How to Tell if a Lawnmower is 2-stroke or 4-stroke?


You just got your new lawnmower, and you are excited to mow your lawn for the first time, but the lawnmower has an empty gas tank. You have fuel, but you do not know if it is the correct type. To determine what fuel you need, you have to figure out if your lawnmower has a 2-stroke engine or a 4-stroke engine first. If you are facing this problem, don’t worry, this article will tell you everything you need to know about 2-stroke and 4-stroke engines and how to tell them apart.

How to Tell if a Lawnmower is 2-stroke or 4-stroke:

Most lawnmowers were 2-stroke engines, but in recent years 4-stroke engine lawnmowers have become much more popular as they are more environmentally friendly. The easiest way to check what type of engine a lawnmower has is by checking its fuel tank. If there is only one port for oil and gas, then it’s a 2-stroke engine, and if there are two ports, then it’s a 4-stroke engine. You will get to learn about this topic in detail in this article.

How to Check the Type of Engine:

The main difference between a 2-stroke and a 4-stroke engine is fueling. Locate your mower’s fuel tank, and if there is only one intake port there, it means the engine is a 2-stroke. 2- stroke engines require the mixing of oil and gas, so there is only one port.

In 4-stroke engines, there are two separate ports for oil and fuel. So, merely observing your fuel tank can quickly tell you if your lawnmower has a 2-stroke engine or a 4-stroke one.

One other method can be by checking their noises. If the noise produced by the mower is thunderous, then it is a 2-stroke engine, and if the noise is normal and bearable, then it is a 4-stroke engine.

You can also see if your lawnmower exhausts a lot of gases or not. If yes, then it is 2-stroke, and if no, then it is 4-stroke. These methods are only applicable if your mower has some fuel and is running correctly. For an empty lawnmower, you will have to reside with the first method.

What is a Stroke?

The piston moves up and down in the cylinder during an engine’s combustion cycle. “Top Dead Center” (TDC) is the piston’s position nearest to the valves, and “Bottom Dead Center” (BDC) is its position farthest from them. When the piston moves from the top dead center to the bottom dead center, it is called a stroke. Moving from the bottom dead center to the top dead center is also called a stroke. The combustion cycle is the complete process of what happens in an engine. We need to be familiar with the combustion cycle before moving on to 2-stroke and 4-stroke engines. The combustion cycle includes the following processes:

  • Intake: Air-fuel mixture is drawn in as the piston moves down the cylinder.
  • Compression: Air-fuel mixture is compressed as the piston moves upwards.
  • Combustion: The spark plug produces a spark that ignites the gas, and an explosion results. The explosion pushes the piston down.
  • Exhaust: The piston moves upward and pushes the burned gas out.

2-stroke Engine:

This type of engine consists only of two strokes; compression stroke and power stroke. These engines work by combining more than one function into one piston movement. The compression stroke is when fuel and air are pulled in the cylinder. Then spark plug causes an explosion that pushes the piston downwards. The exhaust port is uncovered when the piston is pushed down, so the exhaust is driven out of the port due to the cylinder’s pressure. New fuel and air are drawn when the piston gets pushed down even further, and the intake port gets exposed. All these three processes are part of the power stroke. The exhaust port and intake port are the same in these engines. This is called power stroke because it is in these processes that an actual explosion is produced, which results in the creation of power. So, in conclusion, one complete cycle in a 2-stroke engine requires two piston strokes.

2-stroke engines do not have any valves, so they are straightforward. It is very light because there are only a few working parts. They have only one fuel tank, and fuel and oil are mixed before filling it. Fuel and oil should be properly mixed before putting them in the tank; otherwise, the engine can get damaged. They should be mixed according to the oil/gas ratio mentioned in your lawnmower’s user manual.

● Applications:

2-stroke engines are mostly used in small equipment as weed eaters and chainsaws. They are also very popular in racing because of their ability to produce more power concerning their weight. They can run no matter what position they are in. They used to be very popular in old lawnmowers even now some people prefer them because of their high-power output.

