How to distinguish between piston slap and valve noise?

[DawsonMarie]

Piston slap is caused by wear between the cylinder wall and piston, resulting in increased clearance, particularly when the piston skirt wears out. The knocking sound becomes especially noticeable under cold engine conditions or heavy loads. Valve noise primarily occurs due to excessive clearance in the engine's valve train mechanism. Additional information: Piston slap originates from the cylinder-piston assembly, producing synchronous noise matching engine RPM. Valve noise comes from the cylinder head, presenting as scattered metallic sounds - sometimes at twice the engine speed (when both valves produce noise) and slightly offset from combustion pulses. The noise intensity increases with RPM. Note: Some engines use timing chains, whose rattling characteristics resemble valve noise (scattered metallic sounds), but chain noise may disappear at higher throttle openings or exhibit asynchronous behavior with RPM (e.g., guide wheel noise).