I’ve not seen or heard of the two cage halves separating on XT660 motors before. However, to me it looks very much like it has been caused by the motor having run with a loose crank nut for a while (which is a fairly well documented XT660 problem). What’s likely to have happened is that the loose nut has caused a small amount of additional end-float in the crankshaft which has in turn put a lateral strain on the cage(s) and the outer one has given out and separated. The result of this has probably caused the balls in the race to make contact with each other, accelerate wear and led to the bearing failing.

Cage separation like yours is a very common problem on the main shaft bearing of KTM’s pre 2003 LC4 engines. Have a read of this and I think you’ll see the symptoms/results are pretty similar to yours.

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