Chainsaw chain keeps coming off? 6 checks

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1. Make sure it's the right chain

Husqvarna says to check that the chain's pitch, gauge and drive link count all match the guide bar. A chain that's one size off can seem to go on fine and then jump off under load. See how to tell what size chain you need.

2. Set the tension cold

Oregon says to tension the chain only when it's cool, with the engine off:

1. Loosen the bar nuts.
2. Hold the nose of the bar up and turn the tension screw clockwise until the drive links are fully seated in the groove and the tie straps lightly touch the bar.
3. Keep holding the nose up and tighten the bar nuts, back nut first.
4. Pull the chain along the top of the bar with a gloved hand. It should feel snug but still move freely.
5. Do the snap test: pull the chain down on the underside of the bar and let go. It should snap straight back.

Oregon adds that a bar with a sprocket nose needs a little more tension than a solid-nose bar. Husqvarna says a correctly tensioned cold chain doesn't sag below the bar but can still be moved by hand.

3. Recheck a new chain often

Husqvarna says it's normal for a new chain to stretch and need frequent adjustment. Oregon says to check tension often, especially during the first half hour of use. If it gets loose, stop, let it cool and adjust.

4. Don't tighten it hot

STIHL says a chain shouldn't be left tight after cutting, because it shrinks as it cools and can end up too tight on the bar. Loosen it slightly at the end of the job. If you must adjust while it's hot, Husqvarna says to leave some sag below the bar, about the width of a medium screwdriver tip.

5. Look at the drive sprocket

STIHL's guide says never to put a new chain on a worn sprocket, and to replace the sprocket if its wear marks are more than about .02 in. (0.5 mm) deep. Battered drive links can mean a worn sprocket, a sprocket that doesn't match the chain's pitch, or loose tension. STIHL's rule of thumb is one sprocket for every two chains.

6. Look at the bar

STIHL says to check the bar for bent or worn rails, burrs, a spread (splayed) or pinched groove, and a groove that's worn too shallow for the drive links. Clean the groove, file off light burrs, and flip the bar each time you take it off so it wears evenly. A badly damaged bar needs replacing.

And skip the brush

Husqvarna says small branches can lodge between the chain and sprocket and kick the chain off. Use a hedge trimmer or brush cutter for brush instead.

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