Much of the attention paid to Harley-Davidson innovations over the last 100 years usually goes to things like the "Knucklehead" engine, Softail frame, teardrop gas tank, circulating oil system, Hydra-Glide motorcycle front fork assembly and other famous inventions. However, there are plenty of other features that deserve a great deal of praise. All 1914 models featured a new two-speed internal rear hub. This complex piece of equipment was operated by a lever on the left side of the gas tank. Although it would be replaced one year later by the three-speed transmission, it still proves to this day to be an engineering masterpiece.
In 1915, an ingenious system of electrical controls was made available on the "J" and "H" models. Among other things, the electric lighting available that year was not only significantly more powerful than the old acetylene lights of previous years, but was far cleaner and easier to operate. Also available in 1915 was the three-speed sliding gear countershaft transmission, on which today's Harley-Davidson transmissions are largely based.
The 1916 eight-valve racer employed an advancement still in use today. The engine used a total of eight valves, or four valves per cylinder and had one cam gear with four cam lobes. This layout is used in many of today's automotive engines, a testimonial to its performance. The eight-valve was so successful that the class rules were changed in 1922, as it is widely believed, to no longer allow the motorcycle to race.
One of the biggest pre-Knucklehead improvements to Harley-Davidson performance was the Ricardo cylinder head. Famed engineer Harry Ricardo patented in 1919 what he called the "squish principle." Simply put, Ricardo's cylinder head was shaped such that the fuel mixture during the compression stroke was made to rotate in a vortex-type of motion. This translated to more of the mixture swirling around the spark plug meaning a more thorough combustion and more power. It proved to be one of the best developments to happen to the "F-head" engine.
This cutaway rendering of the 1915 three-speed trans-mission was shown in Harley-Davidson's 1915 motorcycle catalogue.