Piston Ring: Testing and Inspection

1. Measure the piston ring end gap using the following procedure:





a. Place the piston ring in the area of the bore where the piston ring will travel (approximately 25 mm or 1 inch down from the deck surface). Be sure the ring is square with the cylinder bore by positioning the ring with the piston head.
b. Measure the end gap of the piston ring with feeler gages. Compare the measurements with those provided below:
^ The top compression ring end gap should be 0.25-0.40 mm (0.010-0.016 inch).
^ The second compression ring end gap should be 0.35-0.50 mm (0.014-0.020 inch).
^ The oil ring end gap should be 0.25-0.76 mm (0.010-0.030 inch).
c. If the clearance exceeds the provided specifications, the piston rings must be replaced.
d. Repeat the procedure for all the piston rings.





2. Measure the piston ring side clearance using the following procedure:
a. Roll the piston ring entirely around the piston ring groove. If any binding is caused by the ring groove, dress the groove with a fine file. If any binding is caused by a distorted piston ring, replace the ring.
b. With the piston ring on the piston, use feeler gages to check clearance at multiple locations.
c. The clearance between the surface of the piston ring and the ring land should be no greater than 0.095 mm (0.004 inch).
d. If the clearance is greater than specifications, replace the piston rings.
3. When replacing the piston rings, only install re-ring sets that have a 1.2 mm thick nitrided steel upper compression ring and multi-piece oil rings. The top compression ring may be installed with either side up. There is a locating dimple on the 2nd compression ring near the end for identification of the top side. Install the 2nd compression ring with the dimple facing up.
4. If the new ring does not reduce the clearance to 0.04 mm (0.002 inch) or less, install a new piston.