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 the same basic dimensions as one of Austin's pre-war sidevalve engines but to an all-new OHV design which had many features copied from the Chevrolet 235 straight-six engine used on military trucks that the Austin works had overhauled during the Second World War. These features included the valve gear and especially the siamesed cylinder head ports. 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 89 mm 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 an Australia only production six-cylinder variant. 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.[1] Petrol versions were produced in the greatest numbers, but diesel versions exist for both cars and marine applications.
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