The MGA pushrod cylinder head is a cast iron unit with integral inlet and exhaust ports, secured to the block by studs and nuts. The head carries the valves, valve springs, rocker shaft assembly, and thermostat housing. While the fundamental design is shared across all three pushrod variants (1500, 1600, and Mk II), there are differences in combustion chamber volume and the bore size of the head-to-block gasket that affect parts selection. The 1489cc and 1588cc heads both carry a '15' casting at the rear and are closely related; the 1622cc Mk II head carries a '16' casting and has a larger combustion chamber volume to suit the increased bore.
Head Gasket Identification
The cylinder head gasket must match the engine's bore size. The 1489cc 1500 engine (73.025mm bore) uses a different gasket from the 1588cc 1600 (75.39mm bore) and the 1622cc Mk II (76.2mm bore). Fitting a gasket with the wrong bore size will either restrict the combustion chamber (too small) or allow the gasket to protrude into the bore (too large), both of which cause problems. The gasket type also changed during production, copper-asbestos composite gaskets were used originally, with modern replacement gaskets using non-asbestos materials.
When ordering, the engine prefix (15GB, 15GD, 16GA, or 16GC) determines the correct gasket. A complete head gasket set includes the gaskets needed for head removal and refitting, covering the rocker cover, inlet and exhaust manifolds, carburettor flanges, air filter mountings, thermostat housing, and heater valve, together with new valve stem oil seals.
Valves and Valve Train
The inlet and exhaust valves are carried in pressed-in guides and seated on machined faces in the head casting. Double valve springs, an outer and inner spring on each valve, maintain valve closure and are available as original-specification replacements. Valve stem oil seals, fitted as O-rings under the spring retainers on the inlet valves only, prevent oil running down the valve stems into the guides; exhaust valves are run without seals because combustion chamber pressure prevents oil ingress through the exhaust guides. When reconditioning a head, the valve seats should be recut and, if necessary, new hardened seat inserts fitted for compatibility with unleaded fuel, the original soft seats were designed for leaded fuel and will erode rapidly without the lead's lubricating effect.
Rocker Gear
The rocker shaft assembly bolts to the head on pillars and carries the rocker arms that open the valves via pushrods from the camshaft below. MGA rocker arms are of the forged type, with an adjusting screw and locknut at the pushrod end of each arm by which valve clearance is set. Factory tappet clearance figures differ between the 1500 and the later 1600 and Mk II engines, and between cold and hot settings, the correct specification for a given engine should be taken from the workshop manual for that variant. Worn rocker arm bushes cause excessive side play, accelerating both rocker arm and valve stem wear, and should be checked when a head is removed for reconditioning.
Thermostat Housing
The thermostat housing is bolted to the front of the cylinder head and carries the thermostat that regulates coolant temperature. The same housing is used across the pushrod MGA range. The thermostat is available in three temperature ratings: 74°C for hot climates, 82°C as standard, and 88°C for cold weather use. A blanking sleeve is available for running without a thermostat, though this is not recommended, the engine will overcool in normal ambient temperatures, run inefficiently, and may fail to warm to its proper operating temperature in cold weather.
Performance Cylinder Heads
Gas-flowed and ported cylinder heads (Stage II specification) are available for all pushrod variants. The Stage II head delivers measurable improvements in airflow velocity and volume through the inlet and exhaust ports, translating directly into increased power and torque. A Stage II head complements an engine rebuild whether the rest of the engine remains standard or is modified, improving airflow and efficiency without requiring supporting modifications elsewhere. The head is supplied fully assembled with valves, uprated valve springs, bronze valve guides, and rocker gear fitted, and is set up for unleaded fuel as standard.
Ordering Notes
When ordering cylinder head components, the engine prefix is essential, this determines the bore size (for gaskets) and identifies any variant-specific differences. For complete head rebuilds, a head gasket set provides all the gaskets required for head removal and refitting. The head gasket set should be used in conjunction with a conversion gasket set (which covers the lower engine gaskets) if a full engine rebuild is being undertaken, timing cover and rear crankshaft seals are purchased separately.