Maintenance Method of Piston Ring in Cummins Diesel Generator Set

The exhaust pipe of Cummins diesel generator set emits black smoke, the engine oil enters the diesel oil and the power drops rapidly. It can be determined that there is a problem with the piston ring. Piston ring is easy to be damaged, and piston ring at the same level of cylinder and piston is generally replaced after damage. When assembling the replaced piston ring, ensure that there is a good fit clearance between the piston ring and the piston ring groove, as well as the inner wall of the cylinder. For this reason, the following inspections should be carried out:

1. Inspection of piston ring end clearance of Cummins diesel genset: the end clearance of piston ring is the clearance at the opening position of piston ring placed in the inner wall of the cylinder. The main purpose of this clearance is to prevent piston ring from being stuck in the cylinder after thermal expansion. During the measurement, if the end play exceeds the value specified in the technical specification, the piston ring shall be re selected. If the measured value is less than the specified value, file one end of the ring mouth with a file.

2. Inspection of piston ring side clearance of Cummins diesel generating set: the upper and lower clearance of piston ring in piston ring groove is called side clearance. During installation, if the side clearance is too large, the sealing effect of the piston ring will be weakened. If it is too small, it may be stuck in the ring groove and cause a cylinder scuffing accident. During inspection, first place the piston ring in the piston ring groove, and then insert a feeler gauge into the upper side of the piston ring for measurement. During measurement, if the side clearance is too small, place the piston ring flat on the place with sandpaper for grinding.

3. Inspect the back clearance of piston ring of Cummins diesel generator: when installing piston ring into cylinder, the difference between the thickness of piston ring and the depth of piston ring groove is called the back clearance of piston ring. During the assembly process, if the back clearance of the piston ring is too large, it will lead to air and oil leakage of the piston ring. If it is too small, it can cause problems such as friction or jamming between the ring and the groove bottom, and it is also unfavorable for the return of oil to the oil ring. Under normal circumstances, the back clearance of the air ring is generally 0.15~0.35, and the oil ring is 0.35~0.70mm. During assembly, the experience to check the side clearance and back clearance of piston ring is: insert the cold ring into the piston ring groove. If it is lower than the edge of the ring groove and can move freely without looseness, it is appropriate.

4. Check the elastic force of piston ring of Cummins diesel generators: the piston ring must have a certain elastic force to ensure that the outer surface of the ring is closely fitted with the cylinder wall. If the elastic force is too small, the ring and cylinder wall cannot fit tightly, resulting in air leakage. If the elastic force is too small, the pressure of the piston ring on the cylinder wall will increase, which will aggravate the wear of the cylinder wall and piston ring.

5. Inspection of piston ring leakage of Cummins genset diesel: piston ring can play a sealing role only when it fits with cylinder wall everywhere. Therefore, light leakage test shall be conducted when selecting piston ring. During the test, first place the piston ring horizontally in the cylinder, cover the inner circle of the ring with a cover plate, and then place a work lamp under the cylinder to observe the fit of the piston ring and the inner wall of the cylinder. During the initial running in process of Cummins diesel generator set, if the leakage of the selected piston ring exceeds the specified standard, the Cummins diesel generator set will have air and oil leakage and other failures. Therefore, when selecting piston ring, it is necessary to check the light leakage.

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