Stihl Chainsaw Throwing Chain (Causes & Fixes)
A Stihl chainsaw throws its chain when the chain climbs out of the bar groove, often because tension is wrong, parts do not match, or the bar, sprocket, chain, or tensioner is worn or damaged. Stop the saw and do not restart it. Inspect the whole cutting system, correct the cause, then check fit, tension, and lubrication before cutting again.
A chain coming off is not a problem to solve by simply tightening it and carrying on. A derailed chain can whip toward the operator, and the parts that allowed it to come off may be damaged. The low-maintenance fix is a correct, matched cutting setup and routine checks, not a shortcut that hides wear.
I start by finding out whether the chain is loose, mismatched, damaged, or being pushed out of a worn bar groove. Work through those checks in order. This can help you avoid buying a chain or bar that does not fit your exact saw.
Why a Stihl chainsaw throws its chain
Chain derailment means the drive links have climbed out of the guide-bar groove, so the chain no longer follows its intended path. It can happen during a cut or while the chain is moving. A loose chain is common, but mismatched parts, wear, damage, or poor lubrication can also be responsible.
Common causes to check first
A chain that is too loose can lift away from the bar and lose its hold in the groove. A chain that fits poorly may not seat correctly even when it looks close. Pitch, gauge, and drive-link count all matter.
- Incorrect tension: A cold chain may be set too loose, or it may loosen during use.
- Mismatched parts: The chain pitch must match the bar and drive sprocket. The chain gauge must match the bar groove. Drive-link count must match the bar length and setup.
- Worn or damaged parts: A worn sprocket, damaged drive links, flared bar rails, a damaged nose sprocket, or a faulty tensioner can let the chain move out of line.
- Poor lubrication: Inadequate oil can increase heat and wear. It is a warning sign to stop and inspect, not a reason to keep cutting.
- Cutting problems: A dull chain, pinched bar, or contact at the bar tip can make the saw behave unpredictably. Do not force the cut.
Wood hardness does not change the required chain fit. A 3/8-inch low-profile chain with .050-inch gauge is one possible configuration, not a universal Stihl setup. Use the markings on your bar and the manual for your exact saw.
What to do after the chain comes off
Stop the engine and do not restart it until you have checked the complete cutting attachment. Engage the chain brake before handling the chain or loosening the cover, and wear gloves. The brake does not make the chain safe to handle; keep hands clear of the cutters.
Inspect the chain, bar, sprocket, and tensioner
Remove the spark-plug boot on a gasoline saw before working near the chain, if the manual directs this step. Follow the manual for your model. Never inspect or adjust the chain with the engine running.
- Check the chain for cracked, bent, or missing parts and damaged drive links. Do not reuse a damaged chain.
- Check that the bar rails are not badly worn, flared, or uneven. Inspect the bar nose sprocket if fitted. Replace parts that are damaged or outside the maker’s wear limits.
- Look at the drive sprocket for wear or damage. Confirm that the tensioner moves the bar as intended and is not broken or jammed.
- Clear sawdust from the bar groove and oil outlet. Check for signs that oil is reaching the bar, using the method in the manual.
If the chain has derailed, inspect every drive link before refitting it. Do not assume the chain is undamaged just because it looks intact at a glance. When you cannot confirm a part is serviceable, have a qualified service shop inspect it rather than testing it under power.
Confirm that the parts match
Find the bar markings and the saw’s model number. Confirm that the bar length is approved for that exact powerhead; do not choose a bar by engine size alone. Match the chain’s pitch, gauge, and drive-link count to the bar, and make sure the sprocket pitch matches too.
| Check | What must match | What to do if it does not |
|---|---|---|
| Pitch | Chain, bar nose sprocket, and drive sprocket | Fit a compatible set listed for the saw |
| Gauge | Chain drive links and bar groove | Do not force the chain into the groove |
| Drive-link count | Chain and bar setup | Use the count specified for that bar |
| Bar length | Bar and exact saw model | Check the model manual or approved parts list |
A chain can appear to fit and still be wrong. If the markings are missing or unclear, identify the bar and chain before buying parts. The manual or an authorized Stihl dealer can help confirm compatibility.
Refit and tension the chain safely
Correct tension keeps the drive links engaged in the bar groove while still allowing the chain to travel around the bar by hand. Follow your model’s manual for the adjustment method and hardware. Do not use a generic measurement or guess at fastener torque.
Set tension, then check it again
With the engine off, engage the chain brake before removing or adjusting the cover. Adjust the tensioner as directed by the manual. To assess the chain, release the brake and wear gloves: the chain should contact the underside of the bar, the drive links should remain engaged in the groove, and you should be able to pull the chain around by hand.
Retighten the cover fasteners as the manual specifies. Do not start the saw if the chain binds, hangs away from the bar, or will not move by hand. After the chain warms, stop the saw and recheck tension. Recheck again after it cools, since a hot chain contracts as it cools.
