Replacing string or a spool on a McCulloch trimmer is a straightforward process that requires no tools. To remove the string head, you need only to remove the locking knob that secures the string head. The string head is the spool that the trimmer string winds around. You can replace the line itself or purchase a replacement spool that already has line on the spool.
Disconnect the spark-plug wire boot from the top of the spark plug. You can pull the boot away from the spark plug with your fingers.
Lay the McCulloch trimmer on its side, with the fuel-fill neck pointing upward.
Hold the string head with one hand, and turn the center knob counter-clockwise with your other hand. Remove the knob from the string head.
Pull the string-head spool out of the housing. Pull the spring that sits between the spool and housing out, and set it aside. The string-head spool is now ready for restringing.
Unplug the McCulloch trimmer from the power cord. Lay the trimmer on its side so you can access the string-head assembly.
Hold the ribbed outer part of the string head with one hand, and push down on the center knob with your free hand.
Twist the center knob counter-clockwise to unlock the string head. Pull the knob and string-head assembly away from the trimmer.