Two stroke motorbikes are old school and awesome, generate more power and are so much fun to ride eg. Yamaha Rx100,Rx135 also the indestructible Rajdoot…. But they’re banned now because they pollute more. So you’re stuck with 4 stroke.

Cubic capacity means the size of the engine, generally more cc’s means more power, a bigger bike profile and a more macho engine sound eg. Royal Enfield.
Remember cc and power are not linearly related, it depends on the engine manufacturer.


In Motorbikes there are Two major divisions in bikes based on commercial uses they are Motor Scooters and motor cycles-

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  • Motor scooters commonly used by ladies , and for person who want more comfort and to satisfy Human factors and ergonomics
  • Motorbikes are commonly by everyone they may use it for various reasons.

Engines In Motorbikes-

Petrol engines are more often used in motorcycles, due to their simplicity. To know more about the reason why petrol engines are used in bikes refer to Why diesel is not used in bikes?.

Petrol engines 

Almost all engines of this generation are Four-stroke engines,Two-stroke engines are almost faced out due to their inefficient operation.
Four stroke petrol engine

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Before going to 4 stroke engines , let’s take a view about what is aStroke????


Stroke is the distance traveled by a piston from TDC (top dead center) to BDC (bottom dead center)and vice versa, during a stroke the crankshaft will rotate 180′.

A four stroke petrol engine follows Otto cycle. Since there are four strokes , a working cycle will be completed in 4 strokes, ie 720, revolution of crankshaft.


Intake stroke-

During intake stroke ,air fuel mixture is taken through inlet valve. during this time the exhaust valve remains closed.Piston moves from TDC to BDC.

Compression stroke-

Both the valves are closed and piston moves from BDC to TDC ,this compresses the air fuel mixture. During compression pressure and temperature rises.

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Power stroke-

Valves remain closed ,At the end of compression stroke ,the fuel is ignited by a spark.Combustion of fuel increases pressure in cylinder and the mixture expands pushing the piston to BDC. (only in power stroke engine delivers power ).

Exhaust stroke –

During exhaust stroke , the exhaust valves open and the piston moves from BDC to TDC pushing all the waste gas out through exhaust valve.

“The power to execute Intake ,compression ,Exhaust stroke comes from Flywheel. 

Starting the engine –

When the key is inserted and turned we are actually closing the circuit between battery and the spark plug.When we are pressing the Stator button , a electric motor ,engages with the flywheel and initiates working of engines. When we stop pressing the button ,the motor input gear disengages from flywheel.


Parts of Motorbike Engine-


  • The piston is a reciprocating part of the engine, which is directly exposed to all products of combustion
  • The crankshaft is an eccentric shaft which converts the reciprocating motion in rotational motion.
  • Piston and crankshaft are connected by a connecting rod, a Gudgeon pin is used to connect a piston with connecting rod
  • The camshaft is used to operate the opening and closing of valves. It is driven by the crankshaft using timing gears.
  • Cylinder is the space in which cylinder reciprocates
  • The gasket is used to seal the gap between the cylinder head and cylinder block
  • spark plugs are used to ignite the fuel mixture
  • a piston ring is generally two types, a compressing ring and oil ring.
  • A compression ring prevents the flow of fluids from above the piston to the crankcase.This is because there is always a gap between piston and cylinder to aid free movement of the piston.
  • Oil ring is used to spread and scrap out the lubricant oil into the crankcase
  • What is a suitable material for the piston of an IC engine?

Terms commonly used with respect to Motorbikes-

CC (cubic centimeter)-

This is displacement or swept volume of  is the sum of volume swept by the piston while traveling from TDC to  BDC  of all cylinders.

What does CC or liter mean when describing the power of an engine?

The power represented by HP horsepower or PS (the German term) .This power is the power available at the crankshaft at any instant.

RPM revolution per minute of crankshaft,ie how fast the crankshaft rotates.

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Torque its is turning moment produced by the engine ie How hard the shaft is rotated.

What is the meaning of torque and power in a car in layman terms?

