Piston and Pin

Piston, Connecting Rod, and Bearings Cleaning and Inspection (Piston and Pin)

Important: Replace the pistons and the pins that are damaged or show signs of excessive wear.

The piston and the pin are a matched set. If service is required, replace the piston and the pin as an assembly.
Do not wire brush any part of the piston.





1. Clean the varnish from the piston and the pin with cleaning solvent.
2. Dry the piston and the pin with compressed air.





3. Clean the piston ring grooves with a suitable ring groove cleaning tool.
4. Clean the oil lubrication holes and slots.





5. Inspect the piston and the pin for the following:
- Cracks in the piston ring lands, the piston skirt, or the pin bosses
- Piston ring grooves for nicks, burrs, or warpage which may cause the piston ring to bind MINOR imperfections may be removed from the piston with a fine file.
- Scuffed or damaged skirts (2)
- Eroded areas at the top of the piston (1)
- Scoring to the piston pin bore (3) or the piston pin

Important: Measurements of components should be taken with the components at normal room temperature.





6. Measure the piston ring-to-piston ring groove side clearance.
6.1. Insert the edge of the piston ring into the piston ring groove.
6.2. Roll the piston ring completely around the piston.
^ If binding is caused by a distorted piston ring groove, MINOR ring groove imperfections may be removed with a fine file.
^ If binding is caused by a distorted piston ring, replace the piston ring.





7. Measure the piston ring side clearance with a feeler gauge.
8. If side clearance is not within specifications, try another piston ring set.
9. The proper piston ring-to-piston ring groove side clearance is:
- The top compression ring side clearance is 0.04 - 0.085 mm (0.00157 - 0.003346 inch).
- The second compression ring side clearance is 0.04 - 0.08 mm (0.00157 - 0.003149).
- The oil control ring side clearance is 0.01 - 0.22 mm (0.0004 - 0.00866).
10. If proper piston ring-to-piston ring groove side clearance cannot be achieved, replace the piston and pin assembly.





11. To determine piston pin-to-bore clearance, use a micrometer and measure the piston pin.





12. To determine piston pin-to-bore clearance, use an inside micrometer and measure the piston pin bore.

Important: The piston and pin are a matched set. If the clearance is not within specifications, replace the piston and pin as an assembly.

13. To determine the proper piston pin-to-bore clearance, subtract the piston pin diameter from the piston pin bore diameter.
The proper piston pin-to-bore clearance is 0.01 - 0.02 mm (0.0004 - 0.00078).





14. Measure the piston for out-of-round.
14.1. With the micrometer at a right angle to the piston, measure the piston at 11 mm (0.433 inch) from the bottom of the skirt.
14.2. Measure the piston at two different points and compare the readings.
14.3. If the piston is more than 0.018 mm (0.0007 inch) out-of-round, replace the piston and pin as an assembly.