Symptoms
- Chain sags noticeably below the bar
- Chain comes off the bar during cutting
- Chain rattles or slaps against the bar at idle
- Cuts are crooked or slow
Likely causes
- CommonNormal chain stretchChains stretch slightly with use and need periodic tension adjustment.
- CommonIncorrect tension after installationA newly installed chain needs proper tensioning before use.
- PossibleWorn or damaged guide barA worn bar groove can let the chain sit loosely or derail.
- PossibleWorn drive sprocketA worn sprocket doesn't grip the chain drive links properly.
What to do
- Shut off the saw and let it cool; wear gloves before handling the chain.
- Loosen the bar nuts slightly and use the tensioning screw to take up slack until the chain sits snug against the bottom of the bar.
- Check the chain can still be pulled around the bar by hand with light resistance, not too tight.
- Retighten the bar nuts while holding the bar tip up.
- Inspect the bar rails for wear or spreading, which can let the chain sit loosely.
- Check the drive sprocket teeth for wear and replace if rounded or damaged.
- If the chain won't stay tensioned properly after adjustment, the bar or sprocket likely needs replacement.
Tools and parts
- Chainsaw scrench (combo wrench/screwdriver)
- Gloves
Chainsaw guide barSearch: “chainsaw guide bar replacement”
Chainsaw drive sprocketSearch: “chainsaw sprocket replacement”
When to call a pro
If the bar or sprocket is worn out, a small-engine or outdoor power equipment shop can replace them.
Safety
Use caution
Always wear cut-resistant gloves when handling the chain, and make sure the saw is off and cool before adjusting tension.