I thought I would put this manufacturer on, since the engine is still commonly used.
Jimbert
JAP Formula 3 500
The single cylinder JAP 4B engine was originally designed for use in speedway bikes during the 1930s. A pushrod design using a total loss lubrication system but light and powerful thanks to the high compression ratio and methanol fuel, it was ideal for 500 cars and ruled the category until the Norton engine became available.
The JAP Origins
Stan Greening had encouraged John Prestwich to pay a visit to Stamford Bridge Speedway track, yet surprisingly he had come away quite unimpressed believing that speedway was little more than another new craze. Fortunately, Stan Greening had more faith in speedway's long-term prospects for he had already been able to observe how the sport was progressing. He retained a keen interest in racing right up to his retirement, completing almost 50 years with J. A. Prestwich and Co. Ltd, and rising to the position of Chief Technical Advisor. The factory’s involvement with speedway racing became the subject for further discussion during the 1929 Motor Cycle Show at Olympia. Bill Bragg who was then Captain of the Stamford Bridge team, called at the JAP stand when Vivian Prestwich was on duty. Vivian realised that perhaps speedway had more to offer than his father had suspected. Through this further representation, John Prestwich changed his mind and gave the project his blessing. Given the go-ahead. Stan Greening started work along the lines Bragg had indicated and in about three months an experimental engine was delivered to Bill.
At the particular time the Rudge engine was taking over from the previously all-conquering Douglas twin, to become the machine on which to win. Unfortunately, the experimental JAP engine was still too heavy and it was also well down on power when matched against the 28 hp of the Rudge.
Wal Phillips, a notable rider of that period had recently switched from his Douglas to the Rudge and as a regular visitor to the JAP factory, he was approached by Stan Greening with a view of stripping down the engine to see how the JAP could be improved upon. Wal agreed, and JAP was receive the breakthrough it needed. By the time the Rudge engine had been stripped down, Stan had made many observations that would be put to good practical use in the JAP engine. Further attention was given to port shapes and angles, without resorting to a 4-valve configuration like that of the Rudge. In addition, the Rudge cams suggested that a revision of the valve timing figures would prove advantageous. Special castings were made and tried, and because the engine was running too cool on alcohol fuel, the cylinder barrel fins were pared off even more. When the new horsepower figures were checked with the Foreman of the Test Shop, they looked good and he agreed to try the engine at Stamford Bridge. A two lap trial had been arranged, before the first race of the evening. After a warm-up had shown the engine was running well, Wal put in a couple of fast laps. When he returned to the pits, the JAP staff were full of excitement, some unofficial timing having shown that he was lapping at over 46 mph, which was more than the track record.
What might have been?
J. A. Prestwich made a wide range of engines including a V twin 1,100 cc. This engine was regularly fitted to Formula 3 cars for use at hillclimbs or in Formula 2. Some manufacturers, notably Cooper, produced long chassis versions of their cars specifically to accommodate these larger engines.
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