FS55R Parts Guide: Fix Your Stihl Trimmer Coil (Expert Tips)

Have you ever been out in the yard, ready to tackle that overgrown patch of weeds, only to be met with the frustrating silence of a dead trimmer? I know I have. And more often than not, the culprit is the ignition coil. It’s a small part with a big job – providing the spark that brings your Stihl FS55R trimmer to life. In this guide, I’m going to walk you through everything you need to know to diagnose and fix a faulty coil on your FS55R, turning that frustrating silence back into a productive buzz. I’ll share expert tips, personal experiences, and even some insights I’ve gained from years of working with chainsaws, wood processing, and yes, even the humble weed trimmer. Let’s get started!

FS55R Parts Guide: Fix Your Stihl Trimmer Coil (Expert Tips)

Understanding the Importance of the Ignition Coil

Before we dive into the nitty-gritty of diagnosing and replacing the coil, let’s understand why this little component is so crucial. The ignition coil, also known as a magneto, is responsible for creating the high-voltage spark that ignites the fuel-air mixture in the engine’s cylinder. Without a functioning coil, your engine won’t start, no matter how much you pull that starter cord.

Think of it like the heart of your trimmer – it’s the source of the vital spark that keeps everything running. A healthy coil ensures efficient combustion, optimal performance, and a longer lifespan for your engine. A faulty coil, on the other hand, can lead to hard starting, poor performance, or complete engine failure.

Key Concepts and Definitions

To make sure we’re all on the same page, let’s clarify some key terms:

Ignition Coil (Magneto): The component that generates the high-voltage spark needed for combustion.
Air Gap: The small space between the ignition coil and the flywheel. This gap is critical for proper coil function.
Flywheel: A rotating component connected to the engine’s crankshaft. It contains magnets that interact with the ignition coil to generate electricity.
Spark Plug: A device that delivers the spark to the combustion chamber, igniting the fuel-air mixture.
Ohmmeter (Multimeter): An electronic instrument used to measure electrical resistance, voltage, and current.

Diagnosing a Faulty Ignition Coil

The first step in fixing your Stihl FS55R trimmer is to accurately diagnose the problem. Don’t assume the coil is bad just because the engine won’t start. There are several other potential culprits, such as a clogged fuel filter, a dirty carburetor, or a faulty spark plug.

Here’s a systematic approach to diagnosing a bad ignition coil:

Check the Spark Plug:
- Procedure: Remove the spark plug and inspect it for signs of damage, fouling, or excessive wear. Clean the spark plug with a wire brush or replace it if necessary.
- Spark Test: With the spark plug removed, reattach it to the spark plug wire and hold the plug against the engine block. Pull the starter cord and observe the spark plug gap. A healthy spark plug will produce a strong, blue spark. A weak, yellow spark or no spark at all indicates a potential problem with the ignition system.
- Personal Experience: I once spent hours troubleshooting a non-starting chainsaw, only to discover the spark plug was the issue. It looked fine, but it was internally cracked. A new spark plug solved the problem instantly.
- Inspect the Ignition Coil:
- Visual Inspection: Carefully examine the ignition coil for any signs of physical damage, such as cracks, melted plastic, or corrosion.
- Wiring Check: Ensure that all wires connected to the ignition coil are securely attached and in good condition. Look for frayed wires, loose connections, or damaged insulation.
- Air Gap Measurement: The air gap between the ignition coil and the flywheel is crucial for proper coil function. Consult your Stihl FS55R service manual for the correct air gap specification. Typically, it’s around 0.010-0.014 inches (0.25-0.35 mm). Use a feeler gauge to measure and adjust the air gap if necessary.
- Data and Insights: An improperly adjusted air gap can lead to a weak spark or no spark at all. Too wide, and the magnetic field is too weak. Too narrow, and the coil can physically rub against the flywheel, causing damage.
- Test the Ignition Coil with an Ohmmeter:
- Procedure: Use an ohmmeter to measure the resistance of the ignition coil. Consult your Stihl FS55R service manual for the correct resistance specifications. Compare your readings to the specified values. A reading outside of the acceptable range indicates a faulty coil.
- Primary Coil Resistance: Measure the resistance between the ignition coil’s primary terminal (the one connected to the kill switch) and ground. A typical reading might be around 2-5 ohms.
- Secondary Coil Resistance: Measure the resistance between the spark plug wire terminal and ground. A typical reading might be around 4,000-10,000 ohms.
- Caution: Always disconnect the ignition coil from the engine before testing it with an ohmmeter.
Check the Kill Switch:
- Procedure: Disconnect the kill switch wire from the ignition coil. Try starting the engine. If the engine starts, the kill switch is likely the problem.
- Explanation: The kill switch grounds the ignition coil, preventing it from generating a spark. A faulty kill switch can ground the coil even when it’s in the “run” position.

