Fitting Pistons & Rings

NOTE: Pistons and rings are available in .50 mm, .75 mm and 1 mm oversize for 3A-C and .01 mm and .02 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 measurements exceed .0008" (.020 mm), refinish bore. When 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 3.0512-3.0524" (77.500-77.530 mm) for 3A-C and 3.1890-3.1894" (81.000-81.010 mm) for 4A-C. Bore wear limit is .008" (.20 mm). Measure piston diameter at right angle to pin and .20" (5 mm) below oil ring groove. Add piston-to-cylinder clearance. Determine finish hone of cylinder.

PISTON DIAMETER SPECIFICATIONS

Application		In. (mm)
3A-C
Standard		3.0468-3.0480 (77.390-77.420)
0.50 mm Oversize		3.0665-3.0677 (77.890-77.920)
0.75 mm Oversize		3.0764-3.0776 (78.140-78.170)
1 mm Oversize		3.0862-3.0874 (78.390-78.420)
4A-C
Standard		3.1846-3.1850 (81.890-81.900)
0.01 mm Oversize		3.1850-3.1554 (80.900-80.910)
0.02 mm Oversize		3.1854-3.1858 (80.910-80.920)

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.
If reusing pistons, decarbon ring grooves with scraper and curved steel wire or piece of broken ring. Clean oil slots in bottom land of oil ring groove. Check for scratches, wear or damage.
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.

Fig 1: Positioning Piston Ring Gaps

NOTE: Ensure ring gaps are not on thrust side of piston and code marks on rings face up.