Core Functions of Engine Cylinder Head Cover (Valve Cover)
The cylinder head cover refers to the stamped or aluminum alloy cover on the top of the engine as you mentioned. It is directly fastened onto the top of the cylinder head and has five core functions:
1. Sealing and oil leakage prevention (primary function)
It covers the valve mechanism on the upper part of the cylinder head. Engine oil splashes inside to lubricate the camshaft and valves.
Sealing is achieved by compressing the valve cover gasket to stop engine oil from leaking out, preventing grease contamination inside the engine compartment and fire hazards caused by oil dripping onto the high-temperature exhaust pipe.
2. Crankcase Sealing and Oil-Gas Separation
Its inner cavity is part of the crankcase. Blow-by gas (mixed gas and exhaust gas) is produced during engine operation. The cover is integrated with an oil-gas separator and a PCV valve.
It condenses oil vapor and lets the engine oil flow back to the oil pan, and guides exhaust gas into the intake manifold for secondary combustion. This prevents excessive crankcase pressure from rupturing oil seals and causing oil leakage, as well as avoids environmental pollution from direct exhaust of waste gas.
3. Dustproof, Waterproof and Protective
It blocks dust, muddy water and foreign matter from entering precise valve train components such as valves and camshafts.
It prevents water intrusion during car washing or rainy weather, so as to avoid engine oil emulsification as well as rust and jamming of parts.
4. Noise Isolation and Operation Noise Reduction
Valves and camshafts generate loud knocking noise when running at high speed. Enclosing these components with the cover can greatly reduce abnormal noises in the engine bay.
An extra stamped decorative cover is installed on the outer layer of many engines to further improve sound insulation and deliver a tidier appearance.
5. Provide mounting reference points
It reserves mounting positions for the oil filler port, waste gas connector and sensors, as well as fixing bolt holes.
On some vehicle models, the ignition coils are mounted directly on the cylinder head cover.
Common Fault Points
1. Aging and hardening of the cover gasket leads to engine oil seepage.
2. Clogged PCV valve causes excessive crankcase pressure, unstable idling, oil seal leakage and increased oil consumption.
3. Deformation of aluminum covers or cracking of plastic covers results in sealing failure and oil leakage.
