Flathead V-Twin Engine

The Harley Davidson Flathead V-Twin was a 45 degree, 45 cubic inch
(742 cc) engine with 22 horsepower that replaced the F-Head or IOE
engine on big twins and was first seen on D-model (the 3-cylinder
Harley Davidson) motorcycles in 1928. 

Photograph courtesy of the Harley-Davidson Motor Company Archives. Copyright Harley Davidson.

This engine was in turn
supplanted by the Panhead engine in 1948, but it appeared on
D-model motorcycles until then.  In 1929, this engine appeared on
V-model Harley’s in a 74 cubic inch version. In 1936, an 80 cubic inch
edition debuted on the Harley Davidson UH and ULH models.  The Flathead
was also used to power the model K Sports Harley in 1952 and was
subsequently used with the Harley Davidson Sportsters from 1957 to
1985. The Flathead was so successful as an engine that it was still
being manufactured and sold up til 1974.

The Flathead was an improvement over the Panhead engine mainly
because of a redesign that made operation less complicated–creating
less problems. This was accomplished by running the valves alongside
the engine and having them open upwards into a new side chamber beside
the main combustion chamber, which removed the need for push-rods or
rocker arms.