Prior to this breakthrough, Harley-Davidson only used a side-valve flathead engine. However, with the new overhead valves, the Knucklehead brought unprecedented power, offering 40 hp with 61 cubic ...

an iconic Harley-Davidson model, boasts nostalgic charm and symbolizes the brand’s triumph over Indian Motorcycles in the 1930s. The innovative Knucklehead engine, featuring overhead valves ...

and the "Knucklehead" engine in 1936, said Bill Jackson, archivist at the Harley-Davidson Museum. Need a break? Play the USA TODAY Daily Crossword Puzzle. “People inside the company are ...