A weed trimmer is an essential tool for most homeowners. It can trim grass in places where mowers can't reach and trim around the edges of sidewalks and walkways, cutting weeds quickly and easily. The tool does require a certain amount of maintenance. If your Troy-Bilt weed trimmer has a stuck bump knob, it will not be able to feed extra cutting line, nor will you be able to replace the cutting line.
Unplug the tool if it is electric. Remove the spark plug if it is gas-powered. Set it on the ground so that you have easy access to the bump knob.
Spray the lubricant around the edge of the bump knob and allow it to soak for about 15 minutes before continuing.
Use the plumber's wrench to grip the bump knob and firmly turn the knob counterclockwise while also pushing the knob in with your other hand. If the knob still does not loosen, continue to the next step.
Grip the knob with the plumber's wrench and begin to turn it counterclockwise while tapping the knob with the rubber mallet. Continue to hit the knob with a bit more force until it comes loose and turns properly.
Bump knobs on Troy-Bilt weed trimmers often become stuck because the cutting line is feeding incorrectly or jammed. You can avoid this problem by using a prewound reel instead of winding it yourself.