Engine and Engine Support Systems
Combustion, breathing and support systems
Diesel engines are compression-ignition: air is compressed until its temperature exceeds the fuel's ignition point, and fuel is injected near the end of the compression stroke. Understand the four strokes, valve events, injection timing and duration, and the relationship between camshaft and crankshaft - timing marks must align or the engine runs poorly, or valves contact pistons. Know firing orders, cylinder numbering as defined by the OEM, valve adjustment procedure and lash specifications, and why overhead-cam and pushrod engines use different sequences.
Support systems carry the marks. Cooling: thermostat opening, the pressure cap raising the boiling point (roughly 3°F per psi at sea level), coolant chemistry, deaeration, belt and fan drive, and the difference between overheating under load and overheating at idle. Lubrication: pump, relief valve, filter bypass, oil pressure versus oil level, and oil analysis as a trend tool. Air handling: intake restriction, charge-air cooler leaks, turbo boost control (wastegate or variable geometry), and exhaust backpressure.
Engine mounts, vibration damper, flywheel/flexplate and belt alignment round out the domain. A failed damper or misaligned accessory drive destroys front-end components quickly.
Worked example - cylinder leak-down. Bring the cylinder to TDC on compression and apply regulated air. Leakage heard at the intake = intake valve; at the exhaust = exhaust valve; at the oil filler or dipstick = rings or piston; bubbles in the radiator = head gasket, cracked head or liner. Rule of thumb: a restricted intake and a plugged exhaust both masquerade as low power, so check both ends before condemning the turbo.