Replacing the Ignition Coil: A Step-by-Step Guide

Once you’ve confirmed that the ignition coil is faulty, it’s time to replace it. Here’s a detailed step-by-step guide:

Gather Your Tools and Materials:
- New ignition coil (Stihl part number 4144 400 1316 or equivalent)
- Screwdrivers (Phillips and flathead)
- Socket wrench set
- Feeler gauge
- Pliers
- Spark plug wrench
- Work gloves
- Safety glasses
Disconnect the Spark Plug Wire:
- Carefully pull the spark plug wire off the spark plug.
Remove the Engine Cover:
- Use a screwdriver or socket wrench to remove the screws or bolts securing the engine cover.
Locate the Ignition Coil:
- The ignition coil is typically located near the flywheel, mounted to the engine block.
Disconnect the Wires:
- Disconnect the kill switch wire from the ignition coil.
Remove the Old Ignition Coil:
- Use a screwdriver or socket wrench to remove the screws or bolts securing the ignition coil to the engine block.
- Carefully remove the old ignition coil.
Install the New Ignition Coil:
- Position the new ignition coil on the engine block, aligning the mounting holes.
- Secure the ignition coil with the screws or bolts. Tighten them securely, but don’t overtighten.
Set the Air Gap:
- This is a critical step! Use a feeler gauge to set the air gap between the ignition coil and the flywheel. Consult your Stihl FS55R service manual for the correct air gap specification. Typically, it’s around 0.010-0.014 inches (0.25-0.35 mm).
- Procedure: Loosen the mounting screws slightly. Insert the feeler gauge between the ignition coil and the flywheel. Rotate the flywheel until the magnets are aligned with the coil. Gently push the coil against the feeler gauge and tighten the mounting screws. Remove the feeler gauge.
- Personal Story: I once rushed this step and didn’t set the air gap correctly. The trimmer ran poorly and eventually stopped working altogether. I had to remove the coil and reset the air gap to get it running properly again.
- Strategic Advantage: Setting the air gap correctly ensures optimal coil performance and prevents premature wear.
Reconnect the Wires:
- Reconnect the kill switch wire to the ignition coil.
Reinstall the Engine Cover:
- Secure the engine cover with the screws or bolts.
Reconnect the Spark Plug Wire:
- Carefully push the spark plug wire onto the spark plug.
Test the Engine:
- Prime the engine and pull the starter cord. The engine should start.

Troubleshooting After Coil Replacement

Even after replacing the ignition coil, you might encounter some issues. Here are a few common problems and their solutions:

Engine Still Won’t Start:
- Possible Causes: Incorrect air gap, faulty spark plug, clogged fuel filter, dirty carburetor, low compression.
- Troubleshooting Steps: Double-check the air gap. Replace the spark plug. Clean or replace the fuel filter. Clean the carburetor. Check the engine compression.
- Engine Runs Poorly:
- Possible Causes: Incorrect air gap, faulty spark plug, dirty carburetor, incorrect carburetor settings.
- Troubleshooting Steps: Double-check the air gap. Replace the spark plug. Clean the carburetor. Adjust the carburetor settings.
- Engine Starts But Stalls:
- Possible Causes: Dirty carburetor, incorrect carburetor settings, clogged fuel filter, air leak.
- Troubleshooting Steps: Clean the carburetor. Adjust the carburetor settings. Clean or replace the fuel filter. Check for air leaks around the carburetor and intake manifold.

Understanding Wood Processing and Firewood Preparation: A Holistic View

While we’ve focused on the ignition coil, it’s important to understand how this repair fits into the bigger picture of wood processing and firewood preparation. Your Stihl FS55R is likely used to clear brush, trim around trees, and maintain a clean worksite, all of which are essential for safe and efficient wood processing.

Felling Techniques and Tool Specifications:

When felling trees, safety is paramount. Here’s a brief overview of key techniques and tools:

Felling Axe vs. Chainsaw: While a felling axe can be used for smaller trees, a chainsaw is generally preferred for larger trees due to its speed and efficiency.
Chainsaw Specifications: For felling trees, I typically use a chainsaw with a bar length of at least 18 inches. My preferred model is a Stihl MS 261 C-M, known for its reliability and power.
Felling Cuts: The bore cut, the undercut, and the back cut are essential for controlling the direction of the fall.
Safety Gear: Always wear a helmet, eye protection, hearing protection, gloves, and chainsaw chaps when felling trees.
Case Study: On a recent project involving clearing a wooded area for a new building site, I used a combination of felling techniques and a Stihl MS 462 R C-M chainsaw to safely and efficiently fell several large oak trees. Careful planning and precise cuts were crucial to avoid damaging nearby structures.

Debarking Logs:

Debarking logs is often necessary for certain wood processing applications, such as milling lumber or preparing logs for construction.

