Riding lawn mower magneto. Are Lawn Mower Ignition Coils Interchangeable? (Find Out)

Are Lawn Mower Ignition Coils Interchangeable?(Find Out)

If you’re a handy homeowner or a professional landscaper, you know that a lawn mower is crucial in maintaining a well-manicured lawn.

But like any machine, a lawn mower can experience issues that require repairs.

One common issue is a faulty ignition coil, which can prevent the mower from starting or cause it to run poorly.

When it comes to replacing a faulty ignition coil, one question that may arise is whether or not different ignition coils are interchangeable.

In other words, can you use any ignition coil with your lawn mower, or do you need to find a specific one that is compatible with your mower’s make and model?

Are Lawn Mower Ignition Coils Interchangeable?

The short answer is that it depends. Some ignition coils may be interchangeable between different brands and models of lawnmowers, while others may not be.

Here are a few factors to consider when determining if an ignition coil is interchangeable with your mower:

Compatibility with the mower’s engine

The first thing to consider is whether or not the ignition coil is compatible with your lawn mower’s engine.

Different engines may have different ignition systems and requirements, so it’s important to ensure that your ignition coil is compatible with your engine.

Brand and model

Even if the ignition coil is compatible with your engine, it’s still important to consider the brand and model of your mower.

Some manufacturers may have specific ignition coils designed specifically for their mowers, and using a different ignition coil may not work or cause damage.

Size and shape

Ignition coils come in different sizes and shapes, and it’s important to make sure that the one you choose will fit in the designated space on your mower.

Measure the space where the ignition coil is located to ensure that the new one will fit properly.


Ignition coils also come in different voltage ranges, so choosing one compatible with your mower’s ignition system is important.

Using a higher voltage ignition coil may cause damage to your mower’s engine, while a lower voltage coil may not provide a sufficient spark to start the engine.

Can you swap ignition coils?

Yes, it is possible to swap ignition coils on a lawn mower or other vehicle as long as the replacement ignition coil is compatible with the engine.

lawn, mower, magneto, ignition

LAWN MOWER SPARK PLUG GAP, if incorrect, it does this to the Ignition Coil

However, it’s important to note that replacing an ignition coil is typically a more involved repair than simply swapping out a spark plug or air filter.

It requires disassembling parts of the engine and electrical system, and it’s important to have some mechanical knowledge and experience to do it safely and properly.

If you’re not comfortable working on your lawn mower or other vehicle’s engine, it’s usually best to seek the help of a professional mechanic or a service center.

They will have the knowledge, tools, and experience to properly diagnose the issue and replace the ignition coil if needed.

How To Test a Lawn Mower Coil

Safety first

Ensure the lawn mower is turned off and disconnected from the power source before starting the testing process.

Locate the coil

The ignition coil is typically located near the engine and connected to the spark plug wire.

Disconnect the spark plug wire

Remove the spark plug wire from the spark plug to prevent accidental engine starting during testing.

Inspect the coil

Visually inspect the coil for any signs of damage, such as cracks, corrosion, or loose connections. If you notice any significant damage, the coil may need to be replaced.

Testing with a multimeter

Using a digital multimeter, set it to the resistance (ohms) mode. You’ll need to refer to the lawn mower’s user manual or the coil’s specifications to determine the appropriate resistance values for your specific model.

Primary coil resistance test

Measure the resistance between the two primary coil terminals (positive and negative terminals).

Connect the multimeter probes to these terminals and check the resistance reading.

If the resistance is significantly different from the specified range, the coil may be faulty and require replacement.

Secondary coil resistance test

Measure the resistance between the positive primary terminal and the spark plug wire connection terminal.

Connect the multimeter probes to these terminals and check the resistance reading.

Again, compare the reading with the specified range in the user manual or coil specifications. If the reading is significantly outside the range, the coil may be faulty.

Additional testing

Some coils have additional terminals or functions, such as a kill switch terminal. If your coil has these, consult the user manual for instructions on testing those specific components.

Replace if necessary

If the resistance readings are outside the specified range or if you suspect the coil is faulty due to visible damage or other issues,

It’s recommended to replace the coil with a new one compatible with your lawn mower model.

What happens if you use the wrong Mower ignition coil?

Using the wrong ignition coil can cause various problems with your Lawn Mower. Here are some potential issues that you might experience:

Poor engine performance

If the ignition coil is incompatible with your mower engine, it may not produce a sufficient spark to ignite the fuel-air mixture in the cylinders. This can lead to poor engine performance, such as reduced power and acceleration.

