What Causes Engine Piston Slap Noise?

[StDeclan]

Engine piston slap noise causes: 1. Bent or twisted engine connecting rod deformation; 2. Excessive carbon buildup in the engine leading to increased compression ratio and detonation; 3. Poor engine lubrication conditions causing abnormal friction between pistons and cylinder walls; 4. Incorrect gasoline grade usage resulting in excessive speed that leads to high cylinder pressure, causing piston skirt to impact cylinder walls and produce knocking sounds. Engine piston slap noise refers to abnormal sounds produced by the piston striking the cylinder walls. The determining factor for piston slap lies in the clearance between the piston and cylinder wall. When piston clearance is too large, slapping is likely to occur. The noticeable manifestation is louder knocking sounds when the car engine is cold (due to larger piston clearance), but as engine temperature rises, piston clearance decreases accordingly, and the knocking sound diminishes.