Verify lubrication and safe operation
Use approved bar-and-chain oil. Check lubrication using the model’s manual; oil type and delivery rate can vary by saw and operating conditions. If the chain is not receiving oil, stop and fix the cause before cutting.
Before starting, inspect the chain brake, chain catcher, throttle lockout, handles, bar, chain, and sprocket. Start the saw using the model-specific procedure on stable ground, with the bar clear of people and objects. Keep bystanders away and maintain an escape route. If the chain loosens, lubrication fails, or the saw acts abnormally, stop work.
Examples: matching the cause to the fix
These are illustrative diagnostic patterns, not reports of a particular customer repair. They show why I check fit and wear before replacing parts. The right fix depends on what inspection reveals.
| What you find | Likely issue to investigate | Next step |
|---|---|---|
| Chain lifts from the bar, but parts appear undamaged | Incorrect tension or tensioner trouble | Reset tension to the manual; inspect tensioner movement |
| New chain does not seat smoothly | Pitch or gauge mismatch, or wrong drive-link count | Compare all markings and fit requirements |
| Chain comes off again after tensioning | Worn sprocket, damaged links, worn rails, or faulty tensioner | Inspect the full system; replace out-of-limit parts |
| Chain runs hot or lubrication seems absent | Oil delivery problem or poor maintenance | Stop, clean the groove and oil outlet, then verify oiling |
| Saw pulls poorly and chain becomes loose | Dull or unevenly sharpened chain, or cutting stress | Inspect sharpening and work setup; do not force the saw |
A repeated derailment is a reason to stop, not to tighten the chain further. Excess tension can add wear and strain. Find the cause before trying another cut.
Prevent the chain from coming off again
Prevention is a short routine: confirm fit, inspect wear, set tension, and verify lubrication. Check the chain and cutting attachment before each use, and clean the bar groove and oil outlet during maintenance. Replace parts based on damage and the maker’s wear limits, not guesswork.
Sharpen cutters evenly. Set depth gauges, also called rakers, with the gauge and value specified for that exact chain type. There is no single clearance for every chain. Too much lowering can raise kickback risk; too little can reduce cutting performance. Do not compensate for a dull chain by lowering rakers excessively or changing carburetor settings.
Keep engine settings model-specific. Idle and maximum RPM must come from the saw’s manual, not a generic target. For STIHL two-stroke saws, the specified mix is 50:1, or 2% oil, when using suitable STIHL two-stroke oil; confirm the manual for your model and market. Never use straight gasoline or an unverified fuel-oil ratio.
After use, switch off the saw, let it cool, clean and inspect the cutting attachment, and store it securely with the chain covered. Follow the manual’s fuel-storage instructions. Recheck fit, tension, and lubrication before returning the saw to service.
Frequently asked questions
These answers cover the most common decisions after a chain comes off. If the chain, bar, sprocket, or tensioner is damaged, do not restart the saw to test it. Use your exact model’s manual for fit, adjustment, and service limits.
Can I keep using a chain that came off?
Only after you inspect the entire chain and cutting system and confirm they are undamaged and correctly fitted. Replace damaged parts; do not restart the saw just to test them.
Should I tighten the chain as much as possible?
No. Set it to the manual’s instructions. The chain should contact the underside of the bar, remain engaged in the groove, and still pull around by hand with gloves.
How do I know which chain fits my Stihl saw?
Check the exact saw model and bar markings. Match pitch, gauge, and drive-link count, and confirm the bar is approved for that powerhead.
Can a worn sprocket make the chain come off?
Yes. A worn or damaged sprocket can affect how the chain engages and tracks. Inspect it along with the chain, bar, and tensioner.
Why does the chain come off after I fit a new one?
Check that pitch, gauge, and drive-link count match the bar and sprocket. Also inspect the bar rails, sprocket, and tensioner, then set tension as the manual directs.
Can a loose chain come off when it gets hot?
A chain can loosen during use, so recheck it after warm-up with the engine stopped. Stop immediately if it becomes loose; do not continue cutting.
Is a chain that feels tight by hand too tight?
Not necessarily, but it must still pull around by hand with gloves and stay seated in the groove. Follow the manual’s procedure and avoid overtightening.
Can I use any bar-and-chain oil?
Use approved bar-and-chain oil and follow the manual. Oil needs can vary with the saw and operating conditions.
Do all Stihl chains use the same raker setting?
No. Use the value and gauge tool specified for the exact chain type. A universal setting can reduce cutting performance or increase kickback risk.
When should I take the saw to a service shop?
Get qualified help if the tensioner, brake, sprocket, bar, or chain is damaged, if the chain repeatedly derails, or if you cannot confirm parts fit and serviceability.
(This article was written by one of our staff writers, Robert Callahan. Visit our Meet the Team page.)
