Learning how to remove a lawn mower spark plug is a simple task that requires a specific socket wrench. This is a fundamental piece of maintenance that every mower owner should know, whether you’re performing a routine check, cleaning, or a full replacement. A faulty spark plug is a common reason for a mower that won’t start, so knowing how to access it is the first step to getting your machine running smoothly again.
This guide will walk you through the entire process safely and efficiently. You’ll learn what tools you need, the step-by-step removal procedure, and what to do with the plug once it’s out. Let’s get started.
How To Remove A Lawn Mower Spark Plug
The core process of removing a spark plug is straightforward, but doing it correctly prevents damage to your engine. The key is to work methodically and use the right tools. Rushing or using incorrect equipment can strip threads or break the ceramic insulator, leading to costly repairs.
Before you touch anything, the most critical step is to ensure your safety. A lawn mower engine can be dangerous if not handled properly.
Essential Safety Precautions Before You Begin
Always prioritize your safety. A moment of caution can prevent serious injury.
- Disconnect the Spark Plug Wire: This is non-negotiable. Locate the rubber boot at the end of the thick wire leading to the top of the engine. Firmly pull it straight off the spark plug. This prevents any chance of the engine accidentally starting.
- Allow the Engine to Cool Completely: Work on a cold engine. A spark plug can be extremely hot after use and can cause severe burns. Wait at least 30 minutes after shutting down the mower.
- Work in a Well-Ventilated Area: Perform this task outside or in a garage with the door open to avoid fume buildup.
- Clear the Work Area: Move away any debris, grass clippings, or flammable materials from around the mower before you start.
Gathering The Necessary Tools And Materials
Having the correct tools on hand makes the job quick and easy. You likely already have most of these.
- Spark Plug Socket Wrench: This is the special tool mentioned earlier. It has a rubber insert inside to grip the ceramic part of the plug and prevent cracking. Sizes are typically 5/8″ or 13/16″.
- Socket Wrench Extension: A short extension bar (about 3 inches) is often needed to reach down into the spark plug well.
- Ratchet: A standard 3/8-inch drive ratchet to turn the socket.
- Gap Gauge Tool: For checking the electrode gap on a new or cleaned plug. A feeler gauge works best.
- Compressed Air or Small Brush: For cleaning debris from around the spark plug hole before removal.
- Anti-Seize Compound (Optional): A small amount can be applied to the threads of the new plug to prevent seizing, but use it sparingly.
- Torque Wrench (Recommended): For installing the new plug to the exact manufacturer’s specification, preventing over-tightening.
Locating The Spark Plug On Your Mower
The spark plug is always on the engine itself, not the mower deck. It’s usally a short, thick, white ceramic cylinder with a rubber boot attached to the top.
- Follow the Wire: The easiest way to find it is to trace the thick, insulated wire from the ignition system. It will lead you directly to the rubber boot covering the plug.
- Look on the Engine Cylinder: The plug is screwed into the cylinder head. On most walk-behind mowers, it’s on the top or front of the engine. On riding mowers, it may be on the side.
- Consult Your Manual: If you’re unsure, your mower’s owner manual will have a diagram showing its exact location.
Common Spark Plug Locations by Engine Type
While generally similar, placement can vary.
- Vertical Crankshaft Engines (common on push mowers): The plug is typically on the top of the engine, facing upward.
- Horizontal Crankshaft Engines (common on some riders): The plug is often on the side of the engine cylinder head.
Step-by-Step Removal Process
Now that you’re prepared and have found the plug, follow these steps carefully.
- Clean the Area: Use compressed air or a small brush to gently remove any grass, dirt, or debris from around the base of the spark plug. This prevents contaminants from falling into the engine cylinder when you remove the plug.
- Remove the Spark Plug Wire: Grasp the rubber boot (not the wire itself) and pull it straight off the end of the spark plug. You might need to twist it slightly if it’s stuck. Set the wire aside where it won’t fall back into contact with the plug.
- Attach the Socket Wrench: Fit the spark plug socket onto the extension bar, then attach it to your ratchet. Carefully lower the socket onto the spark plug. Ensure it is fully seated and straight to avoid rounding the hex head of the plug.
- Loosen the Spark Plug: Turn the ratchet counter-clockwise to loosen the plug. It may be tight initially. Apply steady pressure until it breaks free. Once loose, you can unscrew it the rest of the way by hand.
- Remove the Spark Plug by Hand: Finish unscrewing the plug using just your fingers. This gives you better control and prevents cross-threading. If the plug is difficult to turn by hand, reattach the socket to continue loosening it gently.
- Inspect the Plug and Hole: Once removed, examine the old spark plug’s condition—it can tell you a lot about your engine’s health. Also, take a quick look into the empty spark plug hole to ensure it’s clean.
What To Do After Removing The Spark Plug
With the plug out, you have a few options. You can clean and regap the existing plug if it’s in good condition, or you can replace it with a new one. For most annual spring tune-ups, replacement is recommended.
Inspecting Your Old Spark Plug
The electrodes at the business end of the plug reveal your engine’s condition.
