Knuckleheads are among the most popular motorcycle engines ever produced by Harley-Davidson. Introduced in 1936, the 61-cubic-inch Knucklehead was the first production Harley engine with overhead valves, replacing the longstanding side-valve flathead V-twin.
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Harley-Davidson had built overhead-valve race engines in the past. But the Knucklehead was the company’s first fully overhead-valve powerplant constructed solely for the street. This 1939 Harley-Davidson EL Knucklehead recently offered on eBay is as fine as they come.
Close to Perfection
In another first for Harley, the Knucklehead engine has a fully recirculating oil lubrication system that replaced the old “total-loss” oiling method. It helps keep the engine cool and boosts efficiency. The engine was dubbed the Knucklehead, thanks to its burly polished rocker covers that resemble clenched fists.
The example now on eBay scored 99 out of 100 points in the “Restored” category during a competition judged by the Antique Motorcycle Club of America - opens in new window or tab. (AMCA). The AMCA was founded in 1954 with the “preservation, restoration, and operation of old-time motorcycles” as its mission. It is now one of the country’s most prestigious antique motorcycle clubs.
The AMCA’s National Judging Program evaluates motorcycles in three categories: restored, original condition, and period modified. Judges assign grades using a 100-point scale, measuring against the standard of the bike as it would have appeared when it originally left the factory. This 1939 EL Knucklehead meets the highest standards using period-correct parts, evident by the 99 points awarded by the AMCA.
Once Owned by a Knucklehead Master
This ranking is unsurprising, considering the person who entered the 1939 Knucklehead in the AMCA meet. Carl Olsen is one of the foremost experts on Knucklehead engines.
Since 1982, Olsen has operated Carl’s Cycle Supply out of Aberdeen, S.D. Olsen and his son Matt have built everything from vintage race bikes to ground-up customs. In addition, the father-and-son team competed in the esteemed Motorcycle Cannonball Race, an endurance run across America on antique motorcycles.
Related: A 1915 Indian Owned by Late Founder of Motorcycle Cannonball Run - opens in new window or tab.
The Olsens have a reputation as masters of Knucklehead rebuilds. Considering this motorcycle once belonged to them, you know it’s a runner. More recently, this blue beauty was fully serviced by Stett’s Iron Horse Ranch in El Cajon, Calif. In a video of the motorcycle, its current owner kicked it over on the second try, further testament to this Knuckle’s mechanical soundness.
Art Deco Styling
In addition to its iconic engine and updated oiling system, the EL Knucklehead has many other standout features, including a double-cradle frame and moly-steel springer fork. These features improve ride quality and durability.
Knuckleheads also feature these items:
- An upgraded clutch
- Four-speed transmission with a hand-shifter
- A standard tank-mounted speedometer (another Harley first) that included a mechanical ammeter - opens in new window or tab. and an oil pressure gauge - opens in new window or tab.
Then there’s the EL Knucklehead’s indomitable art-deco styling, from its eye-catching two-tone paint and tank emblems to the light frenched into its front fender. Shiny splashes of chrome trim finish the look.
Nearly 100 years after its birth, the Knucklehead still sets a high standard for Harley-Davidson. It’s a timeless design that makes Knuckleheads irresistible to collectors. Now, consider that this example has ties to the Olsen family. The connection adds a whole new level of desirability to an already incredible motorcycle.
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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.