John Alfred Prestwich's (J.A.P.) Engines

1000-cc J.A.P. Engine

Bonhams 1793 Ltd.

John Alfred Prestwich was an English engineer, designer, and businessman. He is famous for a number of his designs, which included much of the early cinematography equipment, and worked with such luminaries as S.Z. de Ferranti and William Friese-Greene (the cinema pioneer). But for classic motorcycle enthusiasts, he is best known for the range of motorcycle engines his company produced

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Company Founding and First Engines

A 1000-cc J.A.P. Engine. Image courtesy of Bonhams 1793 Ltd.

The company, J.A. Prestwich Ltd., was founded in 1895 when Prestwich was in his early 20s and continued in the production of various components until 1963. The company specialized in precision engineering which led to the development of their first motorcycles—including their own J.A.P. engines. Complete machines were manufactured between 1904 and 1908.

The first motorcycle engine developed and sold by J.A.P. was a 293-cc unit produced in 1903 which was used by the Triumph company for their motorcycles.

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Notable Customers

Although his engines powered motorcycles of his own design for a short time, they earned a reputation for power and reliability needed by other manufacturers. Customers for the J.A.P. engines came, not just from motorcycle manufacturers, but aircraft manufacturers and industrial companies, too. Their engines could, therefore, be found in everything from motorcycles to light rail maintenance trucks.

J.A.P. engines were also exported to many countries including the French ​Terrot and Dresch manufacturers, Ardie, Hecker, and Tornax in Germany, and many manufacturers in Australia such as Invincible.

Customers from the motorcycle manufacturing industry included Brough Superior, Cotton, Excelsior (the British company), Triumph, HRD and Matchless among others. Interestingly, examples can still be seen in specials today such as a J.A.P. engined Norton café racer sold by auctioneers Bonhams in 2008.

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Engines of Note

Two engines stand out from the many produced by J.A.P. because of their contribution to motoring in general and motorcycling in particular. The first is the V-Twin which was manufactured in various capacities from 1905. The V-twin was used in their own motorcycles from 1906.

The main advantages of the J.A.P. V-twin engines were their excellent power to weight ratio and reliability. Although important to motorcycle manufacturers, these attributes were seen as critical to aircraft manufacturers many of whom used J.A.P. engines.

For motorcycle use, the V-twin engine had another attribute: narrowness. With the obvious need to lean a motorcycle over for cornering, the narrower engines were ideal for giving more ground clearance.

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Unique Applications

One of the most popular motorcycle sports in the UK and Australia was Speedway, which along with grass track racing was dominated for many years by J.A.P. engines and, in fact, records show J.A.P. engines were still being used in the 1960s.

Due to the unusual tax laws in the UK, three-wheeled vehicles were taxed the same as motorcycles and many J.A.P. customers used the engines for sidecar work. The V-twin engines were also used in the popular three-wheelers of Morgan cyclecars. Although more like a car than a motorcycle and sidecar, the Morgans were classified for tax purposes the same as sidecars. The engines were front mounted in the Morgan’s and many of the J.A.P. variants were used, including singles, twins, V-twins inside valve and OHV configurations. In conjunction with Morgan, a water-cooled V-twin version was also available.

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Stationary Engines

The versatility of J.A.P. engine design can be seen in their stationary engines, which have powered a wide array of industrial equipment such as generators, rotavator, water pumps, milking machines, hay lifts and numerous machines in the agricultural industry.

During World War II, the company supplied close to one-quarter of a million petrol powered engines in addition to millions of aircraft parts.