9 Part Of Two Stroke Engine With Function

2-stroke engine Components – In a vehicle, the engine is the heart of a vehicle power station. Without the engine, a vehicle will not run unless there are other energy sources such as electric motors. But, in general, vehicles that are currently produced use the combustion engine power source.

Conbustion engine actually can not produce energy because energy can not be made. But this engine is a component of energy conversion from oil (gasoline) to motion energy (rotation).

How to ?

To discuss this we are familiar with 2-stroke engine cycles and 4 stroke engine cycles. What does it mean ?

two-stroke-engine, is a cycle that occurs at one turn of the crank to produce combustion. So every cycle on the 2 stroke engine not only last one round.
four-stroke-engine, is a cycle that has longer stages because in one process of combustion / cycle consists of two times the crank.

Of course, between the 2 stroke engine and 4 tak it has the difference despite having the same fuel. One of them on the components that interact.

In this article, we will discuss what components affect the working principicle of two-stroke engine with each of its functions.

Two Stroke Engine Components And Its Function

1. Cylinder block

Just like the 4 stroke engine, cylinder block is used as a place to make energy changes from the combustion process to produce the energy rotary. The main function of the cylinder block is to place the piston to move up and down. As the name suggests, the shape of this component is like a cylindrical cavity, inside this cavity the piston acts.

2. Head cylinder

The cylinder head has two functions ie as a cylindrical cavity cover and as a place of burning. In theory, engine combustion does occur in the combustion chamber, but the position of this combustion chamber is inside of the cylinder head.

3. Piston

Piston is a tubular component with a certain diameter. The piston diameter is smaller than the diameter of the cylinder, because the piston position is inside the cylindrical cavity. Its function is to adjust the size of the volume of the combustion chamber.

In the cylinder block, the piston only moves up and down. But the up and down movement can cause some conditions, if the piston moves down then the volume of the combustion chamber will enlarge and this makes the gasoline and air mixture sucked into the combustion chamber.

As the piston moves up the volume of the combustion chamber will shrink, this condition causes AFM (air fuel mixture) in the combustion chamber compressed. The result is that the temperature and pressure of the gas increases, if there is a little spark then this gas will burn. And there was a burning process.

But, because the piston’s diameter is smaller than the cylindrical cavity it will leak air from the combustion chamber through the piston gap as the piston rises. To overcome this, there are three rings located on the piston wall. This ring is elastic so it can be attached to the cylinder surface. Through this ring, a gas leak during compression will be prevented.

4. Piston rod

The piston rod or the connecting rod is a part under the piston and above the crankshaft. Its only has one function, connect the up and down motion of the piston to the crankshaft. Although its function is only one, but this component should not be underestimated.

When combustion occurs, the resulting expansion of the combustion process will push the piston down with great power. The piston rod is required to deliver this thrust to the crankshaft without being bent. Therefore, the connecting rod is made of iron.

5. Crankshaft

Crankshaft in principle the same as the stroke on the bike. Its function is to change the up and down motion into a circular motion. As we pedal a bicycle, we subconsciously turn the up and down movement into a circular motion.

On the engine, our leg is assumed as a piston and connecting rod. Just as a connecting rod, the crankshaft is also strongly demanded to withstand the impulse of combustion and strong reverses the spin so that the piston is able to move back up.

For that reason, on a single cylinder engine, crankshaft design usually will be accompanied by silindrical ballance to get more stable rotating.

6. Intake port

The function of this channel is the place for the entry of air and gasoline mixture into the crank chamber. Why go to crank chamber? because in the two-stroke cycle, a mixture of gasoline and air will be channeled into the combustion chamber when finished combustion process. Movement of the piston towards the bottom will push this gas to move up through the transfer channel.

the difference of the 4 stroke engine is the absence of valve mechanism on the 2 stroke engine. That’s because the intake channel is directly connected to the crank chamber. In a two-stroke engine both combustion chamber and crank chamber will affect by the piston movement.

