1940 Flathead on 2040-motos

Harley-Davidson Other description

Harley-Davidson Flathead History

The first flathead V-Twin offered by Harley-Davidson was the D Model, produced from 1929 to 1931. The R model, made from 1932 to 1936, began Harley's side-valve tradition in the 45-cid class. The D and R models were succeeded in 1937 by the W series.  Advantages of a flathead (side-valve) engine over an overhead valve engine were cost of manufacture and simplicity. With valves positioned in the engine block beside the piston (instead of in the cylinder head, as in an OHV engine), pushrods and rocker arms were not needed. Additionally, cylinder heads need only be a simple casting with threaded holes for the spark plugs. During the years 1940 through 1945, Harley-Davidson built over 60,000 side-valve motorcycles for the U.S. and Canadian Armies.  Starting in 1932, the 45-cid side-valve engine powered the Harley-Davidson Servi-Car, whose many uses included police bike, mail carrier, and tow vehicle. Although never selling in large numbers, the three-wheeled Servi-Car stayed in production until 1973, with several reportedly built in 1974.  45-cid Harley flatheads look similar to the Big-Twin Harleys. The easiest way to tell them apart is Big-Twins have their drive chain on the left, the 45's are on the right.