Once an engine makes abnormal noises during operation, it usually indicates that some components have mechanical abnormalities, insufficient lubrication or loose parts, etc. Timely identification of the source of abnormal noise and targeted investigation are important links to ensure the reliability of equipment and extend its service life. The causes of abnormal noises can be analyzed from multiple aspects such as mechanical structure, fuel system, intake and exhaust system, and lubrication system.

Common types of abnormal noises include knocking sounds, tapping sounds, clicking sounds, howling sounds, and vibrating sounds, etc. If abnormal noises occur at the initial stage of engine startup, they may be related to components such as the starter motor, timing belt, and valve clearance. If it occurs in a stable operating state, it may involve parts such as the cylinder block assembly, crankshaft, piston, and intake system.

Piston knocking on the cylinder is a common high-frequency knocking abnormal noise, which usually eases slightly after the engine warms up. The causes may include piston wear, cylinder bore wear, and lubricating oil failure, etc. Long-term use without changing the engine oil or using lubricating oil with mismatched viscosity will accelerate the dry friction of metal parts, causing an increase in the side clearance of the piston and resulting in knocking.

Wear of crankshaft bearings can also cause low-frequency dull abnormal noises. It is especially obvious when accelerating or decelerating. Such abnormal noises are often related to low oil pressure, lubricating oil contamination, and damage to the main shaft bushing. Timely detection of engine oil pressure and replacement of worn parts can effectively reduce risks.

The abnormal noise of the valve mechanism is manifested as a slight knocking sound with a consistent rhythm, which may be caused by excessive valve clearance, wear of the tappet, failure of the hydraulic tappet, etc. If there is a long-term lack of cleaning and maintenance, the carbon deposits in the valve chamber will increase, which will also affect the valve sealing and normal opening and closing, and generate abnormal noise.

If the abnormal noise is similar to a whistling sound, it is often seen that the belt is slipping or the pulley is loose. Checking the belt tension, the coaxiality of the gear train and the lubrication condition of the bearings is helpful for quickly locating the problem. The fan belt is prone to hardening in low-temperature environments, especially when starting up.

Abnormalities in the fuel system may also produce periodic knocking sounds. Problems such as incorrect fuel injection advance Angle, clogged fuel injectors, and poor fuel atomization can all lead to incomplete combustion or runaway detonation, causing obvious abnormal noises. The use of inferior fuel or fuel with a high mixed moisture content can also magnify such problems.

Air leakage in the exhaust system, cracks in the exhaust manifold, loose insulation plates, etc., may also cause sounds similar to "firecrackers" or metal vibrations. The problem can be identified by observing the color of the exhaust gas, the unpleasant smell, or conducting a leakage test on the exhaust system.

It should be noted that some abnormal noises may only occur within a specific speed range, such as frequency band noise caused by resonance or whistling when a turbocharger is operating under high load. For problems where the sound source is difficult to identify, it is recommended to use a stethoscope or infrared temperature measurement device, combined with methods such as cylinder breaking and static inspection, to gradually troubleshoot.