Sort of like the heartbeat of an engine, the spark plug is one of the key components that a lawn mower uses to ignite gasoline and create power. And like a heart, spark plugs work very hard and are constantly firing to keep the engine alive. Because of this, they do wear out over time. But luckily, figuring out how to replace a lawn mower spark plug isn’t anything like learning how to perform heart surgery. All you’ll need is a few simple tools and a bit of know-how to get this job done right.
Why You Might Need to Change Your Spark Plug
As mentioned above, this is a component that will eventually need replacing. Exactly how often a spark plug will need changing does vary, as does the reason for changing them, but there are a few common things (bad spark plug symptoms) to look for. The most typical reasons are: the spark plug has already been used for a season’s worth of time, oil or carbon has soiled it, or the mower has shown less power or fuel economy.
What You Will Need to Change Your Lawn Mower Spark Plug
When actually considering how to change your lawn mower’s spark plug, you’ll probably want to figure out what tools you’ll need first. Though you don’t need a ton of tools for this job, it helps to have the right ones. The things you should gather are:
- Socket wrench
- Spark plug socket
- Clean rag or paper towel
- New spark plug
- Insulated pliers (recommended)
How to Remove a Lawn Mower Spark Plug + Replace
Now that you’ve got all of your tools together, let’s talk about how to change a lawn mower’s spark plug. Make sure to take your time while doing this so that the job gets done smoothly and safely.
1. Stage Lawn Mower
Before you get started, you’ll want to get your lawn mower positioned on a nice, flat, piece of ground. If you have a couple of pieces of scrap wood or small stones, it’s a good idea to block the wheels so that the mower won’t go rolling away.
Also, be sure that you’ve waited for the lawn mower’s engine to cool before you get going on this project. You’ll be working in very close proximity to the engine block and could easily burn yourself. I’d say to wait at least 30 minutes after using your mower before you get started.
2. Disconnect Ignition Cable
Now that your lawn mower is set in place you can locate the spark plug and disconnect the spark plug’s hood and wire that make up the ignition cable. This is something that you should do anytime you’re working on your lawn mower to prevent any chance of unexpected engine ignition.
To do this, I like to use a pair of insulated needle-nose pliers to grab the middle of the hood and gently wiggle it off of the spark plug. You won’t need to use much force to grab the spark plug hood because the pliers will grip the rubber pretty easily. If this isn’t your style, you can just grab the hood with your fingers and pull it off.
3. Remove Old Spark Plug
Figuring out how to remove a lawn mower’s spark plug is arguably the most difficult part of the whole replacement process. Although removal of the old plug can be a little bit annoying, the right tools make a huge difference.
What I do is grab my spark plug socket without putting it on the wrench, and seat in on the spark plug by hand first. This way I can check that it’s making good contact with the spark plug and won’t strip.
Then, grab the socket wrench itself and attach it to the socket that is set up on the spark plug. Apply a little bit of counterclockwise (lefty loosey) pressure to the spark plug at first to be sure that the socket still won’t slip.
Now, apply normal force slowly until the threads come loose. Once the spark plug is loose, it’s easier to unscrew the remaining threads by hand because there will be no resistance and you’ll have a ton of spinning you’ll need to do.
4. Inspect Old Plug
Before you wipe off or throw away your old spark plug (which can go in with your regular garbage by the way), check out its condition. Look for any cracks, burns, or debris on it.
This step isn’t exactly necessary but I would definitely recommend it. Taking a closer look could help you figure out why your spark plug failed.
It’s also really good to know what might’ve made your spark plug stop working in case it is anything other than the usual wear and tear. Oily, sooty, and cracked spark plugs can suggest other possible issues with your lawn mower, like oil in the cylinder for example.
5. Clean and Install New Spark Plug
Once you have your new spark plug unboxed, make sure it’s clean, and also wipe out the top of the cylinder where the spark plug will screw in.
Now start to thread the new spark plug by hand gently until you feel resistance. Once here, get your spark plug socket and socket wrench and tighten it down the rest of the way. You’ll want to secure the spark plug relatively tightly but don’t overdo it.
6. Reconnect the Cable
Before snapping the spark plug hood and cable back on, be sure that the small metal terminal at the top of the spark plug is threaded on completely. Hand-tight is fine, but it’s worth noting because sometimes these little pieces come loose.
All that’s left now is to reconnect the ignition cable as it was before. You should be able to feel the spark plug hood click into place as it slides over the spark plug’s terminal.
How to Remove a Lawn Mower Spark Plug Without a Socket (5 Tricks)
Although a specialized spark plug socket is the most common and recommended lawn mower spark plug removal tool, there are a few things you can do if you don’t have one handy. My advice would be to invest in a spark plug socket if possible. But if you’re in a pinch, and are wondering how to remove a lawn mower spark plug without a socket, here are some other methods you can try.
You may have tried this already, but give your spark plug a firm twist with your fingers if you don’t have the right deep socket to use. Oftentimes spark plugs aren’t installed very tightly or may have loosened over time due to vibrations. If you’re lucky, you just might be able to unscrew your spark plug by hand.
Two things the average DIYer or handyman has laying around are WD-40 (or some other type of penetrating oil) and duct tape. In most situations, one of the two could be of use. Here, grab your lubricant and see if it does the trick.
Spray a small amount at the base of your spark plug if it won’t budge and then wait 5 minutes or so. Then, with the help of your hand or a piece of rubber tubing, grip the spark plug and give it a twist. Using penetrating oil like this can make a really big difference in some situations.
A small length of rubber can help you get a grip and some leverage on your spark plug. Try and find an old piece of rubber tubing that is the same width or just a tad skinnier than your spark plug, slide it over the end, and then grab and twist.
Aluminum Foil Method
If you happen to have some deep sockets but not the correct size, you can give this method a shot. The idea is that you use a wider deep socket and shim it with aluminum foil on the inside of it to try and grip onto the spark plug. I’ve never tried this but have heard of it working before.
Just be careful not to strip your spark plug or shred a bunch of aluminum foil that could fall into your cylinder.
Other Wrench or Pliers (Last Resort)
Well, I would never suggest doing this unless you have a pretty dire need to remove your spark plug right this instant, but you can try gripping the spark plug’s base with a set of pliers or a wrench that you have nearby.
This approach does not work very well and often will cause more harm than good. But, if you’re especially gentle, you may just wiggle it free. However, I would suggest buying a spark plug socket instead of trying this.
How to Change a Spark Plug on a Riding Lawn Mower – Anything Different?
When it comes to how to change a spark plug on a riding lawn mower, the process is pretty much the same as with a push mower. The key difference is how you need to prepare for the removal of the spark plug.
If your riding mower has a keyed ignition, be sure to turn the ignition off, and remove the key. Then, disconnect the battery’s negative terminal and secure it away from the battery. This step is one that you need to do for all riding lawn mowers. It’s actually a good idea to disconnect the battery any time you do work on a riding mower. Then, follow the same steps listed above and reconnect the battery at the very end.