A spark plug for a lawn mower typically costs between $3 and $25, depending on the engine type and brand. While professional replacement services charge extra, doing it yourself saves time and money—especially if you follow our step-by-step instructions. This guide breaks down everything you need to know about pricing, installation, and when to replace your spark plug.
Finding out how much is a spark plug for a lawn mower might seem like a simple question, but the answer depends on several factors—including your mower’s make, model, engine type, and where you buy it. Whether you’re troubleshooting a sputtering engine or planning routine maintenance, knowing the cost and process helps you budget wisely and avoid unnecessary repairs.
In this complete guide, we’ll walk you through everything you need to know about lawn mower spark plugs: from average prices and top brands to step-by-step replacement instructions, common mistakes to avoid, and how to choose the right plug for your machine. By the end, you’ll feel confident replacing your spark plug yourself and saving money in the process.
Key Takeaways
- Spark plug prices vary widely: Expect to pay $3–$25 per plug for most residential mowers, but high-performance or specialty models may cost more.
- DIY replacement is simple and affordable: Replacing your own spark plug usually takes less than 10 minutes and avoids labor fees from mechanics.
- Know your mower’s engine type: Most push mowers use single-cylinder engines (like Briggs & Stratton), while riding mowers often have larger multi-cylinder setups requiring multiple plugs.
- Quality matters more than price: A slightly pricier iridium or platinum plug can last longer and improve fuel efficiency compared to cheap copper options.
- Preventative maintenance saves money: Regularly checking and replacing spark plugs prevents hard starts, poor performance, and costly engine repairs down the line.
- Use the right tools: A spark plug socket wrench (usually 5/8 inch) makes removal and installation faster and safer than using pliers or improvised tools.
- Always consult your manual: Spark plug specifications (heat range, thread size, gap distance) vary by model—never guess what fits your mower.
Understanding Lawn Mower Spark Plugs
A spark plug is a small but vital component inside your lawn mower’s engine. It ignites the air-fuel mixture in the combustion chamber, creating the power that turns the crankshaft and drives the blades. Over time, these plugs wear out due to heat, carbon buildup, and general aging.
Most residential gas-powered mowers—especially those made by Honda, Toro, Craftsman, or Briggs & Stratton—use a single spark plug. Riding mowers with bigger engines may have two or four plugs, depending on whether they’re V-twin or inline configurations.
Unlike car spark plugs, which are designed for high-speed operation over thousands of miles, lawn mower plugs endure frequent short bursts of use. That means they don’t last as long—typically just one season unless properly maintained.
Average Cost of Lawn Mower Spark Plugs
So, how much is a spark plug for a lawn mower? On average, expect to spend between **$3 and $25 per plug**, depending on the following:
– Engine size and type: Smaller 4-stroke engines (common in push mowers) usually use standard copper-core plugs ($3–$8). Larger engines or commercial-grade units may require iridium or platinum plugs ($15–$25).
– Brand reputation: OEM (Original Equipment Manufacturer) plugs from your mower’s brand (e.g., Toro-branded plugs) tend to be more expensive but offer guaranteed compatibility.
– Material quality: Copper plugs are affordable but wear quickly. Iridium and platinum plugs last longer and provide better ignition, especially in humid climates or older engines.
– Seller markup: Big-box stores like Home Depot or Lowe’s often carry mid-range options around $6–$12. Online retailers like Amazon or specialty parts sites may offer bulk discounts or same-day shipping.
For example:
– A generic copper plug from Walmart: ~$3.97
– NGK G-Power or Champion RC12YC: ~$5–$7
– Bosch Double Iridium or OEM Honda plug: ~$12–$18
If your mower has two plugs (like many John Deere riding mowers), double that amount for a full set.
When Should You Replace Your Spark Plug?
Don’t wait until your mower won’t start. Here are signs it’s time for a new spark plug:
– Hard starting: The engine cranks slowly or takes multiple pulls to ignite.
– Misfiring or rough idle: Hesitation during acceleration or vibrations while running.
– Black soot around the plug: Indicates incomplete combustion—often caused by a fouled or worn plug.
– Excessive exhaust smoke: Blue or gray smoke suggests oil burning, which can happen if the plug isn’t sealing properly.
