What causes chainsaw chain to tighten during use?

Answer 1

I am a proffessional Timber faller in Idaho and use Stihlms440,ms460 and ms660 five days a week 7 hours a day in conventional logging operations. The answer to this question has to do with the bar and lubricating system. Most saws now days have an automatic oiler or pump that is enabled only while the saw is running... On your guide bar (if taken off) you will notice a small hole near the powerhead end of the bar. Usually the primary reason for the chain to tighten up is because the lubricating port on the bar ("small hole"as mentioned) is plugged with sadust,saw chips and small woody debris, thus not allowing the oil being pumped to pass through to the guide bar. First I would take a small nail or even a twig and push the debris through the hole. Depending on make and model of the saw and bar there may be two holes. If so clean them both. Now since you have the bar off and in hand you may as well clean between the bar guide rails. (Bar groove) This is most easily is done by using a knife blade. Start up by the bar tip (Sprocket) insert the knife blade into bar groove and carefully pull through the bar groove all the way to the opposite end of the bar. You may have to repeat this step two or three times to completelly break free all of the debris from within the bar groove. Do this carefully and with gloves. complete this on both sides of the bar. This will break loose and woody material that may have clogged the bar groove. Re-assemble the saw,adjust chain tensioner so your chain is at the propper tension and give it a whirl.