The FL Harley model was introduced in 1941 with one knucklehead engine. Bikes with these engines were appropriately nicknamed the "Knuckleheads." Apparently one knucklehead wasn't enough for this rider, former Harley-Davidson dealer Felix Predko. He customized this particular FL 74 OHV Twin with two complete V-Twin Knucklehead engines and transmissions, four pipes, two saddles and two sets of handlebars. Basically, two bikes in one. Measuring more than 13 feet from end to end, the monstrous—and aptly named—"King Kong" bike is one of more than 400 bikes on display at the Harley-Davidson Museum in Milwaukee.