A brief introduction to the v-twin and v-rod engines which power Harley-Davidson motorcycles.
The operational process in the basic air-cooled, V-twin is really quite simple. A spinning cam triggers a spring-loaded valve, that (when open) allows gasoline to flow into a combustion chamber. The gasoline is then compressed by a piston. A spark is introduced to the gasoline filled chamber, by a sparkplug, resulting in an explosion. This explosion releases a substantial amount of gas and energy, forcing the piston violently downward and out of the combustion chamber. Now the piston is at its most southward point and the combustion chamber is filled to its maximum volume with non-essential gas, known as exhaust. The piston once again compresses the chamber, but the valve reopens, allowing the exhaust to escape the combustion chamber. The piston is connected to a crankshaft by a connecting rod, allowing for a double rotation of the crankshaft per engine cycle. A belt-drive is used to externally connect the crankshaft on one end and the rear wheel on the other. As the engine cycles and transfers energy into the crankshaft in the form of motion, the belt is also transferring a greater portion of that energy to the rear wheel in the same fashion.
You will often here the term CC's used as a way to describe the size or power output of an engine. As your engine cycles and the piston moves up and down in the combustion chamber, the area of volume within that chamber changes. The difference between the maximum volume and the minimum volume of the chamber is called displacement. In automobiles this displacement is often measured in liters, but in the smaller engine of a motorcycle it is commonly measured by cubic centimeters, or CC's.
In one cycle of an internal combustion engine, a valve is used to both introduce gasoline to the combustion chamber, and to let exhaust escape from it. When the exhaust escapes the chamber a sound is also emitted that is not unlike the sound of a firecracker. In most automobile engines the greater block size allows for horizontally opposed pistons--as one piston is in the secondary phase of emitting exhaust, another piston is going through the primary phase of combustion. To achieve this separation, the crankshaft has two pins connecting it with the pistons. This allows for an even series of energy producing explosions, and a steady measure of sound. The design engineering on a V-Twin, however, must compensate for a lack of space. In an effort to restrict size without sacrificing utility, the V-Twin engine has two pistons but only one pin. The combustion chambers are set at a forty-five degree angle from each other, preventing the engine from firing on a balanced interval. This is what gives the Harley-Davidson V-Twin its unique sound. Where a normal engine makes an evenly spaced series of noises (bam-bam-bam-bam), the Harley engine makes a noise punctuated by slight pauses (bambam"¦bambam).
The Harley-Davidson engine most commonly manufactured today is its Twin Cam engine. It is named for the double cams used to operate the valves. At 1450 cubic centimeters of displacement (1,450cc's) it is currently the largest production engine on the market. It is still air cooled and operated by overhead valves, and allows plenty of room for aftermarket engine upgrades.
In 2001, Harley-Davidson took its first major step in divorcing itself from the engineering design of its first V-twin. It introduced the Revolution engine onto a brand new frame design, known as the V-Rod. Unlike the V-Twin engines of the past the Revolution is water-cooled, not air-cooled. The angle of the Combustion chambers on the Revolution engine is set at sixty degrees as opposed to forty-five degrees and is fuel injected. It also uses four cams to operate the overhead valves instead of the two cams that are used in the Twin Cam engine. The overall engineering results in a smaller engine that is able to produce substantially more horsepower. The Harley-Davidson motorcycles of today are certainly not for the faint of heart.
