Lawn mower plug gap. Are lawn mower spark plugs pre-gapped

How to Gap a Spark Plug

This article was co-authored by Hovig Manouchekian. Hovig Manouchekian is an Auto Repair and Design Specialist and the Manager of Funk Brothers Auto, a family-owned business operated since 1925. With over 30 years of experience in the automotive industry, Hovig specializes in the process of auto repair and maintenance. He is also very knowledgeable in common automotive issues and needs including engine repair, battery replacement, and windshield accessory and maintenance. Hovig’s knowledge and hard work have contributed to Funk Brothers Auto winning Angie’s List Super Service Award for five consecutive years.

There are 7 references cited in this article, which can be found at the bottom of the page.

wikiHow marks an article as reader-approved once it receives enough positive feedback. In this case, 100% of readers who voted found the article helpful, earning it our reader-approved status.

This article has been viewed 539,767 times.

A properly gapped spark plug is necessary for a properly functioning engine. The gap size affects the spark plug’s firing temperature, which has a direct relationship to the combustion of fuel and air in the engine. Opening the gaps provides a larger spark, useful for some customized engines in maximizing the efficiency. You can learn to properly gap spark plugs by measuring and adjusting accordingly.

Measuring the Gap

• Each vehicle’s measurement will be different, though most are generally somewhere between 0.028-.06 inch (0.15 cm). You can either look in your owner’s manual or go to the auto parts store and have them look it up for you.
• Modified engines require smaller gap settings to account for the amount of power you’re putting through the engine. General rule of thumb: the more power, the smaller the gap.
• A coin-style gap measure is usually the cheapest option, and works by running the edge of the coin through the gap until you reach a point where it stops. The edge is marked like a ruler, designating the thickness of the edge at that point. This is a good tool for older plugs you want to check the efficacy of, but can also inadvertently widen the gaps as you use it.
• A wire coin gap works essentially the same way as the regular coin-style gap, but features different wire measures of varying lengths on the edge around the coin.
• A blade-style feeler gauge is an effective and versatile tool. Built like a.knife, this gauge features different blades of varying widths, some with wire on the end and some without, placed in the gap to check the spacing of the electrodes. You can also use multiple blades to measure larger gaps. These are effective to use while adjusting.
• You can use a little bit of quick-drying (90%) alcohol on the contact points to clean them off if they’re especially dirty. [3] X Research source Lots of build-up or any blackening on the contact points might be a sign of a plug that’s outlasted its prime, however. If they’re especially dirty, you might consider buying new ones.
• There’s a special tool designed for cleaning spark plug—think of it as a sand-filled pouch that’s attached to an air compressor. It cleans the electrode of the spark plug by sandblasting it.

Measure the gap by passing the tool through the electrodes. Place the appropriate blade or wire on your gap tool between the electrode tips of the plug, or pass the coin through the electrodes to determine the measurement.

Adjusting the Gap

• Most spark plugs and iridium plugs manufactured today don’t need to be gapped prior to installing them. If you’ve got a custom modified engine, though, you might be interested in checking or installing plugs at a different spacing. Adjust them accordingly. [5] X Research source
• Never bend more than a few (.02) fractions of an inch. It won’t take much pressure, so be very careful. Spark plugs can be quite delicate, and any fracturing can cause misfires.
• If you’re having trouble using the tool to adjust the gap, consider bending it in using a flat surface like a table to apply some very gentle pressure on the electrode to adjust it.

Re-measure the gap and adjust accordingly. Be very careful not to contact the electrode in the center of the plug and damage the core. If it breaks or shorts you’ll need to toss it and buy a new one.

Be very gentle. Snapping off the electrode will waste your efforts, and it doesn’t take much to do so. Use only a small amount of pressure to bend the electrode and only bend it a little bit.

Community QA

The gap for my car is.054. This is more than double the thickness of the thickest blade on a feeler gauge. Am I supposed to remove several blades from the feeler-gauge assembly and stack them?

Yes. Add more to get the right thickness, if your thickest leaf is too small. It’s a very accurate way to measure or set a gap.

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Thanks! We’re glad this was helpful. Thank you for your feedback. As a small thank you, we’d like to offer you a 30 gift card (valid at GoNift.com). Use it to try out great new products and services nationwide without paying full price—wine, food delivery, clothing and more. Enjoy! Claim Your Gift If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even 1 helps us in our mission. Support wikiHow

NGK offers an extensive book, which is often given away for free at exhibitions and motor fair. You can usually find this sort of information on NKG’s website as well. The correct gap depends on the motor type and may vary from the gap when buying it new.

