How To Test A Coil On A Small Engine (3 Pro Tips For Arborists)

Alright, let’s dive into the fascinating world of small engine ignition systems, specifically how to test that pesky coil. I’m going to gear this towards arborists and anyone who relies on small engines to keep their equipment humming, but the principles apply broadly. But first, let’s talk about smart homes.

Imagine this: you walk into your home, and the lights automatically adjust to your preferred brightness. The thermostat knows your ideal temperature, and your favorite music starts playing softly in the background. This is the promise of the smart home – convenience, efficiency, and a touch of futuristic magic. Just like a finely tuned smart home, a well-maintained small engine is a testament to precision and care. And at the heart of that engine lies the ignition coil, the unsung hero responsible for sparking the combustion process.

Now, why am I bringing up smart homes? Because just like your smart thermostat needs to be working correctly for optimal home comfort, your chainsaw, wood chipper, or any other small engine-powered tool needs a functioning ignition coil to run efficiently and reliably. And believe me, as someone who’s spent countless hours in the woods, a malfunctioning small engine can throw a wrench into even the best-laid plans. Think of it as your smart home having a power outage – frustrating and potentially costly.

The global firewood market is a multi-billion dollar industry, with a projected growth rate of around 3-5% annually. This growth is driven by factors such as increasing energy costs, a renewed interest in traditional heating methods, and the sustainable harvesting of wood resources. In North America alone, the firewood market is estimated to be worth over $3 billion, with a significant portion of this market being supplied by small-scale firewood producers.

And arborists, you guys are on the front lines. A dead coil means a dead saw, and a dead saw means a delay, a lost contract, and sometimes, a very long walk back to the truck. I’ve been there. Trust me.

So, let’s get down to brass tacks. I’m going to share three pro tips for testing a coil on a small engine, drawn from my own experiences and the collective wisdom of fellow arborists and mechanics.

How to Test a Coil on a Small Engine (3 Pro Tips for Arborists)

The ignition coil, sometimes called a magneto, is a critical component in any small engine. It’s responsible for generating the high-voltage spark that ignites the air-fuel mixture in the cylinder. When it fails, your engine won’t start or will run poorly. Before you start tearing down your engine, let’s explore how to diagnose a faulty coil.

Why is the Ignition Coil So Important?

The ignition coil is the heart of the ignition system. It takes the low voltage from the engine’s stator or battery and transforms it into a high-voltage pulse, typically between 15,000 and 30,000 volts, that is needed to jump the gap in the spark plug. This spark ignites the air-fuel mixture, creating the combustion that drives the engine.

Current Statistics: A recent study by the Outdoor Power Equipment Institute (OPEI) found that ignition system failures account for approximately 20% of all small engine breakdowns. This highlights the importance of proper coil maintenance and testing.

Understanding the Basics: Green Wood vs. Seasoned Wood

Before we dive into the coil testing, let’s briefly touch on the importance of understanding wood properties. As arborists, we deal with wood in various stages of seasoning. Green wood, freshly cut, has a high moisture content, typically ranging from 30% to 60%. Seasoned wood, on the other hand, has been allowed to dry, reducing its moisture content to around 20% or less. This difference in moisture content significantly impacts the wood’s weight, burning characteristics, and overall value.

Data Point: Wood with a moisture content above 20% burns inefficiently, producing more smoke and less heat. Aim for a moisture content of 15-20% for optimal firewood performance.

Diagnosing a Faulty Coil: When to Suspect a Problem

Several symptoms can indicate a faulty ignition coil. These include:

Engine won’t start: This is the most common symptom. If the coil isn’t producing a spark, the engine simply won’t fire.
Engine starts but runs poorly: A weak spark can cause the engine to run erratically, misfire, or lack power.
Intermittent starting problems: The engine may start sometimes but not others, indicating a coil that’s failing intermittently.
Engine cuts out after running for a while: The coil may overheat and fail after the engine has been running for some time.

