Changing the string on the Bolens trimmer will depend upon what type of spool you have. The Bolens trimmer uses a spool that accepts standard line and also a spool that accepts a square line known as split line, which is a split table double cord line. The disassembly process is the same for either spool. You can tell which line your spool uses by looking at the holes on top of the inner spool. Square holes indicate you can use split line. If you are unsure, you can purchase pre-wound replacement spools from a home improvement center.
Split Line Trimmer
Unplug the Bolens trimmer spark plug wire from the spark plug with your fingers. Lay the Bolen on its side so you can access the trimmer head.
Hold the spool assembly with one hand, and turn the securing knob in the center counterclockwise with your free hand. Pull the knob off, and inspect the bolt in the bottom of the knob. The bolt should move freely. If the bolt binds, replace the knob with a new one.
Pull the inner spool reel from the outer spool with your fingers. Remove any leftover string from the inner spool reel. Clean the inside of the outer spool with a cloth to remove grass clippings and dirt.
Pull the spring out of the center of the inner spool so that the spring does not get lost. Inspect the teeth around the bottom of the inner spool for wear. Replace the inner spool with a pre-wound replacement if necessary.
Cut 10 feet of new split line with a pair of scissors. Insert one end of the line through one of the line holes in the bottom of the inner spool. Pull the line through until only 4 inches is left out.
Insert the end of the 4-inch line into the second line hole in the inner spool, forming a loop above the spool. Pull the line tight to lock the line in the spool. Split the loose end of the line back 6 inches with a utility knife.
Wind the line tightly around the spool in the direction the arrow points on the top of the spool. Insert the split ends into the two holding slots on the top of the spool.
Insert the inner spool into the outer spool housing, guiding the string ends through the eyelets in the side of the housing. Place the knob over the spool, and turn the knob clockwise to lock the spool in position.
Remove the inner spool as you would for the split line. Cut 20 feet of standard line with a pair of scissors. Fold the line in half, and insert each end of the lines into the two line holes in the top of the spool. Pull the ends through until the loop that forms above the spool is as small as possible.
Wind the lines together around the spool in the direction that the arrow is pointing. Place the final 6 inches of each end into the holding slots on the bottom of the spool.
Insert the inner spool into the spool housing, and guide the string ends through the eyelets in the side of the housing. Place the knob over the spool, and turn the knob clockwise to lock the spool.