Originally Posted by
mconlonx
Was there any issues with the BB that was installed at the factory? No? Then why "fix" something that ain't broke...?
Only upshot here is perhaps the opportunity to screw something up that wasn't wrong in the first place.
Unless you're moving from a cartridge BB to a crankset that uses an outboard bearing system like Shimano Hollowtech II, RaceFace X-type Crankset, FSA MegaeXo, and Truvativ Giga X Pipe - in which case its a different ballgame.
This is a direct quote from the RaceFace website regarding the installation of outboard bearings:
1) FRAME PREPARATION (CRITICAL):
a) BB shell threads must be chased after welding to ensure good alignment between opposing ends of BB shell.
b) BB shell must be face milled on both sides after paint to ensure flat, parallel bottom-out surfaces for BB cups to mate with.
c) Critical!!! BB shell width tolerance after face milling must be:
• 68mm shell = 67.25mm - 68.25mm*
• 73mm shell = 72.25mm - 73.25mm*
Note: BB shell widths outside this specification may result in unacceptable function and life of the BB assembly (too loose or too tight). Out of tolerance BB shells can be compensated for with use of optional preload elastomer and/or spacer(s) (see TROUBLE SHOOTING section.)