Thanks! We’re glad this was helpful. Thank you for your feedback. As a small thank you, we’d like to offer you a 30 gift card (valid at GoNift.com). Use it to try out great new products and services nationwide without paying full price—wine, food delivery, clothing and more. Enjoy! Claim Your Gift If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even 1 helps us in our mission. Support wikiHow

Do not over-tighten the spark plugs. [7] X Research source Most heads are made of aluminum and the threads can strip easily.

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About This Article

This article was co-authored by Hovig Manouchekian. Hovig Manouchekian is an Auto Repair and Design Specialist and the Manager of Funk Brothers Auto, a family-owned business operated since 1925. With over 30 years of experience in the automotive industry, Hovig specializes in the process of auto repair and maintenance. He is also very knowledgeable in common automotive issues and needs including engine repair, battery replacement, and windshield accessory and maintenance. Hovig’s knowledge and hard work have contributed to Funk Brothers Auto winning Angie’s List Super Service Award for five consecutive years. This article has been viewed 539,767 times.

A spark plug gap is the distance between the end of the electrode and the base of the spark plug. If your spark plugs aren’t properly gapped, your engine may not burn fuel properly. Since every make and model requires a different gap size, start by looking in the owner’s manual for your vehicle to find the required gap size, or pull the information up online. Then, grab a gauge tool, and slide the recessed lip under the electrode sticking out from the base of the spark plug. Rotate the disc until you feel a firm resistance and check the measurement next to the lip. If the gap matches your required size, you’re good to install it in your vehicle. If the gap is too small, pull the body of the plug away from the disc with the electrode hanging on the lip to gently force the gap open and re-measure it. If the gap is too big, use the broad side of the gap tool to push the electrode down and make the gap smaller. Continue re-measuring and making minor adjustments until the gap in the spark plug matches your manufacturer’s recommended gap size. For tips on choosing an appropriate gap tool, read on!

Are lawn mower spark plugs pre-gapped?

I am Janine Clarke AKA Equipment Girl, a nerdy girl with an unhealthy knowledge about power tools and gardening! You can contact me here.

I’ve recently been putting together a series of articles all about lawn mower spark plugs, and a running theme throughout most of them is something called the spark plug gap.

Now, I’ve not delved into this topic in great depth before because it deserves an article all of its own, so you can understand why a spark plug gap is so important, whether or not a lawn mower spark plug is pre gapped, and what to do if the correct spark plug gap isn’t as it should be.

Basically, I want to teach you everything there is to know about a lawn mower’s spark plug gap, so you can understand your lawn mower engine better, and fix any problems that should arise with the gap spark plugs are supposed to have.

SO, ARE SPARK PLUGS FOR LAWN MOWERS PRE GAPPED?

Yes, today spark plugs for lawn mowers are usually released pre gapped, because the spark plug gap is so integral to making sure you can start your lawnmower engine, and that the running engine can keep running.

Manufacturers send most lawnmower spark plugs to market pre gapped for convenience, so you don’t have to mess around with the engine when it arrives – the gap is exactly as it should be and the spark plugs can work as they should.

But things can go wrong (and they go wrong often) so as well as talking more about the importance of the right spark plug gap today, I’ll also look at how to double check that you have the right gap before starting your engines.

Ready to find out more? Then join me below.

Your Spark Plug Gap Explained

Spark plugs are rather simple devices operating in a highly complex mechanical engine that rely almost exclusively on electricity to run.

As you’ll already know, most spark plugs work when electricity generated at the ignition coil sends a charge from the spark plug’s center electrode to the ground electrode. The center and ground electrodes are essential in starting the engine.

The center electrode takes the electricity that’s activated when the ignition system is activated (i.e. you turn the lawn mower key, or pull on the start rope) and sends it across the spark plug gap to the ground electrode.

As this happens, a high potential difference is created, and this generates electricity that will cause an electric spark. The spark begins the combustion process in the combustion chamber by burning the air fuel mixture within.

It is this burning that gets the mechanical parts of the engine in working order, which then allows the lawnmower blade to cut, and the engine to continue running as the cycle repeats and the lawnmower can continue in a perpetual motion until the engine is turned off.

But What Happens If The Spark Plug Gap Isn’t Correct?

If the current spark plug gap isn’t exactly as it’s supposed to be according to the engine owners manual, then you’ll notice a few different problems.

ENGINE STRESS

If there is too much space or not enough space between the center electrode and the ground electrode, then the engine will need to work harder to create the spark between the two electrodes.

