Top Ring End Gap is often a major player when it comes to piston problems. Most top land damage on race pistons appears to lift the land into the combustion chamber. The reason is that the top ring ends butt and lock the piston at TDC. Crank rotation pulls the piston down the cylinder while leaving at least part of the ring and top land at TDC. Actual running end gap will vary depending on the engine heat load. Piston alloy, fuel mixture, spark advance, compression, cooling system capacity, duty cycle, and Hp per c.i. all combine to determine an engine's heat load.
Most new generation pistons incorporate the top compression ring high on the piston. The high ring location cools the piston top more effectively, reduces detonation, smog, and increases Hp. If detonation or other excess heat situations develop, a top ring end gap set toward the tight side will quickly butt, with piston and cylinder damage to follow immediately. High location rings require extra end gap because they stop at a higher temperature portion of the cylinder at TDC and they have less shielding from the heat of combustion. At TDC the ring is usually above the cylinder water jacket. The current design KB Pistons do a better job of keeping the rings cool.
If a ring end gap is measured on the high side, you improve detonation tolerance in two ways. One, the engine will run longer under detonation before ring butt. Two, some leak down appears to benefit oil control by clearing the rings from oil loading. A small amount of chamber oil will cause detonation and significant Hp loss. The correct top ring end gap with KB Pistons can be 50% to 100% more than manufacturer's specs. Design changes have been made that reduce top land problems dramatically. Read more detail on this in the "New Piston Improvement" article.
