Piston: Testing and Inspection

CHECK FIT BETWEEN PISTON AND PISTON PIN



1. Try to move the piston back and forth on the piston pin.
2. If any movement is felt, replace the piston and pin as a set.

CLEAN PISTON



1. Using a gasket scraper or other suitable tool, remove the carbon from the piston top.



2. Using a suitable groove cleaning tool or broken ring, clean the piston ring grooves.
3. Using suitable solvent and a brush, thoroughly clean the piston.
NOTE: Do not use a wire brush.

INSPECT PISTON
1. Inspect piston oil clearance as follows:



- Using a micrometer, measure the piston diameter at right angles to the piston pin center line, 34.000 mm (1.3400 in.) from the piston head.

Piston diameter: 85.935 - 85.945 mm (3.3833 - 3.3837 in.)

- Measure the cylinder bore diameter in the thrust directions. (See Cylinder Block Assembly/Testing and Inspection)
Cylinder Block Assembly

- Subtract the piston diameter measurement from the cylinder bore diameter measurement.

Std. oil clearance: 0.055 - 0.078 mm (0.0022 - 0.0031 in.)
Max. oil clearance: 0.100 mm (0.0039 in.)

- If the oil clearance is greater than maximum, replace all the 6 pistons.
- If necessary, replace the cylinder block.

2. Inspect piston ring groove clearance as follows:



- Using a feeler gauge, measure the clearance between new piston ring and the wall of the piston ring groove.

Ring groove clearance:
No.1: 0.011 - 0.070 mm (0.0004 - 0.0028 in.)
No.2: 0.030 - 0.070 mm (0.0012 - 0.0028 in.)

- If the clearance is not as specified, replace the piston.

3. Inspect piston ring end gap.



- Insert the piston ring into the cylinder bore.
- Using a piston, push the piston ring a little beyond the bottom of the ring travel, 105 mm (4.1300 inch) from the top of the cylinder block.



- Using a feeler gauge, measure the ring end gap.

Standard ring end gap:
No.1: 0.300-0.470 mm (0.0118-0.0185 inch)
No.2: 0.350-0.520 mm (0.0138-0.0205 inch)
Oil (Side rail): 0.130-0.450 mm (0.0051-0.0177 inch)

Maximum ring end gap:
No.1: 1.070 mm (0.0421 inch)
No.2: 1.120 mm (0.0441 inch)
Oil (Side rail): 1.050 mm (0.0413 inch)

- If the end gap is greater than maximum, replace the piston ring.
- If the end gap is greater than maximum, even with a new piston ring, replace the cylinder block.


4. Inspect piston pin fit as follows:



- At 80°C (176°F), you should be able to push the piston pin into the piston pin hole with your thumb.

EDITOR'S CAUTION: 80°C is HOT! Wear gloves or exercise caution when handling the piston and pin.