Although most lawnmowers will have a spark plug gap that is correctly set beforehand, this can be moved accidentally during shipping or otherwise changed during use (but more on this later).

If the gap is too large, the engine will work harder to burn the fuel mixture, and if the gap is too small, there might not be enough room for a spark to be created at all, meaning the engine just won’t start.

In many ways, it’s worse for the gap to be too large, though, as the engine will still be able to operate, but the added stress can cause internal engine damage. This sort of damage is common on outdoor power equipment, because many owners think that if the lawnmower is running, then it must be fine. The result? Without the proper gap, your engine could break beyond repair.

ENGINE MISFIRES

Misfires in the engine (specifically the cylinder housing) can occur when the specific width the lawn mower spark plugs gaps are supposed to be aren’t met.

The correct width for each model varies depending on the engine model used, etc., but you can find your exact requirements in the owner’s manual to find all the details you need for your push along lawnmower or vehicle’s recommended setting.

When it isn’t the correct width, engine misfires can occur, meaning it takes a long time for your engine to start, or it will cut out intermittently when in use, depending on your engine type and how poor the spark plug gap is compared to what it should be.

SPARK PLUG WEAR

When installing spark plugs, you have to take extra care to ensure the gap is right. If it’s wrong, then it can lead to spark plug wear, which will then mean you need to replace the old spark plug with a new spark plug much quicker than you ordinarily would.

Again, this comes back to how hard your engine and spark plug have to work when the gap isn’t correct, causing low power over time, or even the engine to break altogether.

What Can Cause Your Pre Gapped Spark Plug To Go Wrong?

I’ve talked about what happens when things go wrong, but what actually causes it to begin with? If manufacturers send out lawn mower spark plugs pre gapped, then what’s causing them to change?

Well, it’s typically for two main reasons:

Shipping

I’ve touched on this already, but it’s one of the most common reasons your lawn mower won’t start when you first get it from the store or have it delivered to your house.

Whilst manufacturers do pre gap spark plugs using a spark plug gap tool or spark plug gauge (A.K.A. a feeler gauge) to make sure they’re perfect, lawn mower spark plugs can be knocked around during shipping. It’s all too easy for the gap to gently bend out of shape, causing the lawn mower spark plug gap to be off ever so slightly. This can lead to the mower performing poorly with lower power, overuse of fuel, etc., or else not starting at all.

Use Over Time

Faulty gaps can occur due to engine heat over time. The heat can cause the ground electrode to move or be eaten away slightly, causing the usually flat, round piece to be misshapen.

This only worsens as the anode gets thinner. The anode, for those of you that don’t know, is a small post covered by a metal tongue at one end of the spark plug – typically found inside the cylinder housing. This anode has the post and the tongue (center and ground electrode), and you can actually manipulate the anode using a spark plug gap tool to adjust it to the correct width.

And doing so is fairly simple…

Adjusting Your Lawn Mower Spark Plug Gap

WHAT YOU’LL NEED

• Spark plug wrench or spark plug socket
• A spark plug gap tool or feeler gauge or gap gauge

THE METHOD

Getting into your lawn mower engine is easy enough with a spark plug wrench or socket because they’re specifically designed to untighten the spark plug so you can manipulate it as you require for a gap adjustment using a gapping tool.

Once loose, just remove it from the correct wire and you’ll be able to use the gap tool to adjust the gap.

Please note: You’ll need to be precise with this task. Only ever stick to the advice in your owner’s manual, or else you may force the gap too wide or leave it too narrow, and you’ll be back to square one again with a lawn mower that performs poorly or doesn’t work at all due to a faulty spark plug gap.

Final Thoughts

Although lawn mower spark plugs are pre gapped, it’s helpful to know the signs that a spark plug gap is faulty so you can fix the issue yourself with an inexpensive gap gauge.

Just remember to consult your owner’s manual, be precise with your measurements, and you should have a spark plug gap that allows the mower to start and continue to run as the combustion cycle repeats itself.

But with mower spark plugs coming with a pre prepared gap to start with, you might get lucky and never need to alter the gap at all until it’s altered over time with continued use.

Now you know everything there is to know about a spark plug gap, I hope you’ll be able to combat any problems should they arise!

Lawn Mower Spark Plug Size: How To Find The Right Plug

Do you need help finding your lawn mower’s right spark plug size? You’re not alone. Finding the correct spark plug size can be challenging, but it doesn’t have to be. With simple steps, you can find the perfect fit and get your lawn mower running like new again in no time!

