Listening to the sound of the diesel engine mean and knowing the fault
The operators who often run excavators are familiar with the sound of diesel engines. The old driver can judge the general working condition of the machine through the sound of the engine, and can also detect some small problems of the engine through the sound. The maintenance master must try the car before repairing the car. The experienced master can judge the fault by the sound.
Today we will talk about the abnormal sound of the engine that the excavator often encounters during use, and the corresponding cause of the fault behind the sound.
1. When the throttle is loose, the top of the cylinder emits a sound of “Dang”, “Dang” and “Dang”.
The specific performance is that when the diesel engine is lowered from high speed to low speed, the top of the cylinder has obvious "Dang", "Dang" and "Dand" impact sounds. This phenomenon is more common. The main reason is that the gap between the piston pin and the connecting rod bushing is too large, and the sudden drop of the rotating speed will produce a lateral dynamic imbalance, causing the piston pin to swing to the left and right, and the striking of the connecting rod bushing. At this time, the piston pin and the connecting rod bushing should be replaced in time to avoid unnecessary waste and loss.
2. When idling, there is a sound of “bar da” and “bar da” near the valve cover.
This kind of sound is mainly caused by the excessive valve clearance of the engine, resulting in the collision of the valve and the rocker arm. When the valve clearance is too large, the displacement between the rocker arm and the valve will be too large, and the impact will produce a metal knocking sound of "bar da" and "bar da". This situation generally occurs after the diesel engine has been working for a long time, indicating that the engine should adjust the valve clearance.
The method of adjusting the valve clearance of the engine:
(1) Open the valve chamber cover.
(2) Rotating the crankshaft to place the piston at the compression top dead center of the cylinder.
(3) Insert the thickness gauge into the gap between the rocker head and the valve, loosen the bolt of the rocker arm to one or two buckles, and adjust the screw with a screwdriver. When the gauge is smooth, the resistance is not met. It is appropriate when it is big.
(4) Make adjustments in the prescribed order.
(5) Continue to drive to the compression top dead center of the six cylinders and adjust other valve clearances in the specified order.
3. During normal operation, the upper part of the cylinder has a crisp sound of the piston striking the cylinder block, that is, "knocking the cylinder"
This is a common fault of diesel engines. The fundamental reason is that the fuel injection advance angle of the diesel engine is too small. In order to make the mixture form normally and burn efficiently, the diesel engine is designed with a certain fuel injection advance angle, so that the diesel fuel is injected into the cylinder and air in advance. If the fuel injection advance angle is too small, the fuel and air injected into the cylinder are not uniformly mixed, resulting in unstable combustion, and the piston is likely to be laterally cheap and collide with the pen contact in the ascending stage, thereby generating a knocking sound.
There are many ways to adjust the injection advance angle. Masters often use a simpler method:
(1) Connect the high and low pressure oil pipes, put the throttle lever in the maximum oil supply position, and supply oil with the oil pump to 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 remove the air in the timing tube. When some of the fuel flows out when the timing tube is shaken, so that the liquid level in the oil pipe is clearly visible, slowly rotate the crankshaft while observing the oil level in the timing tube. At the moment when the oil level rises, the crankshaft is immediately stopped, and a line is drawn on the outer surface of the crankshaft pulley against the gear chamber cover mark.
(4) Continue to rotate the crankshaft clockwise until the mark on the crank pulley is aligned with the mark on the gear chamber cover, and stop the cranking (the piston is at the top end of one cylinder compression).
(5) Measure the arc length between the piston top dead center and the pulley scribe line on the pulley, and calculate the fuel supply advance angle at this time.
(6) Calculate the difference between the measured fuel supply advance angle and the specified advance angle, loosen the fastening bolt of the fuel injection pump, turn the fuel injection pump camshaft clockwise, and finally tighten the bolt.
When the fuel injection advance angle is correct, the sound is eliminated and the diesel engine can work normally and exert its original working efficiency.
4. When the diesel engine is working at high load, there is a heavy, dull and mute knocking sound in the lower part of the collective.This sound is due to the excessive clearance between the crankshaft and the crankshaft bearing, causing friction between the crankshaft bearing and the main journal. If the sound can be heard, the spindle neck and the crankshaft bearing are excessively worn and the engine should be extinguished immediately. If you ignore it, it will be very likely that "holding the tile" and "burning the shaft" will occur when you wear it for a long time.
The maintenance method is generally to remove the engine crankshaft, check the clearance between the crankshaft, the spindle bearing, the main bearing bush and the wear condition, and repair or replace it if necessary.
5. The diesel engine suddenly changes its load, and there is a dull and mute knocking sound near the body.This situation is mainly due to the fact that the gap between the connecting rod journal and the connecting rod is too large, the connecting rod is partially beaten, and then the knocking sound is generated. In this case, the engine should be stopped immediately, then the connecting rods and connecting rods should be removed to check for wear and clearance.
6. During operation, the front cover of the diesel engine has a clear “beep” sound.This is generally the case because the meshing gears inside the front cover of the diesel engine are excessively worn, and the sound cannot be generated by the normal meshing state of the gears.
The repair method is to disassemble the front cover of the engine, check the gear engagement with fuel or paint, and then replace or adjust the gear.
7. During operation, there is a small hammer tapping the sound of the anvil along the upper and lower sides of the cylinder.The main reason for this situation is that the gap between the piston ring and the ring groove is too large, and the piston ring collides with the piston during the up and down movement. When you hear this sound, you should stop the engine work immediately, and find a repairman to replace the new piston ring.
8. During operation, a low knocking sound can be heard on the cylinder stroke.In this case, the gap between the piston and the cylinder is generally too large. When the piston is ascending or descending, the piston moves laterally inside the cylinder, causing severe friction on the cylinder wall, emitting low friction sound, and the diesel engine running at low speed or rotating speed. The mutation is more significant.When this kind of sound occurs, stop working as soon as possible, find a professional maintenance master to identify the engine cylinder liner and piston, and replace the piston or cylinder liner if necessary.