Fitting Pistons
- Inspect pistons. Replace any showing signs of excessive wear, wavy ring lands, or fractures. Replace if sponge-like or eroded surface is on edge of piston top (caused by detonation or pre-ignition).
- If shiny surface on thrust side of piston is found, check for bent connecting rod. DO NOT straighten rod, replace as necessary. Inspect rods for signs of fracture and bearing bores for out-of-round and taper. If bore exceeds limits and/or rod is fractured, replace rod.
- Check pistons for fractures at ring lands, skirts and pin bosses. Check for scuffed, rough or scored skirts. When measuring piston for side clearance or taper, measurement must be made at centerline of pin bore and 90° from piston pin hole.
- Check piston-to-cylinder bore clearance by measuring piston and bore diameters. Ensure piston and cylinder bore are clean, dry and at room temperature 70°F (21°C) during measurement.
- Measure diameter of cylinder bore at top, middle and bottom with gauge at right angle and parallel to centerline of engine. Inspect cylinder walls for scoring, roughness or wear. Check bore for out-of-round and taper. Standard bore out-of-round is .0010" (.025 mm). Maximum is .0020" (.051 mm).
- Cylinder bore taper should not be more than .0005" (.013 mm) for thrust side and .0010" (.025 mm) for relief side. If cylinder wall is severely marred and/or worn, refinishing is needed.
- Before cylinder refinishing, ensure main bearing caps are in place and tightened to specification to avoid distortion during refinishing operation. Pistons are available in standard, standard high limit and .010" oversize.