1 Depressing the clutch pedal is difficult to start

An excavator is equipped with a Mitsubishi S6D115 diesel engine. When the clutch pedal is stepped on, it will be difficult to start the diesel engine, and the hot engine will not start. At this time, if you crank the crankshaft by hand, you will feel that the crankshaft is very difficult to rotate. Only when the clutch pedal is released, the above phenomenon will not occur.

Check as follows: When the diesel engine is running, depress the clutch pedal to the end, and the clutch will make a continuous beep. When the diesel engine is idling, as long as the clutch pedal is stepped on, the engine will stop immediately, and it is preliminarily judged that the clutch is faulty.

Carry out on-vehicle inspection when the diesel engine is stationary. Step on the clutch pedal, the clutch driven disc can rotate freely, and other parts are not damaged or abnormal, but the release bearing cannot rotate.

In order to find the cause of the failure, it was decided to dismantle and inspect the clutch. However, when disassembling the transmission, it was accidentally found that the inner, outer ring and cage of the release bearing were severely ablated and locked. Retry the machine after replacing it with a new release bearing, the malfunction disappeared.

2 The diesel engine cannot start after overhaul

An excavator is equipped with an Isuzu 6B115 diesel engine. The diesel engine cannot be started after overhaul. Although the diesel engine rotates very fast when it is forced to start, there is still no sign of fire.

Check the fuel system and found no pipeline blockage and air leakage. The fuel injection pump pumps oil for each cylinder, and each fuel injection nozzle also sprays well. The cylinder pressure of the diesel engine is normal, and there is no problem with the fuel supply timing. Suspected that the valve clearance was not adjusted properly, and decided to readjust the valve clearance. When adjusting the valve clearance, in order to strive for accuracy, the high-pressure oil pipe was removed and the diesel engine was rotated. When the fuel injection pump high-pressure oil pipe joint of the first cylinder came in, it was found that the first cylinder of the diesel engine was not at the compression top dead center position, while the VI cylinder was in compression Top dead center position.

Rotating the diesel engine clockwise, it is found that the fuel injection pump work sequence is chaotic, the sequence is Ⅳ—Ⅱ—Ⅵ—Ⅲ—Ⅴ—I; while rotating the diesel engine counterclockwise, the working sequence is normal Ⅰ—Ⅴ—Ⅲ—Ⅵ—Ⅱ -IV. This situation is exactly the opposite of the working sequence of diesel engines and fuel injection pumps.

Disassemble the fuel injection pump and check it carefully, and found that the camshaft of the fuel injection pump was reversed. After the camshaft is installed upside down, the diesel engine will have a special malfunction of disordered work order and unable to start. Retry the machine after reinstalling the camshaft in the correct way and the fault is eliminated.

3 Idle speed jitter after diesel engine overhaul

A Mitsubishi S6D110 diesel engine equipped with a certain excavator jittered severely when idling after overhaul. The analysis believes that for a newly overhauled diesel engine, it is most likely that a certain part of the fit clearance is inappropriate during the assembly process. To this end, the diesel engine was disassembled for a comprehensive inspection.

Check the clearance between the main journal of the crankshaft and the main bearing, the connecting rod journal and the connecting rod bearing, the piston skirt and the cylinder wall, the piston and the piston ring, and no problems were found. In the process of disassembling the piston and connecting rod, it was found that the clearance between the small end bushing of the connecting rod of cylinder II and the piston pin was too small, only 0.01 mm.

After the diesel engine is overhauled, the connecting rod small end bushing and piston pin should be able to rotate flexibly. However, the matching gap between the connecting rod small end bushing and the piston pin of cylinder II is too small, which makes the connecting rod difficult to rotate, resulting in the crankshaft not rotating. Jitter due to balance, especially at idling speed, this phenomenon is more obvious. Trim the small-end bushing of the connecting rod of cylinder II with a scraper, and try to fit the piston pin while trimming until the gap between the two meets the requirements. Then the test engine was assembled and the idling jitter of the diesel engine was eliminated.

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