Piston: Testing and Inspection

NOTE: Clean all parts, being sure to remove all gasket fragments, dirt and oil. Be careful not to damage the joints or friction surfaces of aluminum alloy components.

1. Inspect outer circumference of all pistons for seizing and scoring. Replace as needed.
2. Measure outer diameter of each piston at a right angle to piston pin, 0.57 inch below bottom of oil ring. Piston diameter should be 3.7768-3.7779 inches.

Fig. 14 Oversize Piston Selection Chart:

3. Measure piston clearance. Clearance should be 0.0024-0.0034 inch. If clearance exceeds maximum, select an oversize piston to obtain specified clearance, Fig. 14. If a piston is replaced, piston rings must also be replaced.

4. Measure piston ring-to-land clearance around entire circumference by using a new piston ring. Clearance should be 0.0016-0.0033 inch for top ring, 0.0016-0.0033 inch for second ring and snug fit for oil ring. The service limit is 0.006 inch.

Fig. 15 Piston Ring End Gap Inspection:

5. Measure piston ring end gap by using piston to push ring to bottom of travel, Fig. 15. Measure each ring in cylinder of intended use. End gap should be 0.010-0.020 inch for top ring, 0.010-0.020 inch for second ring and 0.015-0.049 inch for oil ring.

Fig. 16 Piston Pine Bore Inspection:

6. Measure each piston pin bore diameter in X and Y directions at four points, Fig. 16. Bore diameter should be 0.9123-0.9126 inch.
7. Measure each piston pin diameter at four points. Diameter should be 0.9119-0.9124 inch for standard pin, 0.9130-0.9133 inch for 0.001 inch oversized pin and 0.9140-0.9143 inch for 0.002 inch oversized pin.
8. Calculate piston to pin clearance. Clearance should be 0.0002-0.0004 inch. If not, replace piston or pin.
9. Correct piston pin length is 3.01-3.04 inches. Replace if necessary.