A motorcycle is a two wheeled machine which is propelled forward by a motor. This motor is generally an internal combustion engine which imparts the forward momentum to the machine. The principle of gyro motion dictates the essence of motorcycle movement forward where the Centripetal and centrifugal forces balance each other while the bike is in motion. Both these forces complement each other and give stability to the bike in motion. A forward momentum (Mass x Velocity) is an essential component for stability of the motorcycle when in motion. This forward motion balances the centripetal and centrifugal forces. This forward movement is achieved through the power supplied by the internal combustion motor or engine. The motorcycle engine may run on gasoline or diesel. But now electric power for traction is another option that is available.
In almost all motorcycles the engine is located just below the petrol tank. This position has the effect of lowering the center of gravity of the bike and gives the machine greater stability. The motorcycle is propelled forward by the engine which supplies its traction power through a steel chain that is connected to the rear wheel. All motorcycles are rear wheel driven. Power is transmitted from the rear wheel by means of this metal chain.
The motorcycle motor’s construction is quite simple. It consists of a single or set of pistons that move in a chamber or a sleeve .The motion is generated by an electric spark. The electric spark ignites a gas and air mixture that releases gases that move the pistons up and down in a cycle. The pistons when they move generate power to a mechanism that moves a connecting chain to the rear wheel. All motorcycles are rear driven.
The power that is generated by the motorcycle engine is through the movement of the piston. When the pistons move they impart the power to the crank which in this case is the chain. The cycle of motion of the piston in the cylinder may follow a two stroke or four strokes. Two stroke engines have a simpler construction and thus are easier to maintain. They also generate more operating power vis a vis four stroke engines. But four stroke engines are more eco-friendly and give a smoother ride on the road. Another advantage of 4 stroke engines is that they can have multiple cylinders. This in turn translates to greater operating power. In two stroke engines very second stroke is the power stroke while in the 4 stroke engines the power stroke is the 4th stroke. A stroke refers to a single movement of the piston.
All motorcycle motors have a rated capacity. This capacity is related to the volume of the chamber in which the piston operates. The capacity of these motors may vary from 25 cc to 1500 cc. The capacity of the pistons and chamber is directly proportional to the output of power. This is also referred to as Brake horse power.
The bike motor is started by means of an electric spark. This in turn ignites the gas air mixture in the chamber and sets the pistons into motion. This spark is generated by a dynamo. Earlier bikes were all kick start. The bike was started by pumping a lever down wards with the leg. But latest motorcycles have incorporated the self start option. In such bikes the pistons are fired by a starter motor.
The older motorcycles had their current supplied by a magneto. Now however the latest bikes are replaced by Capacitor Discharge Ignition. CDI systems provide higher ignition current for starting making the bike easier to start. Kawasaki was the first to adapt this for motorcycles.
Another variant of the bike motor is the diesel engine. Unlike in cars the diesel engine is not adapted for large scale motorcycle use. This is because the diesel engine has a lower efficiency and is also heavier than a corresponding petrol engine. Diesel engines are prone to greater vibration and are generally unsuitable for two wheelers. However a limited variety of diesel powered bikes are in the market.
Bikes with large displacement usually have multi-cylinders. Such motorcycles may have 2, 4 or even 6 cylinders. There are many types of multi-cylinder options available in the market. Cylinders of the bike motors may be positioned in vertical or twin cylinder configuration. They may also be positioned in line. Another development is the Wankel engine made by Felix Wankel (1902 – 1988). Wankel engines generate greater power for the motorcycle. Bike motors can go up to six cylinders. Six cylinders are fitted on the heaviest bikes and include bikes like the Honda CBX and the Kawasaki KZ1300.
Liquied Cooled Engines
Liquid-cooled motorcycles engines are a further development. Such motorcycles engines have a radiator like in a car. The radiator follows the principle of heat dissipation and keeps the engine cool by circulating water or a liquid coolant. Liquid cooled engines can however be fitted only on the larger bikes and are unsuitable for lower displacement bikes. Liquid cooled bikes for a specific displacement generate greater power than air cooled bike engines. They also last longer than an air cooled engine. Air-cooled bikes are however much cheaper to buy and maintain with simpler construction.
However, 4 stroke engines have captured the commercial market. Four stroke engine bikes give a smoother ride on the road and also generate greater power over broader spectrum of speed. But despite this two stroke engines are in great demand in the developing countries, as cost is a big factor there. In the United States and Western Europe the two stroke bike is now an oddity and motorcycle manufacturers mostly market four stroke bike variants.
Another variant of the motorcycle engine is the electric engine. These engines are still in the development stage and are presently only used to power small scooters and mopeds. These electric motors mostly operate on lead acid batteries. However a negative point against these batteries is that they take more than 4 hours to recharge. They also have limitations of speed and performance and unsuitable for heavier bikes. However some concept bikes using a lithium battery have been tested but they are far from commercial production stage due to the prohibitive cost involved.