The MGC is powered by the BMC C-series 2,912cc inline six-cylinder engine, a unit that shares no components with the four-cylinder B-series engine fitted to the contemporary MGB. The C-series has its origins in the 1950s Morris Engines design that powered BMC saloons and the Austin-Healey 100-Six and 3000. The MGC version incorporates a seven main bearing crankshaft derived from BMC Australia's 'Blue Streak' design, in place of the four-bearing crankshaft of the Austin-Healey 3000. With a bore of 83.36mm and a stroke of 88.9mm, the engine produces 145 bhp at 5,250 rpm and 170 lb/ft of torque at 3,400 rpm from a 9.0:1 compression ratio.
A low-compression version was never offered, every MGC engine runs at 9.0:1 regardless of market. The camshaft and valve gear sit on the right-hand side of the engine, freeing the cylinder head for separate ports to all twelve valves where the MGB has siamesed ports. It is a bulky and heavy engine, approximately 2 inches shorter than the Healey 3000 unit but weighing 650 to 700 lb against the MGB engine's 360 lb.
Engine Identification and Prefixes
Every MGC engine carries a prefix identifying its specification, market, and gearbox type. The prefix is stamped on a plate on the right-hand side of the block below the cylinder head, and is the single most important reference when selecting parts. The three engine series are: 29G, the standard 2,912cc engine for home market and most exports; 29GA, the emissions-controlled engine for the USA and (from August 1968) Canada; and 29GB, an under-bored 2,850cc version for the French market, designed to fit below the French 15CV taxation threshold. Within each series, suffix letters denote gearbox type: U for manual, RU for manual with overdrive, and RC for automatic.
All prefixes end with H, denoting high compression. The 29G series ran from 101 to 4969, the 29GA from 101 to 4425, and the 29GB from 101 to 344. Exchange engines carry their own prefixes: 68G347 (manual) and 68G355 (automatic) for 29G units, 68G366 and 68G367 for 29GA, and 68G380 and 68G382 for 29GB.
Engine Finish and Appearance
MGC engines were finished in a distinctive pale silver-grey-green, the traditional Austin-Healey engine colour, not the maroon red of the MGB B-series or the black of the later 18V series. This colour extended to most engine-mounted ancillaries including the oil filter housing and starter motor. On very early cars, approximately the first 100 MGCs, the rocker cover was finished in crackle black. All subsequent cars had the rocker cover in silver-green.
Two self-adhesive labels were fitted to the rocker cover: the front with the MG badge, the rear with Weslake patent numbers.
Production Changes
Although the MGC's two-year production run yielded fewer engine changes than the eighteen-year MGB, several revisions are important for parts selection. The starter motor was modified from engine numbers 29G/624 and 29GA/127, with a new type of solenoid and other changes; the revised type was fitted to 29GB engines from the start of that series. A new oil pressure relief valve was introduced from engine numbers 29G/2756, 29GA/357, and 29GB/171. The most significant change came with the 1969 model year in October, November 1968, from car number 4236 and engine numbers 29G/3201 and 29GA/1401.
The original positive crankcase ventilation system was replaced by a carburettor-based system, the 16AC alternator and separate control box gave way to a 16ACR with built-in regulator, new carburettor specifications were introduced, non-overdrive cars adopted the higher overdrive-car gearbox ratios, and all cars received a revised reverse detent. From August 1968, Canadian cars received the 29GA engine.
Ordering Considerations
The MGC engine shares no internal components with the MGB B-series, all gasket sets, bearings, timing chain components, camshaft, oil pump, pistons, and cylinder liners are MGC-specific. Two gasket set options cover the engine: a top-end set covering the cylinder head, manifolds, carburettors, valve gear, and thermostat; and a bottom-end set covering the timing cover, sump, oil pump, water pump, and lower engine sealing faces. The engine prefix determines which ancillaries are correct for the engine fitted, including alternator type, crankcase breathing components, crankshaft pulley, and carburettor specification. Piston and ring sets for the 2,850cc 29GB engine are typically manufactured to order.
With fewer than 9,000 MGCs built, some exchange components depend on the availability of rebuildable cores.