40. Piston, Connecting Rod and Bearings Clean/Inspect
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.
PISTON MEASUREMENT
The piston skirts are barrel-shaped. To accurately determine the piston diameter, the piston must be measured at a specific gauge point.
The piston gauge point is 65.33 mm (2.575 inch) from the top of the piston.
MEASURING PISTON PIN TO PISTON PIN BUSHING CLEARANCE
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. Subtract 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.
MEASURING PISTON PIN TO PISTON CLEARANCE
1. Measure the piston pin diameter.
2. Measure the piston pin hole inside diameter. Use an inside micrometer.
3. Subtract 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.