This guide will discuss locating and identifying your lawn mower model’s proper spark plug size.

We will also go over some crispy tips and tricks on adequately maintaining and caring for your spark plugs so that they last longer and perform better. So let’s get started.

Are Lawn Mower Spark Plugs Different Than Vehicle Spark Plugs?

Automobile and lawnmower gasoline engines use the spark plug for the same purpose. But it’s important to note that depending on the specific engine, spark plugs may not be interchangeable between automotive and lawn mower applications.

This is because different engines require different spark plug sizes, and other physical differences may also affect compatibility. Let’s have a look.

Thread Size

There is a size variance between the spark plugs used in automobile and lawn mower engines. Most auto engines use a 14-millimeter thread, while many mower engines use a 12- or 10- millimeter thread. Attempting to mate different threads by force can damage the plug, the engine, or both.

Thread Length

The thread length for auto plugs can be 1/2 inch or 3/4 inch long. But many lawn mower engines use a plug with threads only 3/8 inch long. Using the wrong thread length can impair starting or damage the engine.

Gasket Washer Most mower plugs use a metal gasket washer with a cylinder seal, as do many auto plugs. But some General Motors vehicles use a tapered plug that mates with a tapered hole in the cylinder head to seal the cylinder. These plugs wouldn’t fill a lawn mower cylinder and shouldn’t be used.

Are Lawn Mower Spark Plugs A Universal Size?

Different manufacturers produce different kinds of engines, so the size of the spark plug can vary depending on the type and size of the engine. As a result, no universal spark plug size applies to all lawnmowers.

You can use several methods to identify the spark plug size for your specific engine. You can consult the owner’s manual, measure the existing spark plugs or contact the manufacturer directly for assistance.

How Do You Determine Lawn Mower Spark Plug Size?

If you want to determine the correct spark plug size, you can consider the following factors:

Thread Size

The thread size of a spark plug is measured by two distinct dimensions: pitch and diameter. Thread pitch refers to the difference between each thread on the plug, while thread diameter refers to the thickness of the threaded portion of the spark plug. The measurement for the thread size of your spark plug should be printed on each spark plug or found in your mower’s owner’s manual.

Most power spar plug generally comprises 10 millimeters to 14 millimeters thread diameter and a pitch of 1 millimeter to 1.5 millimeters.

Thread Length

The length of a thread, also known as its reach, is connected to its pitch and diameter. Thread length measures the total distance of a spark plug and is essential for proper engine performance. If your lawn mower’s spark plug has an incorrect thread length, it can lead to overheating and oil fouling of the spark plugs.

The thread length of generally in mowers ranges from 3/8 inch to 0.750 inches. If the length is insufficient to reach the engine socket, it may lead to fuel or oil accumulation around the tips.

In contrast, if the thread length is too long, it can cause overheating and damage your mower’s cylinder.

Additionally, the Wrong thread length of the spark plug can also result in the cylinder of your lawnmower needing to be sealed due to ill-fitting components, which would cause your engine to have trouble starting.

Spark Plug Heat Rating

The heat rating of a spark plug indicates its ability to tolerate specific heat levels. The heat rating is measured on a standardized scale, ranging from two to twelve. A spark plug wchis with a six heat rating is suitable for most lawn mower engines, but it’s essential to check your owner’s manual to ensure you’re using the correct heat rating for your specific engine.

If you use a lower heat rating of the spark plug, it will overheat quickly at a lower temperature compared to a higher rate. So make sure you use the correct spark plug with the suitable heat rating to ensure the proper performance of your engine.

Besides this, if you use an incorrect heat rating, your engine may experience pre-ignition or have difficulty operating at any speed. Therefore, using a spark plug with the appropriate heat rating is always essential to ensure your lawn mower is running correctly.

The Spark Plug Gap

As you work on it, check the spark plug gap to determine. This will tell you if the gap between the plug electrodes is set to the correct distance. The gap should be adjusted with a feeler gauge to ensure the plug is not too far apart or too close.

If the gap is too wide, it can cause problems with ignition. If the gap is narrow enough, it could lead to sufficient airflow. Neither of these scenarios is ideal for your mower’s engine, so ensure the gap is set to the proper size according to your engine’s specifications.

Determine the Type of Lawn Mower

Spark plugs for push mowers and riding mowers are slightly different. Push mower spark plugs usually have pitch thread sizes of 1 millimeter to 1.5 millimeters.

Push mower spark plugs typically have a diameter of 10 millimeters to 12 millimeters and a thread length or “reach” of 9 millimeters to 12 millimeters.