If you say a car has a particular torque at 3000 rpm and power at 4500rpm, what does it mean?

In car engines, what is better: 100bhp@1500cc or 100bhp@2500cc


Since there are many reciprocating parts and rotating parts lubrication is necessary.Oil is vital to the operation of your motorcycle and operates in three ways: reducing internal friction, cooling the components of the engine, and flushing the engines debris. Oil lubricates the moving parts in the engine, preventing metal parts from coming into direct contact with each other.

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Cooling of engines

A engine emits large quantity of heat , if not properly removed may lead to thermal strain on engine parts.Bikes are generally either Air or liquid cooled.In air cooling the engines have well defined projections called as fins. These fins are used to increase surface area of engine,there by increasing heat transfer.These air cooled engines depend on Natural convection and Forced convection.
Forced convection comes into play when the bike starts moving or by free flow of air stream (Wind)


Liquid cooled engines are the efficient method of removing heat from an engine, as its capacity is very high.These coolants maintain lower cylinder temperature than air cooling and their efficiency is stable. They use an engine lubricant moving in and around the walls of the cylinder, The cylinder and head have grooves to aid flow of coolant.


Most engine coolant are either simply water or water soluble oils. The hot coolant leaving the engine enters a radiator where they they reject the heat to atmosphere by convection and forced convection.
Electrical systems
There are many systems that require electrical energy,like spark plug,horn,lights,etcAll the power is taken is from  battery . the battery is being constantly charged by a alternator.
AIR Intake system
Air is required for combustion process , the air must be clean and available adequately . Air is drawn into to cylinder due to fall in pressure inside the cylinder during intake stroke.
The principle is simple just like the working of straw , In the image compare the mouth of boy to engines intake effort and replace water by air.

A air filter is used tho filter the air taken in during compression . Most of air filter of bikes and cars are produced

Position of air filter in bikes is shown below

Fuel systems-


  • As  said by all  , its a mechanical system which is used to blend the air  with  fuel mixture ,before the cylinder and before intake manifolds
  • Commonly used in petrol engines
  • The principle is simple and equal to Air pressured water sprayer

Working principle –

  • When air is forced to flow through a tube as in Fig. There is pressure drop in the the tube as air flows (nozzle)
  • This pressure drop is countered by suction of water from the reservoir

The working of carburetor is similar to this above mechanism

  • Air flows through the carburetor is due to suction of  engine
  • And all other principles are same as above mechanism

Controlling the engine

  • The amount of power produced by a engine can be controlled by altering the amount of Air + Fuel mixture present in the cylinder .
  • The amount of fuel supplied to the engine is indirectly controlled by air velocity (mass flow rate)
  • The   amount of Air flowing is again controlled by a throttle valve or a   butterfly valve . This valve is controlled by accelerator pedal .
  • People actually say it as Gas Pedal ,But it just controls amount of Air entering the engine
  • A carburetor consists of various jets or holes to achieve different operation condition. Under heavy loads there will a secondary jet adding more fuel into the venturi.

Cons of carburetor
-The problem is that the carburetor cannot react quickly to a driving conditions. As the amount of fuel supplied is controlled  indirectly by creating vaccum ( this is not applicable to Diesel engines ,as they dont produce vaccum as they dont have throttle valves)
-Most time only air will rush inside the cylinder without carrying away the fuel with it.
-Stratification is not possible and multi jets are not possible
-Engines cant be turbocharged or super charged (complex but possible and inefficient)

Fuel injectors:-

-Two type Direct injection or Indirect injection .
-The fuel injector is electromechanical system controlling amount of fuel injected by a term called PULSE WIDTH  (Metering the fuel )
-The working principle is similar to a syringe
-The fuel injector allows control of fuel stratification and multi jets.
-Fuel injectors can be operated by Piezoelectric crystals  or Using solenoids
-fuel and air are mixed by creating turbulence inside the cylinder
-most bikes use direct injection , at this case only air enters the cylinder during intake stroke and fuel is sprayed when the inlet valves begin to close

