The cylinder head closes off the combustion chamber above the piston. It contains oil and cooling ducts, the inlet and outlet ports, and the complete valve timing mechanism. Building a cylinder head is a complex process, making it one of the most expensive engine parts.
Cylinder head cover
The cylinder head cover sits on top of the cylinder head, covering it like a lid. It is made of sheet metal, cast aluminium alloy or plastic. On vehicle engines it often includes the oil filler pipe, and the engine ventilation line terminates in it. Where possible, the cover incorporates an oil separation chamber for engine ventilation. Its design may furthermore vary with the engine design and noise emission situation.