Engine More sub catagories: Crankshaft Cylinder block Cylinder head Oil filter Oil sump

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After the formation of BMC in 1952, it became a priority to develop a new medium-sized six-cylinder engine to replace the corporation's three different engines in the 2- to 3-litre bracket - the Morris/Wolseley sohc six, and the Austin and Riley fours. The new design was based on the existing 1.2/1.5-litre Austin/BMC B-series whose stroke of 88.9 mm and general layout the new engine shared.

The resulting C-series engine was the work of the engineers of Morris Engines Branch in Coventry where these engines were also made. With a bore of 79.4 mm, the capacity of the original six-cylinder was 2639 cc. This engine was introduced in new Austin, Morris and Wolseley saloons in 1954-55. Depending on carburation and tuning it developed between 86 and 95 bhp in its original form.

Both block and cylinder head were made from cast iron. The crankshaft ran in four main bearings, originally of the white metal lined type, but changed to the lead-indium type in 1959 soon after the introduction of the 3000 model. Originally there were water passages between all cylinders, but on the 3000 engine, which was bored out to 83.4 mm for a resulting capacity of 2912 cc, the cylinders were siamesed in three pairs. The camshaft was on the right-hand side of the engine low down, driven by chain from the crankshaft. A timing chain tensioner was fitted, on the 3000 Mark II and later models supplemented by a vibration damper. The vertical in-line overhead valves were activated by push-rods and rockers.

The potential output of the new engine was originally limited by the fact that the cylinder head had a cast-in inlet manifold. The major change which occured during the production run of the original 100-Six model was the substitution of a much improved cylinder head with a separate inlet manifold and separate ports for all cylinders, known variously as the six-port or the twelve-port engine. At the same time the valves were increased in size, the compression ratio was changed with the adoption of flat-topped pistons, and larger carburettors were fitted. The engine was installed in some cars from car/engine number BN4/48863 in October 1957, and in all cars from 52602 in November 1957. The revised engine was found on all Abingdon-built BN4 models as well as the last Longbridge-built cars, and on all BN6 models. (Cars with the more powerful engine were originally launched in the USA as the 100-Six MM, MM for Mille Miglia).

The next important change was the introduction of the 2912 cc engine in the first 3000 (engine type 29D) in March 1959. Another change which occured early in 3000 production was the substitution of a gear-type oil pump in place of the original Hobourn-Eaton rotary vane type. In March 1961, 3000 MK II models received engine type 29E fitted with the three carburettor manifold, but in the following year, the Mark II Convertible reverted to a twin carburettor set-up on engine type 29F. In October 1962, French export cars became available with the under-bored 2860 cc engine (29FF) to suit French vehicle taxation. The final type of the engine was 29K, introduced in October 1963 for the Mark III Convertible, more powerful still with bigger carburettors. For France this became the 2860 cc type 29KF, although some later French cars reverted to the 2912 cc capacity with engine type 29KFA.

It is not without interest to realise that what was basically the same car, with not a great deal of extra weight, was given almost 50 per cent more power in the course of development.

The original valve size on the first 100-Six was 1.69 in for the inlet valves, and 1.42 in for the exhaust valves. On the six-port engine and on all 3000 engines, valves were increased to 1.75 in (inlet) and 1.56 in (exhaust). With different camshafts used, the valve timing  on 100-Six and 3000 Mark I models was 5°/45°/40°/10°. The 3000 Mark II, until engine number 29F/2285, had valve timing of 5°/45°/51°/15°. Subsequent Mark II BJ7 models from engine number 29F/2286 had 10°/50°/45°/15°. Finally, for the 29K engine in the Mark III, valve timing was 16°/56°/51°/21°. Engine oil capacity was around 12³/₄ imperial pints, including the external oil filter (Tecalemit or Purolator). Normal oil pressure while running was 55-60 lb for the 100-Six, 50 lb at 40 mph for the 3000.

The engine was finished in the same metallic grey-green colour as used on the 100, including the bellhousing, dynamo, oil filter, starter motor and engine mountings. The standard rocker cover was made from pressed steel, painted engine colour, and had a twist-lock oil filler cap with a retaining wire at the front. The maker's name label always read simply Austin. A breather pipe was incorporated at the rear of the rocker cover, of T-shape linking up with a breather pipe from the engine side cover. A cast aluminium rocker cover with a quick release oil filler cap and red Austin-Healey script was a contemporary after-market accessory, not a factory fitting.

Summary of Engine Specification