Engine and Engine Support Systems Servicing
This domain tests the four-stroke cycle, valve clearance, timing, compression, lubrication, cooling, and engine mounts.
Core rules
- Four strokes: intake, compression, power, exhaust; two crank revolutions per cycle.
- Valve clearance is set cold or hot exactly as specified, at TDC compression for the cylinder being adjusted, following the firing order.
- Timing marks on crank, cam, and oil pump must align; never rotate a belt-tensioned engine backwards.
- Compression test: throttle open, all plugs out, good battery; cylinders should usually be within 10% of each other.
- Cooling: correct cap rating, thermostat opening temperature, 50/50 coolant mix, and no air pockets.
- Engine mounts: check for cracked rubber and separated bonding; support the engine before removal.
Worked example
Specifications: intake 0.20 mm, exhaust 0.25 mm, cold, firing order 1-3-4-2. Reasoning: cylinder 1 at TDC compression has both valves closed, so the feeler gauge that drags slightly is correct. Rotate the crank 180° per firing-order step and adjust each cylinder at its own TDC compression. If you adjust at overlap - exhaust closing, intake opening - the clearance reads loose and the valve ends up over-tightened, risking a burned valve or rough idle.
Traps
Adjusting at TDC overlap; using a hot spec on a cold engine; forcing a timing belt over a misaligned mark; reusing a stretched belt; opening the cooling system hot; jacking the engine by the oil pan.