As the piston moves upward, the volume enlargement in the crank chamber will suck air and gasoline into the crank chamber, when the piston moves back down the piston wall closes the intake channel.

7. Exhaust port

Just like the intake port, the exhaust port is the channel that connects the combustion chamber with the exhaust port. Its function, as the exhaust channels of combustion gases. This channel also does not have a valve mechanism because it takes advantage of piston movement to open the channel.

The location is above the intake channel, and this channel will open automatically when the piston moves down. When the air from inside the crank room enters the combustion chamber, it will push the combustion gases move out via exhaust port.

8. Transfer port

the transfer channel is a special channel that connects the combustion chamber with the crank chamber. Just as the two channels above, this channel is also not equipped valve mechanism. Just use the piston movement to set open and close channels.

The function of this channel is to flow AFM inside the crank chamber to the combustion chamber. How does it work ? it’s work by utilizing the piston movement, when the piston moves down automatically open port transfers. While the intake channel will be closed. And this will push the fuel water mixture inside the crank room into the combustion chamber.

9. Spark plug

Spark plugs have function to sparking fire on the gasoline engine. This spark plug works by converting electrical energy into fire, how it work?

Actually, the fire and electricity have ability to burn. So that, to do the burning procces inside combustion chamber, it’s only need to increase the electrical voltage (up to 20KV) so that the electricity can form a spark.

In general 2 stroke spark plugs and 4-stroke spark plugs are same, but the location of the spark plug on the 2-stroke engine is located above the central combustion chamber. So the burning will be more centered in the middle and the power will be straight vertical down.

But, the weakness of 2-stroke engine is related to the level of gasoline consumption and emissions that very bad. That’s due to this engine combustion occurs every crank rotation, while the 4-stroke engine burn every two crank rotation so that the use of gasoline is twice more wasteful than the 4 stroke engine.

While emissions, filled with white smoke coming from side oil. The side oil is a spare oil that lubricates the crank chamber, but the oil will enter the combustion chamber as the piston moves down. As long as the oil will burn and the result is white smoke from exhaust.
— Update: 30-12-2022 — cohaitungchi.com found an additional article Two (2) Stroke Engines – Parts, Working, Application from the website www.mechstudies.com for the keyword parts of 2 stroke diesel engine.

Two (2) stroke engines are described along with all basic details, how does two-stroke engine works, along with many diagrams.

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Let’s begin with two (2) stroke engines!

What are two (2) Stroke Engines?

Two (2) Stroke Engines Basics

The two-stroke engine is part of an internal combustion engine with only two strokes for its working.

It differs from the four-stroke engine based on stroke completed in two revolutions, whereas, in the four-stroke, the operation is completed in four 180 degrees rotations.

The name itself comes from its operation completing process in two revolutions. A stroke means the piston travels along with the cylinder.

Parts of 2 stroke diesel engine
Two 2 stroke engines
  • In the two-stroke engines, the two strokes get activated at the same time.
  • Just like the end of combustion and the compression stroke happen simultaneously, and exhaust entry happens simultaneously.
  • Two-stroke engines have a great weight to power ratio compared to four-stroke engines.
  • The two-stroke engines are commonly seen in dirt bikes, mopeds, small motors, jet skies, etc.
  • They are having limited use now due to their disadvantages in the commercial automobile vehicle sector.

Two (2) Stroke Engines Importance

There are some advantages of the two-stroke engines. We will discuss them later in this post.

  • But the applications for which the two-stroke engines are used is due to they are light in weight due to less moving parts.
  • The main difference between two-stroke and four-stroke is the required crack rotation for the operation.
  • The crankshaft needs to complete about two rotations to complete operation in the four-stroke engine, whereas the two-stroke needs only one crank rotation to complete the operation.
  • But you will not see the two-stroke engines in the car as much as four-stroke engines.

