Engine construction, components and overhaul procedures
Engine construction, components and overhaul procedures covers the block, head, reciprocating assembly, valve train and the measurement discipline that decides whether parts are reused, reconditioned or replaced.
Inspection sequence
- Clean and visually inspect for cracks, scoring and thread damage before measuring.
- Measure cylinder bores at top, middle and bottom in two planes at 90° to each other, using a bore gauge set from a micrometer.
- Check piston-to-bore clearance at the skirt, ring end gap in the bore, crankshaft journal taper and out-of-round, and bearing clearance with plastigauge.
- Check valve stem-to-guide clearance, valve seat recession and head flatness with a straight edge and feeler gauge.
Worked example. Nominal bore 80.00 mm. Top-plane readings are 80.06 mm and 80.04 mm, middle 80.03/80.02, bottom 80.01/80.01. Out-of-round at the top = 80.06 − 80.04 = 0.02 mm. Taper = largest top reading minus largest bottom reading = 80.06 − 80.01 = 0.05 mm. Both are inside a 0.10 mm wear limit, but the ring gap must still be checked in the bore: 0.55 mm against a 0.25–0.40 mm specification is too wide, so the bore is worn or the ring is wrong.
Assembly rules
Torque in the specified sequence and stages, usually three passes. Replace torque-to-yield bolts, gaskets, seals and stretch bolts. Lubricate threads and bearing shells as specified, fit rings with the mark facing up, and time the camshaft to the crankshaft marks before fitting the belt or chain.
Traps
Reusing stretch bolts, fitting rings upside down, omitting the head bolt sequence, and turning a crank with dry bearings.