26. Piston, Connecting Rod, and Bearing Clean and Inspect

CONNECTING ROD MEASUREMENT

IMPORTANT: Do not use a cam or shop towel to dry connecting rod mating surface.





1. Clean connecting rods in solvent and dry with compressed air.
2. Inspect connecting rods for the following:
- Signs of being twisted, bent, nicked, or cracked.
- Scratches or abrasion on the rod bearing seating surface.
3. If connecting rod bores contain minor scratches or abrasions, clean the bores in a circular direction with a light emery paper. DO NOT scrape the rod or rod can.
4. If the beam of the rod is scratched or has other damage replace the connecting rod.
5. Measure piston pin to connecting rod bore using the following procedure:
a. Using an outside micrometer, take two measurements of the piston pin in the area of the connecting rod contact.
b. Using an inside micrometer, measure the connecting rod piston pin bore.
e. Subtract the piston pin diameter from the piston pin bore diameter.
d. The clearance should not be more than 0.021 mm (0.0008 inch).
- If there is excessive clearance, replace piston pin.
- If there is still excessive clearance, replace connecting rod.

PISTON MEASUREMENT





l. Clean piston skirts and pins with a cleaning solvent. DO NOT wire brush any part of the piston.
2. Clean piston ring grooves with a groove cleaner. Make sure oil ring holes and slots are clean.
3. Inspect pistons for the following conditions:
- Cracked ring lands, skirts, or pin bosses
- Ring grooves for nicks, burrs that may cause binding
- Warped or worn ring lands
- Eroded areas at the top of the piston
- Scuffed or damaged skirts
- Worn piston pin bores
4. Replace pistons that show any signs or damage or excessive wear.
5. Measure piston pin bore to piston pin clearances using the following procedure:
a. Piston pin bores and pins must be free of varnish or scuffing.
b. Use an outside micrometer to measure the piston pin in the piston contact areas.
c. Using an inside micrometer, measure the piston pin bore.
d. Subtract the measurement of the piston pin bore from the piston pin The clearance should be within 0.002 - 0.012 mm (0.00007 - 0.00047 inch).
e. If the clearance is excessive, determine which component is out of specification.





6. 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 0.20 - 0.40 mm (0.0060 - 0.015 inch).
- The second compression ring end gap should be 0.35 - 0.55 mm (0.0137 - 0.0216 inch).
- The oil ring end gap should be 0.25 - 0.76 mm (0.0098 - 0.029 inch).
c. If the clearance exceeds the provided specifications, the piston rings must be replaced.
d. Repeat the procedure for all the piston rings.





7. 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 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 top piston ring and the ring land should be no greater than 0.075 mm (0.0030 inch).
d. If the clearance is greater than specifications, replace the piston ring.
e. If the new ring does not reduce the top ring side clearance to 0.075 mm (0.0030 inch) or less, install a new piston.
8. 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.
9. The clearance between the surface of the second piston ring and the ring land should be no greater than 0.069 mm (0.0026 inch).
10. If the new ring does not reduce the clearance to 0.069 mm (0.0026 inch) or less, install a new piston.





11. Measure piston width using the following procedure:
a. Using an outside micrometer, measure the width of the piston 14.5 mm (0.570 inch) above the bottom of the piston skirt at the thrust surface perpendicular to the centerline of the piston pin.
b. Compare the measurement of the piston to its original cylinder by subtracting the piston width from the cylinder diameter.
c. The proper clearance specification for the piston is 0.010 - 0.041 mm (0.0006 - 0.0016 inch).
12. If the clearance obtained through measurement is greater than these specifications and the cylinder bores are within specification, replace the piston.