What is piston slap?

Piston slap is a term used to describe the noise that occurs when a piston moves up and down within a cylinder bore with excessive clearance. This clearance between the piston and cylinder wall causes the piston to "slap" against the cylinder wall, resulting in a knocking or tapping sound.

Piston slap is most commonly heard when the engine is cold and decreases as the engine warms up. It can be caused by various factors, including excessive wear on the piston and cylinder walls, incorrect piston-to-cylinder clearance, or poor engine design.

While piston slap can be an annoyance to drivers, it is not usually a serious problem unless it becomes excessive and affects engine performance. In such cases, it may be necessary to repair or replace the piston and cylinder components to eliminate the noise and prevent further damage to the engine.