How Do Chainsaws Work? 2-Stroke Engines And Carburetors

How does a chainsaw work?

Whether you want to work on your own chainsaws for repairs or modifications, or you just want to understand how chainsaws work for the fun of it, there are some excellent resources that we’ve gathered here.

These are some of the best videos demonstrating and explaining how 2-stroke chainsaw engines work. They’ve come a long way since first being invented!

How A Stihl Chainsaw Engine Works

The man in this first video explains how a chainsaw works on a Stihl MS 261 cutaway.

It’s a helpful way to show how a modern saw works and he also discusses many of the model’s safety features.

Covered in the video:

The type of fuel used in these engines (fresh well-mixed 50:1 fuel oil)
How the pull cord works to move the flywheel
Briefly about how the flywheel creates spark – “it has a magnet that interacts with our module”
How the flywheel directs cool air over the engine because 2 stroke is air-cooled, not water-cooled
How the piston moves up and down in the engine and how the piston rings cause compression in the cylinder
The oil in the fuel provides lubricant for the bottom end containing the crankshaft and bearings
As the piston moves up, there’s an area of low pressure underneath which draws fuel and air through the intake valve into the area under the piston
At the same time, the area above the piston is being compressed and just before it reaches the top there’s a spark that ignites the mixture
The explosion drives the piston down which allows the smoke out of the exhaust port and fresh fuel/air mix to come up through the transfers

You can see all of this happening clearly in the engine cutaway and it’s a good intro to two-stroke engines.

Other videos we’ve shared below go into far greater detail, but this helps to give a first general idea of the parts of an engine and how they work.

The end of the video goes on to explain:

How Stihl’s engines work more efficiently to prevent unburned gasoline escaping (“scavenge loss”)
Chain brake activation by hitting the wrist
Momentum/inertia-activated brake activation by a lead weight in the chain brake
Chain brake engaged through the release of the handle (“Quick-Stop Super”)

How A 2-Stroke Engine And Carburettor Work Together

This next video is excellent!

Craig explains all of the interworking parts and systems involved in a 2-stroke engine and carburetor using drawn illustrations.

In this video, you will learn about:

How air is drawn into the carburetor through the inlet and mixed/atomized with fuel
How fuel is drawn into the carburetted with the movement of the fuel pump diapraghm
How the diaphragm is moved by the pulse line by the movement of the piston
The fuel valve flap
The needle valve
How the atomized fuel/oil and air mixture is drawn into the underside of the piston through a one-way valve
How the mixture is being compressed above the piston until it is ignited by the spark plug
What creates the spark – the flywheels structure, coil pack, magnet
How the magnet creates magnetic energy/electricity which is taken to the plug to create the spark
How the explosion sends the piston flying back down which closes the fuel inlet valve
How the piston begins to compress the mixture below it as it drops
How smoke is released and new fuel/air mixture is brought up through the transfers, pushing out the rest of the combusted fuel
How the piston goes up on its own momentum, and how the weights on the crankshaft help to keep that momentum going
How the fuel inlet is opened up again by the vacuum that is created and fills up below the piston again

He finishes it by explaining the difference between a 4-stroke and a 2-stroke engine and why they have their names.

For a more detailed video on how a carburetor works, see this video by the same guy.

Chainsaw Engine Cutaway Demonstration

Next up is this helpful video from Tinman’s Saws using a Stihl 028 Super that has a cutaway engine.

Throughout the video, he names and describes the different parts of the engine which is great for those learning chainsaw lingo.

Some of the terms you’ll come to understand include spark plug, cylinder, piston, wrist pin, rod (small end/big end), crankshaft, crank bearing, and seals, lower and upper transfers, intakes, and so on.

Also covered in the video:

What happens during a full rotation of the engine
When and how the intake, transfers, and exhaust open and close
How the fuel-air mixture is brought up through the transfers
What is compression
How the fuel fills above the piston on the intake side to push combusted material out
How compression is built

As Tinman states,

It makes more sense now, the cutaway is incredible. Watch the video a couple of times and see how there’s several things going on at once. But it’s simple.

And of course, as we’ve seen in some of the previous videos, there’s even more going on when you bring in the carb, flywheel, and so on.

You can see part 2 here and part 3 here using the same cutaway Stihl chainsaw.

How The Engine Moves The Chain

To finish the ‘how do chainsaws work?’ puzzle, we need to know how the engine movements result in a spinning chain on the chain bar.

This video goes through the entire process ending with this aspect. It’s a little bit robotic and some parts are a bit basic, but the animations are really helpful.

This video shows:

How the flywheel magnets power the spark plug
The entire engine process (as has already been described – though the animation makes things even clearer)
The function of the choke and primer bulb
Some of the reasons your saw may not start (find out how to fix a flooded engine here)
The best fuel for 2-stroke engines
The chain drive system which involves the crankshaft, clutch, throttle
The bar and chain plus the chain bar oil system
Safety features like chain brake and chain guards

And these guys obviously love their ECHO chainsaws!