Starting issues

The ignition coil provides the spark needed to start the engine. If the ignition coil is incompatible with your Lawn Mower, it may not produce enough spark to start the engine or produce an inconsistent spark, causing starting issues.

Damage to the engine or other components

Using the wrong ignition coil can also cause damage to the engine or other components in the ignition system. For example, if the ignition coil produces too much or too little spark, it can cause damage to the spark plugs or other components.

How long does it take to Replace Mower Ignition Coil?

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How to Test A Lawn Mower.Briggs And Stratton Coil Magneto With a multimeter #easy

How to fix a no start condition on a lawnmower with no spark

Lawnmower gasoline engines are pretty basic setups so repairing them normally only takes a few basic tools and a little time and money.

When you are diagnosing a small engine with a no start condition there are three basic things that can cause this:

Air / Fuel Mixture Electrical or Spark Compression

The first two problems are the least expensive and easiest to fix. If you have a problem with low compression in the cylinder then this can point to physical damage or wear that may require a more expensive fix or total engine replacement.

The main way that I diagnose the difference between an Air / Fuel problem and an Electrical Problem is by first checking if there is any gas in the tank. Also is the gas good. meaning that it hasn’t sat in your shed for a few seasons. Normally even gas that sits over the winter will start your engine if it was in a sealed container. If it sits longer than a year you might want to be skeptical about its strength and don’t test it with a match. bad gas will still ignite. its just not strong enough to let the engine run on it.

If you have gas and there aren’t any leaks around the carburetor / air filter then the next thing to do is check the air filter for extreme blockage. The air filter can be blocked with dirt and debris or it can be blocked with oil or even moisture. For the reason of testing clean around the carburetor so there isn’t any dirt and then just remove the air filter and try starting the engine.

If its not air or gas then the next thing to check is spark.

Diagnosing no spark on a Lawnmower engine

There are two different types of ignition and electrical systems on lawnmowers. There is the battery driven and the engines without batteries. If you are pulling a start cord you don’t have a battery.

If you have a engine that is rated under or about 20 horse power your spark is probably generated by what is called a Magneto. If you have a larger engine you may have actual coils like your car and a crank positioning sensor. Coils are not common on consumer grade equipment but they are out there on some engines so keep that in mind.

A Magneto is what supplies electricity to your spark plug. Although your gasoline engine might have a battery and starter the starter only turns the engine to induce the magneto just like you would if you had to hand pull start the engine.

Magnetos work by electrical induction. This is where a magnet that is placed on your flywheel passes by the magneto as the flywheel turns and the magnet causes electricity to be induced into the spark plug.

As you pull start the engine only a few rotations and sparks are necessary to start the combustion process which will take over and keep the engine turning. As long as the magnet is passing by the magneto it will cause a spark and no outside alternator and coil is needed.

It is a great way for small engines to get spark because it means they can run in pretty harsh conditions and a battery is not required.

So, how do you diagnose a bad spark?

The first thing you want to do before you are pulling your engine covers off is pull the spark plug and reattach it to the spark plug wire. Then place the bent L shaped electrode against the metal housing of the engine and see if you can see a spark when you pull the start cord or hit the key.

If you do see a spark it could still be a problem where not enough spark is being made to start the engine. This happens if you have oil on the spark plug or if the gap between the Ground L and center Electrode of the spark plug are too wide or eaten away.

If your spark plug is really wet and oily it will point to internal engine damage and you already should have seen signs of engine damage by blue gray smoke coming from your exhaust for some time.

If plug is dry but the ceramic cone is cracked or the gap on the spark plug is set wrong you should really just replace the plug. You can reset gaps by bending the L shaped Electrode with feeler gauges and a tool but a plug that is worn to that point is probably very old on a small engine and you might as well spend the 3 and get a fresh plug which is pre-gapped at the factory.

Reinstall the plug and see if the engine starts with the regapped or new plug.

If you don’t have a spark at all then your magneto could be bad. They don’t normally go bad but they can. It is not a part that you would normally replace like an air filter or spark plug but if your engine is about 10 years old it could be a magneto.

lawn, mower, magneto, ignition

Unlike automotive engines the wire to the spark plug is normally attached to the magneto and is not replaceable if you have damage to your plug wire you will probably need to replace everything.

The cost of a Magneto is not that bad you can expect to pay 20 on push mowers to 50 on lawn tractors. If you have a Twin Cylinder engine you will have two magnetos and you should replace both of them at the same time if the replacement is due to age and not due to physical damage.

If you need to replace the magneto there are normally only two bolts that hold it in place but when you replace the magneto you must make sure to have a proper gap between the engine flywheel and the magneto fins. Some people place a business card between the fins and the flywheel before they tighten the bolts and this should work however it is best to read the directions or your service manual and set the gap with feeler gauges.

