Fitting Pistons & Rings
NOTE:
Pistons and rings are available in .50 mm, .75 mm and 1 mm oversize for 3A-C and .50 mm oversize for 4A-C engines.
- Inspect cylinder block for cracks or flaws. Using bore gauge, measure for out-of-round or excessive taper. If measurement exceeds .0008" (.020 mm), refinish bore. If one cylinder is bored, all must be bored. Check head gasket surface for warpage. Maximum limit is .002" (.05 mm).NOTE: Before cylinder block machining operations, ensure main bearing caps are installed and tightened to specification. Bore cylinders in order of No. 2-4-1-3 to prevent distortion.
- Determine piston oversize according to cylinder wear. Standard bore diameter is 3.0602" (77.73 mm) for 3A-C and 3.1890-3.1902" (81.000-81.030 mm) for 4A-C. Bore wear limit is .008" (.20 mm). Measure piston diameter at right angle to pin and .20" (5.0 mm) below oil ring groove. See PISTON DIAMETER SPECIFICATIONS table.PISTON DIAMETER SPECIFICATIONS
Application In. (mm) Standard 3A-C 3.0468-3.0480 (77.390-77.420) 4A-C 3.1850-3.1864 (80.90-80.93) - After honing cylinder to final fit, measure piston-to-cylinder clearance with parts at 70°F (20°C). Ensure difference of bore limit between cylinders is .002" (.05 mm) or less. If beyond limit, cylinders must be bored.
- Measure side clearance of rings in grooves as each is installed. Check ring end gap. Install ring squarely in cylinder, using piston. If beyond limits, replace piston and/or rings. When installing rings, ensure code mark faces up. See Fig 1.