История и эволюция двигателей BMC серии B

The BMC B series was a line of straight 4 & straight 6 internal combustion engine mostly used in motor cars, created by British automotive manufacturer Austin Motor Company.

The precursor of the "B" series engine was a 1200 cc Overhead Valve (OHV) engine which was used in the 1947 1952 Austin A40 Devon, and, in slightly modified form, in the 1953 Austin A40 Somerset. This engine had many of the same basic dimensions as one of Austin's pre war sidevalve engines the 1125cc engine fitted in the Austin 10 which had the stroke common to all later B Series engines, allowing the use of much of the same installed equipment to produce the block and crankshaft but to an all new OHV design. Beyond this relationship to the pre war Ten's engine, the lineage of the new OHV 1200cc power unit was somewhat complex in the rest of its design it was in essence a scaled down version of the 2199cc engine introduced in 1945 on the Austin 16 hp. The design of this unit were derived from the much larger OHV engine developed for the wartime Austin K5 military truck, which used a 3995cc straight six engine (minus two cylinders this engine became the 2660cc four cylinder engine used in the Austin A90 Atlantic and the Austin Healey 100). The K5 engine was broadly an Austin version of the 3519cc engine built by Bedford for its military trucks, and in turn the Bedford engine was similar in design to the Chevrolet 235 straight six engine Bedford and Chevrolet both being part of General Motors. The common features found on all these engines, from the Chevrolet 235 to the Austin 1200cc, include the design of the valve gear and the cylinder head, especially the siamesed cylinder head ports. The A40 engine was originally drawn up to be produced in two capacities of 990cc and 1200cc to fall into the Eight and Ten tax horsepower classes. Before the A40 was launched, the British government removed the tax horsepower system in favour of a flat tax rate making the smaller capacity redundant. Therefore only the 1200cc version was built but could not be increased in capacity any further since it was already nearly at the maximum bore and stroke dimensions permitted by the design of the block casting. The long stroke, narrow bore characteristics of engines designed for the British taxation system remained. Austin realised that eventually they would need an engine that could power many of its forthcoming medium sized cars, and this would require an engine of at least 1500 cc capacity. Since the A40 Devon engine could not have its capacity enlarged, a new engine needed to be designed and built. The design of this new engine commenced around January 1952, and was designated as the "B" series. The first production version of the B series retained the same 1200cc capacity as the A40 engine and, superficially, appeared to be identical, with the same valve gear, same cylinder head design, same positioning of its ancillary parts (many of which were interchangeable with the older engine) and so on. But the B series block and head were slightly larger in both length and width and the block had thicker cylinder wall castings making the new engine heavier than the A40 motor. This was to allow room for enlargement of the cylinder bore to provide the larger capacities foreseen by BMC. The stroke was retained at and was never altered. Originally of approximately 1.2 Litre capacity, later displacements ranged widely from 1.2 L to 2.4 L, the latter being a six cylinder variant which was only produced in Australia. The most common engine sizes were 1.5 L and 1.8 L and saw service in a number of vehicles. This included a version of the engine built under license in India by Hindustan Motors for its Ambassador series of cars. Petrol versions were produced in the greatest numbers, but diesel versions exist for both cars and marine applications. Meanwhile the earlier 990cc displacement would later indirectly resurface in Japan from the late 1950s at Nissan after the company had engaged an American engine specialist called Donald Stone formerly of Willys Overland as a consultant, Nissan was trying to develop a new 1 litre engine at the time for the 1957 Nissan Bluebird (210/211), but as Stone pointed out, it would have cost a fortune. His suggestion was to shorten the cylinder block of the 1.5 litre B Series licence built in Japan as the 1H engine, thus the 1 litre Nissan C engine also known as the "Stone engine" was born being manufactured on Austin's old transfer machines. When it was later increased to 1.2 litres from 1958, it was named the Nissan E engine. This was followed by the Nissan J engine, distinctly different from the earlier engines yet similar in many ways.

The engine was of conventional construction with a one piece crankcase and cylinder block in cast iron with the crankcase extending down to the lowest level of the main bearing caps; with a cylinder head, also usually in cast iron, and a sump made from pressed steel for rear wheel drive vehicles. Early engines used a three bearing crankshaft, but later engines used five bearings. On all except the rare twin overhead camshaft variant, the camshaft — which was chain driven and mounted low in the block — operated the overhead valves via pushrods and rocker arms. The two inlet ports in the non crossflow cylinder head were shared between cylinders 1 + 2 and 3 + 4 and the three exhaust ports between cylinder 1, 2 + 3 and 4. Valve clearance was adjustable by screws and locknuts on the rocker arms. Another unconventional characteristic of the engine is that the bore spacing is not constant between all four bores. The distance from cylinder 1 to 2 is 3.4375"; 2 to 3 =3.875" ;and 3 to 4 =3.4375". The B series shares many design features (such as the heart shaped combustion chambers and siamese inlet ports designed by Harry Weslake), as well as its basic layout and general appearance, with the smaller BMC A series engine. However another difference was its block's full depth skirt which provided excellent bottom end strength. This made the engine highly durable and suitable for developing into diesel versions in later years.

2 litre B Series prototype was designed by BMC engine man Stan Johnson in 1964 65. This unit displaced 1,998 cc, power output was 106 hp and featured siamesed cylinder bores and offset conrods in order to use the existing 1.2/1.5 litre cylinder block. This engine never went beyond the prototype stage.

There was a six cylinder unit, named "Blue Streak", which was used in the Australian Austin Freeway and Wolseley 24/80.

There were two series of engine numbers used; BMC changed the system at the end of 1956.

Beginning in the early 1970s the numbering system was simplified to "18 V" plus a serial number, where 18 represents the capacity and V = vertical, i. e. longitudinal (in line, not vee arranged) engine with rear wheel drive, and H = Horizontal, i. e. transverse engine with front wheel drive. There was sometimes a country indicator after the first part of the code, e. g. "18V Z" was used for some United States (except California) MG MGB engines.