Engine Systems: Construction, Operation and Maintenance
Domain 3: Engine Systems: Construction, Operation and Maintenance
This domain examines how a four-stroke engine produces power, the function of major components, and the maintenance tasks that keep it reliable. The exam expects correct terminology, clearances, timing and diagnostic reasoning.
Core rules
- Four strokes: intake, compression, power, exhaust. The crankshaft makes two revolutions per cycle; the camshaft makes one.
- Know the firing order and mark TDC on the compression stroke. Timing marks must align before belt or chain removal.
- Critical clearances include valve clearance, piston ring end gap, bearing oil clearance and cylinder taper. Compare with manufacturer limits.
- Torque fasteners in the specified sequence and stages, especially cylinder heads. Some bolts are torque-to-yield and must be replaced.
- Lubrication and cooling are systems: oil pump, filter, galleries, thermostat, water pump, radiator and fans. Low oil pressure or overheating must be diagnosed, not masked.
- Maintenance includes oil and filter, air filter, coolant condition, drive belts, PCV system and checking for leaks.
Worked example
A four-cylinder engine has low compression on cylinder 2. A wet test is done by adding a small amount of oil to the cylinder and repeating the test. If compression rises noticeably, the oil has sealed worn piston rings. If it stays low, the leak is more likely valve sealing, a head gasket or a cracked head. The reasoning separates bottom-end from top-end leakage before disassembly.
Traps
- Rotating the engine after removing a timing belt without aligning marks.
- Reusing torque-to-yield head bolts.
- Opening the cooling system when hot.
- Using the wrong oil viscosity or coolant type.
- Assuming a misfire is always ignition; check compression, fuel and mechanical condition.