The 45° F-Head V-Twin

The 45° F-Head V-Twin

Harley-Davidson soon realized that the easiest way to significantly increase engine size was to add an extra cylinder. The company built a prototype V-twin in 1907 and four years later the first production V-twins rolled out of the factory. The engine effectively joined two singles on a common crankshaft and cases. If the angle of the “V” was narrow, the new engine could be used in the same frame as a single. Harley chose a 45° “V,” and a motorcycling classic was born. The arrival of the mechanical exhaust valve on the V-twin was also important, allowing engine revs to be increased and thus release more power.

Harley’s trademark is born

Harley's trademark is born

The appearance of the 45° V-twin effectively provided the blueprint for the Harley twin of today. From 1915 it was refined and improved rather than radically altered.

F-Head set-up

These early V-twins were known as F-heads because the inlet valve was positioned in the cylinder head and the exhaust valve was on the side of the cylinder, creating an “F” formation. This incomplete engine is believed to be from a factory race bike.

V-twin operation

V-twin operation

To make a V-twin, the two rods connecting the crankshaft to the pistons have to sit on the same shaft. Harley used “male and female” rods to solve the problem.

“The V-twin opened up America for ordinary riders. It was a giant step forward for the Harley rider.”

Bruce Lindsay (Motorcycle Restorer)

The Competition. 1914 YALE V-TWIN

The Competition. 1914 YALE V-TWIN

Harley wasn’t the only manufacturer to choose the 45° engine layout for its bikes. The Consolidated Manufacturing Company of Toledo, Ohio, built Yales from 1903-15 and this 61cu. in. model had a 45° V-twin engine and mechanically operated inlet valves.