Case Analysis And Explanation

When the engine is working, the engine oil is filled between the cylinder wall, piston ring and piston. When their fit clearance is abnormal, the engine oil between the cylinder wall and the piston will plunge into the combustion chamber, which is the main cause of the oil expelling. After the engine works for a certain period of time, the radial dimension of the piston ring will be reduced, the elastic force will be weakened, the opening gap will be enlarged, and the sealing and the oil scraping action will be deteriorated. The increased gap between the piston ring and the ring groove strengthens the oil pumping action of piston ring. When the piston moves upwards, the engine oil will be scraped into the combustion chamber. The carbon deposit will be generated after oil expelling, to accelerate the cylinder wear and generate a vicious circle. The engine oil will be combusted after the piston ring is jammed. When the piston ring is jammed in the ring groove, the piston ring will lose the elasticity, and the sealing will be deteriorated. In this case, not only a large amount of engine oil will be brought to the combustion chamber when the piston moves upwards, but also a large amount of high-pressure gas will plunge into the crank case when the piston works, to increase the internal pressure of crank case. The spattering engine oil flows into the air inlet pipe through the crank case ventilation device, so that the engine oil and air enter the combustion chamber and are then combusted.

Eliminate the severe gas carry-over of crank case ventilation device (if any), which is mostly caused by jamming of piston ring. The repair quality of engine has a great impact on the oil expelling of cylinder. Excessive cylinder roundness, cylindrical form deviation and surface roughness, matching of piston ring and piston not in accordance with the technical requirements, piston eccentricity in assembly and the non-conforming perpendicularity of cylinder center line and crankshaft rotation center line, etc. all will cause oil expelling. Meanwhile, piston carbon deposit, reverse assembly of piston ring, unreasonable layout of ring port and excessive gap of ring port all will accelerate the oil expelling of cylinder in varying degrees. The oil expelling after the engine runs for a short period is partially caused by non-conforming piston ring quality. The piston ring available on the market has many quality problems such as insufficient elastic force and non-durable elastic force and failure to adapt to the deformation of cylinder liner. These are the main causes of oil expelling in the cylinder after the vehicle travels for certain mileage.