How does a bike engine work?
Today, almost all commercially available motorcycles are driven by conventional
gasoline internal combustion engines, increasingly four-strokes in all size ranges.
This is because 4 stroke engines are more fuel efficient, cause less emissions and
have a longer life than 2 stroke engines.
In a four stroke engine, the working cycle is completed in four strokes of the piston
or two revolutions of the crankshaft. This is achieved by carrying out suction,
compression, expansion and exhaust processes in each stroke. The four strokes of
a petrol engine sucking fuel-air mixture are described below.
- Suction or Charge Stroke: In this stroke, the inlet valve opens
and a mixture of fuel and air is forced by atmospheric pressure into the cylinder
through the intake port. The piston descends from the top of the cylinder to the
bottom of the cylinder.
Compression Stroke: In this stroke, both the valves are closed and
the fuel-air is compressed as the piston moves upwards. This completes one revolution
of the crank shaft.
- Expansion or Working Stroke: Shortly after the piston reaches the
top (during the compression stroke), the compressed air-fuel mixture is ignited,
usually by a spark plug. The resulting massive pressure from the combustion of the
compressed fuel-air mixture drives the piston back down with tremendous force. This
is the is the main source of the engine's torque and power
- Exhaust Stroke: In this stroke, the exhaust valve is open as the
piston moves to top. This movement of the piston pushes out the products of the
combustion from the engine cylinder through the exhaust valve into the atmosphere.
This completes one cycle
Two stroke v/s Four stroke engines
Whereas in a 4 stroke engine, 2 upward strokes and 2 downward strokes constitute
1 cycle, in the two stroke engine, all four events are integrated into one simple
downward stroke, and one upward stroke. In a 4 stroke engine, the spark plug only
fires once every other revolution whereas in a 2 stroke engine,
the engine fires on every revolution. Besides, a 2-stroke engine doesn't
have valves, while a 4-stroke engine does.
In a two-stroke engine, it is necessary to use a mix of gasoline and oil (two-stroke
oil) as fuel. This is used to lubricate the piston and the crank shaft. Such
a mixture is not needed in a 4 stroke engine.
In both types of engine, by means of a crank shaft the up and down motion is converted
into a rotational motion.
Most of the motorbikes can be either liquid cooled, air cooled or oil cooled. Most
air cooled motorcycles take advantage of air blowing past the cylinder and cylinder
head while in motion to disperse heat. Frequent, sustained stationary periods may
cause over-heating. So liquid-cooled bikes are safe to use in a city, where traffic
may frequently be at a standstill. Some manufacturers use a hybrid cooling method
where engine oil is circulated between the engine case and a small radiator. Here
the oil doubles as cooling liquid, prompting the name "oil-cooling."
Coolant is basically a blend of de-ionized water and antifreeze that is circulated
in the engine. It also protects the cooling system by preventing corrosion.
Emissions regulations and the market demand for maximum power are driving the motorcycle
industry to liquid-cooling for most motorcycles
The engine converts the explosive energy to mechanical energy, through the reciprocating
motion to rotary motion. The power developed from rotary motion is controlled by
various systems in a bike. This system is known as the Transmission. The Transmission
consists of the clutch, gear-box & final-drive chain all the way upto the driving
The clutch is a very important "Link" in the transmission of the bike. Its primary
use is to allow the rider to engage and disengage the engine from the wheels. It
also takes up most of the load and vibrations from the engine and does not allow
it to pass onto the rest of the transmission.
After the clutch comes the gear-box. As the name suggests, a box having set of gears.
It allows the rider to use the optimum amount of power from the engine as and how
required. The main function of the gear-box is to reduce strain on the engine by
supplying efficient power at required time. For Instance, the first gear is lowest
and most sensitive gear, which helps in moving of a stationary bike without putting
excessive load on the engine. On the other hand use of second gear requires relatively
more acceleration and gives more strain on the engine and clutch. A lower gear serves
two purposes. They serve as brake and also improve acceleration when required. For
instance, while going downhill on a lower gear provides "Braking Power" and during
uphill provides extra power.
The main components of an electrical system in the bike are the Battery, Alternator/Dynamo/
Generator/Magneto and Ignition/High-Tension Coil(s). The main function of the system
is to provide ignition in the form of a spark to the compressed air+fuel mixture
in the cylinder.
To retain the standard energy of the battery it needs periodical maintenance like
check up of specific gravity, cleaning of terminals, applying a thin film of petroleum
jelly or pure Vaseline (not grease) to keep terminals and connections from corrosion
and sulphation etc
There are two different types of brakes used in bikes, namely: Drum Brakes &
Disk Brakes. The usual arrangement on a good bike is front disk brake and rear drum
The Wheels and Tyres
There are two types of tyres available, the inner tube type and the tubeless type.
In the inner tube type tyre, both the tube and tyre are mounted on the rim. The
tube is like a hollow rubber doughnut. It is inflated with air after it is installed
inside the tyre and the tyre is put on the wheel rim. The inflation causes the tyre
to resist any change of shape.
The tubeless type tyre does not have an inner tube. Instead, the tubeless tire is
directly mounted on the wheel rim so that the air is retained between the rim and