1. Damage to cylinder liners:
The Cummins NT855 diesel engine uses a wet cylinder liner, which is in direct contact with the cooling water of the diesel engine for heat dissipation. The cooling water washes the outer surface of the cylinder liner during the circulation process, which will form cavitation and cavitation on the outer surface of the cylinder liner. Over time, dense pitting will appear on the front surface of the outer surface of the cylinder liner. . In severe cases, insert the hole in the cylinder liner into the oil pan of the diesel engine. To check whether the cylinder liner is punctured or which cylinder liner is corroded and punctured, you can remove the oil pan of the diesel engine, fill the radiator tank with water, slowly crank the diesel engine and observe if water leaks from the cylinder wall or tastestes, if there is coolant leaking, it can be determined that the cylinder liner has been punctured. Additionally, if the cylinder liner water blocking ring is damaged, coolant will also enter the oil pan. Coolant drips from the outer wall of the cylinder liner. This may be due to damage to the rubber water blocking ring. When prying the diesel engine, if rotation is very difficult, do not force it. If this occurs, it may be because coolant has entered the cylinder during the compression stroke. At that time, if you are not careful, the connecting rod. the diesel engine or other parts could be damaged.
2. The oil cooler is damaged:
The heat dissipation of Cummins NT855 diesel engine oil is completed by the barrel type oil cooler installed on theside of the diesel engine. The radiator core is made of a row of copper tubes. The coolant circulates through the copper tubes of the radiator core, and the diesel engine oil circulates outside the tubes. During the flow process, the high temperature oil is cooled by the coolant. ensure a certain oil temperature. When the copper tube of the radiator breaks or the seals at both ends of the radiator core fail, the coolant may enter the oil pan of the diesel engine through the oil passage. When the diesel engine is running, the oil pressure should be higher than the pressure of the circulating water. Under the action of pressure difference, oil can enter the coolant through the cracks in the copper pipe. At this time, it seems that there is oil in the water tank of the diesel engine; when the diesel engineto operate, because the water level in the water tank is higher than that of the oil radiator, under the pressure caused by this height difference, the cooling water will enter through the radiator pipe through the oil passage. In the diesel engine oil pan, it is necessary to determine whether the diesel engine radiator contains oil. When the radiator core copper tube is damaged, use compressed air for inspection. The specific method is as follows: seal the two ends of the radiator core with iron plates, leaving a small hole at one end, and fill the copper tube with water through the tube. small hole. , blow 7 kg of compressed air through the small hole and hold for 5-10 minutes; If water or gas comes out of the radiator oil outlet, it can be determined that the copper pipe of the radiator is damaged and needs to be replaced. In addition, if the joint between theIf the ends of the radiator core and the radiator shell fail, cooling water may also enter the oil pan.
3. Damage to Cylinder Seal:
The Cummins diesel engine cylinder head and diesel engine block are sealed by the cylinder seal. The water channel of the cylinder has a corresponding seal. ring on the cylinder seal to ensure that coolant does not leak. If the flatness error of the cylinder head or cylinder block of the diesel engine exceeds the allowable range, the cylinder gasket will inevitably be poorly sealed and the coolant may leak into the oil pan. Additionally, if the cylinder head bolts of the diesel engine are not tightened as required or the surface is not cleaned during the cleaning process, resulting in non-tightening of the cylinder gasket, coolant leakage will also occur.. It is difficult to determine preciselysion if the cylinder seal is damaged. This inspection can only be carried out after eliminating defects in the cylinder liner and oil cooler.
4. Cylinder head damage:
Once the cylinder head of the diesel engine is cracked, even if there are only small cracks, the coolant will flow into the cylinder and oil bottom from the cracks. when the diesel engine is operating inside the hull. The cylinder head is generally not damaged. To find out if it is intact, you can check it with 7kg of compressed air. Once damage is discovered, they should be replaced immediately.
When using a Cummins diesel generator set, if you find that the engine oil has turned milky white, you should stop for careful inspection and repair, and then continue to work after troubleshooting. Otherwise, due to poor lubrication, the diesel engine may suffer graves mechanical accidents such as delay, cylinder draft or even crankshaft jamming.
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1. There are holes or cracks in the cylinder head in the diesel engine PT fuel pump fuel supply system, the diesel passage is on the cylinder head. There are both oil passages, water passages and diesel passages on the cover. When working, the diesel pressure in the diesel passage on the cylinder head is 0.8-1.2 MPa, the water pressure is lower. than 0.6 MPa and the pressure of diesel is higher than that of water. Pressure, once pores, blisters or cracks appear on the cylinder head, the water channel and diesel channel will be connected, and diesel will enter the water channel.
2. The seal fails or the mechanism is defective. For example, the oil seal of the main shaft of the PT pump falls into panne and the diesel enters the distribution box and then reaches the oil pan. The oil cut-off valve at the diesel outlet of the PT pump is not closed tightly; . Although the diesel engine has been stopped, due to the high position of the diesel tank, diesel fuel can still enter the oil pan through the following path: oil tank → oil line → oil pump PT gears → oil stop. valve (when not closed tightly) → oil pipe → fuel injector (the fuel injector in the oil return and oil measuring stroke, its oil nozzle cavity. The diesel in the fuel tank is connected to the diesel tank, and the diesel drips into the combustion chamber through the nozzle hole under the action of atmospheric pressure) → combustion chamber → oil pan; the injector hole is too large, damaged, or the upper and lower O-ringsior of the injector When damaged, diesel will enter the combustion chamber and then seep into the oil pan; When the one-way valve on the oil return manifold of the PT fuel system fails, diesel will flow through it to the injector and then seep into the oil pan. A manual shut-off valve is installed at the oil pan; outlet from the tank. If the valve core is damaged and not sealed tightly, diesel will flow into the combustion chamber and into the oil pan. The pressure in a certain cylinder is too low, which will cause the cylinder to stop working, resulting in diesel. flow into the oil. Lower case: The diesel engine has insufficient air intake and dangerous combustion will flow into the oil pan along the cylinder wall.
When the diesel engine was dismantled and inspected, it was found that there wast numerous blisters around the injectors of cylinders II and V. Since the diesel pressure is higher than the water pressure when the engine is running, water cannot flow into the diesel passage around the injectors at mid-flow, so that diesel fuel entered the water tank; the top of the injector push rod of cylinder II was broken and the injector push rod of cylinder V was bent, causing the injector push rods of cylinder II and V to lift cannot not be modified precisely. As a result, the diesel fuel could not be completely burned and flow into the oil pan additionally, after removing the oil outlet pipe on the oil pan; PT pump shutdown, it was found that diesel was still flowing out of the oil shutoff valve port. Diesel after cleaning the valve core No more leaking; at the same time, after replacing the new cylinder head and the newit push rod, the fault phenomenon has been eliminated.