GM Service Manual Online
For 1990-2009 cars only

Check the used piston-to-cylinder bore clearance in the following manner:


    Object Number: 4987  Size: SH
  1. Using a telescoping bore gauge located 65 mm (2.5 in) below the top of the cylinder bore, measure the cylinder bore diameter.

  2. Object Number: 4988  Size: SH
  3. Measure the piston diameter at 20°C (70°F).
  4. Measure the skirt at a right angle to the piston pin hole, 25 mm (1.0 in) below the oil ring groove.
  5. Subtract the piston diameter from the cylinder bore diameter in order to determine the piston-to-bore clearance.
  6. Locate the piston-to-bore clearance. Refer to Engine Mechanical Specifications .
  7. Determine if the piston-to-bore clearance is within the acceptable range.
  8. If the used piston is not acceptable determine if a new piston will fit the cylinder bore.
  9. If the new piston will not bring the clearance within tolerances the cylinder bore must be reconditioned. Refer to Cylinder Boring and Honing .
  10. Mark the piston to identify the cylinder for which it was fitted.