The trimmer head on a Troy-Bilt weed trimmer contains the inner reel, cutting line, spring and outer head. These parts can be removed to replace the trimmer head on the trimmer. The trimmer head can break, the spool can crack and the spring may no longer function, all of which will require replacement of the broken part and the cutting head. Clogged weeds can also wrap themselves around the drive shaft, which will also require head removal to fix.
Turn off the power switch on the Troy-Bilt trimmer. Lay the engine flat onto a workbench, head tilted up. Grab hold of the moving head. Unscrew the bump knob counterclockwise. Remove the bump knob and inner reel. Clean the area inside the head with the rag.
Take the spring out of the head if it's still attached. Pull the retainer clip off the arbor bolt with the needle-nosed pliers. Unscrew the arbor bolt's nut, if present, counterclockwise with the wrench.
Grab hold of the shaft and loosen the cutting head in the opposite way it spins during operation, which should be counterclockwise for most Troy-Bilt models. Take the cutting head off the end of the drive shaft.
Set the new cutting head onto the head of the drive shaft. Tighten the cutting head onto the arbor bolt. Fit and tighten the nut onto the end of the arbor bolt if present.
Set the retainer clip into the center. Set the spring into the inner reel. Push the inner reel down into the cutting head. Tighten the bump knob clockwise.