Pruner: Chain Falls Off

The chain rotates inside the channel of the bar. Over time chains will stretch and the drive teeth of the chain will wear down allowing the chain to pop off the bar. At this point the chain must be replaced. To do so, first remove the upper and lower drive shaft from each other by loosening the locking nut and handle. This will make it much easier to work on the pruner head. Remove the cover and pull the chain and bar off, then remove the old chain and clean out the bar. Lubricate the bar with bar oil, then install the new chain around the bar and back onto the pruner head with the chain around the drive sprocket. Install the cover and tighten the nut hand tight. Tighten the cover down and inspect the tension on the chain as it may have been altered by the final tightening of the cover. To complete this repair, you should re-attach the 2 drive shafts.

The bar on your pruner supports the chain for rotation. The bar should be cleaned regularly as a part of your maintenance routine, and should also be checked periodically for signs of wear. Check the bar first by trying to wiggle the chain back and forth inside the rail. If you can wiggle the chain the bar will need to be replaced. If the nose wheel bearing has too much play, the bar will need to be replaced as well. You will also want to check for wear behind the nose wheel. If you discover that the bar is worn on one side you can simply flip the bar, but if it is worn on both sides it must be replaced. To replace the bar, first separate the 2 drive shafts by loosening the locking nut and handle and pulling it apart (this step may not be necessary, but you may find it easier to work on your pruner with the drive shafts separated). Next, remove the cover, pull the bar and chain off, remove the chain from the bar, and discard the old bar. Lubricate the new bar with bar oil, and install the chain onto the bar. Then, install the bar back onto the pruner head, with the chain around drive sprocket. Now you can install the cover with the nut hand-tight. You may have to back off the tensioner to allow it to properly align with the hole in the chain bar. Adjust the tension on the chain by rotating the adjuster screw clockwise. The chain should be tight enough to rotate with one hand and the drive links should not come out of the bar nose. Tighten down the cover and re-check the tension on chain, as it may change after you tighten the cover. Finally, re-attach the 2 drive shafts together.

The cover on your pruner houses the tensioner. If the inside of the cover becomes worn, or if the housing for the tensioner breaks it will not hold tension on the chain. This can cause the chain to fall off. To replace the cover, loosen the nut and check the part that houses the tensioner. If the tensioner is out of place, check for damage in the housing part of the cover. Remove the tensioner screw from the cover by rotating it counter clockwise with a screwdriver, then remove the screw, tensioner and retaining clip. Next, install the retaining clip into the slot in the new cover and install the screw through the retaining slip and tensioner. Continue to thread until the retaining clip snaps over the hub on the screw. Now, rotate the screw counter clockwise to shift the tensioner towards the bottom half of the screw. Follow the relevant steps elsewhere on this page for step by step instructions on returning your pruner to its working condition after making this repair.

The drive sprocket drives the chain around the bar. If the sprocket is worn, it can impact the tension on the chain and cause the chain to fall off. To inspect or replace the sprocket, begin by loosening the locking nut and handle on the lower drive shaft and the upper drive shaft then push the alignment clip in and separate. Next, remove the nut on the cover and the cover itself. With the cover off, inspect the drive sprocket for signs of wear such as worn-down teeth, damaged teeth, chips, grooves, or anything else that looks damaged. To replace the sprocket, remove the E-clip holding it in place, then remove the sprocket. At this point you can install a new sprocket and a new E-clip. Next, re-install the cover with the nut hand-tight. You may have to ease off the tensioner to get it to align with the hole in the chain bar. Adjust the chain’s tension by rotating the adjuster screw in a clockwise direction. The chain should be sufficiently tight so as to rotate with one hand without the drive links coming out of the bar nose. Once you’ve arrived at this stage, you can tighten down the cover and re-check chain tension, as it may have changed after tightening of cover. Re-install the 2 drive shafts back together and tighten down the nut and handle.

The retaining ring holds the adjustment screw that keeps tension on the chain in place. If this ring breaks or becomes damaged it will not hold the screw and tensioner in place, which can cause the chain to fall off your pruner. To check and replace the retaining ring, first remove the cover on the pruner head. At this point the retaining ring should be visible and can be inspected. If it is broken, remove the screw and tensioner. Install the new retaining ring into the retaining slip, then thread the screw through the retaining ring and the 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. Take a look at the “Bars” section on this page for advice on putting your pruner back together to complete this repair.