Maintaining the correct chain tension is rather important - too loose and the chain may derail, too tight and the saw will effectively lose power. Many saws require the operator to carry around a combi-spanner to adjust the tension, but a number of smaller saws are available fitted with a quick tension system. In this article, we'll have a look at them and see how they compare after the jump...
I mentioned above a couple of issues regarding chain tension, but there's more; a chain that's too loose will also not cut as effectively as a correctly tensioned chain. Why? Because as the cutters come in to contact with the wood they sit back slightly, and that results in the cutting angles changing. A loose chain will also wear quicker, as well as increasing the wear on the guide bar. Fortunately you can easily recognise a loose chain - either because it's hanging down from the underside of the bar, or because it revolves around the bar when the engine is at tickover (with idle speed adjusted correctly).
A chain that's too tight will result in the chainsaw using up some of it's power to overcome the friction and that's what results in the lack of apparent power and unwillingness to rev freely. That increase in friction can lead to overheating too. It also puts the bearings of the nose sprocket and drive sprocket under undue stress.
So, convinced of the need to get the correct tension, the easiest and fastest method would seem appropriate; but different saws use different systems. The standard method, shown on the right, uses an adjuster screw that can be accessed through the side panel (although some saws have the adjuster screw at the front, facing forward, next to the guide bar - these are really awkward to use, especially with a combi-spanner). Before we can set the tension, those two nuts holding the panel in place must be loosened first as they're also clamping the bar in position.
Maintaining the tension in this manner requires the user to carry around a combi-spanner (with a flat end, not a Torx-head end). The operator first loosens off the two nuts, sets the tension using the flat screwdriver, and then tightens up the two nuts. Job done.
Nowadays, many users (particularly home-users) don't want the aggravation of having to have the combi-spanner to hand in order to adjust the chain, and manufacturers set about finding an even quicker way of correcting the chain tension with the least amount of fiddling about.
Enter stage left... the quick tension system. The example in the photo here is off of a Stihl MS250C, but it's similar to many other fast tensioners. The photo at the top of the post shows it with the side panel still fitted. You can see on that photo the large 'dial' on the side - this is not the tensioner, but it's a quick release for the side panel. The actual bit that the operator uses is on the top of the side panel - a small black wheel that links in to the cog fitted to the guide bar (that can be seen on the photo to the left).
To adjust this system, all you need do is flick the handle out of the quick release dial, back it off a fraction, then use the adjustment wheel to set the tension and tighten up on the side panel. It is quick and it doesn't require any tools. But is it any good?
Personally, I found it a bit awkward to get the right tension and it's not as finely adjustable as the good old screwdriver adjuster. Having said that, it does work, but I'm not sure I'd want one on a professional saw; for the home- / occasional- user however it's probably ideal. It also means that changing the guide bar is not quite as quick either, as that big cog is bolted to it and should be removed before swapping bars - the other thing that it means is that when it comes to your regular servicing and you turn the bar over to even out wear... you need to take the cog off and swap it over too.
So, for now at least, it's the old way of doing things that wins it for me; not just for setting the tension but also for ease of maintenance.