Piston and Connecting Rod Inspection

1. Clean piston.





(a) Using a gasket scraper, remove the carbon from the piston top.





(b) Using a groove cleaning tool or broken ring, clean the piston ring grooves.





(c) Using solvent and a brush, thoroughly clean the piston.

CAUTION: Do not use a wire brush.

2. Inspect piston and piston ring.
A. Inspect piston oil clearance.





NOTE: There are 3 sizes of the standard piston diameter, marked "1", "2" and "3" accordingly. The mark is stamped on the piston top.





(a) Using a micrometer, measure the piston diameter at right angles to the piston pin center line, 42 mm (1.65 inch) from the piston head.
Piston diameter:
STD
Mark "1": 99.950 - 99.960 mm (3.9350 - 3.9354 inch)
Mark "2": 99.960 - 99.970 mm (3.9354 - 3.9358 inch)
Mark "3": 99.970 - 99.980 mm (3.9358 - 3.9362 inch)
O/S 0.50: 100.450 - 100.480 mm (3.9547 - 3.9559 inch)
O/S 1.00: 100.950 - 100.980 mm (3.9744 - 3.9756 inch)
(b) Measure the cylinder bore diameter in the thrust directions.
(c) Subtract the piston diameter measurement from the cylinder bore diameter measurement.
Standard oil clearance: O.040 - 0.060 mm (0.0016 - 0.0024 inch)
If the oil clearance is greater than maximum, replace all the 6 pistons and rebore all the 6 cylinders. If necessary, replace the cylinder block.





NOTE (Use new cylinder block): Use a piston with the same number mark as the cylinder bore diameter marked on the cylinder block.





B. Inspect piston ring groove clearance.
Using a thickness gauge, measure the clearance between new piston ring and the wall of the piston ring groove.
Ring groove clearance:
No. 1: 0.040 - 0.080 (0.0016 - 0.0031 inch)
No. 2: 0.030 - 0.070 (0.0012 - 0.0028 inch)
If the clearance is greater than maximum, replace the piston.





C. Inspect piston pin fit.
At 80° - 90° C (176° - 194° F), you should be able to push the piston pin into the piston pin hole with your thumb.