1. Abnormal noise is closely related to diesel engine speed
Most common abnormal noises of diesel engines depend on the speed of the diesel engine. When the speed of the diesel engine changes, the speed of each moving part will also change accordingly. Especially when the speed is accelerated or decelerated suddenly, the moving parts will produce a certain acceleration or deceleration. Due to the inertia, on the one hand, it may cause new abnormal noises, and on the other hand, it will make the originally inconspicuous abnormal noises become clear. Therefore, the existence of most common abnormal noise faults of diesel engines depends to a large extent on the speed of the diesel engine.
When analyzing and judging the abnormal noise faults of diesel engines, it is advisable to do more various speed tests to accurately find the cause of the abnormal noise faults.
(1) When the diesel engine suddenly increases the throttle and the speed suddenly increases, there will be more obvious and clear abnormal noises, such as the sound of loose main bearings and connecting rod bearings, and the abnormal noise caused by piston ring friction.
(2) When the speed of the diesel engine is stable, the abnormal noise is disordered. When it is decelerated suddenly, there will be more obvious abnormal noises, such as the sound of loose piston pin bushings and excessive camshaft axial clearance. (3) When the diesel engine is idling or running at low speed, there are more obvious abnormal noises, such as the noise caused by the piston pin or connecting rod bearing being too tight, the abnormal noises caused by the piston pin, valve and valve tappet, etc.
(4) Abnormal noises when the diesel engine is running at medium speed, such as the noise caused by the loose valve seat ring, the abnormal noise caused by the wear of the camshaft outer profile, etc.
2. Abnormal noise is closely related to diesel engine load.
The stress conditions of various moving parts of diesel engines change with the load, and abnormal noise will also change accordingly. Some abnormal noises are alleviated as the load decreases; some abnormal noises are aggravated as the load decreases; and some abnormal noises are generated as the load changes. The abnormal noise caused by the load size has a clear relationship with the cylinder position of the diesel engine. When analyzing and judging the abnormal noise fault of the diesel engine, for a single-cylinder diesel engine, the method of suddenly increasing the load and reducing the speed, or suddenly reducing the load and increasing the speed can be adopted to judge the relationship between the abnormal noise and the load; for a multi-cylinder diesel engine, the method of cutting off the fire of each cylinder or two adjacent cylinders to relieve the load of one or two cylinders can be adopted to conduct experimental judgment.
(1) When the load of a single-cylinder diesel engine increases, the abnormal noise that increases generally includes piston knocking and connecting rod bearing noise; the abnormal noise that appears as the load decreases generally includes valve seat ring noise and the sound produced by individual parts of the valve train.
(2) For multi-cylinder diesel engines, if one cylinder misfires and the abnormal noise is reduced or disappears, it is generally caused by piston knocking, piston ring leakage or loose connecting rod bearing. If one cylinder misfires and the abnormal noise becomes more severe, or there is a noise instead of being there, it is generally caused by a loose piston pin sleeve, connecting rod bearing cover or flywheel fixing bolts. If two adjacent cylinders misfire and the abnormal noise is reduced or disappears, it is caused by a loose main bearing.
3. The abnormal noise is sensitive to the temperature of the diesel engine.
(1) The noise is heard at low temperatures, but it becomes less or even disappears when the temperature rises. The reasons for the noise are: the gap between the piston and the cylinder wall is too large; the piston is not properly lubricated due to the depth and width of the main bearing oil groove; the engine oil pressure is low and the lubrication is poor.
(2) The noise is heard when the temperature rises, but it becomes less or disappears when the temperature drops. The reasons for the noise are: premature ignition caused by overheating; the long and short axes of the piston skirt ellipse are in opposite directions; the piston ellipse is small, the gap between the piston and the cylinder wall is too small; the piston is deformed; the gaps between the piston rings are too small.
