GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Chevy P12 Chassis 🢒 Engine 🢒 Engine Mechanical - 7.4L 🢒 Piston Selection

Tools Required

J 8087 Cylinder Bore Checking Gauge

Important: Measurements of all components should be taken with the components at normal room temperature.

For proper piston fit, the engine block cylinder bores should not have excessive wear or taper.

A used piston and pin set may be reinstalled if, after cleaning and inspection, they are within specifications.


    Object Number: 4972 Size: SH
  1. Inspect the engine block cylinder bore. Refer to Cylinder Boring and Honing .
  2. Inspect the piston and pin. Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .
  3. Use the J 8087 and measure the cylinder bore diameter. Measure at a point 64 mm (2.5 in) from the top of the cylinder bore.

    4. Object Number: 4974 Size: SH
  4. Measure the J 8087 with a micrometer and record the reading.

    5. Object Number: 4988 Size: SH
  5. With a micrometer or caliper at a right angle to the piston, measure the piston 11 mm (0.433 in) from the bottom of the skirt.
  6. Subtract the piston diameter from the cylinder bore diameter in order to determine piston-to-bore clearance. Refer to Engine Mechanical Specifications .
  7. If the proper clearance cannot be obtained, select another piston and measure the clearances.

    8. If the proper fit cannot be obtained, the cylinder bore may require honing or boring.

  8. When the piston-to-cylinder bore clearance is within specifications, permanently mark the top of the piston for installation into the proper cylinder.