Originally Posted by
Burton
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.
Uh-huh.
99% of anyone replacing BB, swapping from cartridge to external, will not have any issues at all, without re-/facing the BB shell. Of those who do, some will screw it up somehow and be worse off for having attempted it, or have a shop do it.
If OP is concerned, remove cartridge BB, think about re-/facing if there's still paint showing on the outside face of the BB shell. Shiny metal? Wouldn't worry about it, and I'd assume that it was faced at the factory or by a shop.