Pruner: Can't Keep Chain Tensioned

The chain rotates around the bar and has all the sharp teeth that do the cutting. Over time and use, these chains can stretch, but more likely is the drive teeth on the chain becoming so badly worn that the chain needs replacement. To do this, loosen the locking nut and handle connecting the lower drive shaft to the upper drive shaft. Next, push the alignment clip in and pull apart. Next, remove the nut on the cover. Remove the bar and chain from the pruner head, then the chain from the bar. Reinstall the new chain over the bar then reinstall back onto the pruner head, making sure to install the chain around the drive sprocket. Scroll to our “Cover” section elsewhere on this page for tips on returning your pruner to working order after making this repair.

The bar provides the channel for the chain to rotate on. Over time, the inside of the bar can become worn and will need to be replaced. To replace, loosen the locking nut and handle on the lower drive shaft to the upper drive shaft. Next, push the alignment clip in and pull apart. Next, remove the nut on the cover. Remove the bar and chain from the pruner head then the chain from the bar. On the new bar, lubricate the inside with a bit of bar oil. Install the new chain around the bar then back onto the pruner head. Make sure the chain is installed around the drive sprocket. Install the cover and hand-tighten the nut. See instructions under “Cover” for re-installation advice.

The cover houses the chain tensioner and keeps debris out of the pruner head. If the inside becomes damaged, preventing the tensioner from being held in place, you will need to replace the cover. Start by loosening the locking nut and handle on the lower drive shaft to the upper drive shaft. Next, push the alignment clip in and pull apart. Next, remove the nut on the cover. Remove the cover. Remove the tensioner screw from the cover by rotating it counter clockwise with a screwdriver. Remove the screw, tensioner, and retaining clip. Install the retaining clip into the slot in the new cover. Install the screw through the retaining slip and tensioner. Continue to thread until the retaining clip snaps over the hub on the screw. Next, rotate the screw counter clockwise to shift the tensioner towards the bottom half of the screw. Install the new cover. You may have to rotate the adjuster screw counter clockwise to properly align the tensioner into the hole in the chain bar, then hand-tighten the nut on the cover and rotate the adjustment screw clockwise to pick up the slack in the chain. (Chain should be tight enough to rotate with one hand and the drive links should not come out of the bar nose.) Tighten the nut on the cover and make sure the chain is tight again, as it may have shifted during the final tightening of the cover.

The drive sprocket drives the chain around the bar for cutting. If the drive sprocket is worn, it can impact the tension on the chain. Loosen the locking nut and handle on the lower drive shaft to the upper drive shaft. The next step is to push the alignment clip in and pull apart. Now you are able to remove the nut on the cover and remove the cover itself. With the cover off, inspect the drive sprocket for signs of wear, such as worn-down teeth, damaged teeth, chips, or anything else you think looks wrong. To replace, remove the E-clip holding it in place and remove the sprocket and install a new one. Re-install the E-clip. Re-install the cover with the nut tightened by hand. See tips under the “Cover” section for advice on re-installation.

The adjuster screw adjusts the tension on the chain. It allows you to set the proper tension on the chain when using your pruner. If the adjuster screw has become stripped or damaged, it may impact the way the adjuster screw holds tension. To replace this part, first loosen the locking nut and handle securing the lower drive shaft to the upper drive shaft. Next, you will have to push in the alignment clip and pull apart. The next step is to remove the nut on the cover. Remove the cover altogether and then remove the tensioner screw from the cover by rotating it with a screwdriver. Remove the screw, tensioner, and retaining clip. Install the new retaining clip into the slot in the cover, then install the screw through the retaining slip and tensioner. Continue to thread until the retaining clip snaps over the hub on the screw. Next, rotate the screw counter clockwise to shift the tensioner towards the bottom half of the screw. Install the cover. You may have to rotate the adjuster screw counter clockwise to properly align the tensioner into the hole in the chain bar. Hand-tighten the nut on the cover. Next, rotate the adjustment screw clockwise to pick up the slack in the chain until it’s gone. (The chain should be tight enough to rotate with one hand and the drive links should not come out of the bar nose). Tighten the nut on the cover and make sure the chain is tight again. Re-install the upper drive shaft to the lower drive shaft by inserting them together and aligning the alignment pin. Tighten the handle and locking nut to complete the process.