Learning how to remove a spark plug from lawn mower is a fundamental skill for any homeowner. Removing a spark plug safely requires the right socket and a careful hand to avoid damaging the threads. This simple maintenance task can help you diagnose engine problems, perform a tune-up, or simply replace a worn-out part. With a few common tools and about 15 minutes, you can complete this job yourself and keep your mower running smoothly.
How To Remove A Spark Plug From Lawn Mower
This section provides the complete, step-by-step process. Before you start, always ensure the lawn mower is on a flat, stable surface and the engine is completely cool. Working on a warm engine is a safety risk and can lead to burns.
Tools And Materials You Will Need
Gathering the correct tools before you begin makes the job faster and safer. You likely have most of these items in your garage already.
- Spark Plug Socket (usually 5/8″ or 13/16″) with a Rubber Insert
- Socket Wrench or Ratchet with Extension
- Gap Gauge or Feeler Gauge
- Clean Rag or Shop Towel
- A Small Amount of Anti-Seize Compound (Optional)
- A New Spark Plug (Recommended to have on hand)
- Safety Glasses
- Work Gloves
Step 1: Disconnect The Spark Plug Wire
This is the most critical safety step. Locate the spark plug wire, which is a thick, rubber-insulated wire leading from the engine to the top of the spark plug. Firmly grasp the rubber boot (not the wire itself) and pull it straight off the plug. This prevents any accidental engine starts while you are working.
Important Safety Note
Some mowers have a safety clip or latch on the boot. If it feels stuck, gently twist it back and forth while pulling. Never yank on the wire, as this can damage the internal connection.
Step 2: Clean The Area Around The Spark Plug
Use your clean rag to wipe away any grass clippings, dirt, or debris from around the base of the spark plug. This prevents foreign material from falling into the engine cylinder when you remove the plug, which could cause serious damage.
Step 3: Loosen And Remove The Spark Plug
Select the correct spark plug socket. Fit it onto the plug, ensuring it is fully seated. Attach your ratchet and extension. Turn the ratchet counter-clockwise to loosen the plug. Once it is loose, you can finish unscrewing it by hand. Carefully lift the spark plug straight out of its port.
If The Spark Plug Is Stuck
If the plug is difficult to turn, do not force it. Apply a small amount of penetrating oil around the base of the plug and let it sit for 10-15 minutes. Then, try again. Forcing it can strip the aluminum threads in the engine head, leading to costly repairs.
Step 4: Inspect The Old Spark Plug
Examining the old plug can tell you a lot about your engine’s health. Look at the electrode (the small metal piece at the tip) and the ceramic insulator.
- Normal Wear: The electrode will be worn down and the insulator may be light tan or gray in color.
- Oily Deposits: Indicates excess oil entering the combustion chamber, often a sign of engine wear.
- Carbon Fouling (Black, Sooty): Suggests a rich fuel mixture, a dirty air filter, or excessive idling.
- White, Blistered Insulator: Points to an engine running too hot, possibly from incorrect fuel or timing issues.
How To Install A New Spark Plug
Installing the new plug correctly is just as important as removing the old one. A improperly installed plug can cause poor performance or damage.
Step 1: Check And Adjust The Gap
Most new spark plugs are pre-gapped, but it’s always wise to check. Find the correct gap specification in your mower’s manual (common gaps are .030″ or .025″). Insert your gap gauge between the center and side electrode. If adjustment is needed, gently bend the side electrode with the gap tool until you feel a slight drag on the gauge.
Step 2: Thread The New Plug In By Hand
This step is crucial. Carefully insert the new spark plug into the socket and lower it into the hole. Start threading it in by hand, turning it clockwise. It should thread in smoothly and easily. If you encounter any resistance, stop immediately. Back the plug out and try again, ensuring it is not cross-threaded.
Step 3: Tighten The Spark Plug
Once the plug is hand-tight, use your ratchet to give it a final snug. For most small engines, a quarter to a half turn past hand-tight is sufficient. Over-tightening is a common mistake that can strip threads or crack the plug’s ceramic insulator. If you have a torque wrench, refer to your manual for the exact specification (usually between 15-20 ft-lbs).
Step 4: Reconnect The Spark Plug Wire
Push the rubber boot firmly onto the end of the new spark plug until you feel or hear a click. Ensure it is seated all the way down. A loose connection will prevent the mower from starting.
Common Mistakes To Avoid
Being aware of these common errors can save you time, money, and frustration.
Using The Wrong Socket
A standard deep-well socket can crack the spark plug’s porcelain insulator. Always use a proper spark plug socket with a rubber or magnetic insert to grip the plug securely.
Forgetting To Disconnect The Wire
Always, always disconnect the spark plug wire first. This ensures the engine cannot start, protecting you from the blade and a potential shock.
Over-Tightening The Plug
As mentioned, this is a frequent error. The threads in the engine head are soft aluminum. Stripping them means you’ll need to perform a helicoil repair or replace the entire engine head.
Not Checking The Gap
An incorrect gap affects the spark’s strength and timing, leading to hard starting, poor fuel economy, and rough engine operation. Taking a moment to check it is always worth it.
When To Remove And Replace Your Spark Plug
Regular maintenance is key to a long-lasting mower. Here are the main reasons you might need to remove the plug.
- Annual Spring Tune-Up: Replace the spark plug at the beginning of each mowing season.
- Engine Won’t Start: A fouled or damaged spark plug is a common culprit for no-start conditions.
- Rough Running or Misfiring: If the engine sputters or lacks power, checking the plug is a good first step.
- After Submersion or Flooding: If the engine was flooded with fuel, removing the plug allows you to crank the engine and clear excess fuel from the cylinder.
- General Inspection: It’s good practice to inspect the plug mid-season, especially if you have an older mower.
FAQ Section
How Often Should I Change My Lawn Mower Spark Plug?
For optimal performance, you should replace your lawn mower spark plug once per season. If you use your mower heavily, consider changing it twice a year. A fresh plug ensures reliable starts and efficient combustion.
What Size Socket Do I Need To Remove A Spark Plug?
The two most common spark plug socket sizes for lawn mowers are 5/8 inch (16mm) and 13/16 inch (21mm). The 5/8 inch size is more prevalent. Check your old plug or owner’s manual to be certain before you buy a socket.
Can I Clean An Old Spark Plug Instead Of Replacing It?
You can clean a lightly fouled spark plug with a wire brush and some solvent. However, for severely fouled plugs or those with a worn electrode, replacement is the better and more reliable option. New plugs are inexpensive.
Why Is My Lawn Mower Spark Plug Black And Wet?
A black, wet, oily spark plug indicates oil is leaking into the combustion chamber. This could be due to worn piston rings, valve guides, or simply the mower being tipped on its side incorrectly. Persistent oil fouling requires further engine diagnosis.
What Happens If You Don’t Gap A Spark Plug?
If the gap is too wide, the spark may be too weak to reliably ignite the fuel mixture, causing misfires. If the gap is too narrow, the spark will be small and may not ignite the fuel properly, leading to poor performance and increased emissions. Always check the gap.