Dirt Bike Engine: [Everything Discussed In Details]


Dirt Bike Engine

Dirt bikes are such a topic that excites many people. I have been a dirt bike fan since my childhood. This fascination for dirt bikes led me to research them and helped me find out many things about dirt bikes and dirt bike engines.

An engine or motor is the powerhouse that supplies power to the dirt bike. The more powerful the dirt bike engine is, the more powerful your dirt bike will be. The maneuver of a dirt bike also depends on the engine of the dirt bike.

If you are planning to buy a dirt bike, you need to know everything about a dirt bike engine thoroughly. This will help you to decide which one you should go for and which one to avoid. Here in this article, I will be talking about all that you need to know about a dirt bike engine. So keep on reading.

An Overview Of The Basic Dirt Bike Engine Components:

A dirt bike or any other vehicle that runs on motors is also known by the term engines. These engines are made up of not only a single component but also various parts. 

These different parts of a dirt bike engine help to determine the strength of that dirt bike engine. 

Not everyone is familiar with the various parts or components of a dirt bike engine. For this reason, before buying a dirt bike, they sometimes fail to understand the engine strength. This confusion leads to a failed attempt to purchase the right bike for oneself. That is why I will now tell you about the different parts of a dirt bike:

Some parts of a dirt bike engine are so basic that you will find them almost in every dirt bike regardless of their version or model type. I will now briefly discuss 4 of the most basic components of a dirt bike engine:

1. Piston:

The job of a piston is to compress the air or fuel mixture, while the job of the spark plug is to ignite it. The subsequent detonation drives the piston downward, spinning the crank. The rotating action is transmitted from the crank to the clutch, gearbox, sprocket, and back wheel. Therefore, forward motion is the outcome of the piston rod getting pushed below by the expansion of burning fuels.

A piston in a bike goes upward and downward almost 200 times per second. Trust me, that is a lot of work. No machine can work that much for too long. So, make sure you replace it from time to time. 

2. Cylinder Block:

The number of cylinders in a dirt bike engine can vary. It can be one or more than one. Usually, the power and torque production of a bike happens in this section. This procedure helps to move the bike forward or backward. A dirt bike engine is usually an internal combustion type where all the activities are performed to maneuver a dirt bike.

Internal combustion engines typically come with vacuum spaces, and that’s why the combustion process happens inside a cylinder of a bike. In the inside part of a cylinder, the air, gas, or fuel mixture is being compressed, which is later ignited by the spark plug. This whole process creates an internal explosion, and through that, it produces the power to run the dirt bike.

3. Fuel Ports (Inlet & Exhaust):

The ports in a bike work for the intake and exhaust of fuel by intaking the fuel through the inlet port. After the air-fuel mixture gets into combustion, the burnt fuel then goes to the exhaust port and is ejected outside. 

4. Crankshaft:

The crankshaft is turned as the pistons rise and fall. The energy from the piston’s lateral motion, or upward and downward movement, is converted into a rotational movement of the crankshaft. This rotating motion is conveyed from the crankshaft to the back wheel of the dirt bike through the clutch and transmission or the gearbox, sprockets, and chain.

How Does A Dirt Bike Engine Work? (Both 2 Stroke & 4 Stroke)

Before buying a dirt bike, you must know the details of the engine of that bike thoroughly.  This is the life of any vehicle. In a dirt bike, the engine is the core determinator of its performance.

The following sections will explain, so you have a better understanding, how these two and four-stroke dirt bike engines work. So, buckle up and keep on reading.

  • 2 Stroke Dirt Bike Engine: 

A two-stroke dirt bike engine works the same as all the other dirt bike engines, but the only difference is a two-stroke dirt bike works in only two piston strokes. A 2 stroke dirt bike engine completes the process by using the crankcase with the help of the moving piston. 

Between the two strokes, one stroke draws the air-fuel mixture to the combustion chamber through the transfer port from the crankcase. After that, the piston of the engine gets close to the top of the combustion chamber, where the ignition of compressed air-fuel mixture happens by the spark plug. The combustion creates high pressure through this process, forcing the piston down on the second of the two strokes.

When the piston rises during the first stroke, the reduced pressure in the crankcase forces more air-fuel mix. This process keeps going on and on, and that is how a two-stroke dirt bike engine works.

  • 4 Stroke Dirt Bike Engine:

In a four-stroke engine, there are four steps of the power-producing cycle, unlike the two-stroke engine. Each of the power-producing components serves its own duty of piston strokes. They are as such intake, compression, combustion, exhaust. 

