The upper engine components sit above the cylinder head and are the most accessible area of the MGA engine for routine maintenance. They comprise the rocker cover, rocker shaft assembly and rocker arms, pushrods, cam followers (tappets), oil filler cap, and associated fixings.
These components are where the owner most frequently interacts with the engine, valve clearance adjustment, oil top-ups, and rocker cover gasket replacement are among the most common service tasks on any MGA.
Rocker Cover
The pushrod MGA rocker cover is a pressed steel item, painted in the same dark red or maroon as the rest of the engine. It seals to the cylinder head via a cork gasket and is held by two centre studs with domed nuts, spacers, and cup washers, the nuts, spacers, and cup washers are also available in chrome-plated alternatives for owners seeking a more polished appearance. At the rear of the rocker cover are two rectangular plates, the MG badge on the right-hand side and the patent numbers plate on the left, attached by small rivets. A brass plate bolted to the rear of the carburettor balance pipe carries the firing order (1-3-4-2) and the factory-specified valve rocker clearance for the engine, providing a useful at-a-glance identification feature on original cars.
An alloy rocker cover with a cast MG logo, chrome filler cap, and chrome or knurled nuts is available as an upgrade, offering both an aesthetic improvement and better heat dissipation. When fitting a non-standard rocker cover, the breather arrangement must be maintained, the crankcase ventilation system draws fumes through the rocker cover, and blocking or removing the breather connection will pressurise the crankcase and cause oil leaks.
Oil Filler Cap
The original oil filler cap is a bayonet type fitted toward the front of the rocker cover. It was finished in cadmium plating and embossed with the brand names of eight recommended lubricants. On early cars, a slightly different cap may be found with a separate top plate carrying the oil brand names printed in black on a tan background. The cap was held against the cover by a short wire tether to prevent loss during oil top-ups.
Reproduction caps to the original bayonet specification are available, as are chrome filler caps that suit alloy rocker covers.
Rocker Gear
The rocker shaft assembly sits on pillars bolted to the cylinder head and carries eight rocker arms, one for each valve. Each rocker arm pivots on a bronze bush pressed into its bore, and it is this bush that suffers wear over time, leading to excessive side play, rocker arm tilting, and accelerated wear on both the rocker shaft and the valve stems. Rocker arms, bushes, and the complete rocker shaft assembly are available as individual replacements or as a fully exchange-reconditioned assembly. Worn bushes should be replaced when the rocker gear is dismantled, as a worn rocker arm left in service will wear the valve stem and shaft in equal measure.
Pushrods and Cam Followers
Eight pushrods connect the cam followers in the block to the rocker arms on the cylinder head. The pushrods are of tubular steel construction with hardened ball ends. The cylindrical cam followers sit in bores in the cylinder block and are lifted by the camshaft lobes rotating beneath them. Worn cam followers develop a concave wear pattern on their face, which accelerates camshaft lobe wear, if the camshaft is being replaced, the followers should always be renewed at the same time.
Cam followers and pushrods are common across the 1500, 1600, and Mk II engines, with one important exception. Tappets and pushrods fitted to early 1500 engines (before engine number 15GB5504) are dimensionally different to the later items and are not interchangeable with the later specification.
Early-engine owners should identify their engine number before ordering, and the early tappets and pushrods must be replaced in matched pairs rather than mixed with later parts.
Twin Cam Upper Engine
The Twin Cam engine has a fundamentally different upper engine arrangement. Instead of a single rocker cover, pushrod, and tappet arrangement, the Twin Cam has two camshaft covers, one for each camshaft, with an MG badge cast into the front of each cover, the letters and octagon picked out in red. The cam covers are finished in natural aluminium rather than painted red like the rest of the engine. The Twin Cam uses inverted bucket tappets operated directly by the camshafts, with shim adjustment rather than the screw-and-locknut arrangement of the pushrod engine.
The screw-in oil filler cap is fitted to the left-hand cam cover adjacent to the MG logo. No Twin Cam upper engine components are interchangeable with the pushrod cars; Twin Cam parts fall outside the standard pushrod range and specialist support should be sought directly from the MGOC Spares team or a recognised Twin Cam specialist.