Riding mower spark plugs typically have a pitch of 1 millimeter to 1.5 millimeters, a diameter of 12 millimeters to 14 millimeters, and a thread length or reach of 15 millimeters to 19 millimeters.

What happens When you use the wrong spark plug type for your mower?

Using the appropriate spark plug for your lawn mower is essential for consistent and efficient performance. If you accidentally use the wrong spark plug type, it can lead to several consequences.

Difficulty starting the mower

it can lead to difficulty starting the mower, leaving you frustrated and exhausted.

Run roughly or misfire

It can cause the mower to run roughly or misfire, decreasing its lifespan.

Excessive fuel consumption and emissions

Incorrect spark plugs can also lead to excessive fuel consumption and emission due to a lack of power from the engine.

Overheating spark plug

It may also lead to overheating the spark plug, resulting in engine damage or costly repairs.

Other Specifications to be Considered:

Specific spark plugs have a center electrode that operates at a higher average temperature than others. Such spark plugs are known as “hotter” and “colder” ones.

Some spark plugs elongated further into the combustion chamber than others, termed “longer” or “shorter,” respectively. Considering these spark plug features when selecting one for your lawn mower engine is essential, as they can affect its starting and running performance.

The features mentioned impact how the engine starts and operates and should be adjusted accordingly to match its specifications. If you use too hot or too cold of a spark plug, your motor may experience pre-ignition or difficulty running at any speed. If the plug is too long or short, it can also cause damage to both the piston and the plug itself.

Taking care of the basic specifications can go a long way in keeping your lawn mower engine running smoothly and efficiently. Please select the right type and spark plug features that best fits your lawn mower’s specifications, and always check the gap between electrodes before installing them. Doing so will ensure that you get the best performance from your engine!

Tips and Tricks

Assuming you have obtained all the technical information, the next step is to buy the correct type of spark plug for your lawn mower. Below are some easy tips to keep in mind before doing so:

Read and understand your owner’s manual

Before purchasing a spark plug, it is essential that you read, understand, and follow all instructions given in your owner’s manual.

Check the spark plug gap

Check the spark plug gap to ensure it is set to the correct size as determined by your mower’s engine specifications.

Purchase quality parts

When shopping for a spark plug, purchase quality replacement parts from a reputable dealer.

Get help from an expert

If you are unsure of which spark plug to purchase, feel free to ask for help from an expert or professional in the automotive industry. You can also contact your manufacturer directly for advice.

Other Method

If you need help finding the information in the online owner’s manual, you can contact the manufacturer through their email addresses, phone numbers, or social media.

Tips For Maintaining Your Spark Plugs

Now that you know the correct spark plug size for your lawn mower, here are some tips to help you keep them in good condition:

• Clean the spark plug periodically with a wire brush or sandpaper.
• Replace the spark plug every 100 hours of use or if it’s damaged or worn out.
• Make sure the gap or corroded.
• Inspect the spark plug regularly for signs of wear or damage.
• Use a spark plug wrench to remove and install the spark plugs – never use an adjustable wrench.
• Ensure the spark plug is gapped correctly to the manufacturer’s specifications before reinstalling it.

These tips will help ensure your spark plugs last longer and perform better, saving you time and money in the long run.

Spark Plug Components:

The spark plug comprises several components: the shell, porcelain insulator, electrodes, electrode tips, and ground straps. Knowing what these parts do is essential if you want to understand how the spark plugs work and determine which type you need for your mower.

The Shell: This component acts as a housing for the spark plug and is usually made of metal. It helps protect the other components from dirt, moisture, and mechanical damage.

The Porcelain Insulator: This acts as an insulator between the outside of the shell and the electrode tip. It prevents electrical current from leaking out and keeps dirt particles away from the electrodes.

The Electrodes: These metal wires carry electricity from the spark plug to the engine’s combustion chamber. They can be single or double ground and come in different sizes, depending on your mower’s engine specifications.

The Electrode Tips: These are located at the end of the electrodes and conduct electricity from the spark plug to the combustion chamber. They need to be periodically replaced, as they can become corroded or worn over time.

The Ground Straps: These metal straps connect the different electrode tips to create a continuous electrical path between them.

By understanding the different spark plug components and their functions, you can be sure you purchase the correct type of spark plug for your lawn mower.

FAQs

Can I use my car spark plug in my mower?

