LONG BLOCK M 20R7050 - Caterpillar

Illustration 1. The 5P3519 Piston Ring Groove Gauge Group, top, and the 5P4812 Keystone Piston Ring Groove Gauge Group, bottom.Procedure To Check Ring Groove Wear On Pistons Which Use Keystone Rings
Remove the rings from the pistons. Clean the pistons with glass beads to remove all carbon deposits from the ring grooves.
It is possible for the glass beads to push some of the material from the iron band into the ring grooves. See Illustration 2. This material can be felt with a fingernail. Carefully remove the small amount of material with a three-corner file before the grooves are checked.
Illustration 2. Metal distortion in the ring grooves caused by glass beads. Carefully remove this pushed-up material with a three-corner file.Use the correct gauge, as shown on the instruction card. Check the grooves at four evenly-spaced places around the pistons. To do this, install the round end of the gauge straight in toward the centerline of the piston. The body of the gauge MUST be over the iron band. See Illustrations 3, 4, 5, and 6. DO NOT use force to push the gauge into the groove.
Illustration 3. Correct use of 5P4812 Keystone Piston Ring Groove Gauge Group in the top ring groove. Any clearance between the body of the gauge and the iron band is an indication the piston can be used again. USE AGAIN.
Illustration 4. No clearance is shown between the gauge and the band. DO NOT USE AGAIN.
Illustration 5. Correct use of the 5P4812 Keystone Ring Groove Gauge Group in the lower ring groove. The gauge is turned over so the body is over the iron band. USE AGAIN because there is clearance between the band and the gauge. Be careful when a direct injection piston is checked; it is difficult to read the gauge because of the gas expansion groove.
Illustration 6. No clearance is shown between the gauge and the band. DO NOT USE AGAIN.With a light behind the piston and gauge, check for clearance between the body of the gauge and the iron band. If there is ANY clearance, shown by ANY light between the body of the gauge and the iron band, the piston can be used again. See Illustrations 3 and 5. The piston must not be used again if, at ANY place checked, the body of the gauge makes contact with the iron band so that no light shows between them. See Illustrations 4 and 6.
There have been reports of worn ends on some of the 5P4812 Keystone Piston Ring Groove Gauge Groups. The worn ends can cause wrong indications. Current gauges have an improved hardness which decreases the wear. Since there is no way to measure this wear with common tools, it is Caterpillar's recommendation that a new gauge group be kept in the tool room for use as a master (main) gauge. If a gauge shows several pistons are not good, check the pistons with the master. If the master shows the pistons are good, use the pistons again. Get a