Replace everything and start your engine you should be ready to hit the lawn.

Final Note

Diagnosing engine problems is pretty easy if you follow basic steps and precautions. You should NEVER try to start your engine with the blade on and the lawn mower in any position other than its normal operating position. Never raise the wheels off the ground to take a look. never place it on the side and pull the starter cord with a spark plug installed or the magneto wire not pulled and then covered with a rubber spark protector.

Just never take the chance because at every professional shop there are people hurt while working on lawnmower repairs.

Pulling the spark plug wire should be second nature. You should do it every time you work on your engine unless you return the mower to standard running position with all guards and safety devices in place.

If in doubt take it to a repair shop or many shops can come to you.

In other how to guides we will cover other no start conditions for lawnmowers and small engines.

How to test a magneto coil with a multimeter

With modern vehicles, there is no end to where problems could come out from. However, the older vehicles and engines present one more component to think about; magneto coils. Magneto coils are important components within the ignition system of small aircrafts, tractors, lawnmowers, and motorcycle engines, among others. A lot of people don’t know how to test these components for problems and we are here to help. In This Guide, You’ll Learn The Following:

  • What Is A Magneto Coil And How Does It Work?
  • Symptoms Of A bad Magneto Coil
  • How To Test A Magneto Coil With a Multimeter
  • And Frequently Asked Questions

What Is A Magneto Coil And How Does It Work?

A magneto is an electrical generator that makes use of a permanent magnet to create periodic and strong pulses of current, rather than a constant supply of it.

Through its coils, it supplies this strong pulse of current to a spark plug which ignites compressed gasses in the ignition control system of an engine.

How is this pulse created?

There are five components that work together to make a magneto work:

  • The armature
  • A primary ignition coil of 200 turns of thick wires
  • A secondary ignition coil of 20,000 turns of thin wire, and
  • An electronic control unit
  • Two strong magnets fitted into the engine flywheel

The armature is a “U” shaped component situated close to the flywheel and on which the two magneto ignition coils are wrapped around.

Going by Faraday’s law, any relative motion between a magnet and wire induces current and flow in the wire.

lawn, mower, magneto, ignition

The engine flywheel has two magnets embedded at a particular point on it.

When the flywheel rotates and this point goes past the armature, it gets periodically supplied with magnetic fields by the magnets.

Remember the coils of wire are on the armature and, per Faraday’s law, this magnetic field supplies the coils with bits of electrical current.

This periodic supply of current builds up in the coils and reaches a maximum.

Once this maximum is reached, the electronic control unit activates a switch, and the contact points open.

This sudden release sends a flood of strong electric current into the spark plugs, firing up the engine. All these take place in a few seconds.

Now, the magneto may stop serving its purpose effectively and the culprits are usually the coils.

Symptoms Of A bad Magneto Coil

When a magneto coil is faulty, you experience the following

  • The engine warning light illuminates on the dashboard
  • Difficulty starting engine
  • distance traveled by gas
  • Lack of acceleration power

If you notice any of these, the magneto coils could be the problem.

Just like when testing other electronic devices and components, you need a multimeter to test these coils.

How To Test A Magneto Coil With a Multimeter

Take off the rubber casing, set your multimeter to Ohms (Ω), and make sure the Ohm range is set to 40k without any auto-ranging. Place the multimeter probes at the magneto copper winding and the metal clip under the rubber casing. Any value below or above the 3k to 15k range implies that the magneto coil is faulty.

This is only the basic and most straightforward description of what you have to do, and further explanation is needed for a proper understanding of the process.

The first step is to detach the flywheel shroud from the whole setup.

The flywheel shroud is a metal casing that covers the magnetic and is kept in place with three bolts.

Engines made in the 1970s typically have four bolts holding the shroud.

Once the shroud has been taken off, you locate the magneto coil.

Finding the magneto coil shouldn’t be a hassle as it is the only component behind the shroud with exposed copper windings or metal core.

These copper windings (the armature) form a “U” shape.

The magneto coil has wires protected by a rubber casing that go into the spark plug. To test it out, you have to take off this rubber casing from the spark plug.

For a magneto coil, you measure resistance. This means that your multimeter dial is set to Ohms represented by the Omega symbol (Ω).

Rather than opting for auto-ranging, you manually set your multimeter to the 40k Ohms range. This is because auto-ranging gives you very unreliable results.

Now, to measure resistance within your magneto coil, there are two things to do. You want to measure the primary and secondary coils.

