How to Replace Stihl Weed Eater Head? Easy Instructions for Stihl Owners

Introduction

Stihl weed eaters are renowned for their durability and performance, but even the best equipment needs part replacements over time. The trimmer head is one of the most common wear parts, and if you’ve been searching for How to Replace Stihl Weed Eater Head? you’ve come to the right place. Replacing a worn or broken head is a simple 10-minute DIY job that costs a fraction of buying a new weed eater, and you don’t need any special tools or mechanical experience to do it. This comprehensive guide covers everything from identifying when you need a new head, to step-by-step instructions for all Stihl head types, to pro tips to make your replacement last for years.

Table of Contents

• Signs You Need to Replace Your Stihl Weed Eater Head
• Tools and Materials You’ll Need
• Types of Stihl Weed Eater Heads
• Preparation Steps Before Replacement
• General Step-by-Step Guide to Replace Stihl Weed Eater Head
• How to Replace a Loop Head on Stihl Models
• How to Replace an AutoCut Head on Stihl Models
• Common Mistakes to Avoid During Replacement
• Tips for Extending Your New Head’s Lifespan
• Comparison of Popular Stihl Replacement Heads
• Frequently Asked Questions
• Conclusion

Signs You Need to Replace Your Stihl Weed Eater Head

Knowing when to replace your weed eater head is key to avoiding damage to your equipment and keeping your yard looking neat. Watch for these common signs that it’s time for a new head:

• Trimmer line breaks constantly: If you’re going through line faster than usual, even with correct usage and the right line size, your spool may be worn out or cracked, causing the line to snag and break.
• Line won’t feed: For AutoCut (bump feed) heads, if bumping the head on the ground doesn’t release more line, the feed mechanism is broken. For loop (manual feed) heads, if pulling the line doesn’t release it smoothly, the spool is damaged or the line is wound incorrectly.
• Cracked or broken head housing: If you hit a rock, curb, or tree root while trimming, the plastic head housing can crack or break. A damaged housing will cause the head to wobble, damage the drive shaft, and make cutting impossible.
• Excessive vibration: A wobbling or vibrating head is usually a sign of a misaligned drive fitting, a loose retaining nut, or a cracked head. Ignoring this issue can cause permanent damage to your weed eater’s engine shaft, which is far more expensive to repair than replacing the head.
• Poor cutting performance: If your weed eater is running but not cutting effectively, even with fresh line, the spool may be worn out and unable to hold the line securely.

Replacing the head is almost always cheaper than buying a new weed eater, and Stihl OEM replacement parts are widely available at hardware stores, garden centers, and online retailers.

Tools and Materials You’ll Need

You don’t need any fancy power tools to replace your Stihl weed eater head – just these basic supplies:

• Replacement Stihl weed eater head compatible with your specific model (verify compatibility using your model number first)
• Correct trimmer line for your new head (most Stihl models use .080″ or .095″ round or square line; check your old head or owner’s manual for the exact size)
• Phillips or flathead screwdriver (depending on your model’s retaining bolt type)
• Work gloves to protect your hands from sharp line and debris
• Safety glasses to protect your eyes from flying debris
• Small cleaning brush (an old toothbrush works perfectly) to remove grass and gunk from the drive shaft
• Light machine oil (optional, for lubricating the drive shaft and spool bearing)
• Torque wrench (optional, but recommended to avoid overtightening the retaining nut)

Types of Stihl Weed Eater Heads

Stihl makes three main types of weed eater heads, each designed for different use cases. Knowing which type you have will help you follow the correct installation and loading steps:

Loop Heads

Loop heads, also called manual feed heads, are the traditional Stihl head design. They feature a removable spool that you manually wind with trimmer line, and you pull the line out by hand to adjust the length during use. They’re extremely durable, making them a popular choice for commercial users and anyone trimming heavy brush, tall weeds, or woody vegetation. Most older Stihl models, like the FS 38 and FS 45, come standard with loop heads.

AutoCut Heads

AutoCut heads are Stihl’s bump feed design, the most common head type on residential Stihl weed eaters. Instead of manually winding the spool, you bump the bottom of the head against the ground while the engine is idling to feed out more line automatically. They’re incredibly convenient for lawn trimming and light edging, and most come pre-wound so you don’t have to load line yourself. Models like the FS 56 RC-E and FS 94 R use AutoCut heads.

