How Do I Tighten the Chain on My Stihl MS 170 Chainsaw?

The MS 170 is one of the chainsaw models manufactured by Andreas Stihl & Co. Like any power tool, the MS 170 requires occasional adjustment to keep it running properly. This is particularly true of the chain tension. The links of a newly installed chain stretch slightly and when this occurs, the tension of the chain needs to be increased accordingly. Failure to do this can damage the guide bar or cause injury if the chain jumps the bar altogether. Depending upon how your MS 170 is configured, adjusting the chain tension is performed using one of two methods.

Front Chain Tensioner

Step 1

Shut off the saw and check to see that the chain brake is disengaged.

Step 2

Loosen the two nuts holding the sprocket cover in place. Turn them counter-clockwise until you can wiggle the guide bar slightly up and down. You will not need to remove the nuts completely.

Step 3

Lift the guide bar. Use the screwdriver end of your adjustment tool to tighten the tension screw by turning it clockwise. The screw is located on the outside of the guide bar slightly below and just ahead of the sprocket cover nuts. Tension the chain until it rests securely against the underside of the guide bar.

Step 4

Continue holding the guide bar slightly upward. With your other hand, use the wrench end of the adjustment tool to retighten the nuts on the sprocket cover.

Step 5

Check the chain tension. With your gloved hand, pull the chain around the guide bar. It should move smoothly and not bind.

Quick Chain Tensioner

Step 1

Shut off the saw and check to see that the chain brake is disengaged.

Step 2

Pull out the hinged clip and loosen the wingnut. The clip and wingnut will be located on the sprocket cover directly below the adjusting wheel.

Step 3

Turn the adjusting wheel clockwise until it stops. This will draw the chain up against the underside of the guide bar.

Step 4

Retighten the wingnut firmly turning it clockwise.

Step 5

Reposition the hinged clip and fold it down over the wingnut.

Step 6

Check the chain tension. With your gloved hand, pull the chain around the guide bar. It should move smoothly and not bind.