How to Change Heads on Stihl Weed Eater? Step-by-Step

Introduction

Changing the cutting head on a Stihl weed eater is a routine maintenance task that keeps your trimmer running efficiently and extends the life of the machine. Whether you are switching from a standard bump‑feed head to a fixed‑line model or simply replacing a worn‑out head, understanding the process saves time and prevents damage to the drive shaft. This guide walks you through every step, from identifying the correct head type to testing the trimmer after installation. By following the instructions below, you will learn how to change heads on Stihl weed eater equipment safely and confidently.

• Understanding Stihl Trimmer Head Types
• Tools and Safety Gear Needed
• Preparing the Weed Eater for Head Change
• Step‑by‑Step Guide: How to Change Heads on Stihl Weed Eater
• Choosing the Right Replacement Head
• When to Replace the Trimmer Head
• Tips for Maintaining Your Trimmer Head
• Common Mistakes to Avoid
• Troubleshooting After Head Replacement
• Frequently Asked Questions
• Conclusion

Understanding Stihl Trimmer Head Types

Stihl offers several cutting head designs, each suited to different vegetation and user preferences. The most common categories are bump‑feed heads, fixed‑line heads, and blade‑type heads. Bump‑feed heads, such as the AutoCut series, release line automatically when you tap the head on the ground. Fixed‑line heads, like the FixCut, hold a pre‑cut length of line that does not advance automatically. Blade heads use metal or plastic blades for heavy brush and small saplings. Knowing which head your model uses is the first step in selecting a compatible replacement.

Model numbers are usually stamped on the head housing or listed in the owner’s manual. For example, the Stihl FS 56 RC‑E uses an AutoCut 25‑2 head, while the FS 131 may accept a FixCut 31‑2. Cross‑referencing the part number with Stihl’s official parts catalog ensures you purchase the correct component. Using an incompatible head can cause vibration, poor cutting performance, or even damage to the gearbox.

Tools and Safety Gear Needed

Before you begin, gather the following items:

• Adjustable wrench or socket set (typically 13 mm or 1/2 in.)
• Flat‑head screwdriver for retaining clips
• Gloves (cut‑resistant preferred)
• Safety glasses or goggles
• Hearing protection if you plan to run the engine during testing
• Clean rag and a small brush for debris removal
• Replacement head (verified for your model)
• New trimmer line (if the head requires fresh line)

Always disconnect the spark plug wire before working on the trimmer. This prevents accidental starts while your hands are near the rotating shaft. Wear gloves to protect against sharp edges on the old head and the new line. Safety glasses shield your eyes from any debris that may fly loose during removal.

Preparing the Weed Eater for Head Change

Start by placing the trimmer on a stable, flat surface. If the unit has a shoulder strap, remove it to give you clear access to the head. Turn the engine off and allow it to cool completely. Pull the spark plug boot off the spark plug and secure it away from the plug. Next, remove any guard or debris shield that covers the head; most Stihl models use a single bolt or quick‑release latch. Keep all removed hardware in a small container so nothing gets lost.

Inspect the drive shaft and the head mounting area for built‑up grass, dirt, or old line fragments. Use the brush and rag to clean the threads and the splined shaft. A clean mounting surface ensures the new head seats properly and reduces the chance of vibration. If you notice excessive wear on the shaft splines, consider having a dealer inspect the gearbox before installing a new head.

Step‑by‑Step Guide: How to Change Heads on Stihl Weed Eater

Removing the Old Head

1. Locate the retaining nut or bolt on the underside of the head. Most Stihl heads use a left‑hand thread (turn clockwise to loosen).
2. Fit the appropriate wrench or socket onto the nut. Hold the drive shaft steady with a strap wrench or by gripping the shaft housing if accessible.
3. Turn the wrench clockwise to break the nut free. Once loose, unscrew the nut completely by hand.
4. Slide the old head off the splined shaft. If it sticks, gently tap the side with a rubber mallet; avoid hitting the shaft directly.
5. Remove any remaining line or debris from the shaft and the head cavity.

Installing the New Head

1. Align the splines on the new head with the splines on the drive shaft. The head should slide on smoothly without forcing.
2. Thread the retaining nut onto the shaft by hand, turning counter‑clockwise (right‑hand thread) until snug.
3. Tighten the nut with the wrench. Torque specifications vary by model; a typical range is 30–40 Nm (22–30 ft‑lb). Consult your manual for the exact value.
4. Reattach any guard or debris shield you removed earlier, ensuring all bolts are secure.

Adjusting the Trimmer Line (If Applicable)

1. If the new head is a bump‑feed type, feed the appropriate diameter line through the eyelets following the arrow direction indicated on the head.
2. Pull the line until equal lengths extend from both sides, usually about 10–12 inches each.
3. For fixed‑line heads, insert the pre‑cut line segments into the designated slots and secure them with the retaining clips.

