Automotive Engine Systems and Overhauling
Engine fundamentals
Understand the four-stroke cycle: intake, compression, power, exhaust. Know bore, stroke, swept volume, clearance volume, compression ratio and engine capacity. Compression ratio = (swept + clearance volume) / clearance volume. Valve timing, overlap, firing order and valve clearance affect breathing and smoothness. Petrol engines use spark ignition; diesel engines rely on high compression for ignition.
Overhauling procedure
Typical sequence: strip, clean, inspect and measure, then recondition or replace, then reassemble to specified torques and clearances. Measure cylinder bore for taper and ovality, piston-to-bore clearance, ring end gap, crankshaft journal wear and bearing oil clearance (plastigauge). Check valve stem clearance, valve seat angle and spring free length. Torque sequences are usually spiral from the centre outward to avoid distortion; some fasteners are torque-to-yield and must be replaced.
Traps: confusing swept volume with total capacity; forgetting that oversize pistons require reboring; mixing up valve lead and lag; ignoring ring gap orientation; reusing stretch bolts; and failing to check crankshaft end float.
Worked example: bore 80 mm, stroke 90 mm, four cylinders. Swept volume per cylinder = pi/4 x 8^2 x 9 = 452.4 cm3; total = 1810 cm3 (about 1.8 litres). Rule of thumb: ring end gap roughly 0.003 to 0.004 times bore in mm for many engines, but always follow the manufacturer's specification.