The earliest Harley-Davidson motorcycles were powered by a single-cylinder engine. However, in 1911, the company introduced the 7D, considered to be the first 45-degree twin-cylinder production model with a displacement of 49.5 cubic inches producing 7 horsepower. Only 27 model 7D motorcycles were believed to have been made in 1911 and just four are still known to exist. Harley-Davidson experienced significant growth in 1911, growing from 150 employees in 1910 to 550 by the end of 1911. The factory produced 5,625 units, all model 7s (27 model 7Ds), more than double the previous year’s output.
Harley-Davidson made several improvements to model 7, including vertical fins on the head, which provided a larger surface area for heat transfer and promoted better cooling. A belt-drive idler assembly allowed a rider to stop the motorcycle without shutting down the engine. While most of the motorcycles used the older technology with a 30 CID single-cylinder engine, the new V-Twin engine in the 7D became the company’s trademark power source in one form or another, giving the Harley-Davidson its identifiable characteristic sound.
According to the Las Vegas Review-Journal, “Some engines hum. Some whine. Others roar. But Harley-Davidson motorcycle engines rumble . . . The sound is so distinctive – and so closely associated with the brand – that Harley-Davidson once sought to have it trademarked (the company ultimately withdrew the application).”
[Featured image by Daniel Hartwig via Wikimedia Commons | Cropped and scaled | CC BY-SA 2.0]
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