Are Lawn Mower Spark Plugs Universal?

Lawn mowers are surprisingly complex machines with quite a few moving parts, any of which could break. Generally speaking, lawn mowers come in two varieties; walk-behind mowers and lawn tractors with a mower blade underneath. There are several small engine manufacturers that build the engines that are found in either of these machines, and where there’s different engines, there’s different parts for those engines. 

Are lawn mower spark plugs universal? Lawn mower spark plugs are not universal. Each engine model has a specific spark plug that will fit it, and swapping out the incorrect spark plug could cause engine failures or damage. Before installing a spark plug, you should ensure it is the right model for your particular engine.

The spark plug is part of the ignition system, which creates the spark of electricity that ignites the air and fuel mixture in the engine. Replacing the spark plug on a lawn mower is a relatively simple process but ensuring you use the correct spark plug for your engine model is critical to keeping your mower running smoothly.

Keep reading to find out all about lawn mower spark plugs and how to replace them.

Are Lawn Mower Spark Plugs Universal?

While specific spark plug models are not universal, all working engines require a spark plug. There are several large manufacturers of lawn mower engines, which are typically a different manufacturer than the lawn mower (for example, Briggs & Stratton supplies the lawn mower engines for Husqvarna brand mowers). 

Each of these manufacturers have a different spark plug, and even some different engines by the same manufacturer have different spark plugs as well. You should always check with the manufacturer or your owner’s manual to find spark plugs that are compatible with your mower. 

How Are Spark Plugs Different?

A spark plug is a component of an engine’s ignition system. In combustible engines, the spark plug provides the small electrical spark that ignites the air and fuel mixture in the pistons, which then creates an explosion that causes the pistons to start pumping, thereby starting the engine.

Because the spark plug is involved in a mini-explosion every time you start the engine, it needs to be made from durable materials

Spark plugs are differentiated by their thread width, the gap they’re designed for, and their heat rating, among other things. The importance of making sure you have the right spark plug for your lawn mower model cannot be overstated.

If you buy a replacement and it doesn’t go in properly, don’t force it, as you may damage the threads in your mower. Without a properly fitting spark plug, you could damage your small engine and void the warranty as well.

How Do You Know Your Spark Plug Needs to Be Replaced?

There are a number of symptoms your lawn mower may exhibit when the spark plug is having issues. Among these are the following:

  • Engine won’t start
  • Engine sputters and starts
  • Engine won’t turn over
  • Engine runs rough

If any of these happen with your lawn mower, one of the first and simplest things to check is your spark plug. Do a visual inspection of the plug, checking to see if there’s any excessive dirt or debris on it, if the electrode is damaged, or if the porcelain portion is cracked. If you can’t clean your spark plug or if one of the parts is damaged, it’s time to replace the plug. 

However, your spark plug may just be dirty and covered with engine dirt and grime. You can remove the spark plug, following the steps outlined in the owner’s manual for your mower, and clean it with a spark plug cleaning brush or rag. 

Spark plugs aren’t expensive, and they’re designed to last for years. Most lawn mower manufacturers recommend that, as part of your yearly maintenance on your machine, you check your spark plugs for serviceability.

How to Find the Right Spark Plug for Your Lawn mower

The spark plug you purchase should be the recommended plug for your lawn mower. The simplest way to make sure you buy the same plug is to take the old spark plug to your local hardware or auto store and buy the identical part. Your owner’s manual or the manufacturer’s website will be a good source of information as well, telling you exactly what sort of spark plug you need to fix your mower. 

Spark plugs are made from a variety of different metals and materials, each of which has differing levels of durability. Copper spark plugs are the cheapest but also last the shortest amount of time, while spark plugs made from platinum or iridium are more durable and will last much longer. 

Of course, the more durable the material, the more expensive the spark plug. A copper spark plug will usually be just fine for a lawn mower, and if you check it at least annually as part of your lawn mower maintenance, it’s quite possible that it lasts as long as the life of your lawn mower.

Walk-Behind Lawn Mowers

Walk-behind mowers have small engines that either come in a two-stroke or four-stroke variety. For these small engines, you’ll likely be using an L-head or side-valve spark plugs because the engines are called either L-head or side-valve engines. 

These spark plugs may be smaller or made from different types of materials than automotive spark plugs, but it’s possible you can find the same spark plug in an automotive store. Your engine’s manufacturer can give you a list of suitable replacement spark plugs.

Lawn Tractor Spark Plugs

Lawn tractors are powered by much larger engines than walk-behind lawn mowers, being more similar to car engines (albeit on a much smaller scale). These engines, which are referred to as overhead valve engines because of their design, can range from 13 to 30 horsepower, though the larger, commercial use lawn tractors can have even higher horsepower ratings. 

These engines will usually need a more durable spark plug than a small walk-behind mower, and you might have better luck finding a suitable replacement at an auto parts store. 

Where Can You Buy Replacement Spark Plugs?

Replacement spark plugs are easy to find. As long as you have the part number your engine requires, you can visit most automobile parts stores or your local hardware store. The hardware store where you purchased your lawn mower is very likely to have the specific spark plugs designed for your engine model. 

You can also have great luck finding replacement spark plugs on your engine manufacturer’s website. Usually, the manufacturer will let you look up your engine by model number, then will have links to be able to purchase suitable replacements.

There might be several plugs that will fit your mower, in which case you might choose according to customer reviews or cost.  A spark plug for your push mower will probably cost you around $5. 

Final Thoughts

Lawn mower spark plugs are designed for a specific engine, and different engine manufacturers require different size or spec spark plugs. If you have a lawn tractor, your engine is different as well and therefore requires different spark plugs. Spark plugs are built to withstand high amounts of heat and pressure, but they can become caked with engine debris or damaged after many uses. 

If you need to replace a spark plug, your best bet is to check with the manufacturer of your lawn mower engine and buy the recommended part number. That way, you can keep your lawn mower starting smoothly and running well for years. 


Peter Toth

Hi! I'm Peter, the owner of BackyardGadget. Working around the house has always been a big part of my life. I've created this site to share my experience, and to help people choose the right tools for the job. Thank you for stopping by!

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