How to do-it-yourself instructional on adjusting a chainsaw for correct chain tension. Shown on Stihl 038AV Super Pro.
Alright today on Repairs101 Iím going to show you how to set up proper chain tension on your chainsaw.
For almost ten years I made my living working behind a chainsaw. And, well this is one of them. Iím quite partial to the Stihls. I do recognize that Husqvarna and Sachs-Dolmar and Echo all make excellent products Ė many other manufacturers do as well. Iím 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 Iíve had for twenty years or thereabouts and it still pulls like a Saint Bernard going after a squirrel.
I always keep my saws disassembled so weíll just pop the cover off and put the bar back on. OK the first thing Iíll show you is you might as well clean it up while youíre in here. If youíve got compressed air thatís going to be the best thing obviously but if youíre out in the woods or up a tree or something, youíre 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 itís 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. So just clean it up. OK now something in particular you want to focus on cleaning is the chain adjusting screw right here. If youíre out in the bush youíre probably just going to have Ė 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-girlfriendís toothbrush for jobs like this. There you go. Get that nice and clean. And weíre ready to put the bar on.
OK so people call this the blade but of course itís not a blade itís called a bar. And the bar has no top, no bottom. Youíll find that one side will wear out. When it does, all you need to doÖ there you go. All you need to do is grab a flat file Ė you want to hold it in your vise. And just cut off the high edges with your flat file.
 
                                  
 
Alright so the next thing is to get your chain on. Itís 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 youíve got chisel chain or chipper chain of course they pull forward Ė that is away from your body Ė on top. You know itís going to be rotating that way.
OK now once youíve 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.
Hereís the adjusting screw and hereís the adjusting pin. Now Iíll just leave my finger there and you can see it tracking back and forth. This screw is moving this pin right here Ė currently Iím going forward and going forward will be pushing the chainsawís bar out and therefore increasing the tension on it.

Chainsaw chain tensioner assembly   

The next thing to show you would be these holes right here on the bar Ė one on either side. OK and what they do is ride on that pin. So we just keep the chain in the barís groove. OK it doesnít 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 Iíve left just a ton of slack here and what weíll do is get the cover back on real quick and then take the slack out using that adjusting screw. OK now Iíve just seated these very, very loosely and as you can see the chain is way too loose here. So weíre 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 itís very important to hold the nose of the bar up when youíre making the adjustment and when youíre doing the final tightening. As I turn this screw up the chain tension comes out of the chain. OK. Now you can see itís getting very, very close. Pull down on it a little bit and thereís quite a bit of teeth still showingÖ so Iím going to pull up on it some more and now although I can expose some teeth Ė 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 Iím good to tighten this up and Iíve got correct chain tension.
 
           
 
OK so itís very important that you only pull the chain towards yourself on the top like that and itís a good idea to wear a glove or have a rag on your hand or something like that so that you donít get cut. But never ever try and pull the chain in the other directon OK because youíre going to cut yourself on the chisels. Now thereís no question that itís going to loosen up after youíve run it for a bit, OK. The chain is going to heat and expand and the chain will loosen up a little bit. 
Checking chainsaw chain tension
So it is a little on the snug side. Trust me. Thatís 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 canít pull very much out of it and when you leave it cold Ė now Iím talking cold before youíve used the saw at all: you do not want to see any slack hanging here OK? Itís 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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