A common question when starting riding is “Which is better, a 2 stroke or 4 stroke dirt bike for beginners?”
I recommend a 4 stroke dirt bike for beginners. In this article I will go through the pros and cons of each type of bike and explain why I believe a beginner should ride a 4 stroke.
My very first dirt bike was a 2 stroke dirt bike. In fact, the vast majority of the dirt bikes I have had through the years have been 2 strokes. The reason for this is at the time I was buying them, 2 strokes were just so much cheaper than a 4 stroke. I didn’t consider all the factors when looking at a 2 stroke or 4 stroke dirt bike.
Recently this trend has shifted and there is not a ton of difference in price between a 2 stroke and a 4 stroke. This could be due to the fact that manufacturers simply aren’t making as many 4 stroke bikes, or it could be nostalgia for the times when 2 strokes ruled the motocross world.
Before we address the pros and cons of each, let’s first talk about how they are different.
- Difference Between 2 stroke and 4 stroke engines
- 2 Stroke Pros and Cons
- Why 2 Strokes Are Great!
- Why 2 Strokes Are Not Great
- 4 Stroke Pros and Cons
- Why 4 Stroke Dirt Bikes Are Great!
- Why 4 Strokes Aren’t So Great…
- Why a 4 stroke is a better beginner dirt bike
- Wrap Up
Difference Between 2 stroke and 4 stroke engines
First let me dispel any myth that a 2 stroke engine will rev higher than a 4 stroke. This might be the case in some applications, but for dirt bikes, both engines are designed to run at very high RPM.
The name 2 stroke and 4 stroke stem from the number of cycles the engine goes through before it has another combustion event.
2 Stroke Theory
In a 2 stroke engine, the engine fires every time that the cylinder reaches the top of the piston (this statement is not technically correct when considering timing, but that is just splitting hairs). When the piston is at top dead center, the gap between the cylinder and the head is small, creating a very high pressure environment that is conducive to combustion. Then the spark plug ignites the mixture and the piston travels down.
This is where things start to get interesting. Through a combination of negative crank case pressure, location of the exhaust port, and the existence of transfer ports, the burned gasses escape out of the exhaust port, and new unburned fuel travels through the transfer ports to provide a fuel mixture for the next combustion event.
As the cylinder gets to the bottom of its travel and begins to start moving upwards again, a negative pressure is created in the crank case. When the cylinder finally travels by the intake port, the port becomes unblocked and the fuel air mixture rushes in to wait for the next combustion cycle.
Here is a simple video of how the process works. 2 strokes have a certain beauty to their simplicity.
4 Stroke Theory
A 4 stroke on the other hand has valves that control when the fuel goes into the cylinder. A 4 stroke can be broken into 4 distinct actions
- Combustion stroke (Top Dead Center to Bottom Dead Center)
- Exhaust Gas Purge (Bottom Dead Center to Top Dead Center)
- Introduction of Clean Fuel (Top Dead Center to Bottom Dead Center)
- Compression Stroke (Bottom Dead Center to Top Dead Center)
In each of these stroke, the valves control whether or not the gases are coming into or leaving the cylinder.
- Combustion Stroke (All valves Closed)
- Exhaust Gas Purge (Only the Exhaust Valves are open)
- Introduction of Clean Fuel (Only the Intake Valves are open)
- Compression Stroke (All Valves Closed)
As a result of how these engines work, there is only one time every 4 strokes that you have a condition that is perfect for combustion, and that is at the end of the compression stroke. So, the spark is introduced once every 4 strokes.
Here is a simple video that shows how the process works for 4 strokes.
Since the crank case of a 4 stroke never gets any fresh air, it has to be oiled. So a 4 stroke engine will have the crank shaft sitting in an oil bath. On the other hand, the crank case of a 2 stroke is constantly getting fresh air, so in order to make sure it stays lubricated, you have to mix oil into the fuel.
From the average user’s point of view, the main difference is going to be between whether or not you need to mix gas in order to run the machine. A 4 stroke requires unmixed gas, and a 2 stroke requires mixed gas (at a ratio typically between 32:1 and 50:1).
So now that you know the difference between a 4 stroke and a 2 stroke, let’s talk about the pros and cons.
2 Stroke Pros and Cons
Here is a quick list of the Pros and Cons of 2 Strokes, discussed more below.
Why 2 Strokes Are Great!
A 2 stroke has very little that can go wrong compare to a 4 stroke. There are no oil changes, no valve adjustments. It is an extremely simply machine with very little to go wrong.
Cheap to Maintain
That is not to say there is no maintenance. A 2 stroke will require a new piston periodically to maintain good compression. Luckily, this is a pretty cheap task. Additionally, some 2 strokes have power valves (essentially a valve on the exhaust port designed to even out the power curve) that will need to be cleaned, but that is a free job that can be done at home.
Because the engine is so simple, the engines are also extremely light weight. Sometimes up to half the weight of a comparable 4 stroke. Think about it this way, weed eaters are almost always 2 strokes because you can actually carry them around easily. A comparably powered 4 stroke weed eater would weight too much to use it often.