  • Hence carburetor are pure mechanical systems ,and fuel injectors are controlled by ECU units

Advanced  systems in engine 

  • Digitized fuel injection and controlled spark plugs have given excellent control of combustion process. This method gives good power with optimum fuel efficiency.APDV (Advanced Pro Series Digital Variable Ignition System)
  • These systems use cam position sensor , crank position sensor for calculating the timing for fuel injection and spark
  • Other system includes creating turbulence inside the cylinder . Turbulence can be created inside the cylinder by altering the direction of air intake , direction of fuel intake,designing suitable piston head like shown below .
  • Such systems are called as ASFS (advanced Swirl flow induction system),ATFT (advanced tumble flow induction technology)
  • To Creating Swirl is something how the water spins inside a washing machine ,and Tumbling you might be aware of the rhymes Jack and jill where the kids might be tumbling down . Thats science 🙂
  • Using more than one spark plugs, allows more heat to be supplied to engine.
  • Some engines have More than one valves ie Two intake valves and two Exhaust valves. This is done to increase volumetric efficiency of engine. Simply saying it admits more charge inside the cylinder
  • DTS -si(digital twin spark Swirl flow induction)
  • Twin cam or Dual over head cams , this system allow to use two independent cams, separate cam for Intake and exhaust valves. (this just increases precision timing of valves, imagine when these engines are running at 1000-10000 rpm ,every milli second counts :P)
  • CVTi used by TVS ( not to confuse with CVT transmission) 
    TVS Motor’s CVTi technology is a design innovation optimizes the  air-fuel mixture in the cylinder with a unique combination of swirl and  tumble motion. This generates a very high in-cylinder charge motion  which in turn facilitates superior pickup, resulting in improved  performance without negatively impacting mileage.


Electronics and electrical take 10-15 % of the parts in a modern motorcycle. These help the mechanical components work in a better way.

Ignition system-

  Ignition system used to create a spark in the cylinder. Ignition system takes care of the spark timing and all advance mechanism .

For a spark to  jump between the spark plug ends , the voltage difference must be 10000-20000 volts. But the battery supplies 14 volts (not sure about this ). So the voltage must stepped up heavily . The below video will show a older type of ignition system with distributor type.

Short wordings on the above video )all are DC current

-Primary current flow from the battery to the ground this happens when the contact breaker is closed.

-When the contact breaker is opened ( by the cam) the current from battery cannot flow to the ground so them magnetic field in the primary coli destroys. While destroying the magnetic flux will be continuously change , causing a a emf to induce in secondary coil.

-At the same time the capacitor will discharge a huge voltage which will accelerate the destroying magnetic field.

Since no of coils on the secondary coil is more , higher voltage is produced in secondary coli ,which later flows through distributor and  reaches spark plug. The spark plug is grounded by connecting to the engine casing or the chassis.

But in modern engine these system have been modified and used as Transistor control ignition , capacitive discharge ignition , digitalelectronic ignition.

Electronic ignition

                 Electronic fuel ignition uses a electronic module , which uses a series of sensors and actuators. the sensors are used to just visualize the working of sensors. They convert the parameters  (temperature , Crankshaft , camshaft position , throttle position ,  air mass flow rate  , Oxygen level in exhaust  ) into electrical signals and fed them to engine. The output of these sensors are analog , so they converted to digital signal before feeding tho the ECU.

            The engine makes decision based on sensor information , and controls the actuators  ( ignition timing , throttle position if its is a Drive by wire, fuel pressure  ) in the engine , to optimize based on the situation. They act as feedback system.

The engine and ECU has a set of preset values called as Engine fuel map. This is like a table which controls the Air fuel ratio with respect to engine Speed. Air fuel is controlled with injecting predefined quantity of fuel based on throttle position.

Most modern engine will have a ECU with sensors and actuators

Refer this to  know more on engine fuel maps 3S Ignition System (DOHC)

A engine can work only a narrow range of RPM , but in actual scenario we require various speed and torque  depending on situation.A transmission is device which can increase speed with expense of reduction in torque and increase in torque by reducing speed ( this is application of law of conservation of energy)
Gif files show gear speed reduction and speed increase , a combination of such gears form a gear train.

