Scuffing (Piston)
A form of adhesive wear on piston skirts and cylinder walls caused by localized frictional heating and oil film breakdown.
Piston scuffing is a severe form of adhesive wear that occurs on the piston skirts and cylinder walls. It is caused by localized frictional heating and the breakdown of the lubricating oil film between the piston and cylinder bore. Without the oil barrier, the metal surfaces contact directly, leading to localized welding and tearing of the metal as the piston travels.
Scuffing is typically triggered by engine overheating, oil starvation, fuel dilution of the engine oil (which washes away the oil film), or tight piston-to-wall clearances. Once scuffing begins, it creates high spots on the piston skirt that generate more heat, accelerating the wear until the piston seizes in the cylinder bore, causing complete engine failure.
Symptoms of piston scuffing include a loud ticking or knocking noise from the engine (piston slap), loss of power, blue exhaust smoke, and metal flakes in the oil filter. Diagnostics involve inserting a borescope through the spark plug hole to inspect the cylinder walls for vertical scoring lines. Scored cylinders require boring the block to fit oversized pistons or rebuilding the engine.