Air cleaner specification on the MGA is one of the clearest visible differences between the pushrod cars and the Twin Cam, and is one of the first areas to check when ordering replacement parts or restoring an original intake. The breather side of the node covers the crankcase ventilation hardware that was built around the engine's rear side cover and the oil filler cap fitted to the rocker or camshaft covers. Both systems were specified to the engine type rather than to the MGA as a whole, so ordering begins with identifying which engine is in the car.
Pushrod air cleaners, 1500, 1600 and 1600 Mk II
All pushrod-engined MGAs were fitted with individual round pancake Vokes air cleaners, one per SU H.4 carburettor, each housing an oil-wetted mesh element and finished in black. Replacement bodies, retaining hardware and elements are available as service items. The round-pancake assemblies mount directly to the carburettor bellmouths via a flange-and-stud arrangement and sit either side of the engine with no remote air inlet ducting. When servicing, the oil-wetted element is cleaned in solvent, allowed to dry and then re-oiled before being refitted, dry elements give reduced filtration and increased intake noise.
Twin Cam air cleaners
The Twin Cam uses a quite different arrangement. Its HD.6 carburettors are paired with an elongated oval Vokes air cleaner specific to the model, again with an oil-wetted element. From car/chassis 2468 the cleaner was modified with a venturi incorporated in each body, which changed the intake characteristic and also altered the internal profile. Twin Cam cleaner bodies and elements are not interchangeable with the pushrod pancake type and should be ordered specifically to the Twin Cam specification.
Owners of early Twin Cams should also check whether their car is pre- or post-2468 when sourcing replacement cleaners, as the venturi-modified bodies are distinguishable from the earlier plain-interior type.
Oil filler caps and rocker/cam cover breathing
Pushrod MGA rocker covers carry a bayonet-type oil filler cap mounted towards the front of the cover. The cap is cadmium-plated and was embossed with recommended lubricant brand names. The cap forms part of the engine's breathing route in combination with the rear side-cover breather. Reproduction caps are available; when sourcing one for a concours-specification car, the embossed lubricant branding and cadmium finish should be confirmed.
The Twin Cam arrangement is different in detail. Its oil filler cap is a screw-in type mounted on the left-hand camshaft cover adjacent to the MG logo, rather than a bayonet fitting on a pushrod-engine rocker cover. The two cap types are not interchangeable and are supplied specifically to each engine family.
Crankcase breather, pushrod cars
Pushrod MGA engines vent through a rear-side-cover breather typical of the BMC B-series architecture of the period, with a road-draught tube routing crankcase vapour to atmosphere under the car. Replacement side-cover gaskets, breather elbows and hose connections are available as service items. When rebuilding, the side cover should be confirmed clean and the breather passage clear, since restricted breathing raises crankcase pressure and promotes leaks at the rear main oil seal.
Crankcase breather, Twin Cam
The Twin Cam uses the same principle of a cylinder block rear side cover breather pipe but with a different routing, and the arrangement was revised in service. At Twin Cam engine number 657 (December 1958) the breather pipe was modified to prevent oil leaking onto the exhaust system, a known early-production issue.
Replacement Twin Cam breather pipes, side cover components and associated fixings should be ordered to the Twin Cam specification and, where relevant, to the post-657 pattern.
Ordering considerations
Because air cleaner and breather hardware is specified to the engine rather than to the car body, the starting point when ordering is always the engine prefix: 15GB or 15GD for 1500 pushrod cars, 16GA for 1600, 16GC for 1600 Mk II, and the separate Twin Cam engine series. Cars that have been re-engined, most commonly with an MGB-type unit, will carry different breather and air cleaner hardware from factory, and the service items required should be matched to the engine actually fitted rather than to the chassis.