The Engine

Power which is required for the propulsion of an motorcycle is developed by means of a Power unit or Engine.

The requisite power is developed by starting the engine. in order to see how the power is developed, is to know how the engine is put into operation. If an engine is in the working order, the following checks have to be made for the development of power:

• Check whether there is fuel in the fuel tank, oil in the oil sump or oil tank, water in the radiator (incase of water cooling) upto the correct level.
• Check whether the battery is properly fitted.
• Check whether gear-shift lever is in the neutral position (engine should be disconnected from the transmission).

After making the above mentioned checks, the crankshaft, to which are connected all the working parts, directly or indirectly, is rotated mechanically by means of a kick-starter; or electrically by means of a electronic starting motor. By moving the crankshaft, all the working parts of the engine are set in motion, which help in completing the cycle of operation. The power impulse is obtained during the Power Stroke which is stored in the flywheel attached with the crankshaft. Due to inertia moments, the flywheel drives the crankshaft for the other strokes to complete the cycle of operation and this way the engine is set in motion.

Mechanical power i.e., Rotary Motion, which is converted from the heat energy by means of engine, is available at the flywheel of the engine, from where it is transmitted to the wheels.

An motorcycle engine is a Prime Mover with the help of which heat energy (which is obtained from the fuel carried in the fuel tank of the motorcycle) is converted into mechanical energy.

Motorcycle engines can be classified with different regards which are as under:

• With regard to the number of cylinders:

1. Single Cylinder Engine.
2. Multi-cylinder Engine.

• With regard to the strokes per cycle:

1. Two Stroke engine.
2. Four Stroke engine.

• With regard to the cooling of the Engine:

1. Air-cooled engine.
2. Water, or liquid cooled engine.

• With regard to the shape of the Engine Block:

1. In-line Engine
2. V-shape Engine
3. Opposed Cylinder Engine

• With regards to the valves of the Engine:

1. SOHC, Single Overhead camshaft
2. DOHC, Double Overhead Camshaft, or Twin Camshaft
3. Desmodromic valves, or Desmos valves

Every type of motorcycle engine contains three main parts:

• Cylinder head.
• Cylinder Block (Engine Block).
• Oil sump or oil pan.

Parts which move in the engine are known as working parts. These can be grouped as under:

• Group A

1. Crank shaft. The crankshaft is the main shaft in the engine which contains cranks in order to convert reciprocating (linear) movement of the piston into rotary motion.
2. Connection Rod. It connects piston with the crank-shaft.
3. Piston. It serves as a moving floor for the combustion chamber and helps in forming different strokes in order to complete the cycle of operation. It transmits the force of the explosion to the crankshaft through connecting rod.
4. Gudgeon Pin (Wrist Pin). A pin which connects the piston with the connecting rod.
5. Piston Rings. Circular Rings which are fitted with the piston and serve as moving seals between combustion chamber and crank chamber and help in retaining compression in the combustion chamber.

• Group B

1. Camshaft. A shaft which contains different accentric cams in order to open and close the different valves in the engine.
2. Tappet. A cylindrical object which serves as rocker between cam and valve or push rod.
3. Valves. Which serve as gates between the combustion chamber and induction and exhaust ports.
4. Valve Springs. Compression springs which help in closing the valves.
5. Collar and Cotter. Which help in retaining valve spring with the valve.

• Group C

1. Timing Gears and Chains. Gears with the help of which movement is affected from the crankshaft to camshaft, either directly or by means of chains, are known as timing gears, since they are timed to give movement in a definite sequence.
2. Oil Pump. A pump which lifts lubricating oil from the oil sump and delivers to oil gallery for the lubrication of different working parts.
3. Oil release valve. A valve which controls the pressure of oil in the pressure feed lubricating system of the engine.

For the correct working of motorcycle engine, modern motorcycles are fitted with with two types of engines, i.e., two-stroke and four-stroke engines, which have a different cycle of operation. For both engines a Spark Plug, Magneto/Distributor, Carburetor/Throttle Body, etc. are necessary accessories.