Fitting Pistons
- Inspect pistons and replace any showing signs of excessive wear, wavy ring lands, or fractures. Replace piston 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. Replace piston and/or rod as necessary. Inspect connecting rods for signs of fracture and bearing bores for out of round and taper.
- If bore exceeds recommended 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. 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 other signs of wear. Check bore for out-of-round and taper. Cylinder bore out-of-round should not be more than .003" (.076 mm). Cylinder bore taper should not be more than .003" (.076 mm).
- Measure outer diameter of piston at centerline of pin bore and 90° to pin bore axis. If cylinder wall is severely marred and/or worn beyond specifications, refinishing will be necessary.
- Pistons are available in four variations each of standard, .020" (.50 mm) and .040" (1 mm) oversize. Measure new piston and hone cylinder to correct clearance.
- Before cylinder refinishing, ensure that main bearing caps are in place and tightened to specification to avoid distortion during refinishing operation. After refinishing operation, allow bore to cool, then clean bore with soap and water solution and oil cylinder walls.