Diagnosing faults by listening to the sound of excavator diesel engines (1)

It is inevitable that a diesel engine will malfunction during long-term work. The usual solutions are to check, ask, listen, and watch. The most effective and direct method is to judge and solve the problem through sound, and can use the sound to judge and solve the problem. Some prescient small faults are nipped in the bud, avoiding the occurrence of major faults. This is also a major advantage of using listening to troubleshoot problems instead of finding faults by looking, looking, and asking questions.

1. When the diesel engine suddenly drops from high speed to low speed, a “dang, dang, dang” impact sound can be clearly heard in the upper part of the cylinder. This is one of the common problems of diesel engines. The main reason is that the piston pin is in the connecting rod. The gap between the bushings is too large, causing a lateral dynamic imbalance caused by sudden changes in machine speed, causing the piston pin to swing left and right while rotating in the connecting rod bushing, causing the piston pin to hit the connecting rod bushing and cause the piston pin to hit the connecting rod bushing. The sound it makes. In order to avoid larger failures, unnecessary waste and economic losses, the piston pin and connecting rod bushing should be replaced in time to ensure that the diesel engine can work normally and effectively.

2. When the diesel engine is running at low speed (idle speed), a metal knocking sound of “bah, bah, bah” can be clearly heard next to the valve cover. This sound is caused by the collision between the valve and the rocker arm. The main reason is that The valve clearance is too large. Valve clearance is one of the main technical indicators of diesel engines. If the valve clearance is too large or too small, the diesel engine will not work properly. The valve clearance is too large, causing the displacement between the rocker arm and the valve to be too large, and the impact force generated by the contact is also large, so a metal knocking sound of “ba da, da da” is made. This sound is caused by the engine working for a long time. It often occurs, so the valve clearance should be readjusted every 300 hours or so of engine operation. The specific method is:
(1) Open the valve cover. (2) Rotate the crankshaft so that the piston is at the compression top dead center of the cylinder. (3) Insert a thickness gauge into the gap between the rocker arm pressure head and the valve, loosen the rocker arm’s locking bolt by one or two buckles, and use a screwdriver to adjust the screw. When the thickness gauge can move smoothly between the gaps and encounter no resistance, It is suitable when it is large. (4) Make adjustments in the specified order. (5) Continue turning to the compression top dead center of the six-cylinder, and adjust other valve clearances in the specified sequence. When the valve clearance is appropriate, the above sound will be eliminated.

3. When the engine is running, a crisp knocking sound of the piston hitting the cylinder can be clearly heard from the upper part of the cylinder, which is often called “cylinder knocking”. The root cause of this failure is the advance injection of the diesel engine. The angle is too small. As we all know, the fuel supply advance angle of a diesel engine is one of the main technical data of a diesel engine. Whether the fuel supply advance angle is correct or not will directly affect whether the diesel engine can work normally, and whether the engine can provide normal power, affecting the entire engine. The working condition of the machinery. In order to ensure that the formation of the mixture and the combustion process can proceed normally, the diesel engine must have a certain injection advance angle. If the injection advance angle is too small, the air injected into the cylinder will form combustible gas and burn, resulting in unstable combustion. In the upward stage, the lateral deflection occurs and the cylinder wall contacts and collides, and knocking on the cylinder produces a knocking sound. There are many ways to adjust the fuel supply advance angle. Now we mainly introduce one of the simpler methods. The specific steps are:
(1) Connect the high and low pressure oil pipes, place the throttle lever in the maximum fuel supply position, supply fuel with a hand oil pump, and remove the air in the fuel system.
(2) Remove the high-pressure oil pipe of the first cylinder and install the timing pipe.
(3) Rotate the crankshaft clockwise to eliminate the air in the timing tube. When shaking the timing tube, some fuel flows out and the liquid level in the oil tube is clearly visible. Then slowly rotate the crankshaft while observing the oil level in the timing tube. At the moment the oil level rises, immediately stop rotating the crankshaft and draw a quarter line on the outer surface of the crankshaft pulley facing the mark on the gear chamber cover.
(4) Continue to rotate the crankshaft clockwise until the mark on the crankshaft pulley is aligned with the mark on the gear chamber cover, then stop turning (the piston is at the compression top dead center of the first cylinder at this time).
(5) Measure the arc length of the piston on the pulley between the compression top dead center of the first cylinder and the pulley mark, and calculate the fuel supply advance angle of the diesel engine at this time.
(6) Calculate the difference between the measured fuel supply advance angle and the specified advance angle, loosen the fastening bolts of the fuel injection pump, turn the fuel injection pump camshaft clockwise, and finally tighten the bolts. When the injection advance angle is correct, this sound will be eliminated, and the diesel engine can work normally and exert its original working efficiency.

4. When the diesel engine is running, a heavy, dull knocking sound can be heard in the lower part of the diesel engine body. Especially when the diesel engine is working under high load, this sound becomes more obvious. This sound is caused by the crankshaft main bearing bush or It is caused by abnormal friction caused by the contact between the crankshaft main bearing and the main journal. The main reason is that the gap between the crankshaft main journal and the main bearing bush or crankshaft bearing is too large, causing inconsistency between the main journal and the crankshaft main shaft bearing or main bearing bush. This heavy, dull knocking sound is caused by abnormal friction caused by uniform wear. When you hear this sound, you should stop the diesel engine immediately, because if you continue to operate the diesel engine without inspection and maintenance after this sound occurs, it is likely to cause “tile holding” and “shaft burning”. In order to avoid such a serious accident, the diesel engine should be stopped and checked to see if the main bearing bolts are loose. If not, the crankshaft and main shaft bearing or main bearing should be removed immediately and have a professional measure it, calculate the gap value between them, and Compare with the specified data, and check the wear of the main shaft and tile shaft at the same time. Repair or replace if necessary.

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