When it comes time to replace the spark plug on your lawn mower, it is important to use the correct socket size to remove and install the new plug. Using the wrong size socket can result in stripping the plug or damaging the engine. In this article, we will look at the common socket sizes used for lawn mower spark plugs.
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The Role of Spark Plugs in Small Engines
In any gas-powered engine, the spark plug provides the spark that ignites the air-fuel mixture in the combustion chamber. This tiny explosion pushes the piston down, providing the power to turn the crankshaft. Spark plugs are a critical component in small engines like those found in lawn mowers, generators, and other outdoor power equipment.
Over time, spark plugs become fouled or worn and need to be replaced. Replacing spark plugs is a routine part of small engine maintenance and prevents issues like hard starting, rough running, and lack of power. When installing a new plug, it must be torqued down to the proper tightness to crush the gasket just enough to seal combustion gases while still being able to be removed later.
Common Lawn Mower Spark Plug Socket Sizes
The most common spark plug socket sizes used for lawn mower engines are:
- 13/16 inch – This is by far the most common lawn mower spark plug socket size. It fits plugs with a 5/8″ hex size.
- 5/8 inch – Some smaller engines use this metric spark plug socket size.
- 3/4 inch – Used on larger V-twin and overhead valve (OHV) engines.
Within these sizes, sockets come in different drive types like 1/4″ or 3/8″ square drive or with a hex drive to fit wrenches. A 3/8″ drive 13/16″ socket is an excellent all-purpose lawn mower spark plug socket.
Determining the Correct Socket Size
If you don’t know the socket size required for your mower’s spark plug, there are a couple ways to determine it:
- Refer to your owner’s manual – The manual should specify the spark plug type and socket size required.
- Physically measure the plug – Use a spark plug (new or old) from your mower to test fit different sockets until you find the one that fits properly.
- Lookup your engine model – Search online for the engine model and find the recommended spark plug specifications.
Using trial and error with different sockets is the most foolproof method. Just insert the plug into various sizes until the hex shape fits snugly into the socket. This ensures you get the right tool for your particular plug.
Using the Wrong Size Spark Plug Socket
Attempting to use the wrong socket size to remove or install a spark plug can cause a number of issues:
- Damaging the spark plug – Using too large of a socket may crack the ceramic insulator. Too small of a socket will likely strip or round off the hex shape.
- Rounding off the spark plug – Not fully gripping the plug hex can wear down the edges, making it near impossible to remove later.
- Stripping the spark plug hole – An improperly sized socket can damage the aluminum threading in the engine cylinder head.
- Under or over tightening – Without the right socket, achieving the proper torque is difficult when reinstalling the plug.
It only takes a moