Stihl Ignition Coil Specs Explained (5 Pro Testing Tips)

Why Understanding Your Stihl Ignition Coil Matters

Before diving into the technical details, let’s emphasize why this knowledge is so valuable. Chainsaws are indispensable tools for anyone involved in wood processing, logging, or firewood preparation. From felling trees to cutting firewood to size, they are vital for cutting efficiency. A well-maintained chainsaw not only improves productivity but also enhances safety. A chainsaw that starts reliably and runs smoothly is less likely to malfunction during operation, reducing the risk of accidents.

Imagine this: you’re deep in the woods, a good distance from your truck, and the sun is setting. You’ve got a hefty oak down and need to buck it into manageable lengths. But your chainsaw sputters, refuses to start, and you suspect the ignition coil. Knowing how to diagnose and potentially fix the issue on the spot can save you a long, frustrating walk back in the dark. That’s the power of understanding your chainsaw’s ignition system.

Ignition Coils: The Spark of Life

At its core, the ignition coil is a simple device that transforms low-voltage electricity from the chainsaw’s magneto into the high-voltage spark needed to ignite the air-fuel mixture in the cylinder. It’s essentially a step-up transformer.

Here’s a breakdown:

Magneto: As the engine’s flywheel rotates, magnets embedded within it pass by the ignition coil, generating a small electrical current.
Primary Winding: This low-voltage current flows through the primary winding of the ignition coil.
Secondary Winding: The primary winding is wrapped around a core, which is also surrounded by the secondary winding. The secondary winding has significantly more turns than the primary winding.
Voltage Transformation: When the magnets pass the coil, the magnetic field collapses rapidly, inducing a much higher voltage in the secondary winding. This voltage can be anywhere from 15,000 to 30,000 volts.
Spark Plug: This high-voltage electricity is then discharged through the spark plug, creating a spark that ignites the air-fuel mixture, driving the piston and starting the combustion cycle.

Common Ignition Coil Problems

Ignition coils are robust components, but they’re not immune to failure. Here are some common issues I’ve encountered:

Cracked or Damaged Housing: Physical damage to the coil’s housing can expose the internal windings to moisture and debris, leading to short circuits and failure. I once dropped a log directly onto my Stihl MS 290, cracking the coil housing. It ran for about 10 minutes and then completely died.
Short Circuits: Over time, the insulation on the windings can break down, causing short circuits. This reduces the coil’s ability to generate sufficient voltage.
Open Circuits: A break in the windings can completely prevent current flow, rendering the coil useless.
Heat Damage: Excessive heat can damage the coil’s internal components, leading to premature failure. This is especially common in older saws or those that are run for extended periods at high RPMs.
Air Gap Issues: The air gap between the ignition coil and the flywheel magnets is crucial. Too much or too little gap can prevent the coil from generating sufficient voltage. I’ve found that the recommended air gap for most Stihl chainsaws is typically between 0.010″ and 0.014″ (0.25mm to 0.36mm). Use a business card or a feeler gauge to set the air gap accurately.
Loose Connections: Corroded or loose wiring connections can disrupt the flow of electricity to and from the coil.

Symptoms of a Failing Ignition Coil

Recognizing the symptoms of a failing ignition coil is the first step in diagnosing the problem. Here are some telltale signs:

Hard Starting: The chainsaw is difficult to start, requiring multiple pulls or extended cranking.
Intermittent Starting: The chainsaw starts sometimes, but not others.
Rough Running: The engine runs roughly, with misfires or a lack of power.
Engine Stalling: The engine stalls frequently, especially when under load.
No Spark: The most obvious symptom – the spark plug is not producing a spark.

Pro Testing Tips: Diagnosing Your Stihl Ignition Coil

Now, let’s get to the heart of the matter: how to test your Stihl ignition coil. I’m going to share five professional testing tips that I’ve learned over the years.

Important Safety Note: Before performing any tests on your chainsaw, disconnect the spark plug wire and ground it to the engine to prevent accidental starting. Wear appropriate safety glasses and gloves.

Tip 1: Visual Inspection

The first step is always a thorough visual inspection. Look for any signs of physical damage to the coil housing, such as cracks, chips, or melted plastic. Check the wiring connections for corrosion, looseness, or fraying. Ensure the spark plug wire is securely attached to the coil and the spark plug. Sometimes, a simple visual inspection can reveal the problem immediately.

I recall a time when my Stihl MS 170 suddenly refused to start. After a quick visual inspection, I noticed a small crack in the coil housing, right near the spark plug wire connection. Moisture had seeped into the crack, causing a short circuit. A new ignition coil solved the problem instantly.

Tip 2: Spark Test

The spark test is a basic but essential test to determine if the ignition coil is producing a spark.

Remove the Spark Plug: Carefully remove the spark plug from the cylinder head.
Reattach the Spark Plug Wire: Reattach the spark plug wire to the spark plug.
Ground the Spark Plug: Hold the spark plug against a clean, unpainted metal surface on the engine (e.g., the cylinder head). This provides a ground for the spark.
Pull the Starter Rope: Firmly pull the starter rope. Observe the spark plug gap.

If the ignition system is working correctly, you should see a strong, blue spark jumping across the spark plug gap. A weak, yellow spark or no spark at all indicates a problem with the ignition system, which could be the ignition coil, the spark plug itself, or the wiring.

Important Considerations for the Spark Test:

Spark Plug Condition: A fouled or worn spark plug can prevent a good spark, even if the ignition coil is functioning properly. Replace the spark plug with a new one before proceeding with further testing. I typically use NGK or Champion spark plugs in my Stihl chainsaws.
Grounding: Ensure the spark plug is properly grounded to a clean metal surface. A poor ground connection can give a false negative result.
Lighting: Perform the spark test in a dimly lit area to make it easier to see the spark.

Tip 3: Air Gap Measurement

As mentioned earlier, the air gap between the ignition coil and the flywheel magnets is critical. An incorrect air gap can significantly reduce the coil’s ability to generate a spark.

Locate the Air Gap: The air gap is the small space between the ignition coil and the magnets on the flywheel.
Use a Feeler Gauge or Business Card: Insert a feeler gauge or a folded business card into the air gap. The recommended air gap for most Stihl chainsaws is between 0.010″ and 0.014″ (0.25mm to 0.36mm).
Adjust the Coil Position: If the air gap is not within the specified range, loosen the screws that hold the ignition coil in place and adjust its position until the gap is correct. Then, tighten the screws securely.

I’ve found that using a business card is a convenient way to set the air gap in the field. A standard business card is typically around 0.012″ thick, which falls within the recommended range for most Stihl chainsaws.

Tip 4: Resistance Testing with a Multimeter

A multimeter can be used to measure the resistance of the primary and secondary windings of the ignition coil. This test can help identify short circuits or open circuits within the coil.

Disconnect the Ignition Coil: Disconnect the ignition coil from the chainsaw’s wiring harness.
Set the Multimeter: Set the multimeter to the resistance (Ohms) setting.
Measure Primary Winding Resistance: Place one probe of the multimeter on the primary winding terminal (usually a small terminal) and the other probe on the coil’s ground terminal. Refer to your Stihl chainsaw’s service manual for the specific resistance values for your model.
Measure Secondary Winding Resistance: Place one probe of the multimeter on the spark plug wire terminal and the other probe on the coil’s ground terminal. Again, refer to your service manual for the specified resistance values.

Interpreting the Results:

Zero Resistance: Indicates a short circuit.
Infinite Resistance: Indicates an open circuit.
Resistance Outside the Specified Range: Suggests a problem with the coil’s windings.

Important Considerations for Resistance Testing:

Service Manual: Always refer to your Stihl chainsaw’s service manual for the correct resistance values for your specific model. These values can vary depending on the coil type and the chainsaw model.
Multimeter Calibration: Ensure your multimeter is properly calibrated for accurate readings.
Temperature: Temperature can affect resistance readings. Perform the test at room temperature for consistent results.

Tip 5: The “Jump Spark” Test (Advanced)

This test is a bit more advanced and requires caution. It involves observing the spark’s ability to “jump” a wider gap than the spark plug gap. This can help identify a weak ignition coil that might produce a spark at the spark plug but is not strong enough for reliable operation.

Remove the Spark Plug: Remove the spark plug from the cylinder head.
Reattach the Spark Plug Wire: Reattach the spark plug wire to the spark plug.
Increase the Gap: Instead of grounding the spark plug directly to the engine, hold it slightly away from the metal surface, creating a larger gap (e.g., 1/4 inch or 6mm).
Pull the Starter Rope: Firmly pull the starter rope.

If the ignition coil is healthy, you should still see a spark jumping across the larger gap. If the spark is weak or non-existent, it indicates that the coil is not producing sufficient voltage and needs to be replaced.

