Paper 1: The B.M.C. ‘A’ Series Engine

Abstract

This engine was first introduced in 800 cm³ form in 1952, and the paper traces its subsequent design history, culminating in the 1098 cm³ version for transverse installation.

Originally designed for the post-war Austin 7 saloon, this engine was reclassified as the ‘A’ series unit at the time of the formation of the British Motor Corporation. It was then decided that this unit and its derivatives would power all the smaller range of B.M.C. cars.

After a logical development to 950 cm³ a new design situation was created by the concept of the ADO.15 which subsequently evolved into the Mini 7 and Mini Minor. During this period both two-stroke engines and a two-cylinder version of the ‘A’ series were developed, but were discarded in favour of the 850 cm³ four-cylinder unit.

The reasons for this decision, which include both economic and technical considerations, are discussed in detail. The modifications required to suit the transverse installations are also considered.

A further design challenge was presented by the power requirement for the ADO.16, especially as the relatively high power/weight ratio of the Minis had set a high standard in this respect. The decision was complicated by the existence of an alternative engine in the design stage, and the rigid limitations imposed by existing production plant on the basic dimensions of the ‘A’ series.

Previous design criteria had to be discarded in order to make the 1098 cm³ possible, and to establish it as a reliable high-performance unit. The situation was complicated by the need for still greater performance in sports car installations.

Apart from specific details of changes in component design which included the adoption of new materials when required, the paper emphasizes the importance of close liaison between design and development.