1
The fit clearance is too large
The fit clearance is an important indicator of automobile assembly quality. When the lubrication, temperature, load, and speed are constant, abnormal noise will increase with the fit clearance. It becomes more and more obvious with the increase of the engine. Due to natural wear and tear, the clearance of some moving parts of the engine increases beyond the range, resulting in abnormal noise, such as the knocking sound of the piston and the cylinder wall, the impact sound of the connecting rod bearing and the journal, etc.
2
Poor lubrication
Lubrication is an important condition for the normal operation of the engine. Lubrication, cooling, cleaning, sealing and rust prevention can be achieved through the lubrication system. When the clearance is matched, When the temperature, load, and speed are constant, the thickness of the lubricating oil film is affected by the pressure of the lubrication system and the quality of the lubricating oil. Good quality lubricating oil and appropriate pressure can produce a better lubricating oil film. The thicker the lubricating oil film, the smaller the mechanical impact. , less prone to abnormal noise. If the lubricating oil film is too thin, resulting in increased wear, abnormal noise will occur, which will be obvious and clear.
3
Loose fasteners
Vibrations are generated during engine operation, causing some parts to become loose and causing impact sounds. If the flywheel fixing bolts are loose, the connecting rod bolts are loose, etc., causing abnormal noise.
4
Individual parts are deformed and damaged
Abnormal noise is caused by deformation or damage of a certain part. For example, the bending of the connecting rod causes cylinder knocking, and the abnormal noise caused by the breakage of the valve spring and the breakage of the crankshaft.
5
Abnormal combustion
The ignition time of the gasoline engine is too early or too hot, resulting in deflagration, and the injection time of the diesel engine is too early, resulting in premature and rough metallurgy. The sound of knocking on the cylinder.
6
Improper assembly adjustment or repair
Improper assembly adjustment or repair results in misalignment of the fitting clearance of the machine parts. Abnormal noise may occur if the piston pin is assembled too tightly or the valve clearance is improperly adjusted.
7
Speed
Generally, the higher the speed, the stronger the mechanical abnormal sound. However, at high speeds, various sounds are mixed together, and some abnormal sounds are mixed together. The noise is difficult to distinguish, so the diagnosis of the speed depends on the abnormal noise situation. For example, when auscultating the valve noise and piston knocking noise, the abnormal noise is very obvious at idle or low speed. When the main bearing noise, connecting rod bearing noise and piston pin noise In severe cases, it can also be heard at idle and low speeds. In short, the diagnosis of abnormal noise should be carried out at the rotation speed with the most obvious noise, and should be carried out at low speed as much as possible to reduce unnecessary noise and loss.
8
Temperature
Some abnormal noises are related to the engine temperature, while some abnormal noises have nothing or little to do with the engine temperature. In the diagnosis of mechanical abnormal noises For fittings with a large thermal expansion coefficient, special attention should be paid to the working conditions of the engine when it is hot, such as the piston knocking on the cylinder. When the engine is cold started, the abnormal sound is very obvious. Once the temperature rises, the sound will weaken or disappear, so diagnose the cold cylinder knocking. The response is performed at low engine temperatures, and temperature has little effect on abnormal noises produced between mating pairs with small thermal expansion coefficients. Abnormal noises such as crankshaft main bearing noise, connecting rod bearing noise, and valve noise have no special requirements for diagnosing temperature.Temperature is also one of the main factors affecting combustion noise. When a gasoline engine overheats, it often produces ignition knocking sounds.