I AGREE that the damage looks very similar to a failed bearing. I had a few bearing cages fail and most or all of the damage is found in the piston, sleeve and head. Seems like a fair amount of metal bits were distributed in the top of the engine. Finding the source will definitely help determine the cause. Can anybody provide some photos of the same areas of a new, unrun engine for comparison. What does the plug look like? It seems inconsistent that the timing could be off enough to cause that kind of damage and still have the engine run as well as you indicate. Please keep us informed of further discoveries.