knulehead/Panhead (jan 1, 1936 – dec 31, 1965)
Description:
 In 1936, Harley introduces the overhead valve EL, a 61 cubic-inch engine with increased horsepower and uniquely shaped rocker boxes that earned the nickname Knucklehead. 
Harley-Davidson adds new features to the 61 and 74 OHV V-twins including aluminum heads, hydraulic lifters, and one-piece chrome-plated rocker covers that resemble cake pans. The name Panhead was a perfect fit. 
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