Chainsaw Chain Keeps Stretching? Why and What to Do

Some loosening is normal — a new chain beds in and every chain slackens as it warms up. A chain that keeps going loose long after break-in usually points to a worn sprocket, a chain at the end of its life, or a bar that isn’t clamped properly. Running it loose does damage: STIHL links loose tension to damaged drive-link tangs and flattened cutter and tie-strap bottoms, and Oregon to chipped bar rails behind the nose (STIHL Sharp Advice, pp. 20–21, Oregon manual, p. 97).

Loose-tension damage shows on the drive-link tangs and on the bottoms of the cutters and tie straps.

1. A new chain bedding in

Even pre-stretched chain needs a break-in run to seat the rivets, and the tension should be readjusted before it goes to work. STIHL says to run a new chain at low speed for about three minutes with plenty of oil (STIHL Sharp Advice, p. 12). Oregon’s break-in steps say to stop, let the chain cool and adjust the tension often during the first use (Oregon manual, p. 38). Expect to retension a new chain several times in its first session; that is not a fault.

2. Heat

A chain loosens as it warms up in the cut. STIHL notes that a chain tensioned in very cold weather will sag once it reaches working temperature, and that a chain shouldn’t be left tight after cutting because it shrinks as it cools — loosen it slightly (STIHL Sharp Advice, pp. 11, 22). Check tension with the saw off, and don’t crank a hot chain tight.

If the chain gets very hot quickly, check that bar oil is reaching it.

3. A worn drive sprocket

A worn sprocket wears chains quickly. Signs on the chain, per STIHL: the front or back of the drive links peened (battered around the edges), or burrs and peening in the notch of the tie straps (STIHL Sharp Advice, p. 21). On the sprocket itself, look for wear marks worn into the teeth.

• STIHL: replace the sprocket when wear marks are more than about .02” (0.5 mm), never fit a new chain on a worn sprocket, and expect a sprocket to last about two chains (STIHL Sharp Advice, p. 17).
• Oregon: replace the rim or spur sprocket after every two chains, or sooner (Oregon manual, p. 10).

The same STIHL page lists a sprocket whose pitch doesn’t match the chain as another cause of peened drive links.

4. The chain is worn out

Chains do wear and lengthen over time. Husqvarna lists a chain that needs frequent tension adjustments, won’t hold tension, or feels loose soon after adjusting as a sign that it may need replacing (Husqvarna). If the tensioner is near the end of its travel on an old chain, see when to replace a chainsaw chain for the other wear limits.

5. The wrong chain

A chain with too many drive links for the bar runs out of tensioner travel before it is tight. Check the drive-link count, pitch and gauge against the bar — see how to read them.

6. The bar is moving

If the chain loosens because the bar creeps back, check:

• the bar nuts or side-cover knob are fully tight (tighten them with the bar nose held up);
• the tensioner pin sits in the hole in the bar;
• the bar’s mounting slot and tensioner hole aren’t worn oval;
• on tool-free tensioners, the adjuster still locks.

A worn bar tail is a reason to replace the bar — see when to replace a guide bar.

Sources

• STIHL USA — Sharp Advice for chain saw owners (PDF): tensioning (p. 11), breaking in (p. 12), drive sprocket care (p. 17), troubleshooting chain wear (pp. 20–21), cold weather care (p. 22)
• Oregon — Safety & Maintenance Manual (PDF): cutting tips (p. 10), breaking in a new chain (p. 38), guide bar troubleshooting (p. 97)
• Husqvarna UK — When should the chain on the chainsaw be replaced?

Checked against these sources on October 1, 2026.