c1921 Harley-Davidson Model J 1000cc Motorcycle

Description

The evolution of the Harley-Davidson twin can be traced back to 1909, although early models were hampered by the use of automatic inlet valves inherited from the early singles and slippage of the belt drive system.  It was Harley's adoption of mechanically-operated inlet valves in 1911 and the switch to a more durable belt-drive system (with a hand-operated tensioning system) that saw sales - and production - take off and the F-head V-twin would remain in production, albeit with periodic revisions, for the next twenty years.  Improvements included the evolution to 61-cid (or one-litre) capacity in 1912, along with a new frame and free-wheel clutch assembly, followed by a two-speed rear hub in 1914 to cope with the demands of sidecar riders, by which time chain drive had also been adopted.  Harley's range of twins had expanded rapidly to include six distinct models by 1915, with the Model J the most expensive and best equipped, featuring a more conventional three-speed sliding-gear transmission, a 'step starter' and full electrical equipment.  Throughout the 1920s, the Model J continued to evolve, with a front brake a big improvement.  The F-head enjoyed an incredibly long career, with production finally discontinued in 1929.