Testing the Trimmer

1. Reconnect the spark plug wire.
2. Start the engine according to the manufacturer’s starting procedure.
3. Allow the engine to warm up for a minute, then engage the throttle gently.
4. Observe the head for smooth rotation, proper line feed, and absence of unusual vibration or noise.
5. If the head wobbles or the line does not feed, shut off the engine and re‑check the nut torque and line installation.

Choosing the Right Replacement Head

Selecting a replacement head involves matching the part number, line diameter, and intended use. Stihl’s AutoCut heads are ideal for general lawn maintenance because they feed line automatically. FixCut heads suit users who prefer a set line length and less frequent line replacement. For heavy brush, a blade head such as the PolyCut or MetalCut provides more cutting power but requires more frequent sharpening or blade replacement. (See Also:How To Clean Weed Eater Exhaust)

Consider the line diameter your trimmer’s engine can handle. Most residential Stihl trimmers accept 0.080‑in. or 0.095‑in. line. Using a thicker line than specified can overload the engine and cause premature wear. The table below compares the most common Stihl heads for quick reference.

When to Replace the Trimmer Head

Regular inspection helps you decide when a head change is necessary. Signs that a head should be replaced include:

• Cracked or deformed housing that no longer holds line securely.
• Excessive vibration that persists after tightening the retaining nut.
• Line feed mechanism that fails to advance or jams frequently.
• Visible wear on the drive splines inside the head.
• Reduced cutting efficiency even with fresh line.

Most manufacturers recommend checking the head at the start of each season and after every 25‑hour operating interval. Heavy‑use professionals may need to replace heads more often, while occasional homeowners can go several seasons between changes.

Tips for Maintaining Your Trimmer Head

• Clean the head after each use to prevent grass buildup that can cause corrosion.
• Lubricate the retaining nut threads lightly with a marine‑grade grease to ease future removal.
• Store the trimmer in a dry place; moisture accelerates rust on metal heads.
• Use only Stihl‑approved line diameters; off‑brand line can be inconsistent in thickness.
• Rotate the head 180 degrees periodically if the design allows, to even out wear on the splines.
• Inspect the line feed spring (on bump‑feed heads) for fatigue; replace if it no longer returns sharply.

Common Mistakes to Avoid

Many users encounter problems because of a few repeatable errors. The most frequent mistake is turning the retaining nut the wrong direction; remember that most Stihl heads use a left‑hand thread for removal. Forcing a head onto the shaft without aligning the splines can strip the splines, leading to costly gearbox repairs. Over‑tightening the nut beyond the specified torque can crack the head housing or distort the shaft. Using the wrong line diameter often results in poor feed and excessive engine load. Finally, neglecting to disconnect the spark plug wire creates a serious safety hazard.

If you encounter resistance while removing the nut, apply penetrating oil and let it sit for a few minutes before trying again. Never use a pipe extension on the wrench for extra leverage; the sudden torque spike can damage the shaft. When installing a new head, double‑check that the line feeds in the direction indicated by the arrow on the head housing.

Troubleshooting After Head Replacement

Even with careful installation, issues can arise. The following table outlines common symptoms and corrective actions. (See Also:How Long To Soak Weed Eater String)

Frequently Asked Questions

Can I use a non‑Stihl head on my Stihl trimmer?

While some aftermarket heads fit the spline pattern, Stihl does not guarantee performance or safety with non‑OEM parts. Using an unapproved head may void the warranty and can cause vibration or premature wear.

How often should I replace the trimmer line?

Line replacement frequency depends on usage and vegetation type. For typical residential lawn care, expect to reload line every 1‑2 hours of operation. Heavy brush cutting may require line changes every 30‑45 minutes.

What is the correct torque for the head retaining nut?

Torque values vary by model, but most Stihl trimmers specify 30–40 Nm (22–30 ft‑lb). Always consult the service manual for your exact model to avoid over‑ or under‑tightening.

Why does my bump‑feed head not release line when I tap it?

Common causes include a worn feed spring, line that is too thick, or debris blocking the feed mechanism. Disassemble the head, clean the interior, and verify the line diameter matches the head’s specification.

Is it necessary to remove the spark plug wire every time I change the head?

Yes. Disconnecting the spark plug wire eliminates the risk of accidental engine start while your hands are near the rotating shaft. It is a critical safety step. (See Also:How To Clean Weed Eater Carb)

Conclusion

Swapping the cutting head on a Stihl weed eater is a straightforward task when you follow the proper sequence: identify the correct head type, gather the right tools, prepare the machine, remove the old head, install the new one, adjust the line, and test the trimmer. Regular inspection and timely replacement keep your trimmer cutting cleanly and protect the drive system from unnecessary stress. By mastering how to change heads on Stihl weed eater equipment, you ensure reliable performance season after season and avoid costly repairs. Keep this guide handy, refer to the comparison table when selecting a new head, and always prioritize safety by disconnecting the spark plug before any maintenance.