So, let’s know more details about the two-stroke engine parts and their work. These parts are the same as for any engine with slight changes.

Components of Two (2) Stroke Engines

The two-stroke engines have almost the same parts as the four-stroke engines, like,

  • Fuel injectors
  • Spark plug
  • Inlet and outlet ports
  • Piston
  • Connecting rod
  • Crankshaft
  • Crank & crankcase
  • Flywheel
  • Counterweight etc.
Parts of 2 stroke diesel engine
Two 2 stroke engines parts

Let’s know the parts of the two-stroke engine in little detail.

Fuel injectors

The two-stroke engines get an advantage from the fuel injection systems rather than carburetors. However, carburetors are not used to that extent right now. Fuel injectors are used in diesel engines or C.I engines.

  • In the case of two-stroke engines, the carburetor causes the problems of air-fuel mixtures directly going out.
  • The direct fuel injection solves this problem.
  • These injectors spray the fuel directly into the cylinder with the amount to the air required to get the correct amount of mixture of air and fuel.
  • The fuel doesn’t pass through the case, so there is a need for lubrication.

Spark Plug

The spark plug as the name suggests it ignites the fuel. It is connected to the battery; the current is received by the spark plug from the battery via a button start or using a kick. Spart plugs are used in a petrol engine or S.I engines.

  • The fuel gets ignited due to the spark plug and the vehicle starts.
  • If sometimes the vehicle is having problems to start, mostly there’s a spark plug problem, or sometimes when the vehicle just starts and stops suddenly.
  • The spark plug has continuous work in case of two-stroke engines.

Inlet, Outlet & Transfer Ports

Just like in the four-stroke engines, there are inlet, exhaust, and transfer ports in the two-stroke engine.

  • The inlet port is located below height compared to the exhaust or outlet port.
  • Transfer port is placed between inlet ports and outlet ports and it helps to transfer the air-fuel mixture from crankcase to cylinder.
  • As the two-stroke are completed simultaneously the intake and exhaust ports are always at work.
  • In the cross-flow arrangements, inlet and exhaust ports are located opposite to each other side.


The piston is one of the important aspects of every engine arrangement. In the two-stroke engine to complete the operation, pistons need to reciprocate which in turn causes the crack to rotate to get the power.

Parts of 2 stroke diesel engine
Two-stroke engine piston
  • The air-fuel mixture gets expanded in the cylinder and the piston moves downward causing the piston to reciprocate hence generating the motion to crack shaft through connecting rod.
  • Piston has the oil rings to stop leakage of oil.
  • The detailed working of the piston we will know in detail in working section.

Connecting rod

The connecting rod is connected to the piston as well as the crack shaft. It’s a long rod in which both the ends are connected to the piston and the crankshaft with the help of pins.

  • The connecting rod accommodates the reciprocating motion of piston transfer to the rotational motion of the crank.
  • Generally, it is made up of the I-beam section.


The crankshaft is responsible for generating power. The motion received from the piston is the reciprocating movement crank converts it into rotational motion.

  • This power is given to the flywheel and to the wheels.
  • The wheels get powered and thus the vehicle propels.
  • Crankshafts need to complete one revolution in the two-stroke engines, to complete the process compared to two revolutions in four-stroke engines.
Parts of 2 stroke diesel engine
Two-stroke engine flywheel

Crank & Crankcase

A crank is a piece of metal that is placed between the piston and crankshaft.

  • It is basically a small arm attached to the rotating shaft at the right angle.
  • It helps to change the circular motion into a reciprocating motion.


It’s the device that stores the generated power. The crankshaft has a connection to the flywheel using bearings and journals.

The flywheel is one that transfers the engine power to the wheels through a transmission.


In the two-stroke engines to avoid imbalance created by the rotating assembly, the crankshaft counterweights are used.

