This usually means the bar nuts aren't tight enough, or the chain tensioning system needs adjustment. Here's what you do.
- First, make sure the saw is off and completely cool. Engage the chain brake for safety.
- Loosen the two bar nuts on the side of the saw—just enough so you can move the bar by hand.
- Use the tensioning screw (located near the front of the saw, just ahead of the bar) to adjust. Turn it clockwise to tighten the chain.
- Lift the tip of the bar up slightly while you tighten. You want the chain to be snug against the bar, but you should still be able to pull the chain around by hand with a little resistance.
- While holding the bar tip up, tighten the two bar nuts firmly. Re-check the tension; it often loosens a bit when you final-tighten the nuts.
If that didn't work, the drive sprocket might be worn out, causing the chain to stretch unevenly. Also check the bar groove for debris—clean it out thoroughly.
Heads up: A chain that's too tight will overheat and damage the bar. A chain that's too loose is dangerous and can derail. Always check tension before each use.