Cylinder Head

Most modern cylinder heads are cast aluminium. They contain the combustion chambers, intake and exhaust ports, valve guides and seats, coolant passages and oil galleries, and mount the spark plugs or injectors. The head is bolted to the engine block with a head gasket between them. Head bolts are tightened in a set order and often to an angle, and many are stretch bolts that must be replaced.

Engines are described by head layout: SOHC heads have one camshaft per bank, DOHC heads have two. Some heads integrate the exhaust manifold to warm up the catalytic converter faster.

Air or mixture flows in through the intake ports past the intake valves, and exhaust gas leaves through the exhaust ports. Coolant flows through the head to remove heat from the combustion chambers and exhaust side.

Severe overheating can warp or crack a cylinder head, which causes coolant loss, overheating and white smoke. After overheating, the head flatness is checked and the head may need machining or replacement. Oil leaking from the valve cover gasket on top of the head is a common, usually minor leak that can drip onto the hot exhaust and smoke.