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How to Change the String on a McCullough Trimmer

Updated July 20, 2017

The McCullough Gas String Trimmer is one tool in the McCullough line of lawn care machinery. It uses nylon string spinning at high speed to cut grass and weeds. Though this nylon string is extremely durable, the high rotation speed and tough materials being trimmed will eventually destroy the string. Once you have used the entire spool of string, you must replace it to continue working.

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  1. Arrange the trimmer so you can easily gain access to the cutting end of the unit. It helps to brace the trimmer against a wall or other support.

  2. Locate the knurled knob at the bottom of the cutting assembly. Remove the knob by turning it counterclockwise. Set the knob aside.

  3. Remove the string spool and spring by lifting them straight off of the spindle. Set the spring aside. Remove any remaining line from the spool.

  4. Use approximately 14 feet of size .080- to .095-inch nylon line to replace the string. Fold the length of line in half. Hook the U-shaped loop formed on one end into one of the slots located on the side of the spool.

  5. Wind the line in a clockwise direction around the spool. Notice that the spool is divided into two sections. Wind one length of the doubled line on either side of the divider and stop once approximately 6" of line remains. Make sure that you keep tension on the line so there is no slack once the line is wound.

  6. Locate the two slots located on the edge of the bottom of the spool. Thread one end of the string through each slot.

  7. Reinstall the spring over the spindle. Replace the spool over the spindle, ensuring that you thread the ends of the string through the eyelets located on opposite sides of the cutting head housing assembly. Verify that the spring and spool are fully seated on the spindle.

  8. Maintain pressure on the spool and tug firmly at each end of the string to detach it from the spool slots. These slots are only used to keep the string in place while you replace the spool. The line now needs to be free.

  9. Replace the knurled knob and tighten it using only your hand. Excessive tightening can strip the threads on the knob.

  10. Trim any excess line so the remaining line is approximately 5 inches at each end. Too much line will add unnecessary strain to the engine when you start it. This completes the string replacement and you can now use the trimmer.

  11. Tip

    Keep and extra spool of string handy when using the trimmer. This will save a lot of time while you are working.


    Make sure the trimmer is cool before you replace the string; the gas engine generates a lot of heat and can cause serious burns. Wear safety goggles, closed shoes and long trousers when operating the trimmer.

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Things You'll Need

  • Replacement nylon line

About the Author

Rex Molder began writing professionally in 1999 and specializes in automotive, technology and travel articles. His articles have appeared at iPad- and SEO-related websites. Rex holds a Bachelor of Arts in Asian studies from University of North Carolina-Chapel Hill.

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