Originally Posted by
jimmuller
Hmm, how's to know? OTOH, one time when I rebuilt a BB in our tandem I found two of the bearings looked like the moons of mars, highly disfigured and, shall we say, not quite complete spheres. Surface hardness may or may not have been a factor. Fortunately the races were okay.
That might suggest that the original bearings weren't of the best quality or that the lubricant layer had broken down in some way. They're subjected to quite high loadings in use.
If the bearing isn't as spherical as it should be or the grease layer fails, then they will quickly mash themselves up and turn very ugly. They don't tend to overheat like a car wheel bearing might do, but they still seem to make quite a mess of themselves.