c1925 Harley-Davidson Model JD 1200cc Motorcycle with Sidecar

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.  Designed to compete with Indian, Harley-Davidson launched its first 74-cid V-twin in 1921, following the same basic F-head layout of the existing 61-cid unit but with new crankcases, cylinders and heads.  Rated at a healthy 18 horsepower, the Model JD used a three-speed gearbox, a dry multi-plate clutch and an ‘automatic’ oil pump. A number of variants were produced, including the sidecar model and the Big Twin was equipped with either a magneto or full electrics consisting of a six-volt generator, battery, contact breaker points and coil for the front and rear lamps.  Harley-Davidson revised the JD in 1925 with a lowered frame, larger teardrop petrol tank and smaller diameter tyres and 9,506 were built that year.  Popular with sidecar riders, the F-head enjoyed an incredibly long career, with production finally discontinued in 1929.