Piston, Connecting Rod, and Bearing Cleaning and Inspection Piston Inspection

Important: 

•	Do not use a wire brush or glass bead blasting.

•	Use a cleaning solution that will dissolve the carbon deposits.

•	Remove the carbon in the ring grooves with a ring groove cleaner.

1. Clean the piston, by removing all of the varnish and the carbon deposits.
2. Inspect the piston for the following conditions:

•	Cracking or wear of the ring lands.

•	Burrs or nicks of the ring grooves.

•	Cracking of the skirts or pin bosses.

•	Cracking of the piston dome (Use Magnaflux Spot-check dye method or the equivalent).

•	Scuffing or deep scratches of the piston skirt.

•	Scuffing of the piston bore.

•	Wear of the piston pin retaining ring or the grooves.




3. Inspect the connecting rod for the following conditions:

•	Cracks or nicks on the connecting rod (Use Magnaflux Spot-check dye method or the equivalent).

•	Scuffing or scratching of the piston pin bushing.

•	Nicks or scoring of the bearing bore.

•	Bent or twisted rods.

4. The connecting rod is not serviceable for the following repairs:

•	Straightening.

•	Bushing replacement.

•	Connecting rod bearing bore enlargement.

The piston skirts are barrel-shaped. To accurately determine the piston diameter, the piston must be measured at a specific gage point.

The piston gage point is 65.33 mm (2.575 in) from the top of the piston.

1. Measure the piston pin to piston pin bushing.
2. Measure the piston pin diameter.
3. Measure the piston pin bushing inside diameter. Use an inside micrometer.
4. Substract the piston pin diameter from the piston pin bushing inside diameter to obtain the clearance.
5. If the clearance is excessive, replace the piston and piston pin. Piston pins are available only with new pistons.
6. If the clearance is excessive with a new piston and piston pin, replace the connecting rod. Piston pin bushings are available only with new connecting rods.

1. Measure the piston pin diameter.
2. Measure the piston pin hole inside diameter. Use an inside micrometer.
3. Substract the piston pin diameter from the piston pin hole diameter to obtain the clearance.
4. If the clearance is excessive, replace the piston and piston pin. Piston pins are available only with new pistons.

Piston, Connecting Rod, and Bearing Cleaning and Inspection Piston Measurement

The piston skirts are barrel-shaped so the piston diameter must be measured at a specific gauge point.

1. The piston gauge is 65.33 mm (2.575 in) from the top of the piston.
2. Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection for procedures on how to measure pistons.

To determine the piston to cylinder bore clearance perform the following measurements:

1. Measure the cylinder bore. If the bore is serviceable, note the lowest bore diameter measurement. Then compare this measurement to the piston measurement.



2. Measure the piston. Compare the piston measurement to the piston-to-cylinder-bore specifications found at the end of this section. Substract the piston diameter from the lowest bore diameter to determine piston-to-bore-clearance.
3. If the used piston is not acceptable, determine if a new piston will fit the cylinder bore using the above measurement procedures.

Piston, Connecting Rod, and Bearing Cleaning and Inspection Piston Pin to Bushing

1. Clean the piston pin and bushing. The parts must be free of oil and dirt. Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection in order to measure piston pin to piston clearance.
2. Measure the piston pin to bushing following these steps:

•	Measure the piston pin diameter.

•	Measure the piston pin bushing inside diameter. Use an inside micrometer.

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Substract the piston pin diameter from the piston pin bushing inside diameter. If the clearance is excessive, try a new piston pin. If the clearance is excessive with a new piston pin , the connecting rod must be replaced. Replacement bushings are not available. Piston pins are available only wilt new pistons.

Piston, Connecting Rod, and Bearing Cleaning and Inspection Pin to Piston Clearance

1. Measure the piston pin diameter.
2. Measure the piston pin to piston clearance.

•	Measure the piston pin hole diameter.

•	Substract the piston pin diameter from the piston pin hole diameter to obtain the clearance.

•	Replace the piston and piston pin if the clearance exceeds specifications. The piston and the piston pin are a matched set and not available separately.