PolyCut Heads

PolyCut heads use fixed trimmer line instead of a wound spool, meaning there’s no line to jam or feed incorrectly. The line is held in place by small plastic blades, and when the line wears down, you just replace the entire line insert instead of winding a new spool. They’re ideal for thick, tough weeds and edging along sidewalks, as they’re less likely to jam on dense vegetation. The FS 80 and FS 90 models often come with PolyCut heads.

Preparation Steps Before Replacement

Before you start any work on your Stihl weed eater, follow these preparation steps to stay safe and avoid damaging your equipment: (See Also:How To Wrap A Double String Weed Eater)

1. Disconnect the spark plug wire: Pull the rubber boot off the spark plug to prevent the engine from accidentally starting while you’re working. This is the most important safety step, as an unexpected startup can cause serious injury.
2. Wear protective gear: Put on safety glasses and work gloves to protect your eyes and hands from sharp trimmer line and debris.
3. Clean the area around the head: Use a brush to wipe away grass, dirt, and debris from the head housing and drive shaft. This prevents dirt from getting inside the drive mechanism when you remove the old head.
4. Verify your model and replacement part compatibility: Locate the model number on the label on your weed eater’s shaft or engine housing. Cross-reference it with the replacement head’s compatibility list to make sure it fits. Stihl’s website has a parts lookup tool where you can enter your model number to find the exact replacement head for your machine.
5. Lay the weed eater on a flat surface: Place it on a work mat or old towel to keep it stable and protect the shaft from scratches while you work.

General Step-by-Step Guide to Replace Stihl Weed Eater Head

These general steps work for every Stihl weed eater model, regardless of head type. Follow them first, then refer to the model-specific sections below for head-specific instructions. This is the core process for How to Replace Stihl Weed Eater Head? that applies to all units.

1. Remove old trimmer line from the spool (if applicable): If your old head still has line in it, pull out all the remaining line and dispose of it properly. For loop and AutoCut heads, you can usually open the spool cover to access the spool and remove the line.
2. Loosen the retaining nut or bolt: Use a screwdriver or wrench to turn the retaining nut or bolt counterclockwise to loosen it. Most Stihl heads use a standard 10mm or 13mm nut, but check your manual for the exact size. Don’t remove the nut completely yet – just loosen it enough to free the head.
3. Slide the old head off the drive shaft: Pull the old head straight off the drive shaft. It may be stuck if there’s built-up debris, so wiggle it gently side to side to loosen it. Avoid using excessive force, as this can damage the drive shaft splines.
4. Clean the drive shaft: Use your cleaning brush to wipe away any dirt, grass, or old lubricant from the drive shaft splines. This ensures the new head seats properly and doesn’t wobble during operation.
5. Align and install the new head: Line up the drive fitting on the back of the new head with the splines on the drive shaft. Slide the new head straight onto the shaft until it seats fully against the shaft housing.
6. Tighten the retaining nut or bolt: Turn the nut clockwise to tighten it. If you have a torque wrench, tighten it to the manufacturer’s specified torque (usually 10-15 ft-lbs for most Stihl models). Overtightening can strip the threads or damage the drive shaft, so don’t exceed the recommended torque.
7. Load the new head with trimmer line: Refer to the head-specific sections below for instructions on loading line for loop, AutoCut, or PolyCut heads. Make sure you use the correct line size for your head – using the wrong size can cause jams or poor feeding.
8. Reconnect the spark plug wire: Push the spark plug boot back onto the spark plug until it clicks into place.
9. Test the head: Start the weed eater (make sure the area is clear of people and pets) and let it idle. For AutoCut heads, bump the head on the ground to test the feed mechanism. For loop heads, pull the line out to make sure it releases smoothly. If the line feeds properly and there’s no wobbling, you’re ready to use the weed eater.

