1967 Sunbeam Imp
1967 Sunbeam Imp. Click image to enlarge

Story and photo by Bill Vance

Very early cars had their engines in various locations, such as under the seat or behind the driver, but the 1900 Mercedes with its engine in front, followed by a four-speed transmission sending power to the rear axle, albeit through chains, established the general configuration of the automobile.

Then in the 1930s along came Ferdinand Porsche with his powerful Auto-Union racers with the engine behind the driver. And when Porsche’s design office engineered the Volkswagen in the mid-’30s he put the engine in the rear. Porsche would follow this pattern with its post-Second World War Porsche sports car. Porsche of Germany, and Hans Ledwinka of Czechoslovakia with the Tatra, were the leading proponents of rear engine placement.

Following the Second World War the Volkswagen became so popular that several manufacturers, including Fiat of Italy, Renault and Simca of France, and NSU and BMW of Germany, took up the idea. American Preston Tucker used a rear engine in his late 1940s Tucker “Car of Tomorrow” that was supposed to revolutionize the industry. And even mighty General Motors succumbed to Dr. Porsche’s spell with the rear-engined Chevrolet Corviar compact in 1960.

The British were largely unmoved, although some smaller makers such as Lotus and Lola did produce rear-engined cars. Then in 1963, the English Rootes Group, makers of Hillman, Singer, Sunbeam and Humber cars, surprised the industry with its rear-engined Imp, sold as a Hillman in England, and a Sunbeam in North America. It was Rootes’s Mini-fighter, and was as technically novel as the Mini.

The Imp used unit construction and was a quite small car, measuring just 3,531 mm (139 in.) long, with a 2,083 mm (82 in.) wheelbase (the Volkswagen was 4,064 (160) and 2,388 (94) respectively). It was not as tiny as a Mini, but it wasn’t much bigger, and in spite of its diminutive size it carried off its “shrunk down Corvair” styling very well.

With rear engine placement in such a small car, the drivetrain had to be light and compact. The Imp had an all aluminum (block, head, sump and valve cover) overhead cam, water cooled, inline four of just 875 cc. It was a development of a Coventry Climax engine that had originally been used to power fire pumps.

To avoid a long, circuitous throttle connection, it had a pneumatically operated throttle, but this proved troublesome and was soon replaced with a cable. With 42 horsepower, it could propel the 744 kg (1,640 lb) sedan to 96 km/h (60 mph) in 25.2 seconds, and to a top speed of 122 km/h (76 mph) (R&T 6/64).

The longitudinally positioned engine was slanted over 45 degrees to the right for a lower profile, and was located behind the rear axle. It drove the rear wheels through a floor-shifted, manual four-speed, all-synchromesh transmission with an aluminum case. An interesting feature was that instead of conventional universal joints, drive axle angularity next to the transmission was taken by big rubber “donuts,” called “Rotoflex” couplings. There were regular universals at the outer ends of the axles.

The all-independent, coil spring suspension was also unusual in that the front wheels were carried on swing axles, which gave them a decidedly cambered look, rather like the Volkswagen Beetle’s bow-legged rear wheels. Semi-trailing arms were used at the rear, and the wheels were just 12 inches in diameter with 5.90 X 12 tires. Braking was by drums all around.

Steering was rack-and-pinion, but with the tie rod ends attached to the middle of the rack, not to the ends as in conventional designs. This allowed the tie rods to exactly follow the path of the suspension arms.

Accommodation for four passengers was adequate, if a bit short on rear legroom. There was a small space for luggage under the hood, with another bin at the rear accessed by the top-hinged rear window. With the rear seat folded the Imp became a generous little hauler.

The Imp was built in a new factory located in Linwood, Scotland, and was manufactured from 1963 to 1976. In typical British fashion it evolved into several badge engineered versions such as the aforementioned Hillman Imp, Singer Chamois, Sunbeam Stiletto and Husky station wagon. Few, if any, of these reached North America.

Although it was a technically interesting little car, the Imp didn’t reach the popularity of the British Motors Corp. Mini. Cars of the Imp and Mini size were considered too small by most North American motorists.

They would accept the Volkswagen, but there was a limited market for anything much smaller. And with our cheaper gasoline the desire for high fuel economy was not as urgent as it was in Europe. Also, the Imp suffered some early problems in such areas as the pneumatic throttle and carburation, although these were corrected. Over a 14-year period approximately 500,000 Imps and derivatives were produced.

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