Spark Plugs

Shop replacement spark plugs for lawn mowers, trimmers, chainsaws, generators, utility equipment and other small engines. Find NGK, Champion and Denso plug applications by plug number, cross-reference, equipment model, engine manufacturer and package quantity.

The correct spark plug must match more than the brand name. Before ordering, verify the complete plug number, thread diameter, reach, seat style, heat range, resistor specification and recommended gap. Similar-looking plugs may use different dimensions or operating characteristics and should not be substituted unless the equipment or engine manufacturer lists the replacement.

How to Find the Correct Spark Plug

• Start with the plug number: Read the code printed on the old plug or use the equipment owner’s manual, engine manual or parts diagram.
• Check cross-reference numbers: Many listings include equivalent NGK, Champion, Denso, Bosch, Autolite or Torch numbers. Use cross-references only when the full specification matches.
• Confirm the engine model: Record the engine manufacturer, model, type and code numbers when available. The mower or equipment model alone may not identify the engine configuration.
• Verify thread and reach: Thread diameter and reach determine whether the plug fits the cylinder head correctly. An incorrect reach can damage the engine or prevent proper combustion.
• Match the seat style: Spark plugs can use a gasket seat or tapered seat. These designs are not interchangeable.
• Confirm resistor requirements: Many modern engines use resistor plugs to reduce radio-frequency interference. Use the resistor or non-resistor design specified for the equipment.
• Check the recommended gap: Even a new plug should be checked against the engine manufacturer’s specified electrode gap before installation.
• Review package quantity: Products in this collection may be sold in packs of 4, 10, 24, 25 or larger shop quantities.

Spark Plug Brands and Cross-References

NGK Spark Plugs

NGK plug codes identify construction, thread size, heat range, reach and resistor features. Match the complete code, including any letters or suffixes, rather than using only the heat-range number.

Champion Spark Plugs

Champion plugs are widely used in lawn mower, handheld and utility engines. Verify whether the application calls for a resistor plug, electromagnetic-suppression design or a specific projected-tip configuration.

Denso Spark Plugs

Denso plugs may cross-reference to NGK, Champion, Autolite and other brands. Confirm that thread, reach, seat, heat range and gap requirements agree with the engine specification.

Understanding Common Spark Plug Features

Resistor vs. Non-Resistor Plugs

A resistor spark plug helps suppress electrical interference that can affect electronic ignition systems, controls and nearby radio equipment. Do not replace a specified resistor plug with a non-resistor design unless the manufacturer approves it.

Heat Range

The heat range describes how quickly the plug transfers heat away from the firing tip. It does not refer to spark intensity. Using the wrong heat range can contribute to fouling, overheating or pre-ignition.

Spark Plug Gap

The electrode gap affects ignition performance. A gap that is too wide can make the engine difficult to start, while a gap that is too narrow can reduce combustion efficiency. Always use the engine manufacturer’s specification.

Pack Size

Many replacement plugs are sold in service or shop packs rather than individually. Check the product title and description carefully so the quantity matches your needs.

Frequently Asked Questions About Small-Engine Spark Plugs

Can I replace a spark plug with a different brand?

Yes, when the replacement is a verified cross-reference with the same thread, reach, seat, heat range, resistor specification and other required features.

Can I identify the plug from the mower model?

Sometimes, but many mower models were produced with more than one engine. The engine model and original plug number provide a more reliable match.

Should I gap a new spark plug?

Check the gap before installation. Shipping and handling can change the electrode spacing, and the required gap varies by engine.

What does the “R” in many plug numbers mean?

It commonly identifies a resistor-style plug, although code conventions vary by manufacturer. Match the complete published plug number.

Why does my engine keep fouling spark plugs?

Repeated fouling can be caused by an overly rich fuel mixture, restricted air filter, excessive oil consumption, incorrect plug heat range, extended idling or other engine problems. Replacing the plug alone may not correct the cause.

How tight should a spark plug be?

Use the engine or spark-plug manufacturer’s torque specification. Over-tightening can damage threads, while under-tightening can cause poor heat transfer or leakage.

How often should a small-engine spark plug be replaced?

Follow the equipment maintenance schedule and inspect the plug during regular service. Replacement intervals vary with engine design, operating conditions and hours of use.

Can I install a longer-reach plug because it fits the threads?

No. Incorrect reach can allow the electrode to extend too far into the combustion chamber or prevent the plug from seating correctly.

Shut off the engine, allow it to cool, disconnect the existing spark plug lead and follow the equipment manufacturer’s service instructions. Start the new plug by hand to reduce the risk of cross-threading.