Gas-powered weed eaters deliver powerful performances to assist you to tackle tough, tall weeds on your lawn. When looking to buy one for your homecare or professional weed trimming needs, you have two options to choose from and these are the 2 and 4-cycle gas engines.
While these engines are aimed at providing the torque to power the trimmer though grass and lawn weed, each of them is unique. They have different characteristics, pros, and cons. While both are gas powered, the manner in which the fuel is converted into power is what sets them apart.
Deciding whether to go for the 2 or 4-cycle gas engines when buying a weed eater is often a perplexing one. Could one be better than the other? How are they different? What are the pros and cons of owning either of them? By going through today’s post, you will be able to pick up all this information and much more.
How Do They Work?
The term cycles or stroke refers to the movement of the engine pistons inside the cylinder, end to end. It is these engine movements that generate the power transmitted to the trimmer heads. Essentially, the number of strokes that an engine makes to complete a power cycle is what gives the engine either a 4 or 2-cycle names.
From the description, a 4 cycle engine makes 4 strokes to produce a single power stroke. All the fours engine piston movements occur sequentially from the first to last. When you assume an engine that is upright, with its plug on top, then here is the sequence of operations.
The first stroke is the downstroke where the engine piston moves downwards as the inlet valve lets in a mixture of air and gas into the cylinder. The second stage starts as soon as the piston reaches the bottom-most part of the cylinder. Inlet valve closes as the crankshaft forces the piston back up.
Stage three (exhaust), which is the upstroke, occurs as the piston is pushed up. All valves close, resulting in the compression of the air-gas mixture. Once at the top, the spark plug ignites the mixture, resulting in an explosion that sends the piston back down.
Stage four is another compression stroke as the piston rises up. In the course of the rise, exhaust valves open to allow the discharge of exhaust gases from the engine. A new cycle starts as soon as the piston reaches up.
In a 4-cycle engine, there are two complete revolutions of the engine crankshaft to complete all the 4 strokes. The closing and opening of the inlet and exhaust valves are coordinated by gears driven by the crankshaft.
- Efficient combustion
- Produces more torque
- Low emission levels
- No mixing of fuel and oil
- Harder to start
- More parts to maintain
- High vibration levels
- Has to be kept level in storage
- Requires regular oil changes
Unlike a 4-cycle engine that generates power after the fourth stroke, a 2-cycle is more conservative. The power is output after every second piston stroke. These two stages combine the functionality of the above four.
The first stroke combines the downward movement (power stroke) and exhaust (up) stroke. On the other hand, the second cycle combines compression and intake. The first two occur at the top of the cylinder, while the last two occur and the bottom. A single crankshaft revolution is facilitating the whole process.
It is the sparking of the plug and the subsequent air-fuel mixture ignition that triggers the strokes. At some point during the downward movement, the piston passes the exhaust hole, allowing for the loss of some of the expanding gases.
Further down, the piston opens the intake hole (located on the opposite side of the exhaust hole). Air and fuel mixture makes entry into the upper combustion chamber and then is forced into the upper part of the cylinder as the piston is pushed down by the combusting mixture.
During the downstroke, the air intake from the carburettor is closed by a valve. In the following upward stroke, the valve opens to let in fuel-air mix into the cylinder.
At the down most position, the crankshaft cams push the piston back up for the second cycle. Intake and exhaust holes are closed, trapping in some air and gas inside the upper part of the cylinder. The mixture gets compressed, and once it’s at the upper part, the spark plug ignites the mixture, resulting in combustion that shoves the piston down for the second time.
As you can see, the lower end of the cylinder always has a mixture of air and fuel and not oil. Therefore, this engine requires the fuel to be mixed with the gas in a specified ration. The oil component lubricates the moving parts such as the cylinder, crankshaft, cylinder, and piston.
- A small number of moving parts
- Easy to maintain
- Requires less storage space
- Low vibration levels
- Easy to start
- Weighs less
- Less torque
- More emissions for the burning of oil
- Mixing of oil and fuel is a hassle
How to Distinguish Between a 4 And 2-Cycle Internal Combustion Engine
After establishing the difference in how these two engines work, then you need to be able to distinguish between the engines just from first looks. I have studied both engines for quite a while now and have developed these criteria for distinguishing between the two.
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- Listen to the sound produced by the engine as it runs. This may be a layman’s way of identification, but it does work at times. A 4-stroke engine runs smoothly with no sound fluctuations. As for the 2-cycle, the engine is renowned for a loud crackling sound as it runs.
- A 4-cycle engine has a separate oil reservoir. If you spot an oil cap, then it’s a 4-stroke. There is none on a 2-cycle since oil is mixed with the fuel.
