Bad piston rings may be related to the air leakage caused by wear or coking of piston ring grooves. At this time, the external sign of the machine in use is that a large amount of exhaust gas leaked into the cylinder body through the piston ring comes out of the vent (or filler). In this case, the cylinder cutoff method can be used to make one cylinder out of service in turn for judgment. If the exhaust gas no longer comes out from the oil filler or the vent after cutting off a cylinder, it indicates that the piston of the cylinder is in poor use.

Reasons for piston ring air leakage

1. The piston ring groove is worn. The wear of the piston groove is mainly on the lower surface of the ring groove. The original chimney causing the wear is the downward impact of the gas ring and the radial sliding of the piston ring in the ring groove, which reduces the sealing effect of the second sealing surface.

2. The piston ring is worn. Because the material of the piston ring is not matched with the cylinder wall (the hardness difference between the two is too large), the sealing of the ring becomes worse after the ring is worn.

3. The piston ring opening clearance is too large or the mixing time is not up to the requirements, the sealing effect of the face ring deteriorates, the throttling effect is reduced, the air leakage channel is enlarged, and the opening clearance of diesel engines is larger than that of gasoline engines, and the first ring is larger than the second and third rings.

4. Unreasonable distribution of piston ring openings. To reduce air leakage, strengthen the throttling effect at the opening of the ring and make the sealing route of the ring long, so the opening of each gas ring is operated as required.

5. When the engine is working, when the balance bucket of various force phases acting on the ring is floating, it can cause the radial vibration of the ring, make the seal invalid, and at the same time, the circumferential rotation of the ring may occur, which will change the staggering degree of the opening during installation, and also cause air leakage.

6. The piston ring is broken, glued, or stuck in the ring groove, or the piston ring is reversely installed, which makes the first sealing surface of the ring lose its sealing effect and cause air leakage. For example, the twisted ring and tapered ring are not installed in the ring groove as required.

7. The cylinder wall is worn or has marks or grooves that affect the sealing of the first sealing surface of the air ring and cause air leakage.

Piston ring leakage inspection

1. Cylinder by cylinder (remove the spark plug or fuel injector) force. Check the cylinder compression pressure with a small amount of lubricating oil. If the cylinder compression pressure rises after adding lubricating oil, it is confirmed that the piston ring is not sealed tightly.

2. The hardness of the selected air ring is appropriately higher than that of the cylinder. The use of soft piston rings will shorten the service life of the rings. For the soft and hard inspection of the ring and cylinder, the lower edge of the cylinder and the ring can be compared with the JJ or the scraping force test.

3. Correctly grasp the timing of ring replacement when the cylinder is worn heavily, the elasticity of the ring does not drop significantly, and the engine fuel and lubricating oil are normal. If the wear of the cylinder is within the allowable range and the clearance of the matching cylinder is too large, replace the piston as soon as possible, or replace the piston ring only. "The failure will occur again because the original piston swings frequently in the cylinder and the piston ring cannot be controlled.

4. When changing the ring, the scraper shall be used to scrape off the "cylinder shoulder" and remove the carbon deposit in the ring groove. The opening of the ring shall be subject to the inspection of the lower part of the cylinder. To avoid being broken by the "cylinder shoulder", the ring is stuck in the ring groove by carbon deposit and expanded and broken due to insufficient ring opening clearance.

5. Before installing the piston ring, the entire ring belt and pinhole of the piston shall be immersed in clean thin lubricating oil for pre-lubrication to prevent the seizure of the new piston pin and the dry friction between the piston ring and the ring groove after the engine starts.

6. Improve the maintenance quality of the engine, make the opening end clearance, edge clearance, back clearance, etc. of the ring meet the technical requirements, stagger the openings reasonably, strengthen the light leakage inspection of the ring, and avoid the installation of the ring. If the end clearance of the o-ring is a straight cut, it should be flat during the repair.