BIKE AT A GLANCE
To adopt the right attitude for riding, it is necessary to understand
the basic mechanism of a bike.
Let's Start with the Engine
The General Mechanism of an Engine:
There are two types of engines commonly used in Motorbikes
the world over, namely: Two Stroke engines and Four Stroke engines.
Majority of engines used today are Four Stroke. The main working
parts of the engine can be divided into two sections: The Reciprocating
and The Rotary Sections.
The Reciprocating section of the Engine consists
of parts like the piston, connecting rods, tappets, valves,
etc, while the Rotary section consists of parts
like the crankshaft, camshaft, ignition, timing gears etc
To make an engine function, an air+fuel mixture containing vaporized
fuel and oxygen (from the air) is supplied into the cylinder
through the carburetor, where a spark ignites it so that it
burns with an explosive force. The explosion, which takes place
in a closed cylinder, tries to push the piston out of the combustion
chamber, thereby causing the piston to move downwards. The reciprocating
action of the piston is converted into a rotary action by the
crankshaft, which uses the momentum of the piston coming down,
to push the piston back up into the combustion chamber. This
causes the piston to move up and down, in the engine. This rotary
movement is then mechanically transmitted to the rear-wheel
by means of a transmission system.
The carburetor is the heart of the engine, which regulates the
petrol and air supply and prepares the air+fuel mixture for
burning. It mixes approximately 15 parts of air with one part
of petrol by weight and creates a fine spray of petrol by means
The air supplied from the carburetor passes through an air filter/cleaner
which prevents dust particles from entering the engine.
The rider controls the amount of the air+fuel mixture entering
the combustion chamber by operating the throttle. When the rider
accelerates, a larger volume of the air-fuel mixture is fed
into the combustion chamber. As a result of this, the intensity
of the explosion taking place inside the closed cylinder increases.
This causes the piston to be pushed out of the cylinder faster,
which leads to an increase in the engine speed. The engine speed
is then transmitted to the wheels which increase the bike's
The Four Strokes:
Majority of internal combustion engines operate on the above
mentioned 4 stroke cycle. The First Stroke or the movement of
the piston from the top of the cylinder to the bottom is called
the Induction (suction) stroke.
The piston while moving towards the bottom of the cylinder creates
a partial vacuum in the top of the cylinder which inducts/sucks-in/draws
the air+fuel mixture through the carburetor (when the inlet
valve is opened - explained later).
By the time piston reaches the bottom of the induction stroke,
the cylinder is filled with the air+fuel mixture. When the piston
moves up (and both valves are closed - explained later), the
mixture is compressed or squeezed. This is known as the Compression
When the piston is about to reach the top of the cylinder, (known
as TDC - Top Dead Center), the compressed mixture is ignited
by a spark from the spark plug. This causes an explosion, which
leads to the rapid expansion of the air+fuel mixture, which
forces the piston to move downwards. This is known as the Power
The momentum of the piston caused by the power stroke causes
the piston to rise up again in the cylinder which finally throws
out the exhaust gases (since the exhaust valve is open - explained
later) caused on account of the explosion of the mixture. This
final movement of piston is called the Exhaust stroke.
(The piston then once again moves into bottom of the cylinder
to start with induction stroke) This is how Four Stroke
The Role of the Valves:
Usually a cylinder has two valves. The valve, which allows
the air+fuel mixture to enter the cylinder, is called the inlet
valve and the valve that allows the exhaust gases to
leave the cylinder is called the exhaust valve.
During the induction stroke the inlet valve remains open and
the exhaust valve remains closed. During the compression stroke
both valves remain closed. Both valves also remain closed during
the power stroke. On the exhaust stroke, only exhaust valve
opens allowing the burnt gases to be forced into exhaust system.
This is how valves enable the sequence of the four stroke operation.
The opening and closing of valves and the sparking on the plug
at the precise moment is obtained by the timing.
The timing is governed by timing gears attached to the crankshaft,
while the current to the spark plug is regulated through contact
breaker points at the distributor.
