Head Gasket

The head gasket sits between the cylinder head and the cylinder (or block). It must seal against high combustion pressure and temperature while also keeping coolant and oil passages separate.

Modern bikes usually use multi-layer steel (MLS) gaskets; older and many two-stroke engines use copper or composite gaskets or O-rings. Gasket thickness affects the compression ratio and the squish clearance, so the correct thickness matters.

Signs of a failed head gasket include coolant loss with no visible leak, white steam from the exhaust, bubbles in the radiator, milky oil or overheating. Always fit a new head gasket when the head is removed and tighten the head bolts in the specified sequence and torque.