Originally Posted by jzeiler
That is not spalling Curtis, those are CRATERS!! No wonder it felt a bit rough.
Actually, this is a pretty typical appearance of failed bearings I have looked at. If anything is unusual, the pitting/cratering is more localized to select areas of the races rather than spread around the circumference of the races.
Having looked at enough of these in various stages of bearing degradation, and asking the riders for a description of events leading up to the problem, I am getting a pretty good sense of how the bearings go.
On bearings where the rider stopped riding as soon a roughness was noted there is limited pitting of the races. In some, the balls have very minor pitting and the retainer is intact. This is an example of a drive where the rider stopped riding relatively soon after noting the roughness.
When the rider has continued to ride, either not having noticed the roughness or simply trying to get further down the road, the pitting of balls and races becomes more severe and more widely distributed around the races; in those cases the retainer has failed and shredded the oil seal.
Based on my observations I would offer the following opinion:
Early detection of impending bearing failure is a crap-shoot. When the bearing starts to go, it goes relatively quickly. If you check for metal chips/flakes on the drain magnet frequently, you might catch it. But I suspect it is just a few hundred miles, if not, just a few thousand between when the chips/flakes start being produced and outright bearing failure.
Play at the rear wheel is probably of no value it detecting impending bearing failure. Even the bearings with broken retainers have very little axial run-out; by the time you can detect play at the rear wheel secondary to crownwheel bearing failure, your seal is shredded and oil is all over the rear wheel. In short, oil leaking is probably going to be an earlier indicator of bearing failure than is detectable play at the rear wheel.
Detectable play at the rear wheel IS probably an indication of bad pivot bearings or other swing arm problem.