What are the causes of abnormal sound of automobile engine? How to deal with abnormal engine noise?

Possible reasons include dirty engine, poor lubrication, abnormal combustion, long-term parking of the car, obvious idling or low-speed operation of the engine, overheating of the engine, etc. Lubrication is an important condition for the normal operation of the engine. The lubrication system can realize lubrication, cooling, cleaning, sealing and rust prevention. When the clearance, temperature, load and speed are constant, the thickness of lubricating oil film is affected by the pressure of lubricating system and the quality of lubricating oil. High quality lubricating oil and suitable pressure can produce better lubricating oil film. The thicker the lubricating oil film, the smaller the mechanical impact and the less abnormal noise. If the lubricating oil film is too thin, resulting in increased wear, the abnormal sound will be obvious and clear.

First of all, you can add lubricating oil to the abnormal noise caused by long-term parking of the car. In fact, this is because almost all the lubricating oil has returned to the oil pan after the car has been parked for a long time. During cold start, the oil pump can't establish oil pressure immediately, and an oil film is formed between components, especially inside the cylinder head. When the valve is not lubricated during cold start, whether it is a hydraulic tappet or a mechanical rocker arm, there will be a certain valve clearance or the timing chain will fail due to insufficient oil pressure. The clicking sound is caused by normal operation. ?

Furthermore, abnormal noise caused by excessive temperature. Some abnormal noises are related to engine temperature, and some abnormal noises have nothing to do with engine temperature. When diagnosing mechanical abnormal sound, special attention should be paid to the working condition of the engine when it is warmed up. For example, when the piston knocks on the cylinder, the abnormal sound is very obvious when the engine is cold started. Once the temperature rises, the sound will weaken or disappear, so the diagnosis of cold ringing should be made when the engine is low temperature. Temperature matching with small thermal expansion coefficient has little effect on abnormal sound. ?

Finally, the abnormal sound caused by air leakage of the valve. You can remove the cylinder head, grind the valve, check the elasticity of the valve spring and readjust the valve clearance. The sound of valve leakage is outside the valve chamber. It is more obvious at high load and low speed. The sound increases with the increase of load. The main reason is that when the valve seat is hinged, due to improper operation or excessive wear of the inner hole of the valve guide, the valve seat is skewed or the valve clearance is small, which leads to valve ablation, resulting in lax valve closure and leaking sound.