How Does a Lawn Mower Engine Work – Complete Review

If you are fed up with spending a lot on the maintenance of your engine I suggest you do it yourself at home. It saves your money and time too. Almost all the engines have the same mechanism with various sizes and you can maintain it by knowing about its working mechanism but before telling you how does a lawn mower engine work? I just want to ask, do you know.

What is an Engine?

The word engine comes from a Latin word Ingenium whose root meaning is ‘to create’.
It is a machine that is the main source of power. It converts the fuel into another form of energy i.e mechanical energy.


The working principle of an engine depends upon the ideal gas principle that is “as the temperature of a gas increases its pressure and volume also increases: the temperature of gas increases when you ignite the chamber that has fuel in it. 


By burning fuel or gas it helps us to do our work.


American George Brayton manufactured the first commercial engine in 1872 that works on liquid fuel. After it, Nikolaus Otto invented a four-stroke cycle engine in 1876 , with his two colleagues, and in 1879 a two-stroke engine was manufactured by Karl Benz.

How is an engine made?

The engine is formed by using a casting process i.e to pour molten metal in the mold cavity and allows it to solidify.
This is a very inexpensive method that helps to fabricate large components

How Does a Lawn Mower Engine Work?

To understand this phenomenon, firstly we need to explore the types of lawn mower engines

What are the types of lawn mowers engine?

Lawn mowers have 2- cylinders or 4- cylinder engines with an internal combustion system. (Fuel combustion takes place inside the combustion chamber with air)

Two-cylinder lawn mowers:

Have 2 strokes with one crankshaft revolution.

  1. Suction stroke  
  2. Power stroke

In the suction stroke, intake of a mixture (fresh fuel and air), its compression and combustion occur. Whereas in power stroke expansion of mixture, refilling of new fresh air, and exhaustion of used air occurs.

Parts of the 2-stroke engine:

  1. Inlet port
  2. Transfer port
  3. Exhaust port
  4. Spark plug
  5. Top dead center (T.D.C)
  6. Bottom dead center (B.D.C)
  7. Combustion chamber
  8. Crankcase
  9. Piston

Working mechanism:

The piston inside the cylinder moves down from T.D.C to B.D.C

It causes the pressure in the crankcase and lets the crankshaft convert the linear motion into rotary motion by compressing the mixture. The mixture moves upward to the combustion chamber. 

The piston inside the cylinder moves down from B.D.C to T.D.C:

It allows the combustion to occur by allowing the spark plug to ignites the fuel and let the mixture expand. 

Again, The piston inside the cylinder moves down from T.D.C to B.D.C:

It causes the opening of the inlet port and lets the fresh mixture enter into the crankcase simultaneously the exhaust port opens to let the used mixture expels out of it.

The piston inside the cylinder moves down from B.D.C to T.D.C:

It allows the fresh mixture to enter in the combustion chamber that completes the one complete crankshaft revolution i.e. 360

  • Manufacturing is very easy
  • Long-lasting plug
  • No maintenance
  • No valve adjustment
  • Have a reed valve that has a very simple mechanism
  • Only 2-strokes means less distribution of power occurs
  • Noisy
  • Bad for environment
  • Very difficult to get oil for it
  • Uses more oil
  • The inlet and exhaustion happen at a same time causing a small amount of fresh air to exhaust without using

Four-cylinder lawn mowers:

Have 4 strokes with two crankshaft revolution.

  • Intake stroke
  • Compression stroke
  • Power or combustion stroke
  • Exhaust stroke

Parts of the 4-stroke engine:

  1. Piston
  2. connecting rod
  3. crankshaft
  4. Fuel injector
  5. Spark plug
  6. intake/exhaust valve

Working mechanism:

Intake Stroke:

This is the first stroke in which the intake valve opens. 
This allows the air and the fuel to enter the cylinder. Air acts as an oxidizer. The fuel is injected through a carburetor. The first crankshaft revolution causes the piston to move in a downward direction.

Compression stroke:

This is the 2nd stroke in which one crankshaft revolution completes. 
In which the upward movement of the piston compresses the mixture and makes the mixture highly combustible.

Combustion stroke:

This is the 3rd stroke that initiates the 2nd half crankshaft revolution.
It allows the piston to move upward which helps to ignite the fuel through a spark plug and causes the expansion of mixture.

Exhaust stroke:

This is the 4th stroke that completes the 2nd crankshaft revolution.
again, the piston goes upward by opening the exhaust valve that helps to release the burnt mixture out of the cylinder.

  • Better Mileage
  • Eco-friendly
  • Oil is easily available
  • Separate intake and exhaust strokes
  • Thermal efficiency is very high
  • Unidirectional
  • Difficult to make or to maintain
  • heavier
  • More expensive

Why Will My Mower Not Start?

More than 80% of the causes of ‘your mower is not working’ is the engine’s carburetor. So to avoid it you should take great care of it.
The root cause of this is related to fuel and spark plug.

Fuel problems:

Quantity of fuel: 

Before starting your mower, check whether there is enough fuel present or not.  Because it causes the wearing of the carburetor.

Stale fuel:

You should avoid the usage of stale fuel.
The gas shelf life is 30 days. The fuel older than this can cause the corrosion of the carburetor as it contains an amount of ethanol. So you should use the fresh oil to avoid this.

 Fuel filter:

It is used to filter the debris and sediments from fuel so its daily cleaning is very much necessary. But if you see the filter is clogged due to stale fuel or sediments, you should have to replace it with a new one.

Air filter:

The carburetor needs air for its working. The air filter filters the air debris and dirt to enter the engine. Clean the air filter regularly to avoid this.

Spark problems:

Check whether the spark lead  is firmly attached to the plug or not.
If it becomes dirty or damaged, replace it immediately.

If both of these problems are sorted out:

  • Check the clutch and gear it may be damaged, if yes replace it with a new one.
  • battery voltage should be nearer to 12 volts. Otherwise, it fails to start the engine.

How The Lubrication Of Engine Can Be Done And Why it is Necessary?

The lubrication can be done by adding one part of oil into the 50 parts fuel. It helps to stop the corrosion of the metal parts of the engine due to the friction.
2-stroke engines don’t have separate ports for oil so you should mix it with the fuel.
4-stroke engine has a separate port for oil that can be stored in a crankcase and the pump helps to circulate it throughout the engine.
Make sure to add the proper amount of oil.
If you add more oil it causes the smoke discharge and the engine becomes more sluggish.  
If you add less oil, the engine becomes hot and will burn it.


After reading this information I hope you know well about how does a lawn mower engine work. And you can fix it yourself at home instead of spending a lot of money.

Sharing is caring!

Related Posts:

Leave a Comment