Motorcycle Mechanics

Motorcycle Mechanics

Motorcycles are not only a source of entertainment; they can also be a source of transportation and income if someone wanted to make a career of them. Motorcycles are used in many aspects of life. Children, as well as adults, ride motorcycles on trails, open fields and on motocross tracks. They may race, jump or do stunts with the motorcycle. Groups, such as Harley Davidson owners, get together to ride for charity events. Because motorcycles are so cheap to ride, they are great source of transportation. A motorcycle can get 60 to 70 miles per gallon whereas a small Toyota Camry can get 18 to 23 miles per gallon. Industries such as farming, delivery, entertainment, aviation and even the military are known for their use of motorcycles within their operations. Due to the popularity of the motorcycle there has been an emergence of self-taught mechanics. Not all these mechanics can keep up with the new technologies and advancements. “The impact of new technology on the motorcycle industry has been dramatic” (Motorcycle 1). Electronic ignitions, fuel systems, drive trains, and turbocharged engines are just a few areas of advancement. Well-trained technicians are needed and sought after. Job opportunities are available for these well-trained technicians. The motorcycle industry has a lot to offer someone who is interested in a motorcycle mechanic career.

It is always a good idea to understand the history of a subject prior to getting into specifics. Motorcycles originally looked like glorified bikes. They had front and rear wheels that were the same size, with a pedal crank mechanism to turn the rear wheel. Gottlieb Daimler is credited with building the first motorcycle in 1885. It was constructed mostly of wood with iron wheels and was powered by a single-cylinder engine. Most of the early models were three and four-wheeled designs. The two-wheeler was introduced in 1892. “It used a 5-cylinder engine built as the hub of its rear wheel. The cylinders rotated with the wheel, and its crankshaft constituted the rear axle” (Tharp 1). It wasn’t until Hildebrand & Wolfnueller invented and patented a two-wheeler in 1894 that the two-wheeler became success. Still production and manufacturing was a slow process and motorcycles were not readily available for purchase. In 1885, the “French firm of DeDion-Buton built an engine that was to make the mass production and common use of the motorcycles possible” (Thorpe 2). The engine was small, light and a four-stroke. It had a battery and coil ignition instead of a hot tube. A lubrication system was invented to drip oil in metered doses. Soon the engine was copied and was used by Harley-Davidson in the United States. The first U.S. production began in 1892 in Waltham, Massachusetts. The motorcycle was called the Orient-Aster and contained the DeDion-Buton engine. Production continued at a slow pace until 1960. Between 1960 and 1970 over five million motorcycles were produced and sold. During the 1970’s oil crisis, the motorcycle became the preferred mode of transportation (Lear 3). Today there are over “10 million motorcycles in the United States that are commonly used for commuting as well as for various racing competitions” (“Motorcycle Mechanics” 338).

Riding safety is an important aspect to the motorcyclist that needs to be addressed. Safety is the responsibility of the rider. “In an average year 166,000 Americans will be hospitalized as a result of a motorcycle accident. 4,700 of them die. Many others will be crippled for life. In some countries the death rate for motorcyclists is up to nine times higher than that for person riding in a car” (“Motorcycle Safety” 1). A motorcyclist needs to ride with extreme care. Steering, accelerating and braking require skill and a high degree of coordination. A motorcyclist should never drive while under the influence of alcohol. It is very important that one learns how to ride and do so safely. Wearing proper attire is also a necessary component to safety. It should not only provide comfort but also visibility and protection. A helmet, eye protection, jacket, gloves, and boots are the basic attire. The helmet is the most important piece of equipment. It should have a snug fit and be fastened securely under the chin. The helmet should also be certified by the Department of Transportation. Goggles or a face shield are both good for eye protection. Being able to see is an important aspect when riding. Wind that blasts into eyes can be very dangerous. Objects blown into the eyes can cause blurred vision. Jackets made of leather provide a great deal of protection. It is wise to wear gloves and boots in order to provide additional protection. Proper riding apparel will not prevent accidents, but it will decrease the chance of serious injuries.

Finally, motorcycles are a great source of income because one could make a career out of repairing motorcycles. Technician, service writer, parts manager and service manager are a few of the careers available within the motorcycle industry. This paragraph will be focused more on the technician’s career. The technician can make or break a facility. If the technician is knowledgeable and does quality work, the reputation of the facility will be good. If, on the other hand, the technician is not knowledgeable and his quality is lacking, the reputation of the facility will be poor and they will lose customers. One of the tasks a technician will perform is rebuilding a motorcycle engine. A motorcycle engine can be either a two-stroke or a four-stroke.