- Normal Wear: The center and side electrodes will be worn down and rounded. The insulator may be light tan or gray in color. This indicates proper engine operation and simply shows the plug has reached the end of its service life.
- Carbon Fouled: A dry, black, sooty coating indicates a rich fuel mixture, a dirty air filter, or excessive idling.
- Oil Fouled: A wet, black, oily coating suggests engine oil is leaking into the combustion chamber, which is a more serious issue.
- White or Blistered Insulator: This points to an engine that is running too hot, possibly from a lean fuel mixture or incorrect ignition timing.
Gapping and Installing a New Spark Plug
If you are installing a new plug, it must be properly gapped before installation.
- Check the Gap: Find the correct gap specification in your mower’s manual (common gaps are .030″ or .035″). Slide the correct feeler gauge blade between the center and side electrode. It should have a slight drag.
- Adjust the Gap: If adjustment is needed, carefully bend the side electrode only, using the gap tool’s bending accessory. Never bend the center electrode, as it can damage the ceramic insulator.
- Thread the Plug by Hand: Carefully insert the new spark plug into the hole and start threading it in by hand. Turning it counter-clockwise first until you feel a drop can help align the threads correctly. Screw it in until it is finger-tight. This is crucial to avoid cross-threading.
- Final Tightening: Use your socket wrench to give the plug a final tighten. If you don’t have a torque wrench, a general rule is to turn it an additional 1/8 to 1/4 turn after it is snug. Do not overtighten. If using a torque wrench, refer to your manual for the exact setting (often between 15-20 ft-lbs).
- Reconnect the Wire: Push the rubber spark plug boot firmly onto the end of the new plug until you feel or hear it click into place. Ensure it is fully seated.
Troubleshooting Common Removal Problems
Sometimes, the plug doesn’t come out easily. Here’s what to do.
Dealing With a Stuck or Seized Spark Plug
If the plug won’t loosen, don’t force it. Forcing it can break the plug off in the head.
- Apply Penetrating Oil: Spray a quality penetrating oil (like PB Blaster or Liquid Wrench) around the base of the spark plug where it meets the cylinder head. Let it soak in for at least 15-30 minutes.
- Use Steady, Careful Force: Try loosening the plug again with the ratchet. Apply steady pressure rather than a sudden jerk. You can try tightening it slightly first, then loosening it.
- Use a Breaker Bar: If necessary, you can carefully use a breaker bar for more leverage, but be extemely cautious not to strip the head or break the plug.
What to Do If the Spark Plug Breaks
If the ceramic insulator cracks or the plug breaks off, stop immediately.
- Remove All Debris: Use compressed air and tweezers to carefully remove any ceramic pieces from the hole to prevent them from falling into the cylinder.
- Use an Easy-Out Tool: A specialized broken spark plug removal tool (easy-out) can be used to extract the remaining threaded portion. This requires patience.
- Seek Professional Help: If you are uncomfortable with this, take the mower to a small engine repair shop. They have the tools and expertise to remove it without damaging the engine head.
Preventative Maintenance Tips
Regular attention can prevent difficult removals in the future.
- Replace Annually: Make spark plug replacement part of your yearly spring mower tune-up. A fresh plug ensures easy starts and optimal fuel efficiency.
- Use Anti-Seize Sparingly: A tiny dab on the threads of the new plug can prevent seizing, but avoid getting any on the electrodes.
- Always Hand-Thread First: This single habit is the best defense against costly cross-threading damage.
- Store Your Mower Properly: At the end of the season, consider removing the plug, adding a teaspoon of oil into the cylinder, and turning the engine over by hand to coat the cylinder walls and prevent corrosion.
Frequently Asked Questions
What Size Socket Do I Need to Remove a Lawn Mower Spark Plug?
The two most common sizes are 5/8 inch (16mm) and 13/16 inch (21mm). The 5/8 inch size is more prevalent on modern small engines. The best way to be sure is to check your owner’s manual or measure the hex head of the old plug with a caliper. A spark plug socket set often includes both sizes.
How Often Should I Remove and Check My Lawn Mower Spark Plug?
You should inspect your spark plug at least once per mowing season, ideally during your spring maintenance. For most residential mowers used weekly, replacing the plug once a year is a good practice. If you notice hard starting or poor performance, checking the plug should be your first step.
Can I Clean and Reuse an Old Spark Plug?
Yes, you can clean a lightly fouled plug to extend its life. Use a wire brush to remove carbon deposits from the electrodes and insulator. You can also use a specialized spark plug cleaner. However, if the electrodes are severely worn or eroded, or if the plug is oil-fouled, replacement is the better and more reliable option. New plugs are inexpensive.
Why Is It Important to Disconnect the Spark Plug Wire?
Disconnecting the wire is a critical safety step that eliminates the risk of an electric shock or the engine accidentally starting while your hands are near the blade or moving parts. Even with the ignition switch off, a static charge or faulty switch could cause the plug to arc.
What Are the Signs of a Failing Spark Plug That Needs Removal?
Common symptoms include difficulty starting the engine, rough idling or running, reduced power and acceleration, increased fuel consumption, and visible black smoke from the exhaust. If your mower exhibits any of these issues, removing and inspecting the spark plug is a logical first diagnostic step.