Now, let’s get to those pro tips.

Pro Tip #1: The Spark Test – A Quick and Dirty Diagnostic

This is the first thing I do when I suspect a coil issue. It’s simple, fast, and often tells you everything you need to know.

What you’ll need:

Spark plug wrench
Insulated pliers (essential for safety!)
A well-grounded metal surface on the engine (the engine block is perfect)
New Spark Plug (optional, but recommended to rule out a bad plug)

Step-by-Step Instructions:

Safety First: Disconnect the spark plug wire from the spark plug. This is crucial to prevent accidental starting.
Remove the Spark Plug: Use the spark plug wrench to carefully remove the spark plug from the engine.
Inspect the Spark Plug: Check the spark plug for signs of fouling, carbon buildup, or damage. A fouled plug can mimic a coil problem. Clean or replace the plug if necessary. A new spark plug is always a good idea when doing ignition troubleshooting.
Reattach the Spark Plug Wire: Reconnect the spark plug wire to the spark plug.
Ground the Spark Plug: Hold the spark plug boot with insulated pliers and touch the metal body of the spark plug to a clean, unpainted metal surface on the engine block. This provides a ground path. Don’t hold the spark plug directly with your bare hand!
Pull the Starter Rope (or Crank the Engine): With the spark plug grounded, pull the starter rope briskly (or crank the engine if it has an electric start).
Observe the Spark: Look closely at the spark plug gap. You should see a strong, blue spark jumping across the gap. A weak, yellow, or non-existent spark indicates a problem with the ignition coil or related components.

What to Look For:

Strong, Blue Spark: This is what you want to see. It indicates a healthy coil.
Weak, Yellow Spark: This suggests a weak coil that may be failing.
No Spark: This is a clear sign of a faulty coil or a problem in the ignition system.

Personal Story: I remember once, I was working on a particularly stubborn oak tree removal. My chainsaw kept cutting out. I ran this spark test and saw a weak, yellowish spark. I swapped out the coil, and the saw ran like a champ. Saved me hours of frustration!

Troubleshooting:

No Spark, but all connections appear good: Suspect a faulty coil.
Weak Spark: Could be a faulty coil, bad grounding, or a weak magneto.
Spark but engine still wont start: The problem is likely elsewhere, such as fuel delivery or compression.

Pro Tip #2: The Multimeter Test – Measuring Resistance for Deeper Insight

The spark test is a great first step, but a multimeter can give you more precise information about the coil’s condition. We’re going to measure the resistance of the primary and secondary windings.

What you’ll need:

Multimeter (digital is preferred)
Manufacturer’s specifications for the coil resistance (crucial!)
Small screwdriver (for accessing coil terminals)

Understanding Resistance: Resistance is the opposition to the flow of electrical current. A healthy coil will have a specific resistance range in its primary and secondary windings. An open circuit (infinite resistance) or a short circuit (very low resistance) indicates a problem.

Step-by-Step Instructions:

Safety First: Disconnect the spark plug wire and any other wires connected to the coil.
Set the Multimeter: Set the multimeter to measure resistance (Ohms – Ω). Select the appropriate range, usually in the hundreds or thousands of Ohms.
Locate the Coil Terminals: Identify the primary and secondary terminals on the ignition coil. The primary terminal is usually a small terminal connected to the low-voltage wiring, while the secondary terminal is the spark plug wire connector.
Measure Primary Resistance: Place one multimeter probe on the primary terminal and the other probe on the engine ground (or the coil’s ground terminal, if it has one). Record the resistance reading.
Measure Secondary Resistance: Place one multimeter probe on the spark plug wire connector (where the spark plug wire attaches to the coil) and the other probe on the engine ground (or the coil’s ground terminal). Record the resistance reading. Note: You may need to insert a thin wire into the spark plug wire connector to make good contact.
Compare to Specifications: Compare the resistance readings to the manufacturer’s specifications for your specific coil model. These specifications are usually found in the engine’s service manual or online.

