Diagnose according to the analyzed causes and fault phenomena.
(1) If the engine starts with less exhaust and is difficult to start, the reason is insufficient fuel supply in the fuel system, diagnosis and troubleshooting shall be carried out according to the faults described in the fuel system.
(2) If the engine starts smoothly, but the exhaust pipe emits black smoke, and the engine speed is not easy to improve. The main reason is that there is too little air entering the cylinder. Check the air filter of the intake part (check the supercharger for the engine with turbocharger) and eliminate it.
(3) If the engine overheats, most of them are caused by too late injection time, which is the fault cause of engine weakness and should be adjusted. The adjustment method is shown in the description of engine failure to start.
(4) If the exhaust pipe of the engine emits blue and white smoke, it indicates that the weakness of the engine is caused by cylinder blow by, which shall be handled.
(5) Check for air leaks
Pry the engine flywheel to compress the piston of the inspected cylinder to the top dead center, remove the fuel injector, shift to low gear and pull off the hand brake, and then use the hose to fill the combustion chamber with compressed air from the fuel injection nozzle hole. At this time, another person listens to the sound of air leakage at the inlet pipe orifice or exhaust pipe orifice, oil filler, cylinder pad or radiator water inlet. If air leakage is heard somewhere, it indicates that the cylinder is poorly sealed. For example, the sound of air leakage at the outlet of the exhaust pipe or intake pipe indicates that the air is not tightly closed, or the sound of air leakage at the water inlet of the radiator indicates that the cylinder gasket is damaged. It shall be eliminated after identification.
(6) Check engine resistance
Pry the engine flywheel with a crowbar. If it feels more laborious than other diesel engines of the same type or in normal use, it indicates that the resistance of the diesel engine is too large. If the diesel engine has just been repaired, it is mostly caused by too tight assembly, so it should be run in or reassembled.
(7) Check valve timing
If the above inspection is normal, the reason for the weakness of the diesel engine may be in the valve timing phase. Then check the valve clearance of the valve mechanism and the crankshaft angle when the inlet and exhaust valves are opened or closed, and then compare it with the valve timing diagram to find out.
Valve timing inspection method: valve clearance adjustment shall comply with the values specified in the technical documents. Open the observation window cover of the engine flywheel housing, pry the flywheel with a crowbar to rotate, compress the piston of the first cylinder to the top dead center, make a 3-fertilizer dial and pointer, fix the dial on the belt pulley, fix the pointer on the front cover plate, and make the pointer point to the “J” of the dial.
Remove the valve cover, place the dial indicator and bracket on the cylinder head, start to pry the flywheel to rotate, and rotate the push rod of the valve mechanism by hand. When the push rod does not rotate, it indicates that the valve is about to open. At this time, the pointer on the dial indicates the valve opening angle; Make the contact rod of the dial indicator against the valve rocker arm (push rod end), adjust the dial indicator to zero, and then continue to rotate the crankshaft. When the pointer of the dial indicator returns to the zero position, turn the push rod by hand, from the immovable to the rotation boundary, the valve is closed. At this time, the indication degree of the pointer on the dial is the valve closing angle.
The included angle turned by the crankshaft from valve opening to closing is the continuous angle of valve opening. Compare the inspection results with the valve distribution phase diagram specified in the technical documents of the machine. If the out of tolerance is large, find out the causes of the out of tolerance, such as serious wear of the transmission gear, correctness of the installation position of the transmission gear, damage of the camshaft keyway and key, and whether the wear of the cam working surface, and eliminate them after finding out.
Generally, only the first cylinder of diesel engine can be checked, and the valve timing of other cylinders is guaranteed by camshaft.
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