A motorcycle is a two-wheeled machine that is propelled by an engine. This engine is usually an internal combustion engine that imparts the forward drive to the machine. The principle of gyroscopic motion dictates the essence of the motorcycle’s forward motion, where centripetal and centrifugal forces balance each other while the motorcycle is in motion. Both forces complement each other and give stability to the bicycle in motion. Forward momentum (Mass x Velocity) is an essential component for motorcycle stability when in motion. This forward movement balances the centripetal and centrifugal forces. This forward movement is achieved through the power supplied by the engine or internal combustion engine. The motorcycle engine can run on gasoline or diesel. But now electric power for traction is another available option.
On almost all motorcycles, the engine is located just below the gas tank. This position has the effect of lowering the bike’s center of gravity and giving the machine more stability. The motorcycle is propelled forward by the engine that supplies its tractive force through a steel chain that is connected to the rear wheel. All motorcycles are rear wheel drive. Power is transmitted from the rear wheel via this metal chain.
The construction of the motorcycle engine is quite simple. It consists of a single or set of pistons that move in a chamber or a sleeve. The electrical spark ignites a mixture of gas and air which releases gases that move the pistons up and down in a cycle. When the pistons move, they generate energy to a mechanism that moves a connecting chain to the rear wheel. All motorcycles are rear wheel drive.
The power that the motorcycle engine generates is through the movement of the piston. When the pistons move, they transmit power to the crank, which in this case is the chain. The cycle of movement of the piston in the cylinder can follow two strokes or four strokes. Two-stroke engines are simpler in construction and therefore easier to maintain. They also generate more operating power compared to four-stroke engines. But four-stroke engines are more environmentally friendly and provide a smoother ride on the highway. Another advantage of 4-stroke engines is that they can have multiple cylinders. This in turn translates into higher operating power. In 2-stroke engines, the second stroke is the power stroke, while in 4-stroke engines, the power stroke is the fourth stroke. A stroke refers to a single movement of the piston.
All motorcycle engines have a rated capacity. This capacity is related to the volume of the chamber in which the piston operates. The capacity of these engines can vary from 25cc to 1500cc. The capacity of the pistons and chamber is directly proportional to the power output. This is also known as brake horsepower.
The bicycle engine is started by an electrical spark. This, in turn, ignites the gas-air mixture in the chamber and sets the pistons in motion. This spark is generated by a dynamo. Previous bikes were all kickstarters. The bike was started by pumping a lever down with the leg. But the latest motorcycles have incorporated the option of automatic starting. In such bikes, the pistons are fired by a starter motor.
Older motorcycles had their current supplied by a magneto. Now, however, the latest bikes are being replaced by capacitor discharge ignition. CDI systems provide a higher ignition current to start, making it easier to start the bike. Kawasaki was the first to adapt this for motorcycles.
Another variant of the bicycle engine is the diesel engine. Unlike automobiles, the diesel engine is not adapted for large-scale motorcycle use. This is because the diesel engine has lower efficiency and is also heavier than a corresponding gasoline engine. Diesel engines are prone to increased vibration and are generally not suitable for two-wheelers. However, there is a limited variety of diesel-powered bikes on the market.
Large displacement bikes usually have multiple cylinders. These motorcycles can have 2, 4 or even 6 cylinders. There are many types of multi-cylinder options available in the market. The cylinders of the bicycle engines can be placed in a vertical or two-cylinder configuration. They can also be placed online. Another development is the Wankel engine made by Felix Wankel (1902 – 1988). Wankel engines generate more power for the motorcycle. Bicycle engines can go up to six cylinders. Six cylinders are fitted to the heaviest bikes and include bikes like the Honda CBX and Kawasaki KZ1300.
Liquid-cooled motorcycle engines are a further development. Such motorcycle 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 liquid coolant. However, liquid-cooled engines can only be fitted to larger bikes and are not suitable for smaller displacement bikes. Liquid-cooled bikes for a specific displacement generate more power than air-cooled bike engines. They also last longer than an air-cooled engine. However, air-cooled bikes are much cheaper to buy and maintain with simpler construction.
However, 4-stroke engines have captured the commercial market. Four-stroke engine bikes provide a smoother ride on the highway and also make more power over a broader speed spectrum. But despite this, two-stroke engines are in high demand in developing countries, as cost is a major factor there. In the United States and Western Europe, the two-stroke bicycle is now a rarity, and motorcycle manufacturers primarily market variants of four-stroke bicycles.
Another variant of the motorcycle engine is the electric motor. These engines are still in the development stage and are currently only used to power small scooters and mopeds. These electric motors are mainly powered by lead acid batteries. However, a negative point against these batteries is that they take more than 4 hours to recharge. They also have speed and performance limitations and are not suitable for heavier bikes. However, some concept bikes using a lithium battery have been tested, but are far from the commercial production stage due to the prohibitive cost involved.