Oregon explains the correct way to tension your chain.
Always make sure the engine is turned off before you begin tensioning the chainsaw chain. Also, saw chain should only be tensioned while it is cool, not hot. For more information beyond here, refer to the operators manual for your saw, the instructions included with your saw chain and/or guide bar, and Oregon support videos.
- Step 1: Locate the chain tension adjustment points on your chainsaw. Common locations for adjustment points include the side cover and the front of the chainsaw. For some chainsaw models, like the Oregon CS300, the adjustment points are housed within a side cover release knob.
- Step 2: Turn the adjustment screw "clockwise" to tighten, "counterclockwise" to loosen.
- Step 3: Adjust the chainsaw chain tension. Use a chainsaw scrench (a combination of a screw driver and a socket wrench) to loosen your tensioning pin. This pin moves the bar for tensioning purposes and is attached to a screw. Hold the nose of the bar up as you adjust the tension (do not let go of the bar nose until after you've tightened the mounting nut in). For a sprocket-nose guide bar, follow the solid-nose guide bar instructions, then give the tensioner another quarter to half turn. The bottoms of the lowest tie straps and cutters will come up and solidly contact the bottom of the guide bar rail. The tension for a sprocket-nose guide bar must be tighter than for the solid-nose guide bar.
- Step 4: As you increase the chain tension, monitor the gap between the under-side of the guide bar and the slack chain. Continue tensioning the saw chain to remove this gap. The saw chain is properly tensioned when the drive links are fully seated into the groove of the guide bar and all chain tie-straps make light contact with the guide bar.
- Step 5: With a gloved hand, pull the chainsaw chain along the top of the guide bar guide bar away from the engine towards the guide bar nose several times. The chainsaw chain should feel snug but still pull freely.
- Step 6: Finally, perform a "snap" test to ensure proper saw chain tension. Simply pull the chain on the underside of the guide bar down so one or two drive links are out of the guide bar rails and release it. The chain should snap directly into position.


Continue to check the saw chain tension regularly, especially during the first half hour of use. If the chain becomes loose, stop cutting and let the saw cool before readjusting the tension. Source