As a rule of thumb, check your spark plug every spring before mowing season begins. If you’ve used your mower heavily all summer, consider replacing it at year-end. Many experts recommend changing the plug annually, even if it looks okay—since internal damage often isn’t visible without disassembly.
How to Choose the Right Spark Plug
Picking the wrong spark plug can cause serious engine problems. Always refer to your owner’s manual first—it lists the exact part number, heat range, and gap measurement required.
But here’s what to look for if you’re shopping online or guessing:
1. Thread Size
Common sizes are 14mm or 18mm threads. Measure the threaded hole in your old plug or count the notches on the side.
2. Reach Length
This is how far the plug sits into the cylinder. Too short? It won’t seal. Too long? It risks hitting the piston. Most mowers use a 5/8-inch reach.
3. Heat Range
Describes how hot the plug gets during operation. Standard mowers usually use a “hot” plug (e.g., Champion RJ19LM). Cold plugs are for high-compression engines; avoid them unless specified.
4. Electrode Material
– Copper: Affordable, good conductivity, lasts 25–50 hours.
– Nitride-coated copper:: More durable than plain copper.
– Iridium/platinum:: Long-life (up to 100+ hours), excellent performance—ideal if you store your mower for long periods.
Step-by-Step: How to Replace a Lawn Mower Spark Plug
Replacing your spark plug takes just five minutes and requires only basic tools. Follow these steps:
What You’ll Need
– New spark plug (correct type for your mower)
– Spark plug socket wrench (5/8 inch works for most)
– Socket extension (optional, for tight spaces)
– Wire pliers (to disconnect the wire)
– Dielectric grease (optional, for better connection)
– Rags (for cleaning)
Step 1: Safety First
Turn off the mower and remove the spark plug wire. Pull it straight off the old plug—don’t yank the wire itself. For added safety, tape the wire end to the mower frame so it doesn’t accidentally reconnect.
Step 2: Remove the Old Plug
Insert the spark plug socket onto the plug head. Turn counterclockwise until loose, then unscrew by hand. Wipe away any debris around the area—you don’t want dirt falling into the cylinder.
Step 3: Check the Gap
Use a feeler gauge to measure the gap between the center electrode and ground strap. Compare to your manual’s specification (usually .030 inches). Adjust if needed by gently bending the ground strap.
Step 4: Install the New Plug
Hand-thread the new plug into the hole first—this prevents cross-threading. Once snug, tighten with the socket wrench—but no more than finger-tight plus 1/2 turn. Over-torquing can strip the threads.
Step 5: Reconnect Everything
Snap the spark plug wire back onto the new plug. Add a dab of dielectric grease to the inside boot for moisture protection. Double-check that the wire clicks firmly in place.
That’s it! Start your mower—it should run smoothly now.
Troubleshooting Common Issues
Even with a new plug, you might still face problems:
Problem: Mower still won’t start
Solution: Check fuel freshness, carburetor function, and battery (if electric-start). Sometimes old gas gums up the system even with a new plug.
Problem: Engine runs rough after replacement
Solution: Verify correct gap and torque. Also ensure the plug is fully seated—loose plugs cause misfires.
Problem: Spark plug electrode melted or cracked
Solution: Likely due to incorrect heat range or overheating. Switch to a colder plug or reduce load (e.g., don’t tow heavy attachments).
Need help diagnosing deeper issues? Our guide on how to check a spark plug walks you through visual inspection techniques.
Pro Tips for Long-Lasting Performance
– Clean the plug yearly: Use a wire brush to remove carbon buildup. Never clean a damaged plug—replace it instead.
– Store mowers properly: Fuel stabilizers and seasonal storage prevent corrosion (see our guide on winterizing your mower).
– Keep spares handy: Especially useful if you rent mowers or have multiple machines.
– Buy in bulk: Purchasing two plugs at once saves money and ensures consistency.
Conclusion
Now you know exactly how much is a spark plug for a lawn mower—and more importantly, how little effort it takes to replace one yourself. With costs under $25 and a DIY job lasting less than ten minutes, there’s no reason to delay this simple but essential maintenance task.
By choosing the right plug, following proper installation steps, and scheduling regular checks, you’ll keep your mower running efficiently for years. And remember: a healthy engine means fewer headaches, cleaner cuts, and a greener lawn.
Ready to get started? Grab your tools, pick up the correct plug for your model, and enjoy the satisfaction of a well-maintained machine—all while saving money along the way.