The ignition of the air+fuel mixture inside the cylinder creates
tremendous heat. Hence to prevent engine from overheating the
engine has cooling as well as lubricating system. In most Indian
built bikes, the forced air-cooling system is used, where in
the air passes through the fins of the engine, which help in
dissipation/dispersal of heat. The lubricating system, on other
hand consists of oil which is kept inside the engine block,
from where it is pumped around the engine to lubricate (almost
160) moving parts of the engine, Temperature over 700 degrees
is produced inside the engine and only part of this heat is
utilized to convert it into power. The remaining heat is thrown
out through exhaust gases.
In order to maintain the engine in good running condition, it
needs to be regularly tuned-up. This is done by cleaning and
adjusting parts like the carburetor, spark plug(s), contact
breaker point(s), air-cleaner/filter, oil-filter, tappets etc
The cooling and lubricating systems also need equal attention
to avoid major pre-matured repairs to the engine.
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 to driving wheel.
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 power transmission is by means of two chains. The primary
chain is enclosed in the clutch case on the L.H.S. of
the bike and runs in an oil-bath. The final or
drive chain connects the gear-box to the drive-sprocket
of the rear wheel. The drive-sprocket is coupled with the brake
drum, which in turn is fit into the rear hub. There are 4 rubber
blocks fitted between the drive-sprocket/brake-drum and the
hub of the rear wheel, which act as efficient dampers, absorbing
practically all the shocks of power and transmission units and
have a very favorable influence on the life of chain as well
as vital engine parts.
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. A battery provides either 6 volts or 12 volts
current. But a voltage thousands times higher is needed to create
a spark from the spark plug, which can ignite the air+fuel mixture.
It's the high tension coil (Ignition coil) which boosts low
voltage current of the battery and provides upto 30,000 volts
to the spark plug. A small spark is generated at the distributor,
which is converted to a high voltage current, which flows to
the spark plug and finally ignites the air+fuel mixture. A contact
breaker and rotor, inside the distributor, ensure correct sequence
of current to the plug while a condenser attached to the contact
breaker serves as a capacitor that minimizes the damage to the
Another part, which is at the heart of the electrical system
is the Alternator/Dynamo/Generator/ Magneto. This provides a
charge to the battery by generating a current. As the generator
output increases with the engine speed a control unit (Cut-out/Regulator)
is provided to regulate the output. This unit prevents the damage
to the generator unit and protects the battery from over charging/discharging.
The stored energy of battery is used for different purposes
such as: ignition, horn, lights etc
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
There are two different types of brakes used in bikes, namely:
Drum Brakes & Disk Brakes.
The Drum Brake has an aluminum/steel/iron drum
to which the wheel is attached. The drum and wheel rotate together.
The brake shoe plate is bolted on to the chassis and inside
the drum lie the brake shoes, which have brake liners on them.
The brake liners are either riveted or moulded onto the brake
When the brake pedal is depressed, a cam (placed between the
brake shoes) rotates such that the brake shoes move towards
the drum. When the brake shoes grip the rotating drum, the rotating
The Disk Brake has a metal disk instead of a drum
fitted to the wheel and the calipers are bolted on to the chassis/shock-absorber
pipe. The calipers have pistons and brake pads. The disk brake
has to be operated hydraulically. The brake fluid and the actuating
cylinder (brake-oil sump) are fitted on the handle bar of the
bike. When the brake lever is pressed a non return brake valve
operates and sends the brake fluids to the caliper and the piston,
the caliper operates thereby forcing the brake pads to move
towards the disk and produce the friction which allows you to
slow down or stop.
The usual arrangement on a good bike is front disk brake and
rear drum brake.
The Front suspension consists of a telescopic fork with
hydraulic dampers. It is the straight slider type with two cylindrical
coil springs. Steel cover tubes protect the suspension elements.
The rear suspension operates on a circular path. The pivoted
rear swing arm is sprung by two cylindrical coil springs and
fitted with hydraulic dampers. The suspension dampers are protected
by chromium plated steel covers.
The Wheels and Tyres:
The Tyres have two functions. First, they
are air-filled cushions that absorb most of the shocks caused
by riding on bad roads. Therefore they reduce the effect of
the shocks. Second, the tyres grip the road to provide good
traction; Good traction enables the bike to accelerate, brake
and make turns without skidding.
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 the