Cylinder head

How it works

The cylinder head closes the top of the cylinder and forms the combustion chamber. It holds the intake and exhaust valves, their springs, often the camshafts, and the spark-plug hole. On liquid-cooled engines it has coolant passages; on air-cooled engines it is covered with fins. Between head and cylinder, the head gasket provides the seal. The head works at very high temperatures: severe overheating can warp it, damaging the gasket and causing compression or coolant leaks. Valve seats and guides also wear with mileage, which can cause loss of compression or oil consumption. Head problems show up as persistent white smoke, coolant that drops with no visible leak, low compression or valvetrain noise. Removing and reconditioning a cylinder head is workshop work.

Maintenance tips

• ✓Keep an eye on engine temperature: most warped heads come from overheating.
• ✓Keep up with valve-clearance checks at the interval in your manual.
• ✓Thick, persistent white smoke from a warm engine, or coolant dropping with no visible leak, points to the head gasket: have it checked.
• ✓Never tighten head nuts at random: the sequence and torque are set by the manufacturer.
• ✓Reconditioning a head (skimming, seats, guides) is a job for a specialist workshop.