Piston Selection
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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 installed if, after cleaning and inspection, they are within specifications.
- Inspect the engine block cylinder bore for scoring or other damage.
- Inspect the piston and the piston pin. Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection .
- With the micrometer at a right angle to the piston, measure the piston. Measure 4.8L and 5.3L pistons 43 mm (1.69 in) from the crown. Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection .
- Record the piston diameter.
- Adjust the micrometer to the recorded piston diameter.
- Insert the bore gage into the micrometer and zero the bore gage dial.
- Use a bore gage and measure the cylinder bore diameter. Measure at a point 64 mm (2.5 in) from the top of the cylinder bore.
- Record the cylinder bore diameter.
- Subtract the piston diameter from the cylinder bore diameter in order to determine the piston-to-bore clearance. Refer to Engine Mechanical Specifications (LR4 VIN V) or Engine Mechanical Specifications (LM7 VIN T) or Engine Mechanical Specifications (LQ4 VIN U) .
- 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.