Troy-Bilt manufactures a wide line of weed trimmers to tackle most trimming jobs around the home. Some of their trimmers use a bump knob on the bottom of the spool to feed line when necessary. When the bump knob is not working properly, the line will not come out. There are two main causes of a bump knob freezing in the head. Either the spring between the spool and housing is stuck or the bolt inside the knob requires attention. Unfreezing a bump knob from a Troy-Bilt weed trimmer involves inspecting both for damage before making minor adjustments.
Unplug the wire from the spark plug on your Troy-Bilt weed trimmer. Place the weed trimmer on its side.
Hold the outside of the spool housing with one hand and twist the bump knob clockwise with your free hand. If necessary, turn the bump knob initially with pliers if it is difficult to turn by hand.
Pull the inner spool out of the outer housing with your fingers. Look for a spring on the top of the spool. Inspect the spring for damage. If the spring is bent, purchase a replacement at a home improvement center.
Hold the bump knob with one hand and turn the bolt on the top of the knob with your free hand. The bolt should turn freely inside the knob. If it does not, look for cracks or damage on the knob. If you find damage replace the knob.
Spray inside the hole where the bolt threads exit the bump knob with silicone, if there is no damage. Turn the bolt left and right to distribute the silicone.
Apply a thin film of petroleum jelly onto the center shaft of the outer housing with your fingers. Clean the inside of the outer housing with a rag to remove any caked-on dirt or grass.
Place the spring over the center shaft of the outer housing and insert the inner spool over the spring with the ends of the line going through the eye holes of the outer housing.
Thread the bump knob onto the trimmer counterclockwise until it is hand tight. Push the end of the plug wire over the spark plug.