There are two upward and two downward strokes in a 4 stroke dirt bike engine. The intake stroke or the fuel valves open to let air and fuel mixture into the combustion. On the compression stroke, the piston goes upward in the cylinder and compresses the air-fuel mix.

The next stage is the combustion stage. At this point, the spark plug ignites the air-fuel mixture that was compressed before. This very stage forces the piston to go down by creating high pressure in the cylinder. Finally, at the last stage, known as the exhaust stroke, the valves are opened, and the burnt fuel is forced out.

2 Stroke vs. 4 Stroke Dirt Bike Engine: A Complete Comparison Table

A 2 stroke dirt bike engine and 4 stroke one have quite a few similarities, but they have tons of differences in a broader sense. While buying a dirt bike, this topic is the most common one that confuses everyone. People seem to be in great dilemma while choosing a bike of 2 stroke engines or 4 stroke engines. 

If you are going to buy a dirt bike or have the desire to do so in the future, then you might think that if you could know the differences between these types of dirt bikes, it would be pretty helpful for you. This will allow you to choose what is best for you and how you can make the best use of your budget as well.  

So, now, to help you clear all your confusion and know a bit more about a 2 stroke dirt bike engine, and a 4 stroke dirt bike engine I will provide a table that consists of the difference between these two types of engines:

2 Stroke Dirt Bike Engine 4 Stroke Dirt Bike Engine 
It has two cycles of the piston for completing total combustion as well as an exhausting cycle.In such bikes, it takes four cycles of the piston to complete a full combustion and exhaust cycle.
One stroke in 2 produces power on such types of engines. One stroke in 4 produces power on a 4 stroke dirt bike engine.
In a 2 stroke dirt bike engine, the crankcase is lubricated through the total loss lubrication system by mixing oil with the fuel.The 4 stroke dirt bike engine uses its constant oil reservoir.
In most 2 stroke engine dirt bikes, the cumulative opening time of the intake and exhaust ports are able to allow some vapors of fuel that are unburnt to depart in the exhaust stream.As we know, a 4 stroke dirt bike engine is more advanced. In this type of engine, the intake and exhaust valve system prevents such type mishaps from occurring.
In the case of burnt fuel, the 2 stroke dirt bike engine contains more oil because the oil is mixed with the fuel just before the combustion.The 4 stroke bike is different. It contains less oil in its burnt fuel.
A 2 stroke dirt bike engine has fewer moving parts than a 4 stroke one.A 4 stroke dirt bike engine has almost 30% to 50% more moving parts than a 2 stroke engine.
As it has lesser parts, it is lighter than a 4 stroke dirt bike engine.This one is lighter than the 2 stroke engine.
A two-stroke engine can produce up to twice the power of a four-stroke engine of comparable capacity.If the capacity is higher than the 2 stroke engine dirt bike, then this one produces more power.

This table will help you clear a lot of confusion about 2 stroke and 4 stroke dirt bike engines. It will assist you in the future if you are planning to buy a dirt bike.

Difference Between 125cc And 250cc Dirt Bike Engine:

Dirt bikes are not the kind of bike which we use on regular roads. People mostly buy dirt bikes to experience a tedious riding journey. These bikes are ideal for off-road biking. Being a dirt bike fan, everything about dirt bikes fascinates me. I have always researched them and not just the models or new releases, I have studied the engines and all the internal parts.

CC means cubic centimeters, which is a unit. This part of the engine indicates the size of the chamber of a dirt bike engine and shows how powerful the dirt bike engine is. Some people get confused about this. I, too, was confused at the start of my research. After going through a lot of articles, research papers, and first-hand experience of mine, I now possess the required knowledge. Now, I will share my knowledge with you.

There are many kinds of bikes available in different cc. Such as 125cc, 150cc, 165cc, 140cc, 250cc, 450cc, etc. Among them, the most commonly bought and used are the 125cc and 250cc ones. 

Now I will be showing you the difference between the 125cc and 250cc dirt bike engines so that you can decide which one is the better and why. They are different in many ways. 

1. 125cc Dirt Bike Engine:

A 125cc dirt bike engine is often considered the best choice for beginners. Some mention-worthy features of a 125cc dirt bike are mentioned below:

  • A 125cc dirt bike’s engine weight is lighter. 
  • The price of a 125cc dirt bike is quite reasonable than the 250cc or other higher cc dirt bikes.
  • The price of the parts of a 125cc bike is lower and less costly than a 250cc dirt bike.

2. 250cc Dirt Bike Engine:

A 250cc dirt bike engine is also considered an ideal beginners choice. For their convenience, some features are mentioned below:

  • The 250cc dirt bike engine makes more power than the 125cc bike.
  • A 250cc bike’s weight is a lot heavier than a 125cc dirt bike’s weight.
  • The parts are costly on a 250cc bike. As a result, the maintenance cost of a 250cc dirt bike is higher than a 125cc one.

