How To Tell If A Lawn Mower Is 2-Stroke Or 4-Stroke


Lawnmower engines have come a long way since they first appeared on the scene over a century ago. Nowadays, we are spoilt for choice by an incredible range of motors that boast several features and statistics. Our inner gearhead is instantly roused by all the talk of horsepower, torque, displacement, and stroke.

For the average mower owner, the type of fuel is the key to determining whether a lawn mower is 2-stroke or 4-stroke. If a mower has one intake fill location taking gas mixed with oil, it is a 2-stroke engine. If there is a gas and an oil intake fill point then it is a 4-stroke engine.

Our focus today is also on more technical ways to determine the differences. We will break down what experts mean when they refer to a motor’s “stroke”. After that, we will help you with identifying 2-stroke and 4-stroke engines, as well as the benefits and drawbacks of each. 

Is My Mower 2-Stroke Or 4-Stroke?

If you are new to engine technology, there is a good chance that you have no idea what the terms “2-stroke” or “4-stroke” mean.

2-Stroke Engines

Basically, a 2-stroke (aka “2-cycle”) motor is so-called because the cylinder pistons literally need two strokes to complete a combustion cycle, which releases energy from the fuel to run the mower. The upward stroke is called the intake and compression stroke, while the downward stroke is called the power and exhaust stroke.

The intake/ compression stroke is when the piston moves from the bottom of the cylinder (which is known as the “bottom dead center”) to the top (or “top dead center”) to suck air and fuel into the cylinder…hence “intake”. 

As the piston approaches the top, it puts additional pressure on the air/fuel mixture (compression). At the same time, the sparkplug produces a little spark near the mixture to produce a mini-explosion known as “combustion”.

The power/exhaust stroke occurs as a result of the piston being pushed back down by combustion. As the piston moves downward, it uncovers an opening known as the exhaust port. This allows combustion waste (or “exhaust”) to leave the engine.

4-Stroke Engines

A similar process occurs in 4-stroke (aka “4-cycle”) motors. However, these engines require four strokes per combustion cycle. Each stroke is dedicated to one particular function of the cycle, which means:

  • One stroke for intake
  • One stroke for compression
  • One stroke for power
  • One stroke for exhaust

Combustion forces the piston to the bottom dead center (power stroke). The force of the combustion is enough to keep the crankshaft spinning, which makes the piston move up again to clear the exhaust (exhaust stroke). The piston moves down again, this time drawing in fuel before the upward compression stroke restarts the process.

If you would like to read more about this and other mower issues, read one of my other articles…

Telling The Difference Between 2-Stroke And 4-Stroke

Now, differentiating between 2-stroke and 4-stroke motors is pretty simple if you know what you’re looking for. Luckily, you don’t have to rip open your mower engine to study how the pistons move!

Fuel Types

The simplest way to tell between the two engine types is to look at how they are fueled. Mowers with 2-stroke engines will have one fuel filler for the gas and oil mix they run on. Mowers with 4-stroke engines have two fillers, one for gasoline and one for oil.

Engine Sound

You can also tell the difference by the sound the mower makes when it is running. Mowers with 2-stroke motors tend to be very loud, with a high-pitched whirring noise. The opposite is true for 4-stroke mowers, which tend to have quieter, low-pitch motors.

Exhaust

Another telltale sign that you have a 2-stroke mower on your hands is high quantities of exhaust. The way 2-strokes operate is less efficient than how 4-strokes work, which is why they produce more smoke and gases. The 4-stroke motor was actually made for improved cleanliness to be onside with environmental regulations. 

How Good Are 2-Stroke Lawn Mowers?

Although 2-stroke mowers have been around for a fair bit longer than 4-strokes, they are not ready to be sent out to pasture just yet. In fact, 2-stroke engines still retain some key advantages.

Advantages Of 2-Stroke Engines

Firstly, because their combustion cycles are shorter, 2 stroke motors tend to have higher engine revolutions per minute (RPM). A higher RPM allows the mower’s blades to spin faster, which means you’ll cover more ground in less time.

Secondly, because 2-strokes use a gas and oil mix, you don’t have to carry out routine oil changes as part of the machine’s service. The oil is “changed” when you re-fuel.

Lastly, 2-stroke engines are generally lighter than 4-strokes. They have fewer parts and a much simpler design than the latter, which also makes them cheaper. Walk-behind mowers with this kind of engine are much easier to push because of this.

Disadvantages To 2-Stroke Mowers

Unfortunately, there is also a downside to 2-strokes.

  • We’ve already mentioned the higher volumes of exhaust they produce.
  • However, you must know that 2-stroke motors have been known to leak fuel out of their exhaust openings too. This means these engines are squarely in the crosshairs of increasingly strict environmental laws.
  • While 2-stroke mowers certainly live fast lives, they rarely live long. If you opt for a 2-stroke mower, be ready to replace it in a couple of years.
  • In addition, mixing oil and gasoline is not the easiest (or cheapest) thing to do. The price of mixing the two incorrectly can also be fatal for the mower.

Also…noise.

How Good Are 4-Stroke Lawn Mowers?

Getting a 4-stroke mower also has its pros and cons.

The first advantage is refinement. The dedicated strokes make 4-stroke engines far more efficient than 2-strokes. They do not waste fuel as much as the often-leaky 2-stroke.

Noise is less of a problem with 4-strokes as well. As are other forms of pollution. These engines are less likely to fall foul of environmental rules because they are so clean.

Mowers with 4-stroke motors do not require you to mix oil and gas, as they take both separately. No risk of damaging your engine with a shady oil/gas blend. 

While they are not as quick as their 2-stroke cousins, 4-stroke engines run much smoother and last much longer. 

Of course, just like 2-strokes, 4-stroke motors also have drawbacks. For one thing, they are significantly pricier. This is due to their more complicated design and longer lifespans. Repairs may also burn a hole in your pocket.

They also tend to weigh more than 2-strokes of equivalent output, which may be strenuous to some users.

Which Is Better: 2-Stroke Or 4-Stroke?

“Better”, in this instance, is quite subjective. Before investing in either one, you must be sure of your specific needs and circumstances.

If you want to cut a small area of grass quickly, then a 2-stroke is the way to go. However, if efficiency is what you want, then go for the 4-stroke.

If you live in close proximity to your neighbors, a 2-stroke mower may see you miss out on barbecue invitations.  A 4-stroke mower is much quieter.

With organizations like the Environmental Protection Agency (EPA) on the prowl, the long-term future of the 2-stroke engine is uncertain. More environmental laws are on the horizon, which only enhances the 4-stroke’s appeal.

Final Touches On Whether A Mower Is 2-Stroke or 4-Stroke…

Telling the difference between 2 and 4 stroke mowers can be as easy as the type of fuel and the filling points on the mower. Deciding if a two stroke engine or four stroke is better for your needs will depend on these differences.

Keep in mind the advantages and disadvantages of each when choosing the right one for your situation.

To read more about mowers, see my other articles…

Reference

https://www.gardentoolexpert.com/how-to-tell-if-a-lawnmower-is-2-stroke-or-4-stroke/#_Advantages_of_a_2-stroke_Engines

https://www.youtube.com/watch?v=0rza6B5mDQ4&ab_channel=ConcerningReality

Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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