How Do You Change the Head on a Weedeater? (Step-by-Step Guide)

Quick Answer: How to Change a Weedeater Head

To change a weedeater head:(1) Turn off the trimer and disconnect power or remove the spark plug wire; (2) Lock the shaft using the built-in tab or an alignment hole; (3) Unscrew the old head—check for a directional arrow since many heads are reverse-threaded; (4) Remove the old head and any spacer parts; (5) Thread the new head on in the correct direction and tighten; (6) Reconnect power or spark plug and test. If you only need to load new trimer line rather than replace the entire head, refer to your specific head type’s line-loading instructions instead.

Changing the Head vs. Changing the Line: What’s the Difference?

Before you begin, clarify what you actually need todo. Many people searching for “how to change a weedeater head” actually want to reload trimer line, not replace the entire head assembly.

• Changing the trimer line: You’re refilling the cutting string inside an existing bump-feed head. This is maintenance youdo every few weeks or months depending on use.
• Changing the head: You’re removing the entire cutting head assembly and installing a new one. This is necessary if the head is damaged, worn out, or you’re switching to a different head type (for example, upgrading from bump-feed to a fixed-line head).

If your trimer head is still intact but you’ve run out of line, you don’t need to follow this guide—look up line-loading instructions for your specific head type instead. Proceed with this guide only if the head itself is cracked, stripped, or needs full replacement.

Identify Your Weedeater Type and Head Type

The removal procedure varies slightly by trimer power source and head design. Take a moment to identify what you have.

Gas-Powered vs. Electric Trimmers

• Gas trimmers: Typically more powerful; require disconnecting a spark plug wire before work.
• Electric trimmers: Corded or battery-powered; require unplugging or removing the battery.

Both use the same basic head-removal procedure, but safety steps differ slightly.

Common Weedeater Head Types

• Bump-feed heads: The most common type. You tap the head on ground to feed out new line. Easiest to load and reload.
• Fixed-line heads: Line is pre-cut and cannot be reloaded. You replace the entire head when line wears out.
• Metal blades: Some trimmers accept interchangeable metal cutting blades instead of string. Rare on consumer models but possible on heavy-duty equipment.

The head type matters because some heads have retaining clips or spacers that must be removed or repositioned during installation. Note the type before removing your old head.

Safety Steps Before Removing the Old Head

Never attempt to remove a weedeater head while the engine is running or the motor is powered. Follow these safety steps first.

For Gas-Powered Trimmers

1. Turn off the engine and allow it to cool for at least 2–3 minutes.
2. Locate the spark plug wire (typically a thick rubber boot connected to the top of the engine).
3. Firmly grasp the rubber boot and pull it straight off the spark plug. Do not pull the wire itself, as this can damage it.
4. Set the wire aside where it cannot accidentally reconnect.

For Electric Trimmers

1. Unplug a corded trimer from the electrical outlet, or remove the battery pack from a cordless model.
2. Wait 30 seconds to allow any residual motor spin to stop completely.

Tools You’ll Need

• Screwdriver or Allen wrench (size varies by trimer model; check your manual or lay it against the alignment hole to determine fit)
• Work gloves (optional but recommended for grip)
• Replacement head (correct model for your trimmer)
• Cleaning cloth (to wipe the shaft before installing the new head)

How to Lock the Shaft

Before you can unscrew the old head, you must prevent the shaft from spinning. Most weedeaters have a built-in locking mechanism.

Finding the Shaft Lock

Look at the trimmer head assembly where it connects to the main shaft. You’ll see one of these:

• A fixed tab or notch: A small protrusion on the head housing that catches a groove on the rotating shaft. Some heads have this molded directly into the housing.
• An alignment hole: A small hole (typically 6–8mm) drilled through the head housing and into the shaft. The hole is used to insert a screwdriver or Allen wrench to lock the shaft in place.

Locking the Shaft Using an Alignment Hole

1. Insert a screwdriver or Allen wrench through the alignment hole. The tool should fit snugly but not force.
2. The tool will pass through the housing and into a notch or groove cut into the shaft itself.
3. Push the tool in gently until you feel resistance. The shaft is now locked.
4. The shaft cannot rotate while the tool is in place. Proceed to unscrew the head.

Why Locking Matters

If you don’t lock the shaft, it will spin freely when you try to unscrew the head. You’ll just twist the entire trimer shaft instead of loosening the head. Locking ensures all your unscrewing force goes into loosening the head fastener.