How to Replace a Loop Head on Stihl Models

Loop heads require a few extra steps for loading line, but the installation process follows the general steps above. Follow these additional instructions for loop head models:

1. Remove the spool from the new head (if pre-assembled): Some new loop heads come with the spool already installed, but you’ll need to remove it to load line. Turn the spool cover counterclockwise to release it, then pull the spool out of the head housing.
2. Wind the trimmer line onto the spool: Take your trimmer line and thread one end through the eyelet on the spool. Wind the line around the spool in the direction indicated by the arrows on the spool (almost always clockwise for Stihl loop heads). Wind the line evenly, without overlapping, leaving 6-8 inches of line sticking out of the eyelet at the end.
3. Reinstall the spool: Slide the loaded spool back into the head housing, making sure the line eyelet aligns with the outlet hole in the head. Turn the spool cover clockwise to lock it in place. If your model uses a retaining clip to hold the spool, make sure it’s fully seated to avoid the spool falling out during use.
4. Thread the line through the head outlet: Pull the loose end of the line through the outlet hole at the bottom of the head, leaving 6 inches of line exposed for cutting.
5. Test the feed: Pull the line out a few inches to make sure it releases smoothly from the spool. If it sticks, check that you wound the line in the correct direction and that it’s not overlapping on the spool.

How to Replace an AutoCut Head on Stihl Models

AutoCut heads are designed for easy, no-fuss line loading, so the installation process is even simpler than loop heads. Follow these steps for AutoCut models:

1. Check if the new head is pre-wound: Most replacement AutoCut heads come pre-wound with line, so you don’t need to load it yourself. If your new head is not pre-wound, follow the steps below to load it.
2. Open the spool cover: Turn the spool cover at the bottom of the head counterclockwise to release it, then pull the cover off to access the spool.
3. Remove the old spool: Pull the old spool straight out of the head housing. If it’s stuck, wiggle it gently side to side to loosen it.
4. Load the new line (if needed): If you’re loading line onto a new empty spool, thread one end of the line through the eyelet on the spool, then wind the line around the spool in the direction of the arrows printed on the spool (usually clockwise). Wind the line evenly, leaving 6 inches of line sticking out of the eyelet at the end.
5. Reinstall the spool: Slide the loaded spool back into the head housing, making sure the line eyelet aligns with the outlet hole. Snap the spool cover back on and turn it clockwise to lock it in place.
6. Test the bump feed: Start the weed eater and let it idle. Tap the bottom of the head against a hard surface (like a sidewalk or piece of wood) 2-3 times. You should see 2-3 inches of new line feed out each time you bump it. If it doesn’t feed, check that the line is wound in the correct direction and that the bump knob is not damaged.

Common Mistakes to Avoid During Replacement

Even a simple DIY job like replacing your Stihl weed eater head can go wrong if you make these common mistakes. Avoid them to ensure your new head works perfectly and lasts as long as possible:

• Buying an incompatible replacement head: Stihl makes dozens of weed eater models, each with a specific head design. A head that fits one model may not fit another, even if it looks similar. Always check your model number and the replacement head’s compatibility list before purchasing to avoid returns and wasted time.
• Overtightening the retaining nut: It’s tempting to crank the nut as tight as possible to keep the head from coming loose, but overtightening can strip the threads on the drive shaft or crack the head housing. Use a torque wrench if you have one, and tighten to the manufacturer’s recommended 10-15 ft-lbs. The nut should be snug, but not forced.
• Using the wrong trimmer line size: Each Stihl head is designed for a specific line size, usually .080″ or .095″. Using line that’s too thick will jam the feed mechanism, while line that’s too thin will break easily and won’t cut effectively. Check your owner’s manual or the old head’s label for the correct line size.
• Skipping the spark plug disconnect: Forgetting to pull the spark plug wire is one of the most dangerous mistakes you can make. If the engine starts accidentally while you’re working on the head, you could suffer serious lacerations or amputations. Always disconnect the spark plug first, before you touch any part of the weed eater.
• Misaligning the drive fitting: The drive fitting on the back of the head has splines that match the splines on the drive shaft. If you don’t align them properly when installing the new head, the head will wobble during operation, which can damage the drive shaft and cause poor cutting performance. Make sure the splines mesh fully before tightening the retaining nut.
• Skipping the test run: Don’t assume the new head is installed correctly just because you tightened the nut. Always do a test run in a clear, open area to check for wobbling, proper line feed, and any unusual noises before using it for trimming.

