MM.....considering the question has been posted in the chainsaw section and the question is about a chain tightening, I would suggest at a guess it's on a chainsaw wouldn't you?
If the adjuster is working correctly I can only assume the chain is the incorrect gauge for your bar. The drive teeth that slot into the bar are made in various thicknesses- some only a hairsbreadth different. If you have a chain that will slip into the groove when cold it is possible if you have the incorrect guage chain that when the chain is running it will get hot and this will expand the drive teeth causing the chain to jam in the groove. Check you have the correct chain with your dealer. Stihl use a very narrow gauge chain of only 1.1mm wide on their cheaper saws whereas most small saws use 1.3mm. If you fit a 1.3mm chain when you need a 1.1mm chain it will fit, but jam when warmed up.
pleasant
April 2011
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix chainsaws.