The abnormal sound is related to the engine's speed, temperature, load, lubrication condition and so on.

(1) speed

In general, the higher the speed, the stronger the mechanical noise. But the high speed of various sound mixed together, some abnormal sound auscultation but not easy to discern. Therefore, the diagnostic speed is not necessarily high speed, to specific response specific treatment. Such as auscultation valve ring or piston knocking, it can be heard very clearly at idle speed or low speed. When main bearing ring, connecting rod bearing ring and piston pin sound more serious, it can also be heard at idle speed and low speed. In summary, the diagnostic response is carried out at the most obvious speed of the sound and is carried out at a low speed as far as possible to reduce unnecessary noise and loss.

(2) temperature

Some of the abnormal reactions are related to the temperature of the engine, and some of the abnormal reactions have nothing to do with or have little relation to the temperature of the engine. In the diagnosis of mechanical noise, special attention should be paid to the heat condition of the engine for the pair with large coefficient of thermal expansion. The most typical example is the piston knocking. When the engine is cold starting, the noise is very obvious, but once the temperature is hot, the sound will disappear or weaken. Therefore, the abnormal response of this type of pair was diagnosed at low temperature of the engine. The abnormal noise produced by the auxiliary pair with small thermal expansion coefficient, such as crankshaft main bearing ring and connecting rod bearing ring, has little effect on the temperature change of the engine, so there is no special requirement for engine temperature when diagnosing.

The temperature of the engine is also one of the factors affecting the abnormal combustion. When a diesel engine is undercooled, the sound of a fire is often produced (rough work).

(3) load

Generally speaking, the influence of the load on the abnormal sound of the crank and connecting rod mechanism is great, but it has no influence or little influence on the abnormal sound of the gas distribution mechanism. Such as Baotou Benz parts of crankshaft main bearing ring, Baotou Benz accessories, Baotou Benz connecting rod bearing ring parts piston cylinder knocking, cylinder leak sound, ignition of the gasoline engine knocking sound, with the load increases, decreases with the decrease of load; diesel engine ignition knock ring as the load increases; valve ring, camshaft bearing ring and gear ring, abnormal sound does not change when load changes.

(4) lubrication conditions

No matter what mechanical noise is, when the lubrication condition is not good, the abnormal sound is generally serious.