require individual spindle lengths to make them line up with the rear cassette?

Splasher

Different cranks need different spindle lengths. Your chainset being XTR, you can only fit an XTR BB from the Shimano Octalink range because the others in the MTB range used longer splines.

That would seem to give you the choice of 112.5 (bizarrely) and 116mm http://www.chainreactioncycles.com/Mode ... delID=1205

brett1980

Many thanks Splasher, but why ate there different lengths of spindle. surely there can't be the need for frame clearence as the bottom bracket is usually wider than the rest of the bike?

supersonic

Different chainlines - some bikes specify a 47.5 or 50mm chainline, the latter often when the frame has an oversized seat tube (the front mech is placed farther to the right because of it)

brett1980

The bike is a Marin Alpine trial. I don't know where to get the literature on the chainline specs. With this is mind would it matter if i took a gamble with the spindle length?

Splasher

I would guess that 112.5 would be the right one on the basis that most (not LX) use a 113mm spindle to acheive a normal chain-line. Why not clean the BB shell and chainset splines, order from CRC, fit the drive side cup only, try the RH crank only and if it works great, if not, remove, clean and return for a longer one.

Otherwise take to your LBS and make it their problem.

brett1980

Many thanks again Splasher!!!!