The answer isn’t a simple yes or no when using a car spark plug in a lawnmower. While it’s possible in some cases, there are a few things to consider first. One of the main factors is the thread size, as automobiles and lawnmowers typically have different thread sizes. The thread length and gap are other essential aspects to remember.

If you want to avoid causing damage to your lawnmower or engine, it’s best to consult the manual and use a spark plug that matches the specifications mentioned. Doing so can ensure optimal performance and longevity for your trusty lawnmower.

Why does the spark plug gap have to be right?

The spark plug is a crucial component of your vehicle’s engine. Ensuring the correct gap between its electrode and center conductor is essential to your engine’s proper functioning. When the gap is too small or too large, it can cause issues with starting your car, engine misfires, or reduced fuel economy.

To ensure that your spark plug gap is correct, it’s essential to consult your vehicle’s owner manual or a reputable mechanic who can help you adjust it if necessary. Remember, checking and adjusting your spark plug gap can save you from costly repairs.

Can I change the gap on my spark plug myself?

Yes, you can adjust the gap on your spark plug yourself. However, it is recommended that you consult a professional technician or manual to ensure that the gap is set according to your vehicle’s specifications. Incorrectly adjusting the spark plug gap can lead to damage and costly repairs, so use caution when attempting any adjustments yourself.

How do I know if my spark plug is bad?

If your vehicle’s engine is producing a sputtering sound, calling out, or starting to miss, it may be a sign that one of your spark plugs has gone wrong and needs replacing. Additionally, you can check the condition of your spark plugs by removing them from the engine and inspecting them for any signs of corrosion, wear, or other damage. If you notice any of these issues, it is time to replace your spark plugs.

What should I do if my spark plug becomes fouled?

If your spark plug becomes fouled, the first step is to remove it from the engine and clean it with a wire brush. If the spark plug is still not functioning correctly, it’s time to replace it with a new one. Check the gap of your new spark plug and adjust it according to your vehicle’s manual if necessary.

Conclusion

In conclusion, understanding a spark plug’s different components and functions is key to keeping your vehicle running smoothly. Regularly inspecting and replacing your spark plugs can help avoid issues with starting or misfiring engines. Consult your owner’s manual or a professional mechanic when changing or adjusting your spark plug gap. Doing so will ensure that your vehicle stays in optimal condition and can help save you from costly repairs in the long run

Douglas Mackalie is a Founder of Mackalies Garden. He is one of the most exciting people you’ll ever meet. He has 25 years of experience in horticulture and gardening, most of which he’s spent outdoors getting his hands dirty.

What Spark Plug to Use for a Lawnmower?

The spark plug is a vital component of gasoline engines where it ignites the compressed air-fuel mixture in the combustion stroke to create a blast for the release of energy. Like automobile gasoline engines, a lawn mower’s gasoline engine needs a spark plug to ignition the air-fuel mixture. All spark plugs essentially have the same basic working principle. However, it is important to note that all gasoline engines need spark plugs, but they don’t need the same kind of spark plug. A spark plug type is characterized by various features such as thread length, thread pitch, and the gap between the two electrodes, etc. So, if you are in some lawn mowing mood on a lovely sunny morning and don’t want to end up just cranking the engine again and again, choose the right kind of spark plug for your lawnmower engine. We don’t want the wrong spark plug choice to destroy your mowing mood.

What Spark Plug to Use for a Lawnmower:

Use a “small engine” Spark Plug as most car engine spark plugs have a larger thread. Ensure that it has the right thread size (usually, 10 to 12mm) and the correct thread length (usually, 3/8 inch). Also, set the proper gap that matches the engine’s gap requirement. Check your Lawn Mower manual for the correct dimensions.

A detailed description of these features will help you understand their significance and how the wrong choice could harm your plug or engine, or both.

Spark Plug Components:

Interchangeability between a lawn mower spark plug and an automobile spark plug is not completely impossible, but generally, the two applications require spark plugs with different physical features. Some spark plugs are “hotter,” some are “colder,” some are “longer,” and some are “shorter.” What do all these nicknames mean, and what are they based on? Let’s have a detailed look at a spark plug’s physical features.

Spark plug components and features are not something all laymen know. But having a basic knowledge of them is not too difficult. A spark plug has four basic components:

• A metal casing or shell that is threaded.
• A central or live electrode: usually contains a resistor and is connected to the ignition coil’s output terminal by a heavily insulated wire.
• An insulator: to electrically isolate the outer shell from the central electrode. It prevents the escape of high voltages from the electrodes.
• An outer or ground electrode: It is also sometimes referred to as the side electrode.

