It occurred to me after I sent the last note that perhaps detonation cased the apex seal grove to wallow out and the apex seal to fail. This is just a guess on my part.

On a piston engine, I have seen severe detonation shear the ring lands right off the pistons. This happened on a supercharged small block with stock pistons. The detonation was very severe, but brief (drag race.) The tops of the pistons did not have time to burn and melt like they would with more marginal, but long-term, detonation conditions. The force of the detonation did the damage directly rather than the high combustion temperatures.

Just a though.

Bill Dube <LED@Killacycle.com>
http://www.killacycle.com/Lights.htm