The C-series cylinder head is a cast-iron unit with separate ports for all twelve valves, six inlet and six exhaust, unlike the B-series MGB engine which has siamesed ports. The individual porting arrangement allows more efficient gas flow and is one of the reasons the C-series produces its characteristically smooth power delivery. The camshaft and valve gear are located on the right-hand side of the engine, freeing space in the head for the separate port layout. The head is secured by fourteen studs in three lengths, seven long, two medium, and five short, with dedicated nuts and washers.
A Welch plug and a thermal transmitter boss plug seal the remaining apertures in the head casting.
Exchange Cylinder Heads
Reconditioned exchange cylinder heads are available for home market and most export cars. These are supplied as lead-free units, complete with valve guides, valves, and valve springs, ready to fit to a prepared block. Cylinder heads for USA and Canadian specification cars, which were originally designed to accept air injection emissions equipment with additional drillings and connections, may be reconditioned on a customer's own unit basis. Contact MGOC Spares for current availability of North American heads, as these are subject to core unit supply.
Valve Guides, Valves, and Springs
The cylinder head uses twelve identical valve guides serving both inlet and exhaust valves. Standard specification guides are available, along with silicon bronze guides as an alternative offering improved heat dissipation and longer service life, silicon bronze's superior thermal conductivity draws heat away from the valve stem more efficiently, which is particularly beneficial on the exhaust valves where temperatures are highest. Six inlet valves and six exhaust valves are fitted, with the exhaust valves manufactured from a higher-grade material to withstand the greater thermal stress on the exhaust side. The C-series uses a dual valve spring arrangement with inner and outer springs on each valve, seated on spring seats and retained by valve caps and split cotters (twelve pairs).
A complete valve spring set covers all twelve valves. Valve stem oil seals (twelve required) should always be replaced during a cylinder head overhaul, worn seals are a common cause of oil consumption and the blue exhaust smoke on start-up that is often incorrectly attributed to worn valve guides or piston rings.
Rocker Assembly
The rocker assembly comprises twelve individually bushed rocker arms mounted on a single rocker shaft, held to the head by seven pedestal bolts with spring washers. The rocker arms can be rebushed individually, each arm uses one bush secured by a rivet. Twelve tappet adjusting screws with lock nuts allow valve clearance to be set. Six double-coil washers space the rocker arms on the shaft. A grub screw locates the shaft in the correct rotational position.
The rocker cover is sealed by a cork gasket and secured by seven screws with plain washers. On non-USA, non-Canadian cars, an MG badge label and a Weslake patent label were fitted to the rocker cover; North American cars carried an emissions label in place of the MG badge.
Head Gasket and Gasket Sets
The cylinder head gasket is available individually, but a complete top-end gasket set is usually the more practical choice for any cylinder head removal. The top-end set includes gaskets for the cylinder head, manifolds, carburettors, air filters, rocker cover, filler neck, and thermostat, plus all twelve valve stem oil seals. A separate bottom-end gasket set covers the timing cover, sump, oil pump, water pump, and other lower engine sealing faces. Fifteen studs secure the inlet and exhaust manifolds to the head, shared between both manifolds.
Thermostat Housing and Heater Connection
The thermostat is housed in a casting on the front of the cylinder head, with the housing cover secured by two studs with nuts and spring washers, sealed by a gasket. Three thermostat temperature ratings are available: 74°C for hot climates, 82°C as standard, and 88°C for cold climates, all fully interchangeable. A filler neck is bolted to the thermostat housing with three screws, sealed by its own gasket and fitted with a plain non-pressure cap (the system pressure cap is on the separate expansion tank). A heater outlet elbow is fitted to the rear of the cylinder head on cars with a heater, providing the hot water feed to the heater matrix; a blanking plate with gasket is used where no heater is fitted.
Both the elbow and blanking plate are secured by two screws with spring washers.