A motorcycle is generally considered a motor with two wheels, but it's constructed with myriad intricate components that work in unison to propel, stop and support the machine. Although motorcycle technology has advanced at a rapid pace, replacing simple carburetors and points-ignition systems with computerized fuel injection and electronic ignition controls, the basic operation of the motorcycle remains the same.
The motorcycle's chassis consists of a metal frame that supports the motor and suspension. Most cruisers and older motorcycles employ a steel-tube frame that cradles the motor. Sport motorcycles, alternatively, use a lightweight aluminum perimeter frame that wraps around the motor and uses it as an additional rigid support. A forklike rear swingarm is mounted on a pivot at the rear of the frame to support the rear wheel, while the front fork clamp is attached to a pivot at the front of the frame called the steering head. Handlebars are mounted to the top of the fork clamp to provide steering inputs and may appear as a one-piece tubular bar or as fork-mounted clip-on bars. Motorcycle wheels are either made from cast aluminum or use steel wire-spoked rims.
A motorcycle's forward suspension can be supplied by a number of fork variations, with telescopic hydraulic forks being the most common. The fork itself is made from two separate fork legs attached to the fork clamp and the front wheel, each consisting of a wide lower stanchion and a smaller upper tube that slides within it. The forks are controlled by a damping rod and a spring immersed in a thick oil, controlling the fork tube's movement as the front wheel encounters a bump. Modern performance forks offer finer damping-control settings and may be inverted for additional strength, placing the wider stanchion at the top of the fork.
Rear Shock Absorbers
Rear shock absorbers function in a similar method as the front fork and are offered as either a twin or a single mono-shock setup. The shock absorbers pivot on the rear swingarm and the motorcycle's frame, allowing the swingarm to rise and fall as needed to compensate for changing road conditions. While twin shock setups were predominant on nearly all motorcycles until the early 1980s, this setup is usually found on cruiser-style motorcycles. The mono-shock setups found on modern sport motorcycles provide lighter weight and improved response at higher speeds.
Fuel, Intake and Exhaust Systems
A motorcycle's fuel supply is held in a steel, aluminum or fiberglass tank mounted on the frame above the motor, although some models will place the tank under the rider's seat. Fuel is delivered via a petcock --- fuel valve --- or a fuel pump under the tank to the carburetor or fuel-injection system. The fuel is mixed into the air drawn in through the carburetor or throttle body and is passed into the motor, where it's combusted and expelled through the exhaust header pipes and the muffler.
Motor and Transmission
Although motorcycle motors differ in sizes and styles, the basic components remain the same. The motor's crankcase houses the crankshaft, which is responsible for generating the spinning motion that drives the motorcycle forward. Pistons are attached to the crankshaft via a steel connecting rod, and they move within the cylinders attached to the crankshaft. Fuel and air pulled into the cylinder are compressed by the piston and ignited by a spark plug, pushing the piston down and turning the crankshaft. The spinning motion is transferred to the transmission by a primary gear and is then transmitted to the rear wheel via a drive chain or driveshaft.
Electrical power is sourced from a lead acid battery, housed under the rider's seat, providing direct current (DC) power to the lights and ignition system. Once the motor is started, a permanent magnet positioned at the end of the crankshaft is spun within an electrically charged coil of wires, called a stator, to regenerate the battery's charge. It's controlled by a voltage regulator to prevent overcharging. A diode-based rectifier transforms the stator's alternating current (AC) into a direct current before reaching the battery.
- "The Professional Motorcycle Repair Program"; Professional Career Development Institute; 1995
- "The Complete Idiot's Guide to Motorcycles"; Darwin Holmstrom; 2001
- Photo Credit engine of a motorcycle image by terex from Fotolia.com
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