For the primary coil, place the red multimeter probe on the “U” shaped winding and ground the black probe on a metal surface.

To measure the secondary coil, place one of your multimeter probes on the “U” shaped metal core (winding) and place the other probe in the rubber casing at the other end of the magneto.

While this probe is in the rubber casing, you ensure that it touches the metal clip on it.

Here is a video that shows exactly how to measure primary and secondary magneto coils.

Once the probes have been placed on the different parts of the magneto, you check the multimeter for readings.

The readings are presented to you in kilo ohms and should be between 3k and 15k, depending on the type of magneto you are testing.

Referring to the manufacturer’s manual helps you with this. Any reading out of this range means that your magneto coil is faulty.

Sometimes, the multimeter may display “O.L”, which means that there is an open-loop or short between those two points. Either way, the magneto coil needs to be changed.

In addition to these, there are certain tips to take note of.

If the multimeter produces a reading higher than 15k, the culprit may be the connection between your high voltage (HV) wire at the coil and the metal clip that goes to the spark plug.

If all these are checked and the magneto produces proper Ohm readings, then your problem may be with the spark plug or weak magnets in the flywheel.

Check these components out before deciding to change the magneto.

Frequently Asked Questions

How Many Ohms Should An Ignition Coil Have?

A good magneto coil produces Ohm reading between 3k to 15k depending on the model it is. Any value below or above this range signals a fault with it and you may need to replace it.

How Do You Test A Magneto For Spark?

To test a magneto for spark, you make use of a spark tester. Connect the alligator clip of this spark tester to the magneto coil, try to power up your engine, and see if this tester produces a flash.

How Do I Test A Small Engine Coil With A Multimeter

Simply place the multimeter probes on the “U” shaped metal core and the spark plug metal clip at the other end. A reading outside the 3k to 5k Ohms range means it is faulty.

How Do You Test A Magneto Condenser

Set your meter to Ohms (Ω), place the red probe on the hot connector, and ground the black probe on a metal surface. If the condenser is bad, the meter doesn’t produce any consistent reading.

How Many Volts Does A Magneto Produce?

A good magneto generates about 50 volts. When a coil is introduced, this value increases to 15,000 volts, and this can be easily measured with the use of a voltmeter.

What Makes a Lawn Mower Coil Go Bad? ( How You Can Prevent This)

It’s very likely that you’ll need to swap out your lawn mower ignition coil at some point during its lifespan. This is a pretty normal replacement that has to be done for all types of lawn mowers, whether it’s a push mower or a ride-on mower. But if you find that your lawn mower ignition coil keeps going bad, then this definitely isn’t normal. So, let’s look at what causes multiple ignition coils to fail and what you can do to prevent it.

What Causes Repeated Ignition Coil Failure? (The Short Answer)

The most common causes of repeated ignition coil failure are engine overheating, defective coil components such as spark plugs and cables, using incorrect parts, and poor maintenance methods. Any one of these causes, or a combination of multiple causes, can lead to your lawn mower coil failing.

What Makes a Lawn Mower Coil Go Bad (6 Possible Causes)

A lawn mower coil is made up of an iron core and copper winding tucked neatly inside the lawn mower’s ignition coil. Every time the magnet attached to the flywheel passes the coil, there is a complex reaction between the iron core, the copper winding, and the magnet that produces an electrical charge. As soon as conditions for this reaction change to less than ideal, the coil suffers. So, let’s take a look at what causes an ignition coil to go bad.

Overheating of the Engine Coil

During the reaction inside the coil, a fair amount of heat is generated on the copper windings. To make sure the windings can cope with the heat, the copper winding is insulated to make sure that the single wire of the winding never touches itself. Now, this insulation is rated to cope with the reaction heat and the heat of the engine. Consequently, the insulation is not rated to take the added heat of an overheating engine.

So, if your lawn mower is low on oil or has a problem with cooling, then it’s probably overheating The result is the insulation loses its integrity, and the copper winding arcs back on itself. The final result is a change in the amount of charge created and the time of release. These changes lead to a burned out ignition coil.

Over Gapped Spark Plug

The charge that is created in the coil needs a method to discharge itself so that it can continue to process and make more charge safely. This is where the spark plug steps in. The spark plug on your lawn mower is basically a grounding point that this charge is attracted to.

So, once the charge gets to the end of the spark plug, it needs to arc over the gap. Now, if the gap is too big and the sparkplug is over-gapped, the arc can’t happen. This makes the coil think that more current is needed, so it increases the charge. Unfortunately, the coil isn’t designed to do this. The result is the coil produces more current and more heat. The one thing that the coil can’t handle is extra heat. So, if your spark plug is over-gapped, your coil is going to quickly burn out.