After seeing the differences above, you will now be able to choose which features suit you the best and what you are looking for in your dirt bike. However, there are many more differences between a 125cc and a 250cc dirt bike. To know more and detail about them, don’t forget to check out this link.

Related Questions Regarding Dirt Bike Engine:

Advantages And Disadvantages Of 2 Stroke Dirt Bike Engine:

As it has been already discussed in the article that a dirt bike can be of two types. The 2 stroke engine is one of them. People often get confused between a 2 stroke and a 4 stroke dirt bike. Below I will be discussing the advantages of a 2 stroke dirt engine. They are as such:

Advantages Of 2 Stroke Dirt Bike Engine:

The advantage of a 2 stroke dirt bike engine is as follows:

  • It Is Lightweight:

The two-stroke dirt bike engine is a lot lighter than a 4 stroke bike with the same amount of power production.

  •  It is Simpler:

It has fewer moving parts than a 4 stroke dirt bike engine. This feature makes it simpler than the other.

  • Easier Maintenance And Easy To Work On:

 

With lesser moving parts, it makes the job easier to maintain the engine and to manufacture the parts required. 

  • Cheaper To Buy And Maintain: 

As previously mentioned, it has fewer moving parts than a 4 stroke dirt bike engine; it costs less to buy or to maintain a 2 stroke engine.

  • If The Engine Gets Swamped, It Is Easier To Clean:

The engines get hardly affected by water as there are fewer parts in them. If water gets stuck in the machine, it is pretty easy to clean in a 2 stroke dirt bike.

  • It Will Provide You With More Power Output:

Your 2 stroke dirt bike engine is able to produce more power than a 4 stroke dirt bike engine. 

Disadvantages Of 2 Stroke Dirt Bike Engine: 

  • It Consumes More Fuel:

 

2 stroke engines are not that efficient. The air and fuel mixture gets lost through the exhaust port, which causes more fuel consumption. 

  • It Has Higher Hydrocarbon Emission Rate:

In a 2 stroke dirt engine, the intake port and the exhaust open at the same time. Because of this, the exhaust port lets out the air-fuel mixture without even burning some fuel.

Advantages And Disadvantages Of 4 Stroke Dirt Bike Engine:

A 4 stroke engine dirt bike is a kind of dirt bike engine that has a 4 stroke cycle in the piston. It is a higher grade than the two-stroke dirt bike. There are a few advantages and disadvantages of using a 4 stroke dirt bike engine. Below I will be mentioning them for your convenience:

Advantages Of 4 Stroke Dirt Bike Engine:

The advantages of a 4 stroke dirt bike engine are mentioned below:

  • They Are More Fuel Efficient:

 

With valves opening and closing, the four-stroke engine prevents loss of air-fuel mixture through the exhaust port.

  • 4 Stroke Bikes Are More Eco-friendly:

Unlike the 2 stroke engine, the 4 stroke bike doesn’t have the system of total fuel loss. This requires less oil to be burnt in the combustion. This is why it burns less oil and releases fewer exhaust fumes. This is how it works for the environment.

  • Cheaper And Easier Lubrication:

 

The 4 stroke dirt bike engine has a sump reservoir lubrication system. This prevents the constant need for refueling.

Disadvantages Of 4 Stroke Dirt Bike Engine:

There are some disadvantages to the 4 stroke engine bike too. They are as such:

  • The Engine Is Heavy: 

This type of engine has about 30% to 50% more moving parts than the 2 stroke one. This makes the machine a lot heavier.

  • The Maintenance Is Expensive:

The maintenance of a 4 stroke bike is more expensive than a two-stroke bike. More moving parts of the engine make it more costly to manufacture and maintain.

  • The Engine Is More Complicated: 

The engine of a 4 stroke dirt bike has more moving parts than a 2 stroke dirt bike. This makes it more complicated.

How Are The Engines Of Dirt Bikes Classified?

Mostly the classification of dirt bikes is done based on their sizes and strokes. Now you might be wondering how these two are different from each other. 

The size of a dirt bike engine is classified based on the capacity of the combustion chamber. The unit is in CC. If you are not familiar with the term CC, but you are with liters, then know that a liter is equivalent to 1000cc. The capacity of a cylinder reaches its highest position when the piston is at the most downward. This happens in the cylinder block. It is known as the bottom dead center. 

The second classification of a dirt bike engine depends on the times of stroke of an engine or cycle of an engine. As I have already discussed, based on stroke, dirt bike engines are of two types. They are:

  • Two-stroke engine 
  • Four-stroke engine

There is also another type of classification that depends on the number of cylinders a bike has.

