Engine Construction, Operation and Overhaul
How the engine works
A candidate must know the major components - cylinder block, head, piston, rings, connecting rod, crankshaft, camshaft, valves, and timing drive - and the four-stroke cycle: intake, compression, power, exhaust. Valve timing, firing order, compression ratio, clearance volumes, and valve overlap must be understood. In overhaul, measure cylinder bores for taper and ovality, check piston-to-bore clearance, ring end gap, crankshaft journal wear, and bearing clearances with Plastigauge. Follow the manufacturer's torque sequence and angle-tightening procedure.
Traps in questions
Questions often confuse TDC on the compression stroke with TDC on overlap; the distributor or timing marks must align with cylinder one on compression. Ring gaps must be staggered, not lined up, and the top ring may have a marked side facing up. Compression ratio is (swept volume + clearance volume) divided by clearance volume, not swept volume divided by clearance volume. Do not assume a rebuilt engine needs no running-in; bed in rings and bearings with controlled load. Another trap is mixing up valve clearance measurement hot versus cold.
Rule of thumb
Measure twice, machine once. If a bore is worn beyond the limit, rebore and fit oversize pistons rather than merely fitting new rings.
Worked example: a cylinder has a swept volume of 450 cm³ and a clearance volume of 50 cm³. Compression ratio = (450 + 50) ÷ 50 = 10:1.