  • It helps to achieve some higher RPM speed and the engine runs smoothly.
  • The weight of the piston and connecting rod combination affects the size and placement of the counterweight.
  • If this is not done, the engine will experience vibrations that will eventually tear up the main bearings and cause damage.

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Now let’s know the detailed working of the two-stroke engines.

Working of the Two (2) Stroke Engine

Though the two-stroke engines do all the four operations like,

  • Intake,
  • Compression,
  • Power and
  • Exhaust

Check a nice VIDEO from Physics and Animation!

These all steps are completed in just two-strokes. You can classify the two-stroke engine operation in two strokes,

  • Compression stroke: It consists of intake & compression
  • Power stroke: It consists of power & exhaust

Compression Stroke

So, the working starts when you start the engine and the spark plug ignites the fuel.

  • The piston moves from the top dead centre (TDC) to bottom dead centre (BDC) causing the admission of the fuel and air mixture.
  • When the piston is moving downward TDC to BDC a vacuum is created which causes the entry of the air-fuel mixture from the inlet port.
  • The inlet gets uncovered and the fuel is entered. Now the main things start, when the piston reaches from the bottom dead centre (BDC) to top dead centre (TDC) the fuel gets compressed.
  • Now again the spark plug fires up and ignites the fuel and the charge gets expanded.
Parts of 2 stroke diesel engine
Two 2 stroke engine compression stroke

Power Stroke

As we have seen in the previous upstroke the inlet port was open it allows the fuel to enter, due to which partial vacuum is created and there’s no fuel left behind.

  • When the piston is reached at TDC the charge gets ignited by the spark plug and immediately the combustion process starts.
  • Hence the compression, as well as the combustion process, start simultaneously. That’s the reason it’s called the two-stroke engine.
  • The piston is doing a lot of work here continuously.
  • In the power stroke, the piston goes downward as well as uncovering the exhaust port the exhaust gases are expelled out of the exhaust port.
  • The exhaust gases get expelled on one side as well as the fuel comes from the inlet port again.
Parts of 2 stroke diesel engine
Two 2 stroke engine power stroke

That’s the amazing thing about the two-stroke engines the two things happen at the same time. Because the two operations happen at the same time it doesn’t need so many moving parts as compared to the four-stroke engines.

Lubrication for Two (2) Stroke Engines

If you ever drive the two-stroke vehicle, you may be noticed that you need to mix up some oil alongside the fuel mixture. When you fill the fuel at any station you had to mix up some oil to run the vehicle, why is that?

So here is the answer, the two-stroke engine needs lubrication oil.

  • In the case of the four-stroke engine, the lubrication system can be made separate without any issue.
  • But in a two-stroke engine, the oil should be mixed with the fuel.
  • In a four-engine the crank case is a whole different part but in two-stroke engine the crank case acts as pressurization chamber and it can’t hold any oil.

So, if you mix up the oil with the fuel it will get entered into the crankcase and the operation will be smoother. If you forget to add up the oil, the engine isn’t going to last long for sure.

The ratio of gas to oil is set by the engine manufacturer but ranges from 30:1 to 50:1 per volume unit.

This is another disadvantage of the two-stroke engines, the oil gets burned along with the fuel. Two-stroke engines suffer oil starvation if rotated at speed with the throttle closed

There are some advantages and disadvantages of two-stroke engines. There are a lot of disadvantages that are the reason it’s not used by modern cars nowadays and its use is limited, one reason is above stated related to lubrication.

Let’s know more advantages and disadvantages of the two-stroke engines.

Advantages of Two-Stroke Engines

The two stroke-engines do not have any valves so it simplifies their construction compared to the four-stroke engine’s construction.

