Introduced in 1926 in a humble but innovatively designed fabric bodied saloon, Percy Riley's ground-breaking Riley 9 engine- a small capacity, high revving unit- was ahead of its time in many respects. Having hemispherical combustion chambers and inclined overhead valves, it has been called the most significant engine development of the 1920s. With twin camshafts set high in the cylinder block and valves operated by short pushrods, it provided power and efficiency without the servicing complexity of an OHC (overhead camshaft) layout. It soon attracted the attention of tuners and builders of 'specials' intended for sporting purposes. One of the most noteworthy was engineer/driver J.G. Parry-Thomas, who developed the Riley 'Brooklands' model in his workshops at the famous banked Surrey circuit. Officially backed by the Riley company, the Brooklands, along with later developments and variations such as the 'Ulster' Imp, MPH, and Sprite, proved some of the most successful works and privateer racing cars of the late 1920s and early 1930s, at Le Mans,the Ulster TT, at Brooklands itself, and at smaller events like hill climbs. They also provided a platform for the success of motorsports' first women racing drivers like Kay Petre and Dorothy Champney.
The engine configuration was extended into a larger 12 horsepower '4', six cylinder and even V8 versions, powering an increasingly bewildering range of touring and sports cars. The soundness and longevity of the engine design is illustrated by Mike Hawthorn's early racing success after WW2 in pre-war Rileys, in particular his father's Sprite. But by about 1936 the company had overextended, with too many models and few common parts, and the emergence of Jaguar at Coventry was a direct challenge. Disagreements between the Riley brothers about the future direction of the enterprise grew. Victor Riley had set up a new ultra-luxury concern, Autovia, to produce a V8 saloon and limousine to compete with Rolls-Royce. By contrast, Percy, however, did not favour an entry into the luxury market, and the Riley Engine Company had been renamed PR Motors to be a high-volume supplier of engines and components. Although the rest of the Riley companies would go on to become part of Nuffield and then BMC, PR Motors remained independent. After the death of Percy Riley in 1941, the company began producing transmission components and still exists today as PRM Marine Limited (formally Newage Transmissions) based in Aldermans Green, Coventry. Percy's widow Norah ran the company for many years and was Britain's businesswoman of the year in 1960.
