2 Cycle vs 4 Cycle Gas Trimmer | What Are the Differences and Which Is Better

If you are shopping for a new trimmer, then you likely feel spoiled for choice.

Lawncare manufacturers realize that trimmers are always in high demand, and they all work hard to put their own little twist on their wares.

Some people with small yards will lean toward electric trimmers or even the newer style trimmer edger combos.

Unfortunately, they tend to lack the power of a gas-powered trimmer.

Most people with larger yards, complex landscaping, and value efficiency tend to lean toward gas-powered trimmers.

There are indeed many little twists and little special features in this niche.

Yet, when you really weed through all the bells and whistles, your choices in gas-powered trimmers will essentially burn down to a two-cycle engine, or a four-cycle engine.

This probably leaves you wondering: What is the difference between a 2-cycle vs a 4-cycle trimmer?

To really understand which one is best we’ll need to take a closer look and the benefits and drawbacks of each.

What Is the Difference Between 2-Cycle vs. 4-Cycle Gas Trimmers

Right off the bat, we need to demystify the technical terms involved.

When a manufacturer uses the term “Cycle” or “Stroke” they are referring to the way the piston moves inside the engine.

With a two-cycle engine, the piston moves twice to effectively produce its rated power.

With a four-cycle or four-stroke, the piston goes through four cycles to produce its rated power.

Depending on the engine’s design, each piston cycle could be upwards, downwards, to the right, or to the left.

This doesn’t matter much between these 2 engine types.

What matters most is the number of strokes before power gets produced.

How Does A Two-Cycle Trimmer Work?

When a two-cycle engine helps in an upright position its spark plug is on top.

When the spark plug fires it sends the first piston downward, this then ignites the compressed mixture of gasoline and air in the upper cylinder.

The exhaust is then vented through the small exhaust port as the piston moves down.

This essentially allows the hot, expanding gas to escape efficiently.

The air intake port is typically located below the exhaust port.

As the piston continues to move down it allows a fresh mixture of gasoline and air to refill the upper portion of the combustion chamber.

In this configuration, the entire two-cycle stroke system relied on easy air intake through the lawn mower carburetor.

Problems with the carburetor or a buildup of carbon or other residue can alter the fuel-to-air ratio, which can cause a whole host of mechanical problems.

Not the least of which is a loss of power, or increased problems with “Flooding” excess fuel into the combustion chamber.

As the piston reaches the bottom of its stroke the rotation of the internal crankshaft essentially forces it back up the combustion chamber.

Technically speaking this is the start of the “Second Stroke” in the process of producing power.

As the piston continues to move up it sequentially seals off the air intake port and the exhaust port.

This essentially traps the air and fuel mixture in the upper portion of the cylinder.

In a split second, the mixture becomes highly compressed, and the crankshaft turns the piston down again, as the lawnmower spark plug fires.

This causes a very brief, yet intense moment of combustion. The force of which pushes the piston back down again.

The basic process of a two-cycle engine means that there is always some degree of air and fuel in the combustion chamber.

In order for everything to move efficiently, the entire system needs sufficient lubrication from oil.

This usually calls for mixing the oil in carefully measured proportions into the fuel. 

How Do I Mix Oil In A Two-Cycle Engine?

The first thing you need to bear in mind is that two-cycle oil and four-cycle are not exactly the same thing.

You can’t just buy the same SAE 5W-30 you would pour in your car and dump a little in the gas tank of your two-cycle trimmer.

It’s also worth noting that there are different types of two-cycle engine oil.

Most gas-powered two-cycle engines use a type of oil rated for “Air Cooled” motors.

Still, make sure to double-check the owner’s manual to make sure you are using the type they recommend. Some will even have brand-specific recommendations.

While you are reading through double-check the mixing ratio, as well as the specific size of your weed trimmer’s gas tank.

This is usually printed on the engine housing, or cowl, or stamped into the metal of the gas tank.

The volume you buy is also a factor. Many two-cycle oil brands will offer you a quart or even a gallon.

These larger jugs are usually offered at a discounted price.

Just like any commodity, the more you buy at one time, the better the price per unit.

The downside of buying a big jug is that you are going to have to do a lot of precise measuring.

If you measure wrong the gas-to-oil ratio will be too lean or too rich.

A lean mixture with too little oil can potentially overheat and damage the cylinder.

An overly rich ratio, with too much oil, can lead to combustion problems and excess smoke in the exhaust.

If you don’t trust yourself to have a steady hand, or you don’t want the hassle required to mix the perfect ratio, many oil manufacturers sell small little, premeasured bottles.

Most are rated for a single gallon of gas. You simply pour it in, give it a little swish and you are ready to go!

Yes, you do pay a little more for that tiny premeasured bottle of two-cycle oil.

Honestly, when it’s sweltering hot outside and I have mosquitos swarming around my head, the last thing I want to do is fiddle around with precise measurements.

For that sake alone, I open up my wallet and pay that extra dollar for the premeasured bottle of oil.

One other thing to keep in mind is that it is far better to measure and mix the oil into a one-gallon gas can than it is to try to mix directly into the trimmer’s gas can.

How Does A 4-Cycle Trimmers Work?

At first glance, the fact that a four-cycle engine needs a full four strokes of the piston to produce its rated amount of power might seem like a disadvantage.

