Are All Lawn Mower Spark Plugs The Same?


All combustion engines, including those on lawnmowers, require a spark for them to convert fuel to power. The aptly named spark plug is responsible for providing this spark during every combustion cycle. While they perform a similar role in different engines, are lawnmower spark plugs the same and interchangeable?

Lawn mower spark plugs are definitely not all the same. Walk behind mowers require less durable spark plugs with smaller thread widths and gaps. Riders require more durable plugs with larger threads and wider gaps. As well, each brand normally uses their own sometimes patented plugs.

That is our focus today, as we look at lawnmower spark plugs and how they are categorized. We will also talk about the effects of using different plugs on a mower. Let’s get started.

Are Lawn Mower Spark Plugs Universal?

Sparkplugs are a vital component in the combustion process, as they provide the spark required to ignite the fuel and air mix in the engine cylinder chamber. The efficiency of each combustion cycle depends on the timing and proximity of the spark.

While the sparkplug’s role is essential, it is still a very singular function, which may lead many mower owners to believe that it can be swapped out with any other spark plug. After all, a spark is a spark, right?

Wrong!

This belief could not be further from the truth. Lawnmower sparkplugs are not universal simply because lawnmower engines are not universal. Sparkplugs are just as diverse as the engines they serve.

Lawn Mowers Use Different Spark Plugs Because They Do Different Jobs

As you already know, lawnmowers come in different shapes and sizes because they all tackle different types of lawn care jobs.

The performance demands on a commercial zero-turn mower, for example, are much different from what you would expect from a 2-horsepower home push mower.

The same goes for sparkplugs, which must be able to contribute to performance while being appropriately durable.

Walk-behind mowers, which consist of push and self-propelled machines, tend to have small engines (2-10 horsepower) and, therefore, require very simple sparkplugs. The most common type is the side-valve sparkplug.

Riding mowers, which include zero-turns and lawn tractors, have bigger engines (12-30+ horsepower) so they make use of bigger and more durable sparkplugs.

Spark Plugs Are Also Designed By Manufacturers To Only Fit Their Mowers

In addition, every engine manufacturer has its own patented sparkplugs that work exclusively with its engines. Currently, there is no universal supplier of combustion engine sparkplugs, although some aftermarket manufacturers are licensed to make plugs for certain major brands.

Sparkplugs can vary in terms of:

  • Their designated gap from the combustion chamber.
  • Their durability (heat rating, etc.)
  • Thread width

Thread width, especially, is a tell-tale sign of whether a sparkplug is designed for your mower. If the plug is too big or too small for the hole, you’ve probably got the wrong sparkplug on your hands.

Your lawnmower’s instruction manual is the best place to start when you want to find a new sparkplug. It will have the exact part number, as well as the engine model number, so you can request a new one from the manufacturer or an auto shop. You can also just take the old sparkplug to an engine shop and have a professional help you out.

To check out the wide variety of mower spark plugs available and their prices, follow this link to Amazon.

If you liked this article, see some of my others here…

Sparkplugs For Lawn Mowers Chart

As we’ve already established, mower sparkplugs come in many different iterations and are made for specific engines from specific manufacturers.

While there is no universal chart for lawnmowers, American small engine giant Briggs and Stratton offers a rough idea of what you should be looking for when your sparkplug needs changing.

The following table is B&S’s guide for the best side-valve sparkplugs for its walk-behind mower engines.

Replacement Part TypeSparkplug replacement part numberSparkplug gap (inches)
Standard resistor796112S802592S50950.030
Electromagnetic Suppression (EMS)6974510.030
Extended Life Series L-Head Spark Plug Platinum7965605062 (5062D, 5062H)0.030
Champion RJ19LMC5918680.020 for engines built after Code Date 110630×0.030 for engines built before Code Date 110701xx
Champion CJ8, RCJ8, RJ19HX, RJ19LM7965605062 (5062D, 5062H)0.030
Champion RJ2YLE7998760.020
Surefire RJ2XYLE for Craftsman Smooth Start5910400.030
Resistor used on Vanguard models 050032 and 0864006920510.030
Resistor (replacing Champion RC12YC)491055S0.030
Electronic Suppression6910437920150.030
Extended Life Series OHV Spark plug platinum6962025066 (5066D, 5066H)0.030
Resistor Spark Plug – hotter spark496018S50920.030
Resistor6920510.020
Electromagnetic Suppression (EMS)6927200.030

What Happens If You Use The Wrong Spark Plug In A Mower?

As you can see, a spark plug can be “wrong” in various ways, each with its own consequences. 

Trying to fit an oversized plug could result in the hole threading being worn out, which would make fitting the correct plug difficult in the future. Even if you could fit it in position, the plug would probably produce excessively large sparks.

An undersized spark plug will have the opposite problems. Firstly, it won’t be secure in its position because you won’t be able to screw it in properly. Secondly, an undersized sparkplug will produce an undersized spark, which may produce weak explosions, and ultimately, lower power output. 

Using a smaller sparkplug than is required will also waste fuel. The plug will not seal the engine cylinder, and force from the explosion may escape. Your lawnmower’s performance may drop noticeably in such an instance.

The gap between the plug and the combustion chamber is another major area of consideration. Each engine requires a specific gap for the combustion process to take place efficiently. If the gap is too small, and the plug is too close, the spark may cause a premature explosion, which may use fuel inefficiently.

If the gap is too wide, and the plug is too far, the spark may reach the combustion chamber later than required, which results in weaker explosions and, ultimately, lower power output.

The long-term effects of the inefficient combustion from a sparkplug that is the wrong size or distance could result in rapid engine wear and tear, as well as more frequent fuel fill-ups. Using the wrong threaded sparkplug will eventually cause engine starter problems.

Can You Use Your Car Sparkplugs In A Lawn Mower?

It is not an unreasonable question to ask. It is understandable when one looks at the large and complex machinery that is being produced for lawn care these days. Some may legitimately want to know if an automobile spark plug will work in their mower.

Generally speaking, lawnmower sparkplugs are not interchangeable with car sparkplugs. There may be some strange exception in some model, but generally automobile spark plugs will not fit or properly function in a walk behind lawn mower or a riding mower.

Automobile sparkplugs are in the ½-inch and ¼-inch range, while walk-behind mower sparkplugs are closer to 3/8 of an inch. It is highly improbable that a sparkplug from a car would fit on a lawnmower. 

The Final Touches On Mower Spark Plugs…

There are no universal spark plugs for mowers of most any type. This especially goes for mowers not made by the same manufacturer. You also cannot use a car spark plug for your mower in most all cases.

These plugs are designed by these companies to be used only in their mowers and sold by their vendors. Though there can be exceptions, this is the general rule.

If you would like to see more articles like this one, check out some of my others here…

References

https://www.briggsandstratton.com/na/en_us/support/faqs/browse/identifying-the-correct-spark-plug-and-gap.html

https://homeguides.sfgate.com/lawn-mower-spark-plugs-different-vehicle-spark-plugs-86256.html

Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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