power output. Sidevalve designs are still common for many small single-cylinder or twin-cylinder engines, such as lawnmowers, rotavators, two-wheel tractors and other basic farm machinery. Flathead cars Multicylinder flathead engines were used for cars such as the Ford Model T and Ford Model A, the Ford flathead V8 engine and the Ford Sidevalve engine. Cadillac produced V-16 flathead engines for their Series 90 luxury cars from 1938–1940. After WWII, flathead designs began to be superseded by OHV (overhead valve) designs. Flatheads were no longer common in cars, but they continued in more rudimentary vehicles such as off-road military Jeeps. In US custom car and hot rod circles, restored examples of early Ford flathead V8s are still seen. Flathead aero-engines The simplicity, lightness, compactness and reliability might seem ideal for an aero-engine, but because of their low efficiency, early flathead engines were deemed unsuitable. Two notable exceptions were the American Aeronca E-107 opposed twin aero engine of 1930 and the Continental A40 flat four of 1931, which became one of the most popular light aircraft engines of the 1930s. Two modern flatheads are the Belgian D-Motor flat-fours and flat-sixes. These are extremely oversquare and compact aero-engines with direct drive to a propeller. Flathead motorcycles Flathead designs have been used on a number of early pre-war motorcycles, in particular US V-twins such as Harley-Davidson and Indian, some British singles, BMW flat twins and Russian copies thereof. The Cleveland Motorcycle Manufacturing Company produced a T-head four-cylinder in-line motorcycle engine in the 1920s. See also Heron Head Notes External links Ford Flathead Engine Images of each style of Harley-Davidson engine Harley-Davidson K-model motorcycles Cam-in-block valvetrain configurations Engine technology Engine valvetrain configurations Harley-Davidson engines Motorcycle engines Piston engines