Chainsaw chain keeps coming loose

Symptoms

• Chain sags below the bar after cutting
• Chain comes off the bar during use
• Rattling noise while cutting
• Chain was tight, now loose again within minutes

Likely causes

• CommonBar nuts not tightened after adjusting tensionTension was set but the nuts were never fully retorqued.
• CommonNormal chain stretch when new or hotNew chains stretch during break-in, and all chains loosen slightly as they heat up.
• PossibleWorn drive links or stretched chainAn old, stretched chain won't hold proper tension even when adjusted.
• PossibleWorn bar railsSpread bar rails let the chain sit loosely even at correct tension settings.
• Less commonFaulty tensioning screw or mechanismA stripped or broken tensioner adjuster can't hold position.

What to do

1. Let the saw cool, then engage the chain brake and remove the plug boot before adjusting.
2. Loosen the bar nuts slightly, then use the tensioning screw to take up slack until the chain sits snug against the bottom of the bar.
3. Pull the chain around by hand; it should move freely with no sag, but not be so tight it binds.
4. Retighten the bar nuts firmly while holding the bar tip up.
5. Check tension again after a few minutes of cutting, since new or hot chains often loosen further.
6. Inspect the chain for stretched links or the bar for spread rails if it won't hold tension repeatedly.
7. Replace the chain and inspect the bar if stretching is beyond the tensioner's adjustment range.

Tools and parts

• Bar wrench / scrench
• Gloves

When to call a pro

If the bar rails are visibly spread or the tensioner mechanism is stripped, have a saw shop replace the bar or tensioner assembly.

Safety