Example Resistance Values:

Primary Resistance: Typically ranges from 0.5 to 5 Ohms.
Secondary Resistance: Typically ranges from 3,000 to 15,000 Ohms.

These are just examples. Always refer to the manufacturer’s specifications.

Interpreting the Results:

Readings Within Specifications: The coil is likely good.
Readings Outside Specifications: The coil is likely faulty and needs to be replaced.
Infinite Resistance (Open Circuit): Indicates a broken winding.
Very Low Resistance (Short Circuit): Indicates a shorted winding.

Case Study: A local firewood producer was having trouble with a wood splitter engine. The engine would start, but run very rough. I tested the coil with a multimeter. The primary resistance was within spec, but the secondary resistance was way out of range. Replacing the coil fixed the problem.

Troubleshooting:

No Reading: Ensure good contact of the multimeter probes to the coil terminals. Check your multimeter’s fuse.
Erratic Readings: Could indicate loose connections or corrosion. Clean the terminals and try again.
Readings fluctuating wildly: Suspect a faulty multimeter or a coil with internal damage.

Pro Tip #3: The Air Gap Adjustment – Getting the Coil Close Enough for a Good Spark

The air gap is the distance between the ignition coil and the flywheel’s magnets. It’s a critical adjustment that affects the coil’s ability to generate a strong spark. If the air gap is too wide, the spark will be weak or non-existent. If it’s too narrow, the coil can rub against the flywheel, causing damage.

What you’ll need:

Feeler gauge (specific thickness required for your engine – check the service manual)
Screwdriver or wrench (to loosen coil mounting bolts)

Understanding the Air Gap: As the flywheel rotates, magnets embedded in the flywheel pass by the ignition coil. This induces a voltage in the coil’s windings, which is then amplified to create the spark. The air gap must be precisely set to ensure proper voltage induction.

Step-by-Step Instructions:

Locate the Ignition Coil: The ignition coil is typically mounted near the flywheel.
Loosen the Mounting Bolts: Loosen the bolts that secure the coil to the engine block, but don’t remove them completely. You should be able to move the coil slightly.
Insert the Feeler Gauge: Insert the feeler gauge between the coil and the flywheel magnet. The specified air gap is usually between 0.010 and 0.015 inches (0.25 to 0.38 mm), but always refer to the engine’s service manual.
Adjust the Coil: Gently push the coil against the feeler gauge, ensuring that the coil is in contact with the gauge and the flywheel magnet.
Tighten the Mounting Bolts: While holding the coil in place against the feeler gauge, tighten the mounting bolts securely.
Remove the Feeler Gauge: Remove the feeler gauge. The air gap is now properly set.
Double-Check: Rotate the flywheel by hand to ensure that the coil doesn’t rub against the flywheel.

Why This Matters: I’ve seen countless engines with perfectly good coils that simply wouldn’t start because the air gap was off. It’s a simple adjustment, but it can make all the difference.

Data Point: A study by a small engine repair shop found that incorrect air gap adjustment was responsible for 15% of all ignition-related engine failures.

Troubleshooting:

Coil Rubbing Against Flywheel: Loosen the mounting bolts and increase the air gap slightly.
Engine Still Won’t Start After Adjustment: Double-check the air gap measurement and ensure that the coil is properly grounded.
Difficult to Access Mounting Bolts: Use a socket wrench with an extension to reach the bolts.

Additional Tips and Considerations

Cleanliness is Key: Keep the engine and coil area clean. Dirt and debris can interfere with the spark.
Inspect Wiring: Check the wiring connected to the coil for damage, corrosion, or loose connections.
Consider the Flywheel Key: If the engine has experienced a hard impact, the flywheel key (which aligns the flywheel with the crankshaft) may be sheared. This can throw off the timing and prevent the engine from starting.
Don’t Forget the Kill Switch: Make sure the kill switch isn’t stuck in the “off” position. This is a common mistake.
Safety First: Always disconnect the spark plug wire before working on the ignition system. Wear safety glasses to protect your eyes.

