What is Engine Piston Slap?
2 Answers
Engine piston slap is a malfunction phenomenon caused by premature ignition. In diesel vehicles, fuel is injected into the cylinder before the piston reaches the top dead center, leading to combustion while the piston continues to move upward, which produces a knocking sound—this is the piston slap phenomenon. In gasoline vehicles, a high-voltage spark is generated before the piston reaches the top dead center, igniting the air-fuel mixture and resulting in the same knocking sound. The main causes of piston slap include: 1. Improper assembly leading to excessive clearance between the piston and cylinder or severe cylinder wear causing excessive gap; 2. Incorrect piston installation direction or piston deformation, disrupting the normal clearance between the piston and cylinder, resulting in piston slap noise; 3. Poor lubrication conditions, low oil pressure, or low oil viscosity, leading to inadequate splash lubrication on the cylinder walls and failure to form a normal oil film between the piston and cylinder, causing direct contact and piston slap.
I've also experienced engine knocking before. To put it simply, it's when a sudden metal knocking sound appears inside the engine, sounding like 'click click click' or 'ding ding ding'. This is mainly caused by issues with piston movement inside the cylinder - either the gap between the piston and cylinder wall has become too large, causing the piston to rattle around; or there's too much carbon buildup in the engine or low-quality gasoline was used, leading to premature spontaneous combustion of the air-fuel mixture and creating intense shockwaves. This problem shouldn't be ignored. When I didn't fix it promptly last time, the piston rings got worn out, and I ended up needing a major engine overhaul that cost me nearly ten thousand yuan.
