In the cylinder-by-cylinder oil cut-off experiment, when the two-cylinder high-pressure fuel pipe is loosened, the sound is immediately weakened and the oscillation sound is significantly reduced. According to common sense, this sound located in the cylinder should be announced by the piston connecting rod assembly of the cylinder, like It is the sound of piston knocking. Remove the injector of this cylinder and inject a small amount of machine into the cylinder
Oil, slowly turn the diesel engine to make the oil adhere between the piston and the cylinder wall. Restart the diesel engine, the noise is significantly weakened immediately, but after a short period of operation, the noise increases again. For this reason, the cause of the fault is determined It should be the piston knocking.
Trouble shooting process:
1 Carefully inspect the components of the second cylinder again, and accidentally found a bright surface with a length of 70mm and a width of 25mm in the middle of the right side of the cylinder liner.There is also a bright surface on the right side of the piston skirt of this cylinder.
2 Remove the piston connecting rod assembly for inspection, the cylinder connecting rod bearing is not ablated, the cylinder liner has no trace of pulling the cylinder, the connecting rod is not tortuous, and the gap between the connecting rod and the piston pin fits the specification. It should be reasonable that no abnormal noise should occur. And oscillate.
3 Put the piston in the cylinder liner to test, the gap between the piston skirt and the cylinder wall conforms to the specification. So, why is the bright surface between the piston skirt and the cylinder wall caused?
4 Further inspection revealed that the thickness of the right side of the piston skirt of the cylinder is thicker than the thickness of the left side of the piston skirt. The difference in wall thickness between the two sides is 0.30 mm. Therefore, it can be determined that the piston knocking of the cylinder is due to the piston skirt Uneven thickness.
5 By replacing a piston that meets the quality specifications and then testing the machine, the fault is removed.
6 Measure the piston and cylinder liner, the piston and cylinder liner are not out of round deformation.
Conclusion:
The reason for this is that the thickness of the two sides of the skirt of the piston is different.After the piston is heated at a high temperature in the diesel engine, the right side of the skirt is more swelled than the left side.When the piston reciprocates up and down at high speed, the skirt The right side of the part will hit the cylinder wall, causing a knocking sound
And cause the diesel engine to oscillate. This problem is special, and it is difficult to find the cause without careful inspection.
After starting the diesel engine of the loader, the diesel engine cannot increase the speed with the increase of the throttle, and the maximum speed can only reach the medium speed. After about 10 minutes, the speed of the diesel engine can reach the normal speed again. This phenomenon does not occur when the hot engine starts.
Disease characteristics:
1 Once a problem occurs, various speeds exist. This problem is only present in lOmin after the cold start, and everything is normal after lOmin.
2 After the fault occurs, the throttle changes, and the fault changes accordingly. This fault cannot be changed according to the throttle.
Diesel engine cold car is difficult to increase the speed troubleshooting process:
1 First, the low-pressure oil circuit was purged of air, but the problem was not eliminated.
2 The new oil pump has been replaced, and the problem remains.
3 Through a second analysis and study, it is believed that the problem is likely to be related to air leakage in a certain part. For this reason, the injector gasket of a certain cylinder was replaced first, and it was found that the speed of the diesel engine increased significantly after starting. Injector gaskets of all cylinders were replaced in full
remove.
4 Conducted a comprehensive inspection of the fuel injection pump, high-pressure fuel pipe, fuel injector and cylinder pressure. It was found that they all met the relevant technical specifications. Finally, the fixing screws of the fuel injector were tightened, and the problem was still not removed.
