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A British made motorcycle in production from 1938-1940 and again after WWII from 1947-1959, it has an overhead valve, v-twin 498cc engine. It has a top speed of 75 mph (121 km/h).
The Triumph Speed Twin is the first parallel-twin design. This concept dominated British motorcycle production during the postwar period, when BSA, Matchless, AJS, and Norton all produced bikes with similar engines. The Speed Twin was made by Triumph at their Coventry factory.
Triumph entered the motorcycle business in 1903, building singles for many years. The Speed Twin represents a cost-effective compromise between the market's desire for something smoother and more powerful than a single, yet less complex and expensive than multi cylinder engines.
Legend has it that Val Page saw an Ariel Square Four engine running on a test stand, minus its front crank-shaft, and noticed its moderate vibration. He thought it might be an alternative to the more complex V-twins, flat-twins, and multis, and the Speed Twin is the result. Traditional roller bearings were replaced with pressure lubricated plain bearings. The Speed Twin was actually lighter than the single-cylinder designs it replaced. The characteristic bulky crankcase encloses a large central flywheel. The overhead valves are operated by fully enclosed pushrods and rocker arms. The chassis is conventional-rigid at the rear with a girder fork at the front. Since its two pistons move up and down together, the engine shakes like a single, but the vibration is less severe because the twin's stroke is shorter. Firing on every revolution, its propulsion is twice as smooth as that of a single, yet it runs well with a single carburetor.
Edward Turner, Triumph's Chief Designer and Managing Director, launched the Triumph Speed Twin at the 1937 National Motorcycle Show. It was a 500 cc OHV vertical twin in a lightweight frame and the first truly successful British twin, setting the standard for many twins to follow. After World War II the Speed Twin was responsible for the survival of Triumph and every major British marque offered a 500 cc twin designed on similar lines to the Speed Twin. Thousands of Speed Twin Triumphs were sold, and the design was later upgraded to 650 and then 750 cc engines. American riders discovered that a light, handy alternative to the heavy Indians and Harleys they already knew did exist in the Triumph Speed Twin.
The Triumph Speed Twin is available for viewing at the Barber Village Motorsports Museum, Birmingham, Alabama.