Cylinder Head
The cast-metal block bolted to the top of the engine cylinders that houses the intake and exhaust valves, spark plugs, and camshafts.
The cylinder head is a massive metal casting—usually made of aluminum or cast iron—that sits bolted to the top of the engine block. It forms the ceiling of the combustion chambers and houses the intake and exhaust valves, valve springs, fuel injectors, spark plugs, and in overhead-cam (OHC) engines, the camshafts. It also contains intricate passageways for engine coolant and oil to circulate.
The joint between the cylinder head and the engine block is sealed by the head gasket, which must withstand high combustion pressures. Because the cylinder head is located at the top of the engine, it is highly sensitive to overheating.
If the engine runs hot, the cylinder head can warp or crack, causing the head gasket to blow, coolant to leak into the cylinders, or oil and coolant to mix. A warped or cracked cylinder head must be machined (surfaced) or replaced to restore proper engine compression and prevent catastrophic engine failure.