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Chainsaws : Correct Chain Tension

Alright today on Repairs101 I’m going to show you how to set up proper chain tension on your chainsaw.

Stihl saws

For almost ten years I made my living working behind a chainsaw. And, well this is one of them. I’m quite partial to the Stihls. I do recognize that Husqvarna and Sachs-Dolmar and Echo all make excellent products – many other manufacturers do as well. I’m just accustomed to and therefore partial to the Stihls. I find them exceptionally tough. Exceptionally reliable. And, this one here is a thirty-eight super-pro that I’ve had for twenty years or thereabouts and it still pulls like a Saint Bernard going after a squirrel.

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I always keep my saws disassembled so we’ll just pop the cover off and put the bar back on. OK the first thing I’ll show you is you might as well clean it up while you’re in here. If you’ve got compressed air that’s going to be the best thing obviously but if you’re out in the woods or up a tree or something, you’re not going to have compressed air. So have a rag handy and try to get any big chunks away from the sprocket, here, because if they get caught in between the chain and the sprocket it’s going to affect your chain tension. Eventually it will destroy it or it will throw it out and then the chain tension will be lost.

Keep it clean

So just clean it up. OK now something in particular you want to focus on cleaning is the chain adjusting screw right here. If you’re out in the bush you’re probably just going to have – and just dig at it very roughly and crudely but of course in the shop you should be able to have something a little more elegant. I like to use my ex-girlfriend’s toothbrush for jobs like this. There you go. Get that nice and clean. And we’re ready to put the bar on.

OK so people call this the blade but of course it’s not a blade it’s called a bar. And the bar has no top, no bottom. You’ll find that one side will wear out. When it does, all you need to do… there you go. All you need to do is grab a flat file – you want to hold it in your vise. And just cut off the high edges with your flat file.

Chain on

Alright so the next thing is to get your chain on. It’s not a bad idea, by the way, to grease the roller tip, OK, the sprocket on the end. And the idea is make sure you get your chain on the right way. Now, whether you’ve got chisel chain or chipper chain of course they pull forward – that is away from your body – on top. You know it’s going to be rotating that way.

OK now once you’ve determined which way your chain is going to go on, put it on the bar and bring the bar up to the mounting studs and then just swing the chain overtop of the sprocket like that.

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Here’s the adjusting screw and here’s the adjusting pin. Now I’ll just leave my finger there and you can see it tracking back and forth. This screw is moving this pin right here – currently I’m going forward and going forward will be pushing the chainsaw’s bar out and therefore increasing the tension on it.

The next thing to show you would be these holes right here on the bar – one on either side. OK and what they do is ride on that pin. So we just keep the chain in the bar’s groove. OK it doesn’t matter how slack it hangs. And then you just want to mount it like that, get the chain all in underneath. Now you can see that I’ve left just a ton of slack here and what we’ll do is get the cover back on real quick and then take the slack out using that adjusting screw.

OK now I’ve just seated these very, very loosely and as you can see the chain is way too loose here. So we’re just going to turn it this way to gain access to the adjusting screw. And then, one of the critical things I learned was that it’s very important to hold the nose of the bar up when you’re making the adjustment and when you’re doing the final tightening. As I turn this screw up the chain tension comes out of the chain.

Tension test

OK. Now you can see it’s getting very, very close. Pull down on it a little bit and there’s quite a bit of teeth still showing… so I’m going to pull up on it some more and now although I can expose some teeth – and it looks like if I pull real hard I can expose perhaps three to perhaps five. It snaps back nice and at the same time the chain runs really smoothly. So I know I’m good to tighten this up and I’ve got correct chain tension.

OK so it’s very important that you only pull the chain towards yourself on the top like that and it’s a good idea to wear a glove or have a rag on your hand or something like that so that you don’t get cut. But never ever try and pull the chain in the other directon OK because you’re going to cut yourself on the chisels. Now there’s no question that it’s going to loosen up after you’ve run it for a bit, OK.


The chain is going to heat and expand and the chain will loosen up a little bit. So it is a little on the snug side. Trust me. That’s what you want. Is it just a little on the snug side and yet still free running like that. OK I have no problem rotating it with your hand but at the same time you can’t pull very much out of it and when you leave it cold – now I’m talking cold before you’ve used the saw at all: you do not want to see any slack hanging here OK? It’s just not safe having slack like that on the chain.

I can tell you with authority that this is properly adjusted.

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