Faulty or Damaged Spark Plug

Other than over-gapping the spark plug, you might have a bad spark plug that needs changing. A bad spark plug is going to have the same effect as a poorly gapped spark plug. The coil is going to overheat because it is not able to discharge. The result is another burned out coil.

Incorrect Spark Plug

Yep, I’m afraid we’re still talking about spark plugs, but this is the last one. If you’re sitting there wondering, “why does my ignition coil keep burning out” it could be because you’re using the wrong spark plug.

Well, you’ll find that you can buy a spark plug that both fits into your lawn mower and that connects to the ignition cable/spark plug cable. But just because it fits doesn’t mean it’s the right one.

What happens if you use the wrong spark plug? Well, inside the spark plug is an electrode that the current reaches before it arcs to the ground. This electrode is designed with a specific resistance. So, if you have the wrong spark plug, the charge can’t pass the electrode. A wrong spark plug is the same as an over-gapped plug and a faulty plug. Once again, the coil produces more charge, more heat and burns itself out.

Damaged Ignition Cable/Spark Plug Cable

The reaction between the protons and the neutrons inside the coil produces an electron, the charge. This electron charge needs somewhere to go, so it heads for the spark plug. Time for the spark plug cable to step in.

Now, some years back, you would buy a coil and cable separately, but nowadays, they come as one item. Before, it was possible to get the wrong combination and mess up your coil. Fortunately, you don’t need to worry about a mix-up these days.

However, you do need to be aware of cable damage. Just like the overheating problems a spark plug can cause, a cable can do the same. If the cable is damaged or broken, the charge will back up in the coil and form the same heat damage.

Poor Practices

Let me ask you a question. Do you think it’s a good idea to test a spark plug that is attached to your lawn mower without it being grounded? Definitely not. Most of us, at some point, have removed the spark plug from the mower and pulled the starter cord to see if it’s working ok.

Well, if you pull the cord and the spark plug isn’t grounded to the mower’s engine, the coil begins to overheat. This is just the same as a bad spark plug or a broken cable. The charge has nowhere to go.

Signs a Lawn Mower Coil is Going Bad

When figuring out what makes a lawn mower coil go bad, you’ll probably be seeing a few symptoms with your lawn mower before the coil burns out. If you notice these symptoms quickly enough, you might be able to avoid another coil replacement. Here’s what to look out for.

Is There Anything You Can Do If Your Mower’s Ignition Coil Keeps Going Bad?

Now that we have been through what makes a lawn mower coil go bad. Let’s have a look at a few things that will help you avoid another replacement. Here are some tips to help keep the coil protected.

Check the Engine Oil Level

A common cause of a lawn mower engine overheating is low oil. A lack of oil in the engine causes the metal parts to rub together and generate excessive heat. I suggest that every time you fill the gas tap, you check the oil level.

Carry Out Regular Oil Changes

As oil is used and heated, it starts to lose its cooling and lubricating abilities. This results in overheating and potential coil damage. I suggest working out an oil change schedule and make sure that you are changing your lawn mower oil often enough.

Clean Out the Air Vane Guard

When I finish using my lawn mower, I always make a point of cleaning off all the grass. I also make sure to clean out the flywheel. Located on top of the flywheel is a fan that cools the engine. It is super important to keep this clean so that the engine can cool efficiently.

Gap the Spark Plug

Gapping a spark plug is a job that a lot of people skip. I’m guessing this is because it’s not always easy to understand why it’s important. But once you know what makes a lawn mower coil go bad, I’m pretty sure you will not skip it again. So, the simple solution is to get a spark plug gapping tool and gap your plug regularly (here’s a post that explains how to gap a mower spark plug).

Double Check the Spark Plug Specification

If you look in your lawn mower manual, you’ll find out what size spark plug your mower needs. If you can’t find it, you can look online or check with your local mower store.

Using the Mower’s Off Switch

Within the electrical circuit of your lawn mower, there is a bypass for the coil. This basically grounds the coil in a different direction than the spark plug. So, if you are doing repairs on your lawn mower that require the flywheel or engine to turn, make sure the lawn mower is switched off. Disconnecting the spark plug will stop the mower from starting, but it won’t protect the coil.

About Tom Greene

I’ve always had a keen interest in lawn care as long as I can remember. Friends used to call me the lawn mower guru (hence the site name), but I’m anything but. I just enjoy cutting my lawn and spending time outdoors. I also love the well-deserved doughnuts and coffee afterward!

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