Harley-Davidson models. In the late summer of 1929, Harley-Davidson introduced its 45 cubic inches (737 cm³) flathead V-Twin to compete with the Indian 101 Scout and the Excelsior Super X. This was the "D" model, produced from 1929 to 1931. Riders of Indian motorcycles derisively referred to this model as the "three cylinder Harley" because the generator was upright and parallel to the front cylinder. The Great Depression began a few months after the introduction of their 45 cubic inch (737 cm³) model. Harley-Davidson's sales fell from 21,000 in 1929 to 3,703 in 1933. Despite this, Harley-Davidson unveiled a new lineup
Harley-Davidson Shovelhead engine from the enclosed chain, along with a 5-speed transmission and rubber motor mounts to help reduce vibration. In 1981, Harley Davidson purchased AMF's share of the company back, adding a new oil pump, improved valve guides, and lowering the compression to help the engines run on the lower quality gasoline in the United States. The engine was produced until 1984, where the Evolution engine, which had aluminum heads and barrels, began to take over on most models. The engine could still be found in certain models such as the FLH in 1985, but was shortly replaced by the succeeding Evolution