Tips for Extending Your New Head’s Lifespan

Replacing your Stihl weed eater head is an investment, so you’ll want to make it last as long as possible. Follow these tips to extend the life of your new head and keep your weed eater running like new:

• Use Stihl-approved trimmer line: Cheap generic trimmer line is more likely to break, jam the feed mechanism, and wear out the spool faster. Stihl’s own round and square trimmer line is designed specifically for their heads, is more durable, and feeds smoothly. For heavy brush, use Stihl’s heavy-duty square line for better cutting power.
• Keep the head clean after each use: Wipe off grass, dirt, and debris from the head housing and spool after every use. Built-up gunk can cause the spool to jam and the feed mechanism to fail. Every few uses, remove the spool and clean out any grass or dirt that’s gotten inside the head housing.
• Lubricate the spool bearing occasionally: Add a drop or two of light machine oil to the spool bearing every 10-15 hours of use. This reduces friction, prevents the spool from seizing, and extends the life of the head.
• Don’t let the line get too short: If your trimmer line wears down to less than 2 inches, replace it instead of forcing the feed mechanism to release more line. Forcing the feed can damage the spool teeth and cause the line to jam.
• Avoid using the weed eater on hard surfaces: Trimming along concrete, gravel, or rocks wears out the trimmer line and spool much faster. If you need to edge along a hard surface, use a dedicated edger or adjust the line length to minimize contact with the hard surface.
• Store the weed eater properly: Keep your weed eater in a dry, sheltered place when not in use. Exposure to rain and snow can rust the head components and cause the spool to seize. If you’re storing it for the winter, remove the trimmer line and clean the head thoroughly before putting it away.

Comparison of Popular Stihl Replacement Heads

If you’re shopping for a replacement head, it’s helpful to compare the most popular Stihl options to find the right one for your needs. Below is a comparison of three top-rated Stihl replacement heads:

As you can see, each head is designed for a specific use case, so choose the one that matches your typical trimming needs. If you’re unsure which head is right for your model, Stihl’s parts lookup tool or a local Stihl dealer can help you find the perfect fit.

Frequently Asked Questions

Here are answers to the most common questions Stihl owners have about replacing their weed eater head: (See Also:How To Remove Poulan Pro Weed Eater Head)

How often do I need to replace my Stihl weed eater head?

Most Stihl weed eater heads last 1-3 years with regular residential use (5-10 hours per week). If you use your weed eater for commercial purposes (20+ hours per week), you may need to replace the head every 6-12 months. Proper maintenance, like cleaning the head regularly and using the correct trimmer line, can extend the life of your head significantly.

Can I use a generic replacement head instead of a Stihl OEM part?

Yes, as long as the generic head is explicitly listed as compatible with your Stihl model. However, Stihl OEM replacement heads are manufactured to tighter tolerances, use higher-quality materials, and are tested to work seamlessly with your weed eater’s drive mechanism. Generic heads are often cheaper, but they may wear out faster, have feeding issues, or even damage your drive shaft if they don’t fit properly. For most owners, the small extra cost of an OEM part is worth the reliability and longevity.

Why is my new Stihl weed eater head wobbling after installation?

A wobbling head is almost always caused by one of two issues: misalignment of the drive splines, or a loose retaining nut. First, double-check that the drive fitting on the back of the head is fully aligned with the drive shaft splines – you should feel it seat fully before tightening the nut. Next, tighten the retaining nut to the correct torque specification (10-15 ft-lbs for most models). If the head still wobbles, check that the drive shaft itself is not bent, which can happen if you hit a rock or hard object while trimming.

Do I need to break in a new weed eater head?

No, Stihl heads do not require a break-in period. However, you should always do a test run after installation to make sure the line feeds smoothly and there’s no wobbling before using it for heavy trimming. Run the weed eater at idle for 30 seconds, then test the feed mechanism (bump for AutoCut, pull for loop heads) to confirm it’s working correctly.

Can I replace just the spool instead of the entire head?

Yes, for most Stihl models, replacement spools are available for purchase separately, and they’re much cheaper than replacing the entire head. This is a good option if the head housing is intact and not cracked, but the spool is broken or the feed mechanism is damaged. Check your model number to find the correct replacement spool for your head. (See Also:How To Put String On Hart Weed Eater)

Conclusion

Replacing your Stihl weed eater head is a simple, quick DIY task that saves you money on repair shop visits and keeps your equipment running at peak performance. By following these instructions for How to Replace Stihl Weed Eater Head? you can tackle the job in 10 minutes or less, even if you have no prior experience with small engine repair.

Remember to always prioritize safety by disconnecting the spark plug before starting work, use the correct replacement parts for your model, and follow the model-specific instructions for your head type. With proper maintenance, your new head will last for years, keeping your lawn and yard looking neat and tidy with minimal effort. If you run into any issues during the replacement process, consult your Stihl owner’s manual or contact Stihl’s customer support team for model-specific guidance.