  • It doesn’t have lots of moving parts and that contributes to its simplicity.
  • It gives one power stroke per revolution of the crankshaft.
  • High power to weight ratio and significant power boost.
  • The two-stroke engines get a power boost because two-stroke engines fire once every revolution. Power is produced once during 2 strokes of the piston.
  • Two-stroke engines are lighter comparatively.
  • It has a high weight to power ratio.
  • It is almost 30% lighter in weight compared to a four-stroke engine.
  • The produced torque is uniform in the case of two-stroke engines because the power is produced during every alternate stroke of the piston.
  • Due to a smaller number of parts, these are compact in nature. This is the reason these are suitable for small machinery like grass cutters.

Disadvantages of Two (2) Stroke Engines

  • The life of the two-engines is not longer as compared to the four-stroke engines.
  • Parts of the two-stroke engines are associated to wear a lot faster.
  • As we have discussed before we have to use oil with the air-fuel mixture. If the two-stroke engine was used in a car you could burn a gallon of oil for 1000 miles of travel. Hence, they are more expensive to use.
  • They are less efficient, produces lots of carbon deposits due to incomplete combustion, oil-burning along with the air-fuel mixture.
  • The pollution is a lot and maybe these engines may disappear soon. The oil burned along with the air-fuel mixture then produces a lot of smoke.
  • We have seen the working of the two-stroke engines when the intake valve is opened the fuel enters and sometimes some part of the fuel directly goes to the exhaust port. Because of this, you will get less fuel economy and fuel will be wasted.
  • Since the power stroke is produced after every stroke, the engine will heat very quickly. So again, well lubrication and oiling are very necessary to keep the engine running in good condition.
  • High vibration and noisy operation.

So, where these two-stroke engines are used? Let’s know them, as they have limited use now.

Applications of Two (2) Stroke Engines

  • These engines are selected when there is a need for an excellent weight to power ratio.
  • The handheld power tools are one of the good applications of these engines. By employing the oil use they can be handled with any orientation.
  • Commonly used in outdoor power tools, like lawnmowers, chainsaws, and weed whackers.
  • Two-stroke engines are used in motorcycles, etc.
Parts of 2 stroke diesel engine
Two 2 stroke engine applications

In the past, the two (20 stroke engines were used in lots of main-stream vehicles. Like Swedish Saab, Japanese Suzuki, Subaru. In major bike racing events, the two-stroke powered bikes were so much popular in 1970s days. As compared to four-stroke engine these were emitting lots of pollution which caused their discontinuation from the automobile market.

These were used till the 1990s maximum in mopeds and dirt bikes. But due to the strict pollution guidelines and the disadvantages as stated above the use was slowly reduced and they are gone now from the vehicle market and are limited to small applications

High Rated Automotive Engineering Course


So, finally, we have got the basic idea of two (2) stroke engines along with the working principle. Thanks for being with us.

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Further Study

— Update: 30-12-2022 — cohaitungchi.com found an additional article Two Stroke Engine : Parts , Cycle , Diagram , Working , Application from the website learnmech.com for the keyword parts of 2 stroke diesel engine.

A two-stroke (or two-cycle) engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a “four-stroke engine”, which requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust (or scavenging) functions occurring at the same time.
Two-stroke engines often have a high power-to-weight ratio, power being available in a narrow range of rotational speeds called the “power band”. Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and so can be more compact and significantly lighter.


1. Piston 
In an engine, the piston is used to transfer the expanding force of gases to mechanical rotation of crankshaft via a connecting rod. The piston is able to do this because it is secured tightly within the cylinder using piston rings to minimize the clearance between cylinder and piston.

2. Crankshaft
A crankshaft is a part which is able to convert the reciprocating motion to rotational motion.

3. Connecting rod
A connecting rod transfers motion from a piston to crankshaft which acts as a lever arm.

4. Counterweight 
The counterweight on the crankshaft is used to reduce the vibrations due to imbalances in the rotating assembly.

5. Flywheel
The flywheel is a rotating mechanical device which is used to store energy.

6. Inlet & Outlet Ports
It allows to enter fresh air with fuel & to exit the spent air-fuel mixture from the cylinder.

7. Spark Plug
A spark plug delivers electric current to the combustion chamber which ignites the air-fuel mixture leading to an abrupt expansion of gas.

