Piston Selection

1. Measure the piston diameter. Remove the piston pin in order to measure the piston for size or taper.
2. Replace the piston with a standard or an oversized piston if the piston is damaged.

NOTE: Consider both the piston condition and the cylinder bore condition when fitting the pistons. Production and service pistons have the same nominal weight. Production and service pistons can be intermixed without affecting engine balance. If necessary, fit used pistons selectively to any cylinder of the engine. Ensure that the pistons are in good condition.

3. Measure the cylinder bore. If the bore is worn beyond specifications, rebore the cylinder bore. Use the following procedure in order to hone the cylinder bore to the correct size:
a. Select a piston.
b. Hone the cylinder bore in order to obtain the recommended clearance.
c. Scrub the cylinder bore and the piston with soap and water. Remove all foreign material. Dry the cylinder bore. Rub clean engine oil into the cylinder bore.
4. Use the following procedure in order to measure piston to cylinder bore clearance:





a. Measure the cylinder bore with a telescoping gauge. If the cylinder bore is damaged, rebore or hone the cylinder bore to size.
b. Subtract the piston diameter from the cylinder bore diameter in order to determine the piston-to-bore clearance.
c. Compare the piston-to-bore clearance with the specifications in order to determine if the clearance is in an acceptable range.
5. If the used piston is not within an acceptable clearance range, check the service piston sizes in order to determine if a new piston can be selected. Service pistons are available in standard and 0.508 mm (0.020 inch) oversize.
6. If the cylinder bore needs reconditioning, measure the new piston diameter and hone the cylinder bore to the correct clearance.
7. Select a new piston. Mark the piston in order to identify the corresponding cylinder.





8. Select a set of new piston rings.
9. Place the piston into the cylinder at the bottom of the ring travel.
10. Place a position ring on top of the piston.
11. Back off the Piston.





12. Measure the ring gap.
13. If the ring gap is not within an acceptable specification range, increase the ring gap. Do this by carefully filing any excess material from the ring gap.





14. Measure the piston ring side clearance (compression rings).

CAUTION: Do not cut the ring groove with a file or a rough edged tool. Good performance and durability depends on the straightness and smoothness of the ring groove.

15. Use the following procedure in order to measure piston ring side clearance:
a. Measure the amount of piston compression ring side clearance.
b. Roll the piston ring around the groove.
c. Measure the side clearance.
d. If the ring is too tight, check for nicks or burrs. Use emery paper in order to remove burrs.
e. Determine if the ring is within specifications. If necessary, replace the ring.