Do u remember the thing which i said in starting about two types of bikes, this comes under this topic .

Transmission in Motor bikes-

Almost all motor bikes use Sequential transmission . This type of transmission is similar to a manual transmission in car . This system is used because the amount of area available is less .The method of engagement mechanism is different from those in cars.
Its working is hard to be stated in words just check out ths video .

The final drive is a chain drive.

Transmission in Motor scooters
Motor scooters use a kind of automatic transmission  called as CVT ( continuously variable transmission).this kind of transmission is also used  in atv and cars.
This systems consists of two seamless tapered cylindrical surfaces engnaging together,mostly a belt is used to transmit power between these two.
Variable gear ratio are created by sliding contact between belt and surface of cones

The motion between pulley is controlled , component called a variator.The variator function is similar to a centrifugal clutch.

Clutch –

The clutch is device which is used engage and disengage power from a engine.A engine will keep rotating even when we are idling or coasting or while running
If there is no such device called Clutch then in order in slow down or stop , we must switch of the engine.. but this is a inefficent process
Hence a clutch is a device which is used to disengage power from engine , when we are standing still , now the engine can move rotate freely(idling) as there is no load.

Clutches in motor bikes
                Motor bikes use a manual clutch similar a cars clutch the principle is similar
Whats happens when u try to stop a rotating object  using ur hands, yes our hands try to rotate with the rotating element this is due to friction.
This is the principle used in a clutch . It consists of friction surfaces enganging together to transmit power. When the clutch is pressed the friction surfces move away from each other hence power is not transmitted

Most bike use multi plate clutch , if its a wet multi plate the the whole clutch is immersed in transmission oil.
Advanced clutches

  • Rekluse clutch used in Harley davidson,Slipper clutch (available in KTM 200,390)

Motor scooters clutch
                           They use a automatic clutch mostly of centrifugal type. the working principle is very simple.
Tie a heavy object or stone  to one end of thread and rotate it. The object will rotate as shown in fig.

What will happen if u increase speed of rotation , yes the radius of rotation increases.and if speed is reduced the rotation radius also reduces.
This principle is used to engage the centrifugal clutch .similar to the above example , a rotating mass or the brake shoe which expands is used here.
Working is simple ,while we are idling the engine RPM is very less . so the Rotating masses rotate in lesser radius , so power is not transmitted to wheels . When speed increases the centrifugal force causes the rotating masses to expand and comes in contact with wheel hub.hence power is transmitted

Thats it

  • Centrifugal clutch and  CVT together experience transmission loss so only they are not used in Motor bikes.They are used in motor scooters due to their simplicity

Braking system-

         Braking system is similar in both scooters and bikes.there are two commonly used brake system . A mechanical or hydraulic brake is used in  motor cycles.Braking action is caused due to Frictional force between the contacting surfaces.And later this energy is converted into heat energy.

Further some bikes use Drum brakes while some bikes use Disc brake.
Drum brakes
          Drum brakes are simpler and efficient method used for braking. most drum brakes are mechanical actuated

The above diagram shows a hydraulic actuated drum brakes. the working is  simple. when hydraulic fluid is forced inside the cylinder ,the piston  pushes the which in turn pushes the brake shoes against the rotating  drum.braking force is due to friction between the shoes and the drum.  The drum is directly attached to the wheel.

Above image shows the mechanical link to actuate a drum brake (rear wheel), THe working is very simple and slef explanatory after seeing the video below.

If it is a mechanical actuated brake the piston is replaced by a S cam.

Disc brake
               Disc brakes are hydraulic actuated brakeBefore entering into into Disc brakes its required to know about Hydraulic brakes.

The working is effected by basic laws called as Pascals law and hydro static laws .

The main component of hydraulic brake is the master cylinder . A master cylinder working is similar to squeezing tooth paste.