Safety Precautions for the Jump Spark Test:

Insulated Pliers: Use insulated pliers to hold the spark plug to avoid electrical shock.
Dry Environment: Perform the test in a dry environment to minimize the risk of electrical shock.
Avoid Contact with Metal: Avoid touching any metal parts of the chainsaw while performing the test.

Case Study: Diagnosing a Stihl MS 271 Ignition Coil Failure

I recently encountered a problem with my Stihl MS 271 chainsaw. It was becoming increasingly difficult to start, and when it did start, it ran roughly and stalled frequently. I suspected a problem with the ignition system, so I decided to perform a series of tests to diagnose the issue.

Visual Inspection: I started with a visual inspection of the ignition coil. I didn’t find any obvious signs of physical damage, such as cracks or broken wires.
Spark Test: I performed a spark test, and the spark was weak and yellow. This confirmed that there was a problem with the ignition system.
Air Gap Measurement: I checked the air gap between the ignition coil and the flywheel magnets. It was within the specified range of 0.012 inches.
Resistance Testing: I used a multimeter to measure the resistance of the primary and secondary windings of the ignition coil. The resistance of the secondary winding was significantly higher than the value specified in the service manual.
Jump Spark Test: Finally, I performed the jump spark test. The spark was unable to jump a gap larger than the spark plug gap, further confirming that the ignition coil was weak.

Based on these tests, I concluded that the ignition coil was faulty and needed to be replaced. I ordered a new ignition coil online and installed it on my Stihl MS 271. After replacing the ignition coil, the chainsaw started easily and ran smoothly. The problem was solved.

Choosing a Replacement Ignition Coil

If your testing reveals that your ignition coil needs to be replaced, it’s essential to choose the right replacement. Here are some factors to consider:

OEM vs. Aftermarket: You can choose between Original Equipment Manufacturer (OEM) ignition coils and aftermarket coils. OEM coils are manufactured by Stihl and are generally considered to be of higher quality and more reliable. Aftermarket coils are manufactured by third-party companies and are often less expensive. I generally prefer OEM coils for critical components like the ignition coil.
Compatibility: Ensure the replacement ignition coil is compatible with your specific Stihl chainsaw model. Refer to your chainsaw’s parts manual or the manufacturer’s website to find the correct part number.
Warranty: Look for a replacement ignition coil that comes with a warranty. This will protect you in case the coil fails prematurely.

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

Replacing an ignition coil is a relatively straightforward process, but it’s essential to follow the steps carefully to avoid damaging your chainsaw.

Safety First: Disconnect the spark plug wire and ground it to the engine.
Remove the Starter Housing: Remove the starter housing to access the ignition coil. This usually involves removing a few screws.
Disconnect the Wiring: Disconnect the wiring from the ignition coil.
Remove the Old Coil: Remove the screws that hold the ignition coil in place and carefully remove the old coil.
Install the New Coil: Install the new ignition coil in the same position as the old coil.
Connect the Wiring: Connect the wiring to the new ignition coil.
Set the Air Gap: Set the air gap between the ignition coil and the flywheel magnets using a feeler gauge or business card.
Reinstall the Starter Housing: Reinstall the starter housing.
Connect the Spark Plug Wire: Connect the spark plug wire to the spark plug.
Test the Chainsaw: Start the chainsaw and test it to ensure it is running properly.

Preventative Maintenance for Your Ignition Coil

While ignition coils can fail, there are steps you can take to prolong their lifespan and prevent problems.

Keep the Chainsaw Clean: Regularly clean your chainsaw to remove dirt, debris, and moisture. This will help prevent corrosion and damage to the ignition coil.
Maintain Proper Air Gap: Check the air gap between the ignition coil and the flywheel magnets periodically and adjust it as needed.
Use Fresh Fuel: Use fresh, high-quality fuel and oil mixture. Old or contaminated fuel can cause engine problems, which can put stress on the ignition coil.
Avoid Overheating: Avoid running your chainsaw for extended periods at high RPMs. Overheating can damage the ignition coil.
Store the Chainsaw Properly: When storing your chainsaw, keep it in a dry, protected location. This will help prevent corrosion and damage to the ignition coil.

The Importance of Proper Fuel and Oil Mix

I can’t stress enough the importance of using the correct fuel and oil mixture in your Stihl chainsaw. Using the wrong mixture can lead to a variety of problems, including:

Engine Seizure: Insufficient lubrication can cause the piston to seize in the cylinder, resulting in catastrophic engine damage.
Carbon Buildup: Using too much oil can lead to carbon buildup in the combustion chamber, which can reduce engine performance and cause starting problems.
Ignition Coil Stress: A poorly running engine puts extra stress on the ignition coil, potentially shortening its lifespan.

