Preignition damage to top of piston from continental engine.

Cause: Jet fuel mixed into aviation gasoline lowered fuel octane

Swirl markings on top of piston are normal combustion pattern markings. They show how the hemispherical (dome shaped) cylinder head and the induction system swirls the mixture for better mixing and burning.

Erosion damage to side edge of piston is normal location for burning. Burning typically progresses behind the top ring land until a hole forms in the piston. When hole forms preignition stops but pressures blow engine breather. Typically the first notification the pilot receives is when the oil pressure drops to zero because oil has blown out of engine breather.

Scuffing marks are caused by piston overheating and expanding into the cylinder barrel.