A lot of things have changed ever since the first lawn mower was produced. Manufacturers have been working on making them easier to use, more efficient, and more durable.
But one thing remains — the engine. Of course, lawn mowers do have differently designed engines too. But the basics upon which they operate remains the same.
They are either four-stroke or two-stroke. So which one is used in most lawn mowers?
Are lawn mowers two-stroke? Older lawn mowers used to be two-stroke, but they are being phased out. The new emissions regulations call for more environmentally clean lawn mowers. As a result, modern lawn mowers are four-stroke.
While I was doing my research on this topic, I was surprised to find out that two-stroke lawn mowers are getting extremely hard to get by.
If you want to find out more, read on.
What Engines Do Lawn Mowers Have?
Lawn mowers can be gas-operated, electric, and battery-powered (these are also called cordless). The last two don’t have an engine the same way gas-powered ones do. They have an electric motor that is powered by electricity.
However, the gas-powered lawn mowers come with two different engines:
- A two-stroke engine; and
- A four-stroke engine.
What Is a Two-Stroke Engine?
While an engine runs, it goes through a combustion cycle, which repeats thousands of times every minute.
During each cycle, the piston moves up and down. The top position of the piston is called “Top Dead Center” (or TDC), and the bottom position is called “Bottom Dead Center” (or BDC).
The piston motion is created with two strokes:
- First stroke: Compression and combustion;
- Second stroke: Exhaust and Intake;
The first stroke compresses the fuel mixture, which is ignited by the spark plug when the piston reaches TDC.
As this explosion pushes the piston down, we enter the second stroke. During this stroke, the exhaust gas is being pushed out as the fresh fuel mixture is pushed into the cylinder through the transfer port.
For a very cool visual display and explanation of how a two-stroke engine works, make sure to check out the video below.
How to Identify a Two-Cycle Lawn Mower?
The easiest way to find out what engine your lawn mower has is by taking a look at the number of fill ports and fuel tanks.
Generally speaking, two-cycle mowers will have one fill port, while four-stroke engines will have two fill ports (one for fuel and one for oil).
Usually, the caps are clearly labeled.
On a two-stroke lawn mower, you should be able to see a fuel pump and oil can icons. There can also be additional information like the oil to fuel ratio and the maximum ethanol content.
Last but not least, if you are not sure, make sure to double-check the information provided by the manufacturer in your operator’s manual that came with the mower.
Can You Run a Two-Stroke Lawn Mower Without Oil?
While a four-stroke lawn mower will have two separate tanks for oil and fuel, two-stroke engines need to have the oil and fuel premixed.
You should not run your two-stroke lawn mower without oil no matter what. The oil and fuel have to be premixed before pouring them into the fuel tank of the lawn mower.
There have been multiple instances of people that forgot to add oil to the fuel before running their lawn mower. The end result? A damaged and even seized up engine.
Can You Use a Two-Stroke Fuel in a Four-Stroke Engine?
It is not recommended to use a two-stroke mixed fuel in a four-stroke engine. The oil in the fuel can foul the spark plug and produce more smoke as it burns.
Conversely, if you have a lot of it lying around, it can be used in a four-stroke engine, but it needs to be diluted with regular fuel.
Some people even use it for their cars by diluting a 1/2 gallon of mixed fuel with at least 10 gallons of standard fuel, though I have to say I would not recommend doing this.
Is a Two-Stroke Lawn Mower Better Than a Four-Stroke?
Both types of engines have pros and cons. Older mowers usually have a two-stroke engine while the newer models are four-stroke.
And there is a good reason for that. So let’s take a look.
Two-stroke engines are typically a lighter as fewer parts are needed for them to work. The overall construction of the engine is also a lot simpler.
For example, a two-stroke engine can be 2/3 of the weight of a comparable four-stroke engine.
This means that a two-stroke lawn mower is going to be lighter, easier to maneuver, and there will be less risk of damaging the soil or creating ruts while you are mowing.
Two-stroke engines produce more torque at higher RPM, whereas four-stroke engines produce more torque at lower RPM.
Torque is the force that is generated by the engine that makes an object rotate on its axis.
This is very important for lawn mowers as the blade is exactly that kind of object – it rotates around its axis. And the more force it has, the better and cleaner the cut.
This often makes two-stroke mowers a lot noisier compared to four-stroke mowers.
Fuel Consumption and Efficiency
Here the two-stroke engines are going to fall behind.
There is an extra stroke in four-stroke engines during which the exhaust gases are pushed out. And this is not the case with two-stroke engines. This can leave more exhaust gas in the cylinder, which interferes with the fuel mixture and air.
Additionally, two-stroke engines are going to use more fuel on average.
For comparison, in a two-stroke engine, fuel is being consumed every two strokes, while in a four-stroke, every four strokes.
This means two things. A two-stroke lawn mower will consume more fuel and produce more pollution.
Wear and Tear
A two-stroke engine will run at higher RPM with a lot more combustion cycles per piston revolution. Taking into consideration these facts, you can expect a two-stroke lawn mower to last for a shorter period time.
Although a two-stroke lawn mower will be more powerful, it may also be less durable.
Maintenance and Repairs
A two-stroke engine has fewer parts and overall simpler design.
This makes it easier to repair and maintain.
One of the cool things about two-stroke engines is that they can run in almost any position. You can place them on their side, and they will still run smoothly – this is actually one of the main reasons they use two-stroke engines in chainsaws.
Four-stroke engines, on the other hand, have to be leveled out as they can run into problems with the internal oil flow.
On average, a four-stroke lawn mower is going to be more expensive compared to a two-stroke model.
However, a two-stroke engine requires mixed fuel to run properly. Mixed fuel is fuel mixed with oil. Constantly adding oil to the fuel can get very expensive, very fast.
Additionally, the only way to use a two-stroke lawn mower nowadays is by buying an old and used model, which can lead to higher upkeep due to the normal wear and tear.
Are Two-Stroke Lawn Mowers Still Being Sold?
One of the things that you may have noticed above was that I said two-stroke lawn mowers create more pollution and emissions.
This has impacted the two-stroke engines in a big way throughout the years.
Two-stroke lawn mowers are being phased out in America, Europe, and throughout the rest of the world due to the strict emission regulations that are taking place.
This may seem like an unnecessary action, but the numbers can truly be startling.
Some data suggests that a push lawn mower can produce in just one hour the same amount of CO emissions that a car will after being driven for 401 miles.
And one research carried out during the 1990s in Australia concluded that some lawn mowers could produce as many emissions as 40 cars.
This is not just bad for the environment but for your health too. Just think about it, you are staying super close to the lawn mower while you are cutting your gas and inhaling the exhaust gasses.