Grass roots; 500cc racing

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Out of austerity

In searching for the best value in motor racing, it must be logical to look for the smallest car with a single-cylinder engine — all costs being relative to size and the number of pots under the bonnet. The advent of the single-cylinder, 500cc racing car at the end of the Second World War resulted from the desire to find a means of racing cheaply in those austere days. A simple formula was devised which enabled any competent enthusiast to build his own car at home.

Following the early example of Colin Strang, many home-made cars appeared in the years 1947-50. But alongside these enthusiasts, commerce was soon at work, with the Cooper brothers first building their own car and then, seeing the business potential, selling fully-prepared cars until the late 1950s.

Today, a good Cooper can be bought (depending upon its history, originality and condition) for about £8000. And as long as one has some mechanical skills, the cost of running the car should be no more than £1200 for a full season.

The Cooper approach was to build a light, aluminium-panelled, tubular chassis with independent suspension by front and rear upper transverse leaf-springs over lower wishbones, incorporating telescopic dampers. The steering was rack-and-pinion, with hydraulic drum brakes all round. The driver sat low in the car in the upright position; behind him was bolted a JAP air-cooled engine running on methanol fuel.

Engine power was tranferred by chain to a separate four-speed Norton gearbox, and then to a solid back axle. Overall weight was about 540 lb. A good power-to-weight ratio gave a responsive car, which was at its best on hill-climb and sprint courses. Lack of overall power and air-cooling made the cars somewhat vulnerable to the rigours of circuit use, but there is a growing band of Historic owners who, thanks to the Monoposto Club, are currently competing in a class for front-engined Formula Junior cars.

The 500 Owners Association was set up to help preserve these early cars and keep them in regular use at a variety of circuit, hill-climb and sprint meetings. In recent years the club has broadened its scope to cater for the resurgence of interest in modern 500cc cars, which has been a mirror-irnage of those earlier post-war years, with individual enthusiasts building their own one-off cars and then some offering further cars for sale.

This time around it is John Corbyn from Wellingborough in Northamptonshire who is the leading constructor, building his Jedi cars for those who have approximately £4000 to spare for a car which comes complete except for engine and gearbox. The well-designed spaceframe chassis is built from 1in and 3/8in square tube, to which are bronze-brazed all the various mounting points. The aluminium floor pan and side body-panels are riveted on to add further strength. Upper bodywork consists of three removable GRP sections.

The rear suspension is attached to an upright fabricated from 18-gauge sheet steel to take a twin-bearing hub; to this is fixed a lower wishbone and a single link, both with trailing arms. At the front, a Mini stub-axle is grafted into a fabricated tube upright to which are fitted unequal-length upper and lower wishbones. Adjustable Spax shock absorbers within coil-springs are fitted all round.

The 13in x 6in split-rim alloy wheels are shod with either Avon or Yokohama slick tyres, to give excellent adhesion which has now been further improved by the fitting of front canard fins and a rear single-post wing, all with Gurney edges. This completes an attractive and compact body. All pedal controls and the Knight rack-and-pinion steering are adjustable to suit the driver. Minifin hydraulic drum brakes are used all round to give excellent braking for the lightweight frame.

Choice of power-unit is left to the customer, but John will install the required engine mountings. Regardless of which engine/gearbox unit is used, power is transmitted by chain to the final-drive assembly, consisting of a Mini diff with its crown wheel converted to a sprocket carrier. Mini driveshafts take the power out to the wheels.

Enthusiasm for modern 500s has mushroomed to the point where David Tearle of Corby-based Phoenix Foods Ltd has stepped in to provide a sponsored championship. This has given the whole movement the transfusion of status necessary to carry the class to a full revival.

Another link in this renaissance is being forged by David Peers from Kidderminster in Worcestershire, who recently unveiled his Hi-Tech 500, which is aimed primarily at circuit racing. The complete car will cost £6000, coming in kit form to suit the customer’s pocket.

Its power-unit is an Australian-built KTM water-cooled 500cc single. The engine, gearbox and diff are together, and the final drive is made from modified Mini parts. Suspension is by unequal-length, rear jointed wishbones, which are adjustable, and incorporates coil-spring and damper units; steering is by a lightweight rack-and-pinion assembly. The Hi-Tech’s very attractive body consists of four GRP mouldings with side pods — one housing the radiator, the other the fuel tank. It has the appearance of miniature Grand Prix car, and production examples will be fitted with canard fins on the nose and a single-post rear wing. This newcomer is due to receive its race baptism in a seven-race pre-series Championship to be called Formula 500S. MM

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