Despite the increasing popularity of its Knucklehead (overhead valve) engine in the late Thirties, Harley-Davidson continued to offer traditional flathead Big Twin powerplants on its bikes. An 80-cubic-inch flathead joined the existing 74-inch mill late in the 1935 model year, and for 1937, both gained the recirculating oiling system first seen on the Knucklehead. More … Continue reading Classic Bike: 1938 Harley-Davidson UL