The leader of the engine design section for the, A30 was W.V.Appleby who was later
to become Chief Designer of engines and gearboxes for BMC. The photograph below
shows him inspecting an example of an engine he designed 30 years ago.
Reference has already been made to experiments with a twin cylinder version of the
A40 engine, but Bill Appleby says that this engine was almost impossible to balance
satisfactorily and difficult: to mount in the car if vibrations were to be to an
acceptable level. In any case, the cost of producing a vertical twin in water cooled
form would only have been about 12.5% cheaper than a four cylinder engine of twice
the capacity. This is because the twin cylinder engine need a larger flywheel and
large balance weights have also to be built into the crankshaft. Furthermore, all
engine ancillaries are just as expensive as in the four cylinder unit.
A three cylinder in-line unit gave similar problems, and so the four cylinder in-line
unit was favoured because the two firing strokes per revolution were the least required
for the stand of smoothness they were wanting. As Bill Appleby put it, they had
come to precisely the same decision as had Herbert Austin when he designed the original
Having determined the type of engine, the next step was to decide on the stoke/bore
ratio. The A40 engine had proved a great success and so the same stroke/bore ratio
was retained (1.3:1) giving a bore of 59mm and a stroke of 76mm in the case of the
A30 and since the actual stroke was shorter this meant a useful reduction in piston
speed of some 14%.
The electrical equipment was fitted on the opposite side of the engine to the carburettor
in order to keep it away from the heat of the exhaust manifold and also from possible
petrol drips. The oil pump was to be driven from the rear of the camshaft in order
to reduce the cost of providing another gear but this resulted in the pump being
above the oil level in the sump and so the pump would require priming after an engine
strip down. (Take note you engine strippers!) Bill Appleby was not happy about this
arrangement but Johnnie Rix, Chief Designer, insisted that it was a necessary economy.
Austin were proud of the superior pulling power and general efficiency of their
engines compared to say the equivalent Fords of the time and careful attention was
given to the features that produced these characteristics such as large valves and
comparatively heavy flywheels wheels. The cylinder head incorporated the Weslake
form of combustion chamber which is heart-shaped and directs the incoming gas towards
the plug due to the plug being situated. at the apex. Several other details of the
chamber led to excellent efficiency and Zenith remarked more than once that combustion
in the A-Series engines was more constant than any other engines they were testing
at the time. In 1951 only Pool petrol was available in this country and so the compression
ratio was restricted to 7.2:1. In the A35 the C.R. was raised to 8.3:1 as Premium
petrol was then available.
The A-Series engine must surely rank as one of the greatest small engines ever produced
and since its introduction in the A30 it has been used in a whole series of BMC
and BL small cars right through to its present day use in the A Plus form installed
in the Austin Metro. Its designers have good reason to feel fairly satisfied that
they 'had just about got it right'.
© Reproduced by kind permission of the author, Barney Sharratt