Piston: Testing and Inspection

1. Clean the piston skirts and the pins with a cleaning solvent. DO NOT wire brush any part of the piston.
2. Clean the piston ring grooves with a groove cleaner. Make sure oil ring holes and slots are clean.
3. Inspect the 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
^ Piston pin retainer grooves for burrs
^ Scuffed or damaged skirts
^ Eroded areas at the top of the piston
^ Worn piston pin bores or worn piston pins
4. Replace pistons that show any signs or damage or excessive wear.
5. Measure the 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 not exceed 0.002-0.013 mm (0.0001-0.0005 inch).
e. If the clearance is excessive, determine which piece is out of specification.





6. Measure piston width using the following procedure:
a. Using an outside micrometer, measure the width of the piston 50 mm below the crown (top) of the piston at the thrust surface which is 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 0.020-0.051 mm (0.0007-0.00020 inch).
7. If the clearance obtained through measurement is greater than these specifications and the cylinder bores are within specification, replace the piston.