Designs for a small engine, with a displacement of 7.07 cubic inches (116 cc) and 4-inch (102 mm) flywheels, were drawn up by 20-year-old William S. Harley in 1901, with the intention of using the engine on a regular bicycle frame: a motorized bicycle. Harley and his childhood friend Arthur Davidson worked on their motor-bicycle over the next two years at their friend Henry Melk’s machine shop at his north side Milwaukee home.
With the help of Arthur’s brother, Walter, they finished their prototype engine in 1903. While experimenting with their motorized power-bicycle, Harley and the Davidson brothers found it wasn’t able to climb the hills around Milwaukee without assistance from manual pedaling. They quickly put this failed motor-bicycle experiment behind them and chalked it up as a valuable learning experience.
They immediately began improvising a new and improved second-generation motorized wheeled apparatus. This first “authentic” Harley-Davidson motorcycle had a larger engine, approximately 3.5 times bigger than the 1903 motor-bicycle engine, and weighed 28 lbs. (13 kg).
The machine’s advanced loop-frame design was similar to the 1903 Milwaukee Flying Merkel motorcycle, designed by Joseph Merkel, that was already in production.
The larger engine and loop-frame pattern moved the machine from the motorized-bicycle class and immediately pointed the way to future motorcycle designs. Outboard engine developer Ole Evinrude, who was then manufacturing his design of gasoline engines for automotive use at his own shop on Milwaukee’s Lake Street, also provided some aid to the boys with their bigger engine.
The prototype of the new loop-frame Harley-Davidson engine was created and assembled in a small shed in the Davidson family backyard. Most of the original parts, however, were made elsewhere.
Some were probably engineered at a Milwaukee railway machine shop where oldest brother William A. Davidson was then a tool crib foreman.
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This original motorized machine was operational by September 8, 1904 – the date in which it competed in one of the first motorcycle races ever held at the Milwaukee State Fair Park. It was driven by Edward Hildebrand and finished in fourth place. This race is the first recorded appearance of a Harley-Davidson motorcycle in history.