- For the same weed eater specifications, a 4-cycle engine is considerably heavier than a 2-cycle.
- A 4-cycle produces less smoke when starting the engine in comparison to the 2-cycle with considerate amounts of smoke.
Differences between 4 and 2-Cycle Engines
Apart from the working principles and oil fuel mixing, there are a couple of differences between a 4 and 2-cycle engine.
1. Lubrication Principles
In a 2-cycle engine, you have to mix oil and fuel in differing ratios. These often range from a single part of oil to about 50 gasoline parts or 1 part of oil to 20 gasoline parts. These ratios are indicated on the engine label.
The reason why you must mix the two is due to the contact between crank, piston, cylinder and the fuel mixture. In a 4-stroke engine, this contact is eliminated. Instead, a different lubrication system is put in place with an oil reservoir within the crankcase. This oil requires topping and replacement after a period of running hours.
2. Weight to Power Ratio
Another difference is in the amount of power generated by the two engines in comparison to their weights. First, 2-cycle engines are lighter than their 4-cycle counterparts. Therefore, the latter produces more power from their relatively lighter engines.
A 2-cycle packs more horsepower at higher speeds since a complete power stroke only requires a single crankshaft revolution. More horsepower is then produced at high revolutions per minute. Also, this power has no significant decrease when cutting through dense grass growths.
However, a 4-cycle engine with low power and speed output delivers more torque. This turning force is what allows you to cut through tough grass with ease. For heavy-duty uses, a 4-cycle guarantees better efficiency.
3. Fuel Economy
This is another area where the 4-cycle engine outperforms their 2-cycle competitors. In the 4 strokes, the engine has a stage for individual air delivery, and discharge of exhaust gases. As a result, the engine uses less fuel and combusts most of the fuel.
The major flaw in a 2-cycle engine is that the exhaust gases are never eliminated entirely from the combustion chamber before the inlet of a fresh mix of fuel, oil, and air. Part of this exhaust is ignited, while some of the fresh mixture introduced is let out during the discharge of exhaust fumes. This mixture does not do any work in the first place but exits the engine.
4, Amount of Noise Produced
Typically, a 4-cycle is quieter than a 2-cycle engine. The reason for this difference is the dedication of a third stroke for the function of ignition as well as combustion. During this phase, both inlet and outlet valves are closed, completely sealing the cylinders.
As it enters the fourth cycle, most of the fuel has already burnt. Thus, as the exhaust gases exit the chamber, little noise filters out. Note that the noise is not completely non-existent, but it is not as pronounced as in the case of a 2-cycle engine.
The design is a little different in a 2-cycle engine. Every down stroke is accompanied by combustion, which still goes on even as the exhaust gas exits the chamber. Usually, when the air-fuel mixture is ignited, a mini-explosion occurs which filters out as the exhaust gases is discharged. Noise levels depend on how large the engine is and the volume of the air-fuel mixture.
5. Weed Eater Costs
A 2-cycle engine has a simpler design with fewer moving parts, which explains the relatively low prices in comparison to a 4-stroke engine. Any equipment powered by a 4-cycle engine is more expensive than a 2-cycle one, and not only for weed eaters. Therefore, if you are on a budget, then you are better off with a 2-cycle weed eater.
6. Maintenance Requirements
While 4-cycle engines do not require oil to be mixed into their gases, 2-cycles do. If you do not get the ratio right, the engine might develop mechanical problems. However, with the availability of pre-mixed fuels, you do not worry about this eventuality.
A 4-cycle has lots of complex moving parts. These many items increase the likelihood of something breaking. The cost of repair and maintenance frequencies is also higher than in a 2-cycle engine.
7. Impacts On the Environment
Both engine types run on gas, which still leads to emissions that have an impact on the environment. Nevertheless, between the two, a 4-cycle is the lesser evil since it is more fuel efficient and quiet in comparison to a 2-cycle.
Then, there is also the issue of oil being burnt in the latter type of engines, further worsening the environmental impact. So, if you are an environmentalist, then an electric weed eater is probably your only option.
After noting the differences between these two weed eater types, a fundamental question arises over which of the two is better. Each of them has their pros and cons, but owning a 2-cycle weed eater provides you better value for your money than the other option.
For the most part, 2-cycle weed eaters reign supreme as they are reliable, easy to use, start, and require fewer maintenance costs. Alternatively, if your key consideration is the amount of torque output, then I recommend sticking to a 4-cycle weed eater.
Nonetheless, stronger environmental regulations being drafted may doom your 2-cycle options. Because of their high environmental impacts, these stricter emission guidelines may soon face them out; unless the manufacturers make the technology used better or improve on the weaknesses of the 4-cycle engines.