The Infamous F Head

In February 1907, a prototype model with a 45-degree V-Twin engine was displayed at the Chicago Automobile Show. Although shown and advertised, very few Vee-twin models were built between 1907 and 1910. By 1911, some 150 makes of motorcycle had already been built in the United States of America, although just a handful would survive the depression of the 1910s. However, the design focus on performance and low compression power production ensured the success of Harley-Davidson and by the 1920s, Harley-Davidson was the largest motorcycle manufacturer in the world with its motorcycles selling in over 67 countries. 1909 marked the appearance of Harley-Davidson’s first Vee-twin, though it was not until the adoption of mechanically operated (push rod) inlet valves in 1911 (replacing the ‘atmospheric’ type inherited from the single), that the Harley-Davidson Vee twin was truly practical. Known by the sobriquet ‘pocket valve’, this ‘F-head’ (inlet-over-exhaust) engine – built in 61ci and 74ci capacities (1,000cc and 1,200cc respectively) – would remain in production for the next 20 years. The Harley’s singles transmission arrangements (direct drive by means of a leather belt) were continued at first on the twin, but the need to make better use of the engine’s power characteristics, particularly for sidecar pulling, prompted the introduction of a two-speed rear hub for 1914, by which time chain drive and a proper clutch had been adopted. At its peak (1919) Harley-Davidson was selling seven sidecars for every ten bikes before Ford’s Model T became cheap enough to offer a more comfortable alternative. Technical innovation of the F head continued with the introduction of conventional, three-speed, sliding-gear transmission with the ‘step starter’ being introduced on the top-of-the-range version of the twin which, with full electrical equipment, was listed as the Model J, which is what is presented here. Previously belonging to Ross Duncan’s collection, this is a wonderfully maintained example of what is arguably Harley-Davidson’s most influential period.