The two-stoke is preferred by racers and will be the one discussed in this paper. “A two-stroke engine is a simply constructed engine. Two-stroke engines do not have valves, which simplifies their construction and lowers their weight. This makes the two-stroke engine lighter, simpler and less expensive to manufacture and repair. The piston, cylinder, and crankcase serve dual roles in developing power” (“Motorcycle Mechanics” 74). The engine is made up of two parts: a top end and bottom end. The top end contains the cylinder, the cylinder head, piston, the piston rings and the wrist pin. The bottom end contains the crankshaft, the crankcase, the seals, the bearings and bushings. The cylinder’s job is to seal and guide the piston so that it can react to the power of the expanding gases. There are a series of passageways called ports that move gases in and out of the engine. According to David, former motorcycle mechanic, the cylinder head is the area where the gas and oxygen mix on the down stroke, but on the upstroke it is compressed and ignited by the spark plug to produce a mini explosion, which creates power. The cylinder head vibrates constantly and is subject to high temperatures. During a rebuilding job, the cylinder must be inspected thoroughly to make sure there is no warping. If warped, sanding it with emery paper can repair it. The main job of the piston is to hold the ring. The ring must be tight in order to get a good tight seal in the cylinder. If the seal is tight there will be good compression. Lack of compression means a lack of power, preventing the engine from working efficiently. The piston and the piston pin need to be checked for scratches and cleanliness during a rebuild. If any dirt or deposits are left on the piston or the ring it will cause the rings to stick and lead to power loss. So it is very important to take the time to thoroughly check and clean the piston and the piston pin. When replacing a piston, make sure there is enough clearance in the cylinder. Motorcycle books can be purchased with exact measurements and clearance values in them. If there is not enough clearance the piston will shake (seizure) resulting in noise, damage to the cylinder wall and loss of power.

In the bottom end of the engine, the crankshaft continually spins giving the piston the power to continue to work. The crankcase houses the crankshaft. It operates under conditions of high stress. “Atmospheric pressure and the partial vacuum created by the piston causes air to flow through the carburetor to pick up a charge of fuel and then to flow into the crankcase and later in to the cylinder. When the piston has closed off the intake port, the crankcase is sealed” (Motorcycle Mechanics 78). With the continued motion of the piston, the fuel mixture in forced through the transfer ports. Crankcase seals are used to prevent leakage so pressure can build in the crankcase. It is very important to locate and correct crankshaft problems to prevent more serious trouble later. The crankshaft must be measured according to specific measurements. If the crankshaft is seriously damaged, it is better to throw it away and buy a new one. Oil seals are also important during a rebuild job. The seals prevent loss of oil from the engine. The seals also prevent compression leaks. Since compression is needed to move the piston, the seal is important. In addition to preventing leaks, oil seals prevent entry of dirt and particles. During rebuilding jobs, oil seals must always be replaced. Never try to reuse and old oil seal. Finally, the bearings should always be checked whenever the engine is disassembled. Always check for wear (pit marks) and cleanliness. Spin the bearing, listening for noise and roughness. Make sure the spinning is done while the bearing is lubricated. Never spin a dry bearing. All these parts work together to create enough power to move the motorcycle. It all starts when the spark plug fires. Fuel and air in the cylinder have been compressed so when the spark plug fires the fuel ignites. This small explosion causes the piston to go downward. As the piston is moving downward it is compressing the fuel mixture in the crankcase. Once the piston starts reaching the bottom of its stroke, the exhaust port is uncovered. The pressure that has been built up in the cylinder now forces out the exhaust gases. By the time the piston is all the way at the bottom of its stroke the intake port opens. The fuel mixture rushes in the cylinder, filling it up with fresh fuel. During this time, the crankshaft is moving and it forces the piston upward towards the spark plug, which is called the compression stroke. As the piston compresses the fuel, a vacuum is created opening the reed valve and forcing fuel into the carburetor. As the piston reaches the top of its upward stroke, the spark plug fires again. This repeats over and over again.

Two stroke engines require a special fuel mixture. Two-stroke oil must be mixed with the gasoline. In most cases, the mixture is a 32:1 ratio, which means thirty- two parts gas with one part oil. The oil seems excessive, but it is needed in order to keep all moving parts lubricated. The oil lubricates the crankshaft, connecting rod and the cylinder walls. If the gas is not mixed with oil, the engine will run poorly.

There is a lot more to motorcycle riding than meets the eye. A motorcyclist has many responsibilities. It doesn’t matter if a person rides for entertainment, sport, or necessity: the responsibility is the same. Motorcycles are very powerful and must be driven responsibly. Proper riding techniques, safety gear and proper maintenance are key to long and happy riding. If lucky, motorcycle riding can lead to a satisfying career.


Lear, G. Motorcycle Mechanics. Englewood Cliffs, NJ:Prentice-Hall Inc.,1977.

Motorcycle Mechanic Institute. The Complete Guide to Motorcycle Mechanics. Phoenix, AZ:

Prentice Hall, 984.

Motorcycle Safety. 4 Dec. 2003.

Tharp, Dave.Virtual Museum Curator. The First Motorcycle. December 2002. Motorcycle

search. 6 Dec. 2002.

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