How Do You Rebuild A Top End On A 2 Stroke Engine?

Rebuilding your dirt bike engine is a part of the maintenance process. It ensures the health of an engine. Below I am mentioning the steps to reconstruct a two-stroke engine top end:

  • First, set the workspace and wash the bike.
  • Secondly, flush out the coolant.
  • Remove the parts like the seats, gas tank, top unit of the engine, the head of the cylinder.
  • Open the valves.
  • Inspect the piston and replace it if needed.
  • After that, reinstall all the parts that you removed earlier.

How Much Does It Cost To Rebuild A 2 Stroke Dirt Bike Engine?

Engines are a form of machine. A 2 stroke dirt bike engine is no exception to that. The main reason behind it is to ensure the top-notch performance of the engine as well as the bike. From time to time, the rebuild of your engine can help you maintain your bike in many ways. 

Two-stroke engines are simpler, and they have fewer moving parts. So they are cost-efficient and budget-friendly. That is why they can be rebuilt more often. It costs around USD 50 to USD 500 to rebuild a two-stroke dirt bike engine.

How Do You Rebuild A 4 Stroke Top End?

As I have already said, it is essential to rebuild your bike’s engine once in a while to ensure the longevity of your bike’s engine. Now I will be mentioning the steps to rebuild a 4 stroke bike in a concise manner:

This process is divided into two parts. The first one is as below:

  • First, disassemble the parts of your 4 stroke bike’s engine and inspect them. Clean if there is any carbon build-up. Check for any other damages.
  • Further check for any damages in the internal components.
  • Reassemble the parts. 
  • Check the valve clearance. 

The second part of the process is related to the piston. That is as below:

  • Remove all the major parts such as seat, gas tank, spark plug, clutch cable guides, cam cover, etc.
  • Inspect and clean the components. Look for any other significant issues within.
  • Reassemble all the components back.

How Much Does It Cost To Rebuild Your Four Stroke Dirt Bike Engine?

A four-stroke engine is different from a two-stroke one. But it too needs to be rebuilt once in a while. It can save you from costly maintenance fees. It can also protect you from accidents on off-road biking, which can be caused due to poor engine conditions. 

A four-stroke engine has more moving parts that make it more complex than the two-stroke one. It takes hours and a really long process to rebuild a 4 stroke engine. The cost is also significantly more than rebuilding the 2 stroke one. The cost is around USD 1100 and higher.

How To Wash Your Dirt Bike Engine?

Dirt bikes are off-road bikes. This means they have to go through stricter situations like mud, sand, and other things than an average bike. For this reason, the dirt bike engine can get dirtier than other bike engines quite easily. So now I will be talking about how you can clean your dirt bike engine.

Sometimes bike riders soda blast their own bikes, which involves sandblasting the dirt bike with industrial-grade baking soda in a pressurized vessel. It’ll be a thrill. However, you’ll require the blaster, which will add up to your expenses. Some riders start the cleaning process by spraying the whole bike with cleaning agents like the Bio Wash. If you are tight on budget, then you just use a regular dishwasher with warm water. But using the store-bought surfactants makes the job easier.

How Long Does A Dirt Bike Engine Last?

A dirt bike engine is the powerhouse of the dirt bike. It is the soul of the bike. Like mitochondria is the powerhouse of a human cell, engines give energy to the vehicle. But unlike the mitochondria, the machine has a short life expectancy. It needs to be rebuilt from time to time to ensure longevity. 

If you are someone interested in dirt biking, you might be curious about the engine’s life expectancy. Usually, a high-powered engine gets worn out easier than the low-powered one. 2-stroke bikes need frequent rebuilding to prolong their life expectancy. That is why it is said that 2 stroke bikes get worn out more easily than 4 stroke bikes. If you take good care of your engine and maintain them from time to time, they can last up to 8 years.

Final Verdict:

A dirt bike engine can be a very complex issue to understand. But it is one of the vital factors of any vehicle. You should pay a hefty amount of time researching the engine before you buy a dirt bike. Take your sweet time reading this article. You may also check out other dirt bike-related articles by clicking the link.

You may also want to read:

Is A 125 Dirt Bike Too Small For You? 

What Kind Of Gas Does A Dirt Bike Take?

Dirt Bike Laws Of 50 States:

Md. Saifur Rahman

Dirt bike riding was a fascination for Saifur since he was a child. Later that fascination turned into a passion and his profession. Apparently, it may seem that tips and tricks are useless for bike riding sometimes, but you may find them really useful after reading his blogs. Saifur is a regular rider.

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