When a diesel engine suddenly drops from high to low speed, a distinct "clink, clink, clink" impact sound can be heard at the top of the cylinder.

This is one of the common issues with diesel engines, primarily caused by excessive gaps between the engine cylinder liners and the crankshaft sleeve, leading to a lateral dynamic imbalance due to sudden changes in engine speed. This results in the cylinder liners rotating and swaying left and right inside the crankshaft sleeves, causing collisions that produce a loud noise. To prevent more severe issues and unnecessary expenses and property damage, it is imperative to immediately replace the cylinder liners and crankshaft sleeves to ensure the diesel engine operates normally and rationally.

2. At low speeds (idle), a distinct "clack, clack" metallic tapping sound can be heard near the valve cover.

These noises are caused by the collision between the valves and the rocker arms, primarily due to excessive valve clearance. Valve clearance is one of the critical technical indicators of diesel engines. Either too large or too small valve clearance prevents the diesel engine from running normally. Excessive valve clearance leads to excessive displacement between the rocker arms and valves, resulting in a greater impact force upon contact, hence the "clack, clack" metallic impact sound. This sound is commonly heard after the engine has been running for a long time. Therefore, the valve clearance should be re-adjusted approximately every 300 hours of engine operation.

When the engine is running, a clear, crisp knocking sound can be heard at the top of the cylinder, which is commonly referred to as "knocking the cylinder."

The root cause of such issues is the excessively small injection timing angle in diesel engines. As is widely known, the fuel injection timing angle is one of the critical technical data points for diesel engines. The accuracy of the fuel injection timing directly affects whether the diesel engine can operate normally and whether it can provide regular power output, thereby influencing the overall performance of the machine. To ensure the normal formation and combustion of the air-fuel mixture, diesel engines must have a certain injection timing angle. An insufficient injection timing angle leads to the formation of combustible gases in the cylinder, causing unstable combustion. This results in side displacement and contact with the cylinder wall during the upward stroke of the piston, leading to collisions and knocking sounds in the engine block.

4. When the diesel engine is running, a heavy, muffled knocking sound can be heard at the bottom of the diesel engine body, especially when the engine operates under heavy load for an extended period of time, during which the noise becomes more pronounced.

These noises are caused by abnormal friction resulting from the contact between the engine crankshaft main bearing or the engine crankshaft main bearing and the main journal, with the key reason being an excessive gap between the main journal and the bearing or shaft sleeve, leading to uneven wear between the main journal and the engine crankshaft main bearing or sleeve, which causes these heavy, dull impacts. Upon hearing such noises, the operation of the diesel engine generator set should be immediately stopped, as continuing to run the set without conducting an inspection may likely result in "bearing seizure" or "shaft burnout." To prevent such severe accidents, work should be halted immediately to inspect whether the main bearing bolt is loose; if not, the engine crankshaft and main bearing or sleeve should be removed promptly.