Are Chainsaws Two Stroke?

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One of the most common questions soon-to-be chainsaw owners have is about the engines chainsaws have. Many of them are concerned about the inconvenience caused by having to mix oil and petrol. So, what’s the answer?

Are chainsaws two stroke? Almost all of them are, unless we are talking about electric chainsaws. Chainsaws that run on gasoline all have 2-stroke engines, except some STIHL chainsaws that have a hybrid engine that is essentially 4-stroke, but still uses the same petrol-oil mix as 2-stroke engines.

There are some very good reasons for all of this, and in this article I’m going to talk about them in detail.

Why are chainsaws 2-stroke?

To answer this question, first we have to understand what advantages do 2-stroke engines have over their 4-stroke counterparts.

Advantages of 2-stroke engines

First of all, they have less moving parts and therefore they are smaller. This is a very important factor for chainsaws and other power tools because people often use them for hours, which wouldn’t be possible if they were overly heavy. A 2-stroke engine will always be more powerful than a 4-stroke engine of the same size.

This also makes chainsaws much smaller, which comes in handy when you have to use them in situations where a bigger chainsaw would be in the way. For example, when climbing a tree to get rid of a dangerous branch. But it also makes storing them much easier.

Another factor to consider is that 4-stroke engines can’t function if you turn them on their side or upside down. This is because their oil system is gravity dependent, and not getting sufficient amount of oil would quickly lead to malfunctions.

On the other hand, 2-stroke engines have no such problems because the oil is mixed into the fuel. You can turn them however you want, they will still function. It’s easy to see why this is important for chainsaws. When felling a tree, you will always hold them sideways which wouldn’t be possible if they had a 4-stroke engine.

Also, a 2-stroke engine will go from idle to top speed in a much shorter time frame than a 4-stroke – although 4-stroke engines have a much higher torque at lower speeds.

So in short, chainsaws use 2-stroke engines because:

They are smaller and lighter.
They offer higher speed and acceleration.
4-stroke engines can’t function properly if you turn them sideways or upside down.

Disadvantages of 2-stroke engines

Apart from the advantages I pointed out above, 2-stroke engines have their own downsides too.

First of all, 2-stroke engines are much louder, which is why you should always wear some form of ear protection when operating your chainsaw.

They also use fuel less efficiently than 4-strokes, and generate more smoke in the process. They also need more maintenance because of this – you will have to clean the spark plug and the carburetor more frequently, although this is a fast and painless procedure with today’s chainsaws.

You also have to pay attention to use the correct fuel/oil ratio for your chainsaw or you risk malfunction (more on this later).

Conclusion

As you can see, the pros still outweigh the cons in the case of chainsaws – there isn’t a better option than 2-stroke engines at the moment. But that’s not to say that technology isn’t getting better. Today’s 2-stroke engines are a lot more efficient than their predecessors.

For example, Husqvarna chainsaws are built using their new X-Torq technology that offers up to 20% lower fuel consumption and 60% lower emission compared to traditional 2-stroke engines.

They achieve this by using duel flushing ducts. One of them is for the fuel and air mixture, while the other one is for clean air. The clean air is used to press out the burnt gases, and after that the air and fuel mixture gets flushed in.

The video below can show you how it works.

Are there 4-stroke chainsaws?

None than I know of, at least not “traditional” 4-strokes. As I’ve mentioned earlier, STIHL created a new type of engine that is basically 4-stroke, but still uses mixed fuel. It’s called the 4-MIX engine, and you can read more about it here.

It has some nice advantages over 2-stroke engines such as lower emission and better fuel efficiency, and it’s also less loud. I would say it’s a hybrid between a 2-stroke and a 4-stroke.

But then again, if you are looking into 4-stroke chainsaws to avoid having to mix fuel, you are out of luck unfortunately.

What is the fuel mix ratio for a 2-stroke chainsaw?

Most 2-stroke chainsaws use the 50:1 ratio for their fuel mixture. This means that you should mix:

2.6 ounces of oil for every gallon of gasoline (or 20mls of oil for every litre of gasoline for you people not in the US).

This can vary a bit depending on the chainsaw’s manufacturer, so always check your user manual for the recommended ratio if you aren’t sure.

Also, if you don’t use your chainsaw very often you can just buy pre-mixed fuel. This is more expensive than mixing it yourself, but it’s worth it for that peace of mind if you just aren’t sure.

Can I run a 2-stroke chainsaw on unmixed fuel?

No, you should never do this. It will ruin your engine in a matter of minutes without exceptions. The reason to this is that the oil serves as a lubricant for the pistons inside the engine.

Without lubrication, they will keep grinding on the inner parts of the engine causing them to get scarred all over the place. This will also cause friction, which generates heat. In time, this heat will be great enough to melt the pistons and they will stop moving for good.

While doing research on this topic, I came across this video. It shows you what happens exactly if you use the wrong type of fuel in a 2-stroke engine. Although it’s a leaf blower in the video, the same principle applies to chainsaws.

What happens if I put too much oil in the fuel mix of a 2-stroke chainsaw?

Fortunately, this isn’t nearly as bad as running your chainsaw with unmixed fuel. Your chainsaw will have lower performance, give off way more smoke than it should, and may even stop working eventually if you really went overboard with the oil.

Also, too much oil can cause the spark plug to start fouling, which usually means you’ll have to clean it or replace it.

To fix this situation, try to drain as much fuel from your chainsaw’s tank as possible, then fill it with fuel that has the correct oil/gas ratio. Once this is done, check if your spark plug needs cleaning (if it’s entirely black, it does).

Once everything is in order, start running your chainsaw for a few minutes. This should be enough for the bad fuel mix already in the fuel lines to clear up. If this part is done too, your chainsaw should be back to normal.