So, this rod is in a motorcycle, but I posted it here as it is more of a general engine oil question, not specifically motorcycle related. I just had a new con rod (roller bearing type) pressed in my crank, the old con rod bearing failed in a relatively short period of use. I suspect detonation was the cause, but want to make sure that my alternative oil weight choice was not at fault- before I choose a new oil for the repaired engine. The bike is a KTM 350 4-stroke, and it specs a 10-50 and 10-60 oil. It specifies Motorex oil, after searching here, Motorex oils seem to be on the light side of the viscosity range, so I figured Redline 10-40 (with a little 20-50 mixed in in the summer) should work well as Redline oil tends to be on the thicker side. The engine has a high stock compression of 13.5 to 1, which must be hard on the crank. I realize that the failure is probably not oil related, but I don't want to go through this again. I got the old con rod back from the machinist, and it was hammered, from TDC to about 90 degrees around. I said that I suspected detonation, but I have only heard knocking a handful of times, though I realize that I may not always be able to hear it over the engine noise. Could the lighter viscosity been at fault?