Parts of 2 stroke diesel engine
two stroke engine


1. Intake
The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston. The illustrated engine features a poppet intake valve; however, many engines use a rotary value incorporated into the crankshaft.

2. Crankcase compression
During the downward stroke, the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.

3. Transfer/Exhaust
Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixtures is usually expelled as well.

4. Compression
The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

5. Power
At the top of the stroke, the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle. (At the same time, another crankcase compression stroke is happening beneath the piston.)


Down Stroke

First, the piston is moved downside from TDC to BDC to let the fresh air enter into the combustion chamber. The fresh air-fuel mixture gets into the combustion chamber through the crankcase. Crankshaft rotation – 180°

Up Stroke 

Here happens all the magic. The piston is pushed up from BDC to TDC. The fuel-air mixture gets compressed & spark plug ignites the mixture. As the mixture gets expanded, the piston moves down. During the upstroke, the inlet port is opened. While this inlet port is opened, the mixture gets sucked inside the crankcase. When the mixture is pushed up into the combustion chamber during the previous upstroke, a partial vacuum is created as no mixture is left behind in the crankcase. This mixture is ready to go into the combustion chamber during a downstroke but remains in the crankcase until the piston goes up till TDC. Crankshaft rotation – 360°

Two strokes get completed along with one power cycle.

From the 2nd downstroke onwards the exhaust gases get expelled out from one side while a fresh mixture enters into the combustion chamber simultaneously due to the partial vacuum created in the combustion chamber after removal of exhaust gases. This is the beauty of the engine. Both things happen at the same time which makes it a 2 stroke engine.

Two-stroke diesel cycle goes like this:

1. When the piston is at the top of its travel, the cylinder contains a charge of highly compressed air. Diesel fuel is sprayed into the cylinder by the injector and immediately ignites because of the heat and pressure inside the cylinder.

2. The pressure created by the combustion of the fuel drives the piston downward. This is the power stroke.

3. As the piston nears the bottom of its stroke, all of the exhaust valves open. Exhaust gases rush out of the cylinder, relieving the pressure.

4. As the piston bottoms out, it uncovers the air intake ports. Pressurized air fills the cylinder, forcing out the remainder of the exhaust gases.

5. The exhaust valves close and the piston starts traveling back upward, re-covering the intake ports and compressing the fresh charge of air. This is the compression stroke.

6. As the piston nears the top of the cylinder, the cycle repeats with step 1.


Advantages of two-stroke engines

1. For the same dimensions, the power developed is twice to that of four stroke engines
2. Power required for exhaust and suction stroke is saved
3. More uniform turning moment compared to four-stroke engines hence a lighter flywheel is required
4. For the same power output, the two-stroke engine occupies less space
5. Two-stroke engines are lighter than same power four stroke engine
6. Construction and working of a two-stroke is simple
7. Less maintenance is required
8. High power to weight ratio

Disadvantages of two-stroke engines

1. High-speed two-stroke engines are less efficient due to reduced volumetric efficiency
2. In the case of the two-stroke engine running on Otto cycle, a considerable amount of fresh charge is lost due to poor volumetric efficiency
3. Effective compression is less due to the provision of ports for intake and exhaust
4. More consumption of lubricating oil
5. At high loads, the two-stroke engine does not run smoothly due to dilution of charge


Due to increased regulation of air pollution, the use of two-stroke engines is decreased but they are still used in many low power applications. Such as
1. Outboard motors
2. High-performance, small-capacity motorcycles, mopeds, and dirt bikes
3. Underbones, scooters, tuk-tuks, snowmobiles, karts
4. Ultralight airplanes, and model airplanes and other model vehicles
5. They are also common in power tools used outdoors, such as lawnmowers, chainsaws, and weed-whackers.

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