A master cylinder acts like heart of the brake pumping braking fluid to to all chambers under pressure.

The red color rod is attached with brake handle, when this is pressed the hydrualic fluid is squeezed and actuates the piston.
Here is the position of master cylinder of bike.

Disc brake

When the pedal is pressed , the hydraulic fluid is forced to flow out from mater cylinder ,this forces the piston in caliper to expand and squeezes the rotor and wheels get retarded.

Motorcycle frames-

A  motor cycle frame is a just a piece of metal which hold all the parts of  motorcycle.It is sum thing like trunk of the tree holding huge mass above it.Therefore a motorcycle frame must be stiff enough to support all the accessories of a bike . It must also be capable of absorbing the impacts during crash and to safe gaurd engine and the rider
              Often steel tubes are used they are made hollow to reduce their weight while providing class performance.Cast aluminum ,and carbon fibres are used to reduce their weight.
The stiffness of  a frame is reinforced by diagonal members .Stiffness of a frame depends on  Proper triangulation.

Triangulation means all the members of the frame must form common node point.If proper triangulation is not formed any load one the frame will cause a bending load one the adjacent frame.
If properly triangulated ,there will be either tensile are compressive loads acting at the node . (metals have better tensile strength than bending strength)

Before going to the types a simple topic is called as Stressed member.

               A stressed member is frame or component which directly recieves force and transmit that force to other members of a frame.

Types of frames

–    Backbone frame – This is one of the simplest frame ,used in older vehicles,they mostly used engine as a stressed member.The rigidity of the bike is not the best as there is not reinforcment for the neck (which may result in bending ).Below image showing frame of  CD 100 series honda bikes.The engine is supported by a sub frame.
The pipe with larger diameter is called the back bone.From which ,there are many sub frames.


        –      Diamond tube:A diamond tube is just similar to a Backbone frame ,except that a Dwon tube extends from the neck to support the engine.This type also uses engine as a stressed member.They are light is weight and simple in construction to other frames.
Used in :
Bajaj: Pulsar 135LS
Hero: CBZ Xtreme, Hunk, Achiever & Karizma R/ZMR
Honda: CB Twister, CB Shine, CBF Stunner, CB Unicorn, CB Unicorn Dazzler, CBR150R, CBR250R
Royal Enfield: Bullet 350, Bullet Electra, Classic 350/500, Thunderbird 350/500
Suzuki: Slingshot, GS150R
TVS: Flame, Jive, Max 4R, Sport, Star City
Yamaha: YBR125, SS125, SZ, FZ, Fazer

These frames can also be of cradling type, ie the down tube from neck will join the the frame below the engine (either of single down tube or double down tube)

    –     Cradling type:These type are extension of a diamond tube except that the down tube from the neck extends to the frame below the engine.Here engine is not a stressed member .These frames are build to last long and are more stiffer than previous types.

Here the above image is Single cradling type as only one  Dwon tube is used,it can also be a Double down tube.

Single down tube

Double down tube

List of bikes with cradling type:
Bajaj: Platina 100, Discover 100/125/150, Pulsar 150/180/220, Avenger 220
Hero: CD Dawn/Deluxe, Splendor, Splendor NXG, Passion, Super Splendor, Glamour
TVS: Apache RTR 160/180
Yamaha: Crux, YBR110
               –  Trellis frame: This frame is formed by welding series of tubes together forming a cage like structure.They dont have a back bone or diamond or a cradle.The engine is well secured between the cage.Its commonly used in sports bikes.Construction is complex.Handling is sharper with sportier appearance

These frames are used in KTM Duke 200 and 390 models.

           –  Perimeter frame: Perimeter frames also known as Twin spar/beam frames.The main frame usually connects the rear swing arm frame,while the engine is suspended from the frame.The engine can be said to be held around the “perimeter” of the frame.(something like a helmet fro the engine) .Manufaturing such frames is costly and used in sports bikes.Used for sharp and stable handling and brakings.

