In 1901, William S. Harley designed a small engine with a displacement of 7.07 cubic inches (116 cc) and four-inch (102 mm) flywheels intended for use in a regular pedal-bicycle frame. With the help of Arthur's brother Walter Davidson, it was finished in 1903. To help keep the engine in top shape, make sure you have a handy Harley-Davidson service manual.
In 1907, they began selling their motorcycles to police departments. All motorcycles produced in 1905 and 1906 were all single-cylinder models with 26.84 cubic inch (440 cc) engines. By 1911, the company unveiled an improved V-Twin model and mechanically operated intake valves. Though it was small in size, performance-wise, it provided better power. After 1913, most of the bikes manufactured by Harley-Davidson were V-Twin models.
In 1912, Harley-Davidson launched their patented ""Ful-Floteing Seat"" which was suspended by a coil spring inside the seat tube. Harley-Davidson used these seats up until 1958. Harley-Davidson was the largest motorcycle producer in the world by 1920. In 1921, Otto Walker set a world record on a Harley-Davidson motorcycle being the first to average speed greater than 100 mph (160 km/h) during a race.
In 1929, Harley-Davidson debuted its 45 cubic inches (737 cc) flathead V-Twin to compete with the Excelsior Super X and the Indian 101 Scout. This was the ""D"" model manufactured from 1929 to 1931. In 1941, the 74 cubic-inch ""Knucklehead"" was unveiled as the F and the FL. The US Army also asked Harley-Davidson to produce a new motorcycle with many of the features of BMW's side-valve and shaft-driven R71.
In the eighties, Harley-Davidson claimed that Japanese producers were importing motorcycles into the US in such volume as to threaten domestic manufacturers. After an investigation was conducted by the US International Trade Commission, President Reagan imposed a 45% tariff on imported bikes with engine capacities greater than 700 cc in 1983.
Rather than trying to compete with the Japanese imports, Harley -- under new management -- decided to start to produce bikes that echoed ""retro"" appeal of the feel and look of their earlier motorcycles and the following customizations that were common of that era. Many components such as forks, brakes, shocks, electrics, carburetors, and wheels were outsourced from foreign manufacturers, technical improvements were made, quality increased, and buyers slowly returned. And if you ever find yourself having to work on one of these beauties, having a Harley-Davidson repair manual can make the job go more smoothly.