In addition to these four basic components, spark plugs have other components, too, such as a ring, packing washer, center shaft, glass seal and gasket, etc., that make its working smooth.

The choice of lawn mower spark plug should be based on these features’ specifications since certain specifications will best meet your lawn mower engine’s requirements while others won’t.

Spark Plug Size:

Size is an important specification that must be considered when choosing a spark plug for your lawnmower engine. Size is one of the few parameters that makes a lawn mower spark plug different from an automobile engine.

For the threads to fit together, the thread sizes must be similar. If the threads don’t have similar sizes, they just won’t fit. If you try to fit together threads of different sizes by applying force, you’ll damage the spark plug or the engine or both. It is highly inappropriate to mate threads of different sizes forcefully for your engine’s health and spark plug. After all, we all want to keep our machines in order, working, and healthy.

Lawnmower engines usually use smaller thread sizes as compared to automobile engines. Most automobile engines use spark plugs with a thread size of about 14mm, whereas most lawn mower engines use spark plugs with a thread size of about 10 to 12mm. Because the size specifications are different, the two spark plug types can’t be interchanged. They won’t fit in the same unit.

So, next time you go shopping for a spark plug for your lawnmower, keep in mind the spark plug size. You can check the spark plug size of your lawnmower engine from the user manual, or you can go on the internet to get spark plug size info from the model number of your lawnmower engine.

Spark Plug Thread Length:

The second important specification that differentiates between an automobile engine and a lawnmower engine is the thread length.

Here again, lawn mower spark plugs usually have smaller thread lengths as compared to auto engines. Threads on automobile plugs are usually between 1/2 inch to 3/4 inch long. On the other hand, lawnmower engines usually use spark plugs whose threads are only 3/8 inch long.

What happens when you don’t use the right thread length?

Many engines use a tapered spark plug that fits with a tapered hole in the cylinder head. The mating of the two features seals the cylinder. If the right thread length is not used, the components would not fit together, and the lawnmower cylinder won’t be sealed. The use of the wrong thread length will impair the lawnmower engine’s starting or damage the engine or do both.

So, the spark plug thread length is another consideration to be kept in mind while choosing one for your lawnmower engine. Remember the golden rule: Right plug for the right application!

Spark Plug Gap:

As mentioned earlier, a spark plug has two electrodes. There is a live electrode in the center and a ground electrode on the side. Spark is generated at the live electrode, and it travels to the ground electrode across a gap between the two electrodes. The spark plug gap is something that can be changed. If your engine has a problem starting, check if the spark plug gap is right. If it’s not, you can adjust it to match the spark plug packaging or engine manual’s gap specification.

The spark plug gap can change during shipping or handling or if the plug falls on the floor or if the anode gets thinner. So, always check the gap before installing a spark plug.

Why does the spark plug gap have to be right?

Depending on the type of engine your lawnmower uses, the gap between the two electrodes must be set to a specific width. If the gap between the live and ground electrodes is too small, there is not enough space for the spark to be generated with enough power to ignite the cylinder’s air-fuel mixture. On the other hand, if the gap is too wide, the spark generated at the live electrode won’t travel to the ground electrode, and there will be no ignition.

You can use a feeler gauge to measure the gap on your spark plug and compare it to the gap requirement. The feeler gauge has many stripes of different thicknesses. Adjust the gap width to the required specification and check if the stripe with that thickness passes through the gap without any clearance. If it does, your plug is good to go, and so are you!

Other Specifications to be Considered:

Some spark plugs have their center electrodes operating at a higher mean temperature than the other spark plugs. Such spark plugs are called “hotter spark plugs.” Similarly, there are “colder spark plugs,” too.

Furthermore, some spark plugs extend further into the combustion chamber as compared to others. Such plugs are called “longer.” Similarly, there are shorter “plugs,” too.

Such features affect the starting and working of an engine and must be optimized based on its specifications. If the spark plug you are using in your lawnmower engine does not have the right features, it will cause problems and cause some symptoms to emerge that will indicate the problem.

Using a too hot plug for your engine may cause pre-ignition, while a too cold plug might result in your engine’s poor ability to run at any speed.

If the plug is too long, the piston will touch the plug, and both will be damaged, while if the plug is too short, the spark is not created in the right location in the cylinder, resulting in poor running characteristics.

Taking care of the basic specifications can help you avoid such problems. Just make sure that the size, thread length, and gap, etc., match your lawn mower engine’s requirements based on the specifications provided by the manufacturer.