Yet if we take a closer look at the finer points, a four-cycle engine does have some advantages that make it appealing for powering a trimmer.

When the engine is kept in the upright position, with the spark plug at the top, the very first “stroke” of the piston sends it downward.

As this happens a mixture of fresh, pure gasoline and air is essentially forced into the cylinder.

Once it reaches the bottom of the stroke the inlet valve seals shut, and the crankshaft turns the piston upward.

This is the start of the second cycle. 

However, as the piston moves upward all the valves remain closed as the fuel-air mixture is compressed.

The piston then reaches its highest point and the spark plug fires which then ignites the compressed gasses.

This creates the “Power Stroke” of the third stroke, forcing the piston back down again.

Once the piston reaches the bottom of the power stroke it is pushed back up again by the motion of the crankshaft.

During this fourth stroke of the process, the exhaust valve opens and allows the recently burned gasses to escape.

When the piston reaches the top of the cylinder, the process essentially restarts to the first stroke.

Does A Four-Cycle Engine Need Mixed Oil?

It’s important to note that the valves are controlled by small special gears which are essentially powered by the motion of the crankshaft.

This configuration means that the gasoline does not need to be mixed with oil in a four-cycle engine.

It also means that a four-cycle engine is easier to set up, burns cleaner, and is overall more fuel-efficient than a two-stroke engine.

While a four-cycle mower spares you the hassle of mixing oil, they do tend to cost a little more.

You do occasionally need to drain the oil and replace it, just like changing the oil in your car’s engine.

2 Cycle vs. 4 Cycle Trimmer: Which is Right for You?

This is one of those gray-area questions, where there really isn’t a right or wrong answer.

Perhaps the best way to choose the one that is right for you is to compare the key features of each side by side.

Which One Has More Power?

On paper, the two-cycle engine will produce more power than a 4-cycle engine of the same size.

When dealing with most average trimmer lawn care issues power isn’t really a big factor, unless you are planning to tackle some overgrown brush.

Is Weight A Factor?

The fact that a two-cycle engine produces more power for its size, means that you might be able to get away with a smaller engine.

This ultimately can save you some weight, which could be a factor if you have a large yard, one with a lot of trees, or complex landscaping features.

Read Next: Best Lightweight Weed Eaters for Your Yard

Is There A Fuel Efficiency Difference?

There’s no doubt about it, a two-cycle engine will consume more fuel than a four-cycle. They also tend to produce a lot more exhaust.

If you have a small lawn that doesn’t need a lot of trimming, then you probably won’t notice a difference in fuel cost between a two-and-four-cycle engine.

If you have a large yard, with complicated landscaping features or a lawn that is rife with trees, the four-stroke can save you a little money.

It might also spare an eco-friendly person some of the guilt that comes with a smoking, gas hog of a two-stroke engine.

Which One Makes More Noise?

By the nature of their design, two-cycle engines make a lot more noise than their four-cycle cousins.

If you have neighbors living close by with small children, you might want to gently inquire about their naptime before you fire up a two-cycle.

At the very least, you should consider wearing ear protection.

Which One Requires More Maintenance?

Two-cycle engines require a little more maintenance, this is largely due to having to mix the oil with the gasoline.

For some people, this is a major hassle, that steers them away from anything two-cycle.

Honestly, in the early days of using two-cycle engines, I was a bit frustrated and even standoffish.

In time though, I think you’ll find yourself getting used to mixing the ratio correctly. At that point, there is little difference in maintenance requirements.

With a four-cycle engine, you do need to perform a periodic or seasonal oil change.

This is sort of the trade-off for not having to mix the two-cycle oil.

Beyond the oil difference, both two-cycle and four-cycle engines require the same basic stuff like air filter changes.

The occasional replacement spark plug is bound to come up with both.

One minor issue that can turn itself into a big problem is the carburetor.

Two-cycle engines are more likely to have residue and buildup in the carb.

In the long-term, this could lead to issues like a tough start, or possibly your weed eater won’t start, or perhaps even more frequent spark plug replacement.

Is There A Difference In Cost?

Four-cycle engines are inherently more complicated than their two-cycle counterparts.

This usually means you have to pay more for the same amount of power and performance.

One would hope you could make up for the difference in fuel efficiency.

Still, I don’t think you’ll notice much of a shift on the bottom line unless you have a very large, complex yard or you are thinking about starting your own lawn care business.

Two-cycle engines tend to have more problems with the carburetor and spark plug, which means you will likely be paying for repairs sooner.

However, when a four-cycle engine breaks down, it’s typically more expensive to repair.

Conclusion

Like a lot of important purchases, it can help you to sit down and imagine yourself using it.

If your lawn is small, relatively simple, and you don’t have neighbors right nearby, you can probably get by on the cheap with a two-cycle gas trimmer.

Don’t let the oil and gas mixing intimidate you.

I’m sure you will get used to it in time.

Especially, if you buy small premeasured bottles of oil.

If you have a large lawn or a lot of complex landscaping, or you simply live in tight quarters, then I would lean toward the four-cycle gas trimmer.

However, if your landscaping is on the smaller side, we’d recommend you get a weed eater-blower combo type of setup.

It’s also the more environmentally friendly way to make your lawn look beautiful.