Tools: A drawknife, a debarking spud, or a log peeler can be used to remove the bark.
Benefits: Debarking prevents insect infestation and decay, and it can also improve the appearance of the wood.
Data and Insights: Debarking green wood is generally easier than debarking seasoned wood, as the bark is more tightly attached to seasoned wood.

Splitting Firewood:

Splitting firewood can be a physically demanding task, but it’s essential for preparing firewood for burning.

Tools: A splitting axe, a maul, or a hydraulic log splitter can be used to split firewood.
Hydraulic Log Splitter: A hydraulic log splitter significantly reduces the physical effort required to split firewood. I use a 25-ton hydraulic log splitter, which can handle logs up to 24 inches in diameter.
Wood Type Selection: Different types of wood have different splitting characteristics. Hardwoods like oak and maple are more difficult to split than softwoods like pine and fir.
Moisture Content Targets: Firewood should be seasoned to a moisture content of 20% or less before burning. This ensures efficient combustion and reduces the risk of creosote buildup in the chimney.

Firewood Stacking:

Proper firewood stacking is essential for efficient drying and storage.

Methods: The most common methods are the rick method, the holz hausen method, and the linear stack method.
Strategic Advantages: Stacking firewood off the ground and allowing for good air circulation promotes faster drying.
Timing Estimates: Firewood typically takes 6-12 months to season properly, depending on the type of wood, the climate, and the stacking method.
Case Study: I experimented with different firewood stacking methods in my own backyard. I found that the holz hausen method, which involves stacking the firewood in a circular pattern, provided the best air circulation and the fastest drying time.

Green Wood vs. Seasoned Wood:

Understanding the difference between green wood and seasoned wood is crucial for successful wood processing and firewood preparation.

Green Wood: Freshly cut wood with a high moisture content. It’s heavier than seasoned wood and more difficult to burn.
Seasoned Wood: Wood that has been dried to a moisture content of 20% or less. It’s lighter than green wood and burns more efficiently.
Benefits of Seasoned Wood: Burns hotter, produces less smoke, and reduces the risk of creosote buildup.

Safety Considerations

Working with chainsaws, axes, and log splitters can be dangerous. Always follow these safety precautions:

Wear appropriate safety gear, including a helmet, eye protection, hearing protection, gloves, and chainsaw chaps.
Read and understand the operating manuals for all tools and equipment.
Inspect your tools and equipment before each use.
Keep your tools sharp and in good working condition.
Work in a clear and well-ventilated area.
Never work alone.
Take frequent breaks to avoid fatigue.
Be aware of your surroundings and potential hazards.

Strategic Insights and Tactical Instructions

Here are some strategic insights and tactical instructions to help you with your wood processing and firewood preparation projects:

Invest in Quality Tools: High-quality tools will last longer and perform better than cheaper alternatives.
Maintain Your Tools Regularly: Regular maintenance will prolong the life of your tools and ensure they operate safely and efficiently.
Plan Your Projects Carefully: Planning ahead will help you avoid mistakes and ensure that you have the right tools and materials for the job.
Learn from Experienced Professionals: Seek advice from experienced professionals or take a wood processing or firewood preparation course.
Practice Safety at All Times: Safety should always be your top priority.

Next Steps and Implementation Guidance

Now that you have a better understanding of how to diagnose and fix a faulty ignition coil on your Stihl FS55R trimmer, as well as the basics of wood processing and firewood preparation, it’s time to put your knowledge into practice.

Here are some practical next steps and implementation guidance:

Diagnose and Repair Your Stihl FS55R Trimmer: If your trimmer is not starting or running properly, follow the steps outlined in this guide to diagnose and fix the problem.
Start a Small Wood Processing Project: Choose a small wood processing project, such as building a birdhouse or a small garden bed. This will give you an opportunity to practice your skills and learn from your mistakes.
Prepare Firewood for the Winter: If you have a wood-burning stove or fireplace, start preparing firewood for the winter. This will help you save money on heating costs and enjoy the warmth of a wood fire.
Take a Wood Processing or Firewood Preparation Course: Consider taking a wood processing or firewood preparation course to learn more about these topics and improve your skills.
Connect with Other Woodworkers and Firewood Enthusiasts: Join a local woodworking club or online forum to connect with other woodworkers and firewood enthusiasts. This will give you an opportunity to share your experiences, learn from others, and get advice on your projects.

Conclusion

Fixing a faulty ignition coil on your Stihl FS55R trimmer is a manageable task with the right knowledge and tools. By following the steps outlined in this guide, you can save yourself time and money by repairing your trimmer yourself. Furthermore, understanding the broader context of wood processing and firewood preparation will help you maintain a safe and efficient worksite. Remember to always prioritize safety and invest in quality tools. With practice and patience, you can become a skilled woodworker and firewood enthusiast. Now, get out there and get to work!

FS55R Parts Guide: Fix Your Stihl Trimmer Coil (Expert Tips)