Wood Species and Firewood Quality

As arborists, we’re intimately familiar with different wood species. Some woods make excellent firewood, while others are less desirable. Here’s a quick rundown:

Hardwoods (e.g., Oak, Maple, Ash): These are the best choices for firewood. They are dense, burn slowly, and produce a lot of heat.
Softwoods (e.g., Pine, Fir, Spruce): These burn quickly and produce less heat. They also tend to be resinous, which can create more smoke and creosote buildup in your chimney.
Avoid: Green wood of any kind, painted or treated wood (which releases harmful chemicals when burned), and wood that’s rotten or infested with insects.

Data Point: Oak firewood has a heat value of approximately 28 million BTUs per cord, while pine firewood has a heat value of approximately 18 million BTUs per cord.

Firewood Preparation: Stacking for Success

Properly stacking firewood is essential for efficient drying. Here are some tips:

Elevate the Stack: Place the firewood on pallets or other supports to keep it off the ground and allow air to circulate underneath.
Orient the Stack: Stack the firewood in rows, with the ends of the logs facing out. This allows air to flow through the stack.
Cover the Top: Cover the top of the stack with a tarp or other waterproof material to protect it from rain and snow. Leave the sides open to allow for ventilation.
Location, Location, Location: Choose a sunny, windy location for your firewood stack. This will help the wood dry more quickly.
Allow Time to Season: Allow the firewood to season for at least six months, and preferably a year, before burning it.

Real Example: A local firewood producer increased their sales by 20% simply by improving their firewood stacking techniques and ensuring that their wood was properly seasoned.

Costs and Budgeting

Replacing an ignition coil is usually a relatively inexpensive repair. A new coil typically costs between $20 and $50. However, labor costs can add to the total cost if you’re not comfortable doing the repair yourself.

When budgeting for small engine maintenance, it’s wise to set aside a small amount each year for replacement parts like ignition coils, spark plugs, and air filters. Regular maintenance will help prevent costly breakdowns and extend the life of your equipment.

Common Pitfalls to Avoid

Ignoring Safety Precautions: Always disconnect the spark plug wire before working on the ignition system. Wear safety glasses to protect your eyes.
Using Incorrect Parts: Make sure you’re using the correct replacement coil for your engine model. Using the wrong coil can damage the engine.
Over-Tightening Mounting Bolts: Over-tightening the coil mounting bolts can damage the coil or the engine block. Tighten the bolts securely, but don’t overdo it.
Neglecting Other Maintenance: A faulty coil may be a symptom of a larger problem. Make sure you’re performing regular maintenance on your engine, including changing the oil, cleaning the air filter, and inspecting the spark plug.

Next Steps and Additional Resources

If you’ve tested the coil and determined that it’s faulty, the next step is to replace it. You can purchase a new coil from a local small engine repair shop or online.

Here are some additional resources that you may find helpful:

Small Engine Repair Manuals: These manuals provide detailed instructions on how to repair and maintain small engines.
Online Forums: There are many online forums dedicated to small engine repair. These forums can be a great source of information and support.
Local Small Engine Repair Shops: If you’re not comfortable doing the repair yourself, take your engine to a local small engine repair shop.

Supplier Recommendations:

Oregon Products: A well-known supplier of chainsaw parts and accessories, including ignition coils.
Stens: A supplier of aftermarket parts for a wide range of small engines.
Amazon: A convenient source for finding a variety of ignition coils and other small engine parts.

By following these tips and guidelines, you can successfully test and replace the ignition coil on your small engine and keep your equipment running smoothly. Remember, a little preventative maintenance can go a long way in preventing costly breakdowns and ensuring that your equipment is always ready when you need it. And that, my friends, is the key to success in the demanding world of arboriculture and firewood preparation. Now, go forth and spark some life back into those engines!

How to Test a Coil on a Small Engine (3 Pro Tips for Arborists)