● Advantages of a 2-stroke Engines:

  • Simple design because of no valves.
    • Cheaper to manufacture because they have lightweight.
    • Require less maintenance.
    • Have twice the power of a 4-stroke engine of the same size and weight.
    • Have higher power output than a 4-stroke engine because it fires only once per revolution.
    • Beneficial for small equipment.

● Disadvantages of 2-stroke Engines:

  • Produce more pollution compared to 4-stroke engines.
    • Produce more smoke, and the oil/gas mix leaks out through the exhaust post sometimes.
    • Mixing oil and gas can be expensive.
    • Have a shorter life than 4-stroke engines.
    • Have less efficiency than 4-stroke engines.
    • It can get damaged because of even a little mistake in mixing oil and gas.
    • Very noisy.
    • Do not work that well in bigger equipment.
    • Becoming less popular day by day because of the environmental issues.

4-stroke Engine:

As the name suggests, this engine works on four strokes; compression stroke, power stroke, exhaust stroke, and an intake stroke. The compression stroke is when Air and fuel mixture is compressed on a piston moving upwards. A combustion stroke is when the spark plug produces a spark that ignites the gas, and an explosion happens. That explosion pushes the piston down. The exhaust stroke is when the piston moves upward and pushes the burned gas out. An intake stroke is when the air-fuel mixture is drawn in as the piston moves down the cylinder. In conclusion, the power is produced only once every two revolutions, i.e., 4-strokes.

In this engine, the oil used to lubricate different engine parts is flowed back to the crankcase and is not consumed. 4-stroke engines are good at protecting valve train and keeping the engine clean. The oil is kept in the crankcase. The oil needs to get changed after certain hours, and its level should be checked frequently. They have two separate ports for oil and gas, and mixing is not required. You can locate the ports on your engine and fill the fuel. They weigh a lot since a lot of functions are being performed in them. They can only operate in an upright position because otherwise, their internal oil flows. They have been popular recently due to their environmentally-friendly features. Modern lawnmowers use these engines a lot.

● Advantages:

  • Have fewer exhaust flames.
    • Environmentally-friendly.
    • Quiet and reliable.
    • Better and longer life than a 2-stroke engine.
    • Mixing oil and fuel is not required, so these engines cannot get damaged as easily as 2-stroke engines.
    • Expenses due to the mixing of oil and gas are cut down.
    • Produce less pollution.
    • Have more efficiency than a 2-stroke engine.
    • Run smoother than 2-stroke engines.

● Disadvantages:

  • They have valves, so their design is complicated.
    • Difficult to manufacture and repair.
    • Less powerful than 2-stroke engines because of fewer stroke fires per revolution.
    • A lot heavier than 2-stroke engines.
    • More expensive.
    • Difficult to maintain because of the complex design.

Which Engine is Better for Lawnmowers:

The engine to be used in a lawnmower is based on customer requirements. If the customer wants more power, then a 2-stroke lawnmower is preferred, and if the customer wants more efficiency, then 4-stroke lawnmowers are preferred. 2-stroke lawnmowers used to be more popular back in the days, but now 4-stroke lawnmowers are selling more. 4- stroke lawnmowers are preferred by the audience nowadays because of their environment-friendly nature. With an increase in pollution, people prefer that the mowers they use do not contribute to it. But then again, that depends on what kind of function you require from the engine. You can buy any type, depending on your needs.

Related Questions:

● Is a 4-stroke engine more powerful?

This question does not have a single answer. Four-stroke engines are usually bigger than two-stroke engines, so they have more power. But a two-stroke engine is more powerful than a four-stroke engine of the same size and weight. In short, two-stroke engines have a better power-to-weight ratio.

● Can you use diesel in a 4-stroke gasoline engine?

No. Never try this. Diesel is self a self-igniting fuel. Using diesel in a gasoline engine will cause catastrophic damage.

Final Remarks:

Knowing the type of lawnmower is very important since both types have different fueling techniques. Checking if your lawnmower is 2-stroke or 4-stroke is also very easy and straightforward; you have to see if your fuel tank has one port or more. Both 2-stroke and 4-stroke engines have their unique functions. 2-stroke engines lack in some areas in which 4-stroke excel and vice versa. It depends on which one you want to use. To keep your lawnmower in good condition, you have to use high-quality fuel no matter what type.

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