What are the causes of piston knocking noise?
2 Answers
The causes of piston knocking noise are as follows: 1. It may be due to excessive piston clearance or piston deformation. Since the piston clearance is larger in cold conditions, the knocking noise is naturally more severe. When the engine temperature rises, the piston expands, reducing the clearance, and thus the knocking noise diminishes. 2. It could also be caused by severe carbon buildup in the combustion chamber. Excessive carbon deposits in the combustion chamber increase the compression ratio of the diesel engine, leading to excessively high gas pressure and temperature. When atomized diesel fuel is injected into the cylinder and encounters this high-temperature, high-pressure gas, it ignites and burns, causing what is known as detonation. During detonation, the flame spreads outward at an extremely high rate, even before the gas has time to expand, causing a sharp rise in temperature and pressure, forming pressure waves that propagate forward at the speed of sound. When these pressure waves strike the cylinder wall, they produce a sharp knocking noise.
The sound of piston slap in the car is like metal knocking, and I've encountered it several times, most noticeable during cold starts. The main reason is the increased clearance between the piston and cylinder, possibly due to worn piston rings or insufficient expansion caused by engine overheating. If there's insufficient oil or poor lubrication, increased friction can cause the piston to swing and hit the cylinder wall. Improper assembly or prolonged use leading to part aging can also cause problems. I recommend getting it checked immediately, don't wait until the sound gets worse. Take it to a repair shop to measure cylinder pressure and clearance size with a diagnostic tool, and replace piston rings or adjust assembly if necessary. For regular maintenance, make sure to change the oil on time with good quality oil, keep the lubrication system functioning properly, and avoid prolonged high-speed driving to prevent overheating and increased wear. Ignoring this issue can damage the engine, leading to high repair costs and potential hazards.
