Ring butting (below) happens more often than most people realize. It can cause rapid ring wear and in severe cases it can destroy the whole engine. The basic cause is that the top ring gets extra hot and the ring end gap closes completely. If the ring temperature stays the same, or goes down, the only symptom may be shiny ring ends. If ring temperatures continue to increase, the ring increases pressure on the cylinder wall to the point of high wear, scuffing, or even sticking and breaking the top land of the piston off. It is not good to have loose pieces of anything in the cylinder. The rim of the piston is usually the hottest piston area. If it exceeds 600°f it can become its own ignition center, causing runaway detonation.
The moral of the story: Make sure your engine does not run lean at full power, don't skimp on ring end gap, choose fuel, compression ratio, camshaft, and timing that keeps you out of the detonation zone.
By John Erb