The difference between the two abnormal noises is still very large. The most obvious difference is that the engine noise is in the middle and lower part of the engine, while the valve noise is in the upper part of the engine.

There are two types of bearing bushes on the engine: crankshaft bushes and connecting rod bushes. The scientific name of the crankshaft bush is the crankshaft main bearing, commonly known as "big bush". Its sound is characterized by a heavy "boring" metal knocking sound in the crankcase. The sound is rhythmic and increases with the increase of engine speed and load. And enhance.

There is no obvious change in the noise when the single cylinder is cut off, and the noise is weakened when the adjacent two cylinders are cut off; the scientific name of the connecting rod bearing is the crankshaft connecting rod bearing, commonly known as "small tile", and its noise is characterized by slow and heavy in the crankcase. The rhythmic "Dangdang" sound, the sound is clearer when the engine is at medium speed, it does not change with the engine temperature, and the sound weakens or disappears after the single cylinder is cut off. When the bearing burns, it will make a "squeak" metal friction sound. Generally, abnormal noises in these two parts are caused by poor lubrication, which is a serious engine mechanical failure.

The abnormal valve noise occurs on the top of the engine. It will make a continuous and rhythmic "click" sound, which is most obvious and clear at idling speed, but not obvious at high speed. The sound of single-cylinder fire and oil cut-off basically does not change, and is not affected by temperature. The main reason for abnormal valve noise is that the valve clearance is too large. In addition, poor valve lubrication and abnormal wear of the valve rocker arm will also cause abnormal valve noise. Now many passenger car engines use hydraulic valve lifters, and abnormal valve noise generally does not occur.