34. Piston Selection

Important: Measurements of all components should be taken with the components at normal room temperature.
For proper piston fit, the engine block cylinder bores must not have excessive wear or taper.
A used piston and pin set may be reinstalled if, after Clean and Inspect, they are within specifications.





1. Inspect the engine block cylinder bore for scoring or other damage.
2. Inspect the piston and the piston pin. Refer to Piston, Connecting Pod, and Bearings Clean and Inspect.
3. With the micrometer at a right angle to the piston, measure the 4.8/5.3 machined dome piston 0.15 mm (0.006 inch) from the bottom of the skirt.
4. Record the piston diameter.





5. Adjust the micrometer to the recorded piston diameter.
6. Insert the bore gauge into the micrometer and zero the bore gauge dial.





7. Use a bore gauge and measure the cylinder bore diameter. Measure at a point 64 mm (2.5 inch) from the top of the cylinder bore.
8. Record the cylinder bore diameter.
9. Subtract the piston diameter from the cylinder bore diameter in order to determine the piston-to-bore clearance.
The proper piston-to-bore clearance should be 0.03 - 0.07 mm (0.0012 - 0.00275 inch) for 4.8/5.3 liter engines.
The proper piston-to-bore clearance should be 0.032 - 0.072 mm (0.0013 - 0.00283 inch) for 6.0 liter engines.
10. If the proper clearance cannot be obtained, select another piston and measure the clearances.
If the proper fit cannot be obtained, the cylinder bore may require boring and honing for an oversize piston or engine block replacement.