What Spark Plug to Use for Lawn Mower

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All gasoline engines have a spark plug that ignites the fuel. However, the spark plugs of cars are not quite like the lawn mowers spark plugs. You can hardly use one for the other.

The question is, which spark plug suits your lawn mower?

This article talks about how spark plugs work, the unique features of a lawn mower spark plug, and how to choose one a suitable one for your lawn mower.

How Do Spark Plugs Work?


Spark plugs are found in combustion engines that run on gasoline. They are located on the cylinder head of the internal combustion engine. They ignite compressed aerosol gasoline by creating an electric spark. They also move heat away from the combustion chamber.

A spark plug ignites the piston-compressed air-fuel mixture with a spark. This moves from the end of the centre electrode to the ground electrode. Lawnmower spark plugs use the high voltage spark to ignite fuel combustion.

What Spark Plug to Use for Lawn Mowers? 

We understand the temptation to use any engine spark plug for your lawn mower. However, a lawn mower does not use just any kind of spark plug. No, a car spark plug won’t work.

Spark plugs differ in the gap between electrodes, thread length, and thread pitch.

Let’s look at how to consider these factors when getting a spark plug:

Thread Size

This is a very important factor when choosing a spark plug. Thread sizes differentiate a car spark plug from that of a lawnmower.

Thread Length

This is another factor to consider. Generally, lawn mower spark plugs have shorter thread lengths only about ⅜ inch long. This is unlike car spark plugs which have spark plugs up to half an inch long. 

Using a spark plug with an inappropriate thread length can impede the engine from starting, or cause engine damage.

Tip: use your old spark plug as a guide.

Spark Plug Gap


Remember what we said earlier about a spark plug having two electrodes? Spark travels in a gap between the live center electrode and the ground electrode. The gap should be set to a particular width depending on the engine of your lawn mower. 

If the electrodes are too close, the spark generated is too weak to produce efficient air-fuel ignition. If the electrodes are too far apart, the spark from the live electrode will not reach the ground electrode so ignition does not occur.

Many mowers have a spark gap recommendation of 0.030 inches. Check for your lawn mower’s gap requirements. Use a feeler gauge to check the spark gap on your plug and compare it with the requirement. Adjust the gap as necessary.

Spark Plug Length

Spark plugs vary in their level of extension into the combustion chamber. Longer plugs extend farther than others.

A replacement spark plug that’s too long can damage your lawn mower engine. Meanwhile, one that’s too short will reduce gas mileage and cause fouling of the spark plug.

Spark Plug Heat Range

Heat range is the specific range of heat under which a lawnmower’s spark plug can function optimally. Spark plugs may be hot or cold.

Generally, lawn mowers work well with a hot spark plug such as a 4 heat range. The heat range is usually specified in numbers. Lower numbers are for the hot spark plug type while cold types have higher numbers.

Hot spark plugs have a low heat range. That is, they heat up easily and attain optimal temperature. They have longer insulator noses and burn off carbon deposits. Their tips also remain hot for longer.

Cold spark plugs, on the other hand, transfer heat more quickly. They do not burn off enough carbon deposits so they can get dirty more quickly. They have shorter insulator noses. The tips also remain cooler for longer.

Spark Plug Types

Let’s take a quick look at common spark plugs suitable for certain engines.

Champion CJ8, RCJ8, RJ19HX, J19LM, and RJ19LM    

These models are suitable for Briggs & Stratton engines

Champion RJ19LMC

This is suitable for quantum engines

Champion RJ2YLE 

This model is used in Quantum Series 625, 675, & 725 engines with date codes later than 110701xx

Surefire” RJ2YXLE

It is used in Craftsman Smooth Start (MRS) lawn mowers.

Top 5 Best Spark Plugs for Lawn Mowers

Now that you know what spark plug is suitable for a lawn mower, and how important it is to get one, let’s look at the top 5 spark plug options to go for.