Stihl recommends a fuel-to-oil ratio of 50:1 for most of their chainsaws. This means that for every 50 parts of gasoline, you should add 1 part of two-stroke oil. Always use a high-quality two-stroke oil that is specifically designed for air-cooled engines. I personally prefer Stihl’s own two-stroke oil, but other reputable brands like Echo and Husqvarna are also good choices.

Chainsaw Safety: A Constant Priority

Throughout this guide, I’ve emphasized the importance of safety. Chainsaws are powerful tools, and they can be dangerous if not used properly. Always wear appropriate safety gear, including:

Eye Protection: Safety glasses or a face shield to protect your eyes from flying debris.
Hearing Protection: Earplugs or earmuffs to protect your hearing from the loud noise of the chainsaw.
Gloves: Heavy-duty gloves to protect your hands from cuts and abrasions.
Chaps: Chainsaw chaps to protect your legs from accidental cuts.
Boots: Steel-toed boots with good ankle support.

Always follow the manufacturer’s instructions for operating and maintaining your chainsaw. Never operate a chainsaw if you are tired, distracted, or under the influence of drugs or alcohol.

Dealing with Green Wood vs. Seasoned Wood

As someone who processes a lot of wood, I know that the type of wood you’re cutting can affect your chainsaw’s performance. Green wood, which is freshly cut wood, is much heavier and more difficult to cut than seasoned wood, which has been allowed to dry.

Green Wood: Green wood has a high moisture content, which makes it harder to cut and can cause the chainsaw chain to bind. It also tends to produce more sawdust, which can clog the chainsaw’s air filter and cooling fins.
Seasoned Wood: Seasoned wood has a lower moisture content, which makes it easier to cut and reduces the risk of binding. It also produces less sawdust.

When cutting green wood, it’s important to keep your chainsaw chain sharp and to clean the air filter and cooling fins frequently. You may also need to adjust your cutting technique to avoid binding. Seasoned wood is generally easier to cut, but it’s still important to maintain your chainsaw properly.

Strategic Considerations for Firewood Preparation

Preparing firewood efficiently requires more than just a sharp chainsaw. Strategic planning can save you time and effort.

Wood Selection: Choose wood species that are known for their high heat output and ease of splitting. Oak, maple, and birch are excellent choices.
Felling Techniques: Use proper felling techniques to ensure the tree falls in a safe direction and minimizes the risk of damage to the surrounding environment.
Bucking Techniques: Buck the logs into manageable lengths that are appropriate for your wood stove or fireplace. I typically buck my logs into 16-inch lengths.
Splitting Techniques: Use a log splitter to split the firewood. Hydraulic log splitters are the most efficient, but manual log splitters are also a viable option.
Stacking Techniques: Stack the firewood in a way that allows for good air circulation. This will help the wood dry more quickly. I prefer to stack my firewood in rows, with gaps between the rows for ventilation.

Costs Associated with Wood Processing

It’s important to consider the costs associated with wood processing when planning your projects. These costs can include:

Chainsaw Purchase and Maintenance: The cost of purchasing a chainsaw, as well as the ongoing costs of maintenance, such as chain sharpening, oil, and fuel.
Log Splitter Purchase or Rental: The cost of purchasing or renting a log splitter.
Fuel and Oil: The cost of fuel and oil for the chainsaw and log splitter.
Safety Gear: The cost of safety gear, such as eye protection, hearing protection, gloves, and chaps.
Time: The value of your time spent processing wood.

By carefully considering these costs, you can make informed decisions about your wood processing projects and ensure that they are cost-effective.

Inspect Your Chainsaw: Start by inspecting your own Stihl chainsaw. Check the ignition coil for any signs of damage or wear.
Perform a Spark Test: Perform a spark test to ensure that your ignition coil is producing a strong spark.
Measure the Air Gap: Measure the air gap between the ignition coil and the flywheel magnets.
Consult Your Service Manual: Refer to your Stihl chainsaw’s service manual for specific information about your model.
Practice Safe Chainsaw Operation: Always practice safe chainsaw operation. Wear appropriate safety gear and follow the manufacturer’s instructions.

By taking these steps, you can ensure that your Stihl chainsaw is running smoothly and reliably, allowing you to tackle your wood processing projects with confidence. And remember, a little knowledge and preventative maintenance can go a long way in keeping your chainsaw running for years to come.

Stihl Ignition Coil Specs Explained (5 Pro Testing Tips)