Removing the Old Head: Thread Direction Matters

This is where many people get stuck. Not all weedeater heads use standard right-hand threads. Many are reverse-threaded, meaning you turn clockwise to loosen (the opposite of most fasteners).

Check for a Directional Arrow

Before you turn anything, inspect the head for an arrow or label. Look around the base where the head connects to the shaft. You may see:

• An arrow indicating LEFT (turn counterclockwise to loosen) or RIGHT (turn clockwise to loosen).
• Text reading “RIGHTY TIGHTY” or “LEFTY LOOSEY” or similar.

If you find a label, follow it exactly. If there’s no visible label, check your trimer’s manual or the manufacturer’s website.

Universal Reverse-Thread Rule

If you cannot find a label and have no manual, here’s the common pattern: Most consumer-grade weedeater heads (particularly Poulan Weed Eater brand and similar models) use reverse threads. This means you turn the head clockwise (when looking down at the head from above) to loosen it and counterclockwise to tighten.

The reasoning: Reverse threads prevent the head from unscrewing during operation due to the centrifugal force and vibration.

Step-by-Step Removal

1. With the shaft locked (tool inserted in the alignment hole), grip the head housing firmly with your other hand.
2. Try turning the head clockwise first. Apply steady, firm pressure. Do not jerk or yank.
3. If the head moves slightly and you hear a creaking sound, you’re on the correct rotation direction. Continue turning clockwise in quarter-turn increments.
4. If the head doesn’t budge or you feel extreme resistance, stop. Try the opposite direction (counterclockwise). One direction will be correct.
5. Once the head begins to losen, continue turning until it spins freely by hand.
6. Unscrew the head completely and set it aside.

Removing Spacers and Retaining Parts

Once the head is off, you may see:

• A rubber or plastic spacer washer between the head and the shaft.
• A metal retaining ring or clip.
• A metal washer.

Remove these and set them aside. Check your replacement head to see if it requires the same spacers. Many replacement heads come with their own spacers, so do not assume you need to reuse the old ones. Consult the new head’s manual if included.

What If the Head Won’t Budge?

If the head is stuck despite correct direction and good force:

• Let it soak: Spray penetrating oil (like WD-40) around the base where the head threads onto the shaft. Wait 15–30 minutes and try again.
• Use a strap wrench: Wrap a rubber strap wrench around the head housing for better grip and leverage, then turn.
• Tap it gently: Use a rubber mallet to tap around the base of the head. This can help break up corosion. Tap, wait a moment, then try turning again.
• Heat it slightly: For gas trimmers, run the engine for a few seconds to warm aluminum head slightly, which can expand it and losen corosion. Stop the engine, disconnect the spark plug, and try again immediately while still warm.

Do not use excessive force, as you risk damaging the shaft or stripping the threads.

Installing the New Head

Once the old head is removed and the shaft is clean, you’re ready to install the replacement.

Prepare the Shaft

1. With the shaft still locked (alignment hole tool still inserted), wipe the shaft where the head threads on using a clean cloth.
2. Remove any debris, corrosion, or old grease.
3. The shaft should be clean and dry.

Thread the New Head On

1. Position the new head at the end of the shaft so the internal threads align.
2. By hand, begin turning the head in the same direction as your new head’s manual specifies, or use the same thread direction as the old head (likely clockwise for reverse-threaded systems).
3. Turn slowly and feel for the threads to catch. You should feel a slight resistance and hear a faint threading sound.
4. Once hand-threading feels snug, stop.

Tighten Using the Shaft Lock

1. Keep the shaft locked with your alignment hole tool.
2. Grip the head housing and turn it toighten. Use firm, steady pressure—do not over-tighten.
3. Tighten until the head feels solid and doesn’t wobble when you shake it.
4. You should not hear any clicking or movement between the head and shaft.
5. Remove the shaft lock tool and gently try to turn the head by hand. It should be tight and not spin.

Avoid Cross-Threading

Cross-threading happens when the threads misalign, stripping both the head and shaft. To avoid it:

• Start by hand-threading very slowly.
• Feel for smooth resistance—threads catching smoothly.
• If you feel grinding, clicking, or sudden tightness at an od angle, stop immediately.
• Back the head off completely and restart.
• Never force a head onto the shaft if it doesn’t thread smoothly.

Reconnecting Power and Testing

Now that the new head is installed, restore power and perform a test run.