Your Guide to Buying the Right Spark Plug for your Lawn Mower:

You already know about the basic components of a spark plug. You can check their required specifications from the user manual or can get them from the internet. But where do you buy a spark plug from?

Spark plugs are a vital engine component and are therefore very popular. You can easily find them in engine spare parts stores. If you know of a store that sells lawnmowers, they will surely have the spare parts.

Or you can buy online from popular online shopping websites and have the right spark plug delivered to your doorstep. Make sure to buy from a credible website and a seller with a positive customer rating. Don’t forget to go through the customer reviews to be sure.

All you need before going shopping is the required specifications. You can either use the old spark plug as a reference for them or using the user manual.

Related Questions:

Can I use a car spark plug in my lawnmower?

Automobile and lawnmower spark plugs are interchangeable in some cases, but not always. The two types usually have different thread sizes, thread lengths, and gaps, etc. So, use a plug for your mower whose specifications match the ones mentioned in the manual.

Can I change the gap on my spark plug myself?

Yes. It’s quite simple. Use a feeler gauge to check the thickness and adjust it till it matches the requirement.

Final Remarks:

The right spark plug is essential for your lawnmower engine’s smooth performance and, ultimately, your lawnmower. The spark plug needs to ignite the air-fuel mixture to start the engine and needs to be capable of surviving the cylinder environment. So, always get the right spark plug for your lawnmower engine based on the features specifications that we just discussed.

What You Should Know About Spark Plugs, Their Adjustment, and Their Replacement (2023)

Spark plugs are inside every gasoline car engine, but most vehicle owners know little about these small but vital engine parts. Knowing more about their operation, maintenance and replacement is one key to making sure your engine runs well. Below is more information about spark plugs, how you can check them for proper adjustment and functioning, and how to know when it is time to replace them.

The Purpose of Spark Plugs

The basic operation of an internal combustion engine, which describes your car’s gasoline motor, is not particularly complex. The motor first mixes gasoline and air in small quantities and then ignites the mixture inside a cylinder with an electrical spark.

As the hot gases from the explosion expand, they push a piston, which in turn is linked to a shaft that transfers power to the transmission and ultimately the wheels. This process occurs thousands of times per minute, but for it all to work, the source of the sparks, the spark plugs, must fire consistently.

The Anatomy of a Spark Plug

Spark plugs are constructed of an insulating material and a metallic conductor. At the top end of the plug, the tips connect to the spark-plug wires and send an electrical current down the interior of the plug to the electrodes. There are two electrodes separated by a small gap; as the current approaches the end of one electrode, it effectively jumps across the gap to the opposite electrode and creates a visible spark.

The Spark-Plug Gap

One of the key factors that makes a spark plug work well, or not, is the size of the gap between the electrodes. If the gap is too small, the spark will likely be too weak and cause the engine to run poorly or with poor efficiency. However, if the spark plug gap is too large, the spark is unlikely to consistently jump across the long distance between electrodes, thus leading to a rough-running engine or one that doesn’t run at all.

Fortunately, spark-plug gaps can be easily adjusted by mechanics, including many amateur do-ityourselfers. A spark-plug gap gauge both measures and adjusts the gap and is inexpensive and simple to use.

There are different types of gap gauges, but they all basically function the same way; simply locate the recommended gap for the spark plugs in your vehicle and then insert the gauge edge into the gap and measure the distance between the electrodes.

Should the gap be too narrow, the mechanic will gently pry the gap apart with the gauge. On the other hand, should the gap be too wide, it can be narrowed by the mechanic’s squeezing the electrodes closer together with a tool or pushing the bottom electrode down onto a tabletop.

Replacement of a Spark Plug

Spark plugs undergo a remarkable amount of stress because they experience electrical currents of tens of thousands of volts, hundreds of degrees of heat, and constant vibration. Eventually, all spark plugs will wear out and need to be replaced. Knowing when a spark plug needs replacing is sometimes a matter of knowing the lifespan in terms of miles, but the presence of certain engine symptoms can provide clues. Here are some things that can help you know when it’s time to install new spark plugs:

• Difficulty starting the engine, especially during a cold start
• Poor running or idling at any point
• Lack of acceleration when pedal is pushed
• High fuel consumption unexplained by other factors

If your car is experiencing problems that lead you to believe your car’s spark plugs need replacing, then contact a qualified automotive technician for assistance. They can perform spark-plug replacements and offer sound guidance about other plug-related issues.

If you find that the issue isn’t with the spark plugs, and you end up deciding to get a new car, consider donating your old car to Newgate School, which teaches disadvantaged young adults auto mechanics skills.