The 1275cc cylinder head is a cast iron design with siamesed inlet ports on the same side as the exhaust ports, both inlet and exhaust manifolds bolt to the same face of the head. (The head is therefore not a true crossflow design.) It is secured to the block by nine studs and nuts, with plain washers fitted beneath the nuts on five specific stud positions. Head studs should be tightened to the correct torque in the specified sequence, tightening in the wrong order or to the wrong torque can distort the head, causing gasket failure and coolant or oil leakage.
Thermostat Housing
Three different thermostat housing covers were used during 1275cc production: a vertical-flow type for early cars with the thermostat outlet pointing upward, and crossflow types for later cars with the outlet directed to the left-hand side of the radiator. The correct cover must be matched to the cooling system layout. The thermostat housing gasket is specific to each cover type.
Valves
Valve sizes on the standard head are 1.31 inches (inlet) and 1.15 inches (exhaust). Valve guides are common to both positions. Valve springs are a dual arrangement with an outer and inner spring on each valve, and inlet valves carry an oil seal on the stem. The rocker shaft assembly bolts to the head via four pillars, and three distinct rocker arm types were used across production, forged, pressed, and sintered, each with its own specific adjusting screw.
Mixing rocker arm types with incorrect adjusters results in poor valve clearance control and potential valve train damage.