Acceptable loss is ''zero''. Correct breakin is for work hardening the parts and marrying them to each other. If there's wear, there's grit. And when you have grit, you have wear......
On that groove, yes it's there and it's awful. I was told by a cam manufacturer years ago that flat cams have the groove and rollers don't. The only way to get a flat cam without the groove is to have it spray welded and reground (and hope the machinist does it right).
The bearing getting the raised channel is definatly a thing. And it's made worse by HV pumps, jacked up springs pressures, and people that feel the need to run 20W50.
On that groove, yes it's there and it's awful. I was told by a cam manufacturer years ago that flat cams have the groove and rollers don't. The only way to get a flat cam without the groove is to have it spray welded and reground (and hope the machinist does it right).
The bearing getting the raised channel is definatly a thing. And it's made worse by HV pumps, jacked up springs pressures, and people that feel the need to run 20W50.