Outstanding Power Output
CC for CC, a 2 stroke is going to make more power. This is why when 4 strokes were introduced into the racing scene, a 250cc 4 stroke raced with 125cc 2 strokes. A 2 stroke makes roughly double the power per cc of engine that a 4 stroke does. This is rather obvious because it is firing twice as often.
Why 2 Strokes Are Not Great
Uneven Power Output
Because of how 2 stroke engines work, when you are at half throttle, you are not getting half the power. You are getting far less. However, as you advance to full throttle, you quickly get a shot of power. This is called “coming on the pipe.” Essentially it is a strong burst of power that is only seen at the upper ends of the throttle curve.
This makes it a little bit difficult to control because there is a very fine line between low power and getting full power. For racers that still ride 2 strokes, most of them are going to be staying at that full power area throughout the race, and controlling the power output by slipping the clutch.
One of the biggest complaints about 2 strokes is their unreliability. I would argue that this is more of a result of the owners neglect than anything else. Still, since the oil and gas mixture has a tendency to gum things up, a poorly maintained 2 stroke will be unreliable.
If you look closely at the video showing how a 2 stroke works, you will see that some fresh fuel can escape out the exhaust unburned. This is just plain inefficient. A 2 stroke is essentially venting a small amount of unburnt fuel into the air.
Let’s face it. Mixing gas is a pain and can be expensive. For every gallon of gas you buy you have to add a certain amount of oil. If you fill your gas tank up and its some portion of a gallon (for example 1.25 gallons) then you are going to have to do math.
Frequent Piston Changes
You are going to have to replace the piston in your 2 stroke pretty often if you are riding a decent amount. Somewhere between every 10 to 20 hours is the average. So, if you are riding all weekend, you will need a new piston every weekend. If you are racing, you probably will want to put a new piston in after every race.
Replacing a piston doesn’t take a ton of time after you have done it a few times, and pistons are cheap, but it is something that has to be done.
4 Stroke Pros and Cons
Here is a quick list of the Pros and Cons of 4 Strokes, discussed more below.
Why 4 Stroke Dirt Bikes Are Great!
The power output of a 4 stroke is linear. If you are at half throttle you are going to be getting half power. Full throttle, full power. This power is much more manageable, meaning that you don’t have to do tricks to keep it right where you want it.
A 4 stroke is a very reliable motor. As long as you have oil in it, a clean air filter and some gas it will generally run. You don’t have to mix any oil, so the gas stays clean.
No Oil Mixture
4 strokes have an oil bath that the crank sits in. This means that you don’t need to constantly introduce more oil. Just put gas in it and go!
Like a 2 stroke, a 4 stroke has relatively low maintenance. For the most part you will be spending your maintenance time changing the oil.
Why 4 Strokes Aren’t So Great…
Expensive to Maintain
So they are relatively low maintenance, but they are expensive to maintain when that maintenance is required. For instance, I recently had a 4 stroke dirt bike come in that had a messed up head. A complete used replacement head was around 700 bucks.
With 2 strokes you have to do pistons frequently, with 4 strokes, its valves. A valve adjustment is quite a bit easier than a piston replacement, but it is still work that has to be done to keep it running in tip top shape. It is also not something that you want to ignore because should you let a misadjusted valve go to long you risk ruining the head.
A comparable 4 stroke dirt bike is going to have roughly double the displacement of a 2 stroke. This means it’s going to be quite a bit heavier than the 2 stroke. The head assembly also adds quite a bit of weight to the overall motor. What this means for the rider is that there is just more bike to wrestle with in a given class size.
A 4 stroke has an insane number of moving parts. The valves, springs, cams, cam chain, the list goes on. Each one of these parts is prone to failure. Granted most of them don’t fail often, but as with most things, the more parts there are the more there is to break.
Why a 4 stroke is a better beginner dirt bike
So we have gone through how the two different types of engines work and the pros and cons of each. Now, why is a 4 stroke a better beginner bike than a 2 stroke?
It comes down to frustration level. A 4 stroke is simply going to be easier to keep running with a more manageable power output. Sure a 4 stroke is heavy, but at least it won’t get away from you as easily as a 2 stroke will.
Ultimately, success in riding a dirt bike comes down to practice, and if you have a machine that is a headache to ride then you are much less likely to practice. For beginners especially, you don’t want the bike to seem unmanageable and a 2 stroke will certainly seem unmanageable at times.
So, if you have a choice between a 2 stroke or 4 stroke dirt bike as a beginner, get a 4 stroke. There is a reason all the pros have moved to 4 strokes. Do as they do!
I hope this article didn’t come off like a 2 stroke bashing article because that truly was not the intent. My first bike was a 2 stroke and they will always have a special place in my heart. I just believe that a 4 stroke is a much more manageable machine that is much easier to own.
At the end of the day most of us just want a bike we can start and ride without having to worry about all the ins and outs of 2 stroke ownership. Sure they are cheaper, but that is only one factor when thinking about a 2 stroke or 4 stroke dirt bike.
Regardless of which direction you decide to go, remember to take your time and ride within your skill level. Stay safe out there!