1. Hilom- Champion RC12YC

  • Brand: Hilom
  • OEM part number: 71
  • Product Dimensions: ‎3.7 x 1.97 x 0.71 inches
  • Copper core
  • Ultra-seal and TinTac shell
  • SAC-9 semiconductor resistor


  • Compatible with all lawn mower engines
  • Increases fuel consumption efficiency
  • Reduces smoke emissions
  • Improved replacement for all spark plug types


  • Poor functioning when the engine is hot

This spark plug is a dependable option on the market. It has a long lifespan. Hilum-Champion-Stratton is made with an ultra-seal, TinTac shell and a copper core.

The shell is resistant to corrosion and is non-stick. The copper core controls the heat level of the plug to prevent overheating. Heat control improves durability. It comes with a SAC-9 semiconductor resistor which ensures utmost RFI and EMI electromagnetic suppression (EMS).

The Hilom- Champion RC12YC spark plug model is a great choice as it works well with all lawn mowers.

2. Briggs-Stratton-796112-2pk

  • 2 spark plugs in a pack
  • High voltage generation
  • Suitable for l-head, sprint and classic engines
  • Quality OEM replacement parts


  • Resistant to corrosion
  • Affordable
  • Easy-to-use
  • Replacement part


  • Not suitable for all engines

Perfect for any flathead engine, the Briggs-Stratton-796112-2pk spark plug is a good option for Briggs & Stratton engines.

 Its electrodes are sharp and clean, making ignition easy and efficient.  The quality OEM replacement part is resistant to corrosion and suitable for long term use. It is suitable for classic, sprint and side valve (L-head) engines.

3. Champion RJ19LM Spark Plug

  • Copper built
  • Flat seat type
  • 14mm thread diameter, 21mm hex size


  • Affordable
  • Can be run on a cold engine


  • Not suitable for hot engine

Regardless of the size of your lawn, the Champion RJ19LM Spark Plugs supplies enough power to your lawn mower. 

It is unique in that it can be used to run a cold engine test without damaging it. It is made of quality copper material for durability. This mower spark plug is used for Craftsman, Troybilt, Sears, Tecumseh and MTD lawn mowers

4. NGK-BPM8Y Spark Plugs

  • Trivalent metal casing technology
  • Innovative design
  • Spark plug gap resistor made of glass and carbon mixture 
  • The pack has 2 plugs
  • Corrosion-resistant
  • Durable


  • Works for other engines
  • Can run vehicles and other power equipment
  • Easy to use


  • Fairly expensive
  • Spark plug packaging may be poor

Get two quality spark plugs in one pack with the NGK-BPM8Y. The manufacturer is renowned for producing excellent replacement parts. 

The powerful spark plugs are designed with a trivalent metal case which makes them resistant to corrosion and wear. 

Their durability is coupled with a unique electrode design that produces sharp sparks. This gives the engine a smooth response and improved power. The reason for its carbon-glass resistor is to ensure top performance.

What’s more? The  NGK-BPM8Y spark plugs can be used for other engines, both big and small. It is suitable for automobiles. Original NGK spark plugs have a date code you can interpret by reading their website chart.

5. Champion RJ19HX

  • Copper core electrode
  • OEM Champion replacement part, part number 973
  • Specifications: check gap is 0.0276 to 0.0315 inch
  • Product dimensions: 4×3.9×1 inches


  • For lawn and garden use
  • Can be used for pressure washers and other engines
  • Increased conductivity
  • Good heat control
  • Good overall wear
  • Resistant to fouling and corrosion
  • Reliable performance


A lot of users prefer the Champion RJ19HX because of its ease of installation and durability. This copper spark plug made by the Champion brand is a quality OEM Champion replacement part. 

The Champion RJ19HX comes in a 4-in-1 pack so you have an adequate supply for many years. It is recommended for Craftsman and Briggs and Stratton mowers. It is easily fixed with a 13/16 spark plug wrench.

Final Verdict

The right spark plug contributes to a smooth mowing experience. A good spark plug improves engine performance and fuel combustion. 

Our number #1 recommended lawn mower spark plug is the Briggs-Stratton-796112-2pk.