Used in Pulsar 200 NS and RS and R15

                              Red circled part is the swing arm ,for the rear wheel.
      – Under bone frame (used only on scooters):This frame just consists of simple construction ,with a large tube acting as bone ,which runs as a single tube from neck and runs down the bike as twin tube.
The rear wing arm will be fixed to the supports as shown by red circle .

Suspension system-

A suspension system is used to connect the un sprung mass of system ( wheel hub ,wheels ) to the sprung mass (all other parts ).
              They generally contain a shock absorber and and coil springs.
A shock absorber consist of a Spring and damper. The spring is used to transfer the load or shock  gradually form wheels to sprung mass.
The damper is component which is used to dampen out vibrations by converting them to friction energy using fluids.

Nitrox suspension????????
After seeing the above video , its evident that during shock the fluid is transfered in and out of the two tubes.Then why does a nitrox name sit in there ,lets see

What happens when u shake a Tin can of oil .The oil will foam (aeration ),so the can will be filled with bubbles.

If this is the case ,The same will happen inside a damper ,the fluids continous movement may result in aeration or formation of  bubbles .To prevent it the air is evacuated and filled with Nitrogen .
This concept will be explained in the following video

Most commom suspension used in bikes
-A coils over at rear (either monoshock or dual shock)

-Telescopic suspension at front

It may be telescopic (left img) or Inverted fork (right img)

Swing arm suspension
                        The swing arm suspension is like our hand and elbow joint (fulcrum) this allows the rear frame of bike to move relative to from front frame.

Other aspects :Tires –

Radial tires
From the name suggest here each layer of  tire known as Ply are placed radailly to contribute as various layers of a tire.Plys are plced along circumference of tire radially.
             This alignment gives reinforcement for tires  in the faces ,mostly  radial tires have weak side walls.Most radial tyres are reinforced with steel meshes.
          While taking a turn radial tires allow side walls to compress more ( as they are not reinforced) there by increasing the friction contact.

Cross ply tires
                   This type of tires were the  , the plies are arranged in direction parallel to axis of tire.These tires are pioneering types . Currently they are out fashioned and are used only is roads which are very rough and hard terrains where the side walls are to be reinforced.

Look at the image below , It will tough to identify a radial or cross ply tire by the outer appearance

The answer can be read by reading marks on tire Its called manufacturers code
-B stands for Cross ply or bias ply
-R stands for Radial type…

In recent trends tubeless tires are being used , this tire is simple that  the tire and tube are integrated together so that the tube does not blow off during a punctured like a balloon.

  • Tires are either treaded or non treaded (slick tyre ) based on use .The treaded tires are mostly used for wet or off road purpose.The treads are used to prevent hydroplaning while riding in wet conditions.
  • These grooves or treads are used to transfer water away from tire to prevent hydroplaning

Difference between a Scooter and a bike’

  • Most scooter use a automatic gearbox (CVT) with automatic clutch (centrifugal type).While bikes use manual gear box (Sequential type) and a manual clutch (wet or dry multiplate)
  • The suspension of scooters are tuned for comfort ,while for bikes they are performance.
  • Most bikes shock aborbers are adjustable , a person can adjust the ride comfort of rear absorber. for example FZ 2.0 comes with 7 step adjustable monoshock,using a puller wrench.Its rare to find such set ups in scooter .
  • Most scooters use rear suspension as a swing arm suspension with a monoschock.

Do It Yourself- Adjusting Monoshock Suspension Of Yamaha FZ-S V2.0

  • The wheel base of scooter(around 1250mm)  is smaller than motorcycle (around 1375) ,Also the tire diameter is around 10 inch for scooters and for motorcycles is around 18 inches (im not sure of this values hope some one can correct
  • Engine and transmission  is mounted on rear swing arm for scooters,while engine is mounted on main frame for bikes.

And finally i wanted to add something there is some thing callled high beam in a bike , plz dont use these lights while driving,unless required.This high beam will be irritating for most other users on road

This is represented by this symbol on the dashboard , plz identify and adjust to normal beam.


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