1939 Harley-Davidson Model EL "Knucklehead" , Engine no. 39EL 3505

1939 Harley-Davidson Model EL "Knucklehead"
Engine no. 39EL 3505

"Knucklehead" first appeared in 1936, the nickname knucklehead alluding to the bulbous rocker boxes atop the engine. Although the depression had severely curtailed motorcycle sales, company management had decided in 1932 to develop a 1000cc overhead valve vee-twin with recirculating oil system. Nearly five years in development, the motorcyclists dream, more horsepower, had arrived. The knucklehead combined engine design and styling in the fashion of aircraft engines, with the higher compression EL producing 37 horsepower, enabling a stock machine to touch 100mph. Other technical features included a four-speed gearbox and a double-loop cradle frame. To Milwaukee's good fortune, the Knucklehead came to market just as the depression was on its way out. Harley-Davidson sent racer Joe Petrali to Daytona, Florida in March of 1937 who put the Knucklehead through the timing lights at 136mph. For model year 1941 the engine capacity was increased to 1200cc and designated the F series. No other motorcycle had captured the attention of American riders in the way that the knuckleheads had. They would stay in production for 12 years, and gave Milwaukee another great stride on Springfield.