For Gas Trimmers

1. Reconnect the spark plug wire by pushing the rubber boot firmly back onto the spark plug until you feel a click.
2. Check that the boot is fully seated and not loose.
3. Perform a visual inspection: the new head should be centered and not wobling.
4. Start the engine and let it idle for 10 seconds.
5. Increase throttle to full speed and listen for any vibration, rattling, or unusual noise.
6. The trimer line should spin smoothly without stuttering.
7. If something sounds off, stop immediately, disconnect the spark plug, and inspect head installation.

For Electric Trimmers

1. Reinsert the battery or plug the corded unit back in.
2. Perform a visual inspection: the new head should be centered and not wobbling.
3. Turn on the trimmer at low speed for 5 seconds.
4. Increase to full speed and listen for vibration, rattling, or noise.
5. The trimmer line should spin smoothly.
6. If something sounds wrong, turn off immediately, unplug or remove the battery, and check the installation.

If the trimmer operates smoothly with no unusual vibration or noise, the head installation is successful.

Loading Trimer Line (For Bump-Feed Heads)

If you’ve installed a new bump-feed head, you’ll need to load it with trimer line before use. Most bump-feed heads come empty or with minimal line.

Note: Line-loading procedures vary significantly by head design. Consult the specific manual for your new head’s model, as the process differs between brands and head types. Some common steps include:

• Removing a spool or cover from the head.
• Winding new line (typically 0.065″ to 0.095″ diameter) onto the spool in the direction indicated by an arrow.
• Threading the line through eyelets or guides.
• Reinstalling the spool cover.

Do not guess the line-loading procedure—incorrect loading can prevent the bump mechanism from working or damage the head. Look up your specific head model’s instructions online or in the manual.

Troubleshooting Common Head-Change Issues

The New Head Spins But Won’t Tighten

Cause: Possible cross-threading or worn shaft threads.

Solution: Remove the head and inspect both new head’s internal threads and the shaft threads for visible damage or debris. If threads look intact, try reinstalling with slower, more deliberate hand-threading. If the head still spins, the shaft threads may be worn and may require professional repair or shaft replacement.

The Trimmer Vibrates More Than Usual After Installing the New Head

Cause: Head is not centered or is fully tightened.

Solution: Disconnect power, lock the shaft, and verify the head is tight by turning it clockwise (or according to its manual) with added force. Ensure the head is perfectly centered where it meets the shaft. Remove the head, inspect for debris, and reinstall, ensuring full seating.

Trimmer Line Won’t Spin After Head Installation

Cause: Line is tangled, incorrectly loaded, or the head is not properly installed.

Solution: Verify the head is tight and properly seated. If the head is secure, remove and reinspect the trimer line loading. Ensure line is wound in the correct direction and seated in all guides. If a bump-feed head, test the bump mechanism by tapping the head on the ground lightly to see if line extends.

Oil or Coolant Leaking From the Head After Installation

Cause: Over-tightening can crack the head housing, especially if it’s plastic.

Solution: Do not over-tighten. Tighten until snug and the head is secure, but not with maximum force. If the head is cracked, it must be replaced. In the future, tighten with steady, moderate pressure only.

Frequently Asked Questions

Are all weedeater heads reverse-threaded?

No, but most consumer-grade weedeater heads are reverse-threaded to prevent them from unscrewing during operation due to vibration and centrifugal force. However, some brands use standard right-hand threads. Always check for a directional label on the head or consult your manual before removing it. Attempting to unscrew in the wrong direction could damage the threads.

Can I use a replacement head from a different brand on my weedeater?

Not reliably. Weedeater shaft sizes and thread types vary by manufacturer and even by model year within the same brand. Using a head with incorrect threads or fit can result in a loose, unsafe head or cross-threading. Always purchase a replacement head designed for your specific trimer model. Check your manual or the trimer’s model number before ordering.

How often do I need to change the weedeater head?

If the head is intact and functioning, you typically do not need to change it. Bump-feed heads may last many years with only occasional line reloading. Replace the head if it cracks, the threads strip, the housing breaks, or the bump mechanism fails. Most homeowners never replace the head during the trimmer’s useful life unless there is physical damage.

Why is my weedeater head stuck and won’t losen?

A stuck head is usually caused by corosion, dirt buildup, or over-tightening from the previous installation. Try applying penetrating oil around the base, waiting15–30 minutes, and attempting again. For stubborn heads, use a strap wrench for better leverage or gently tap the base with a rubber mallet. Avoid excessive force to prevent thread damage.