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Harley-Davidson Knucklehead | Wisconsin Historical Society

Historical Essay

Harley-Davidson Knucklehead

Wisconsin Historical Museum Object – Feature Story

Harley-Davidson Knucklehead | Wisconsin Historical Society
EnlargeHarley-Davidson Knucklehead

Harley-Davidson Knucklehead, 1941

Source: Wisconsin Historical Museum object #2003.19.1

EnlargeModel FL "the Line"

Model FL "the Line", 1941

Overview of the Model FL, showing “the Line.” The Line is more pronounced with the saddlebags removed and the rear hub entirely visible. Source: Wisconsin Historical Museum object #2003.19.1

EnlargeDetail of Model FL

Detail of Model FL, 1941

Detail of engine, with rocker boxes - the source of the “Knucklehead” nickname - highlighted in orange. Source: Wisconsin Historical Museum object #2003.19.1

1941 Model FL motorcycle manufactured by the Harley-Davidson Motor Co., Milwaukee, Wisconsin, 1941.
(Museum object #2003.19.1)

The FL was Harley-Davidson's first modern "heavyweight" motorcycle. Introduced in 1941, the FL featured the high compression version of the company's first 74-cubic-inch overhead valve V-Twin "Knucklehead" engine. Only 2,452 FL's were built in 1941 before the company converted from civilian to military production for World War II. The FL is generally considered among the best looking motorcycles ever produced, and, because of its limited production, is one of the most sought after by collectors.

The early history of this particular motorcycle is unclear. Built in 1941, it was well used and eventually junked. However, it is hard for a bike this appealing to stay junked. The motorcycle was rehabilitated and re-titled in 1985. Most of the major components, including the frame, engine, transmission, fenders, gas tank, seat, springer front suspension, handlebars, footboards, clutch assembly, kick start, rear brake pedal, and rear center bike stand are original.

Despite coming to rest in a museum, this bike is no "museum piece." It was restored to be ridden, and shows the wear and tear of heavy, regular use, as well as the results of a minor accident. To date, museum curators have chosen to preserve the bike in its current state, which documents its history of use, rather than to restore it to a showroom appearance.

Harley-Davidson – one of Wisconsin’s and America’s signature brands — got its start in a tiny garage in Milwaukee. There, childhood friends William Harley and Arthur Davidson began tinkering with motors in 1901. Later assisted by Arthur’s brothers, William and Walter, the pair produced a motorized bicycle in 1903. The following spring, the four partners produced their first recognizable motorcycle, featuring a newly designed, 24.74 cubic inch engine. The company established by Harley and the Davidson brothers has lasted more than a century. (The early, myth-clouded years of the Harley-Davidson Motor Co. are examined in detail in 'At The Creation: Myth, Reality and the Origin of the Harley-Davidson Motorcycle, 1901-1909', a book published by the Wisconsin Historical Society Press.)

In a field crowded with fledgling motorcycle manufactures, the Harley-Davidson Motor Co. made its mark before World War I by building powerful, durable machines. By 1920, Harley-Davidson had grown into the largest motorcycle manufacturer in the world. Reliable and continuously improving technology was one reason for their success, and one of the company’s most enduring designs was the overhead valve V-Twin engine, introduced in 1936 with a 61-cubic-inch displacement.

Riders nicknamed the engine the "Knucklehead" because of the distinctive shape of the polished alloy rocker boxes atop each cylinder. The Knucklehead provided vastly increased horsepower and durability, and became the bedrock of Harley-Davidson engine design for the next 65 years. The Knucklehead was the heart of a boldly redesigned and reengineered cycle, the revolutionary Model E.

Besides bearing a remarkable engine, Harley-Davidson big twin motorcycles of the mid-20th century are among the most beautiful ever made. These models all share "The Line," a dramatic diagonal slash from the top of the teardrop gas tank back to the rear axle. The "Line" first appeared on the 1936 Model E and continued through 1958, when the introduction of rear shock absorbers on the Duo-Glide realigned the frame into a more horizontal look.

The combination of a legendary engine, dramatic styling, and low production numbers makes the 1941 FL, according to one motorcycle historian, "a classic among classics."

[Sources: Wagner, Herbert. At the Creation: Myth, Reality and the Harley-Davidson Motorcycle, 1901-1909 (Madison; Wisconsin Historical Society Press, 2003); David K. Wright. The Harley-Davidson Motor Company: A 100-Year History (North Branch, MN: SalCarTech, 2002); Rafferty, Tod. The Complete Harley-Davidson (London: Salamander Books, Ltd., 2001); Wilson, Hugo. The Ultimate Harley-Davidson Book (New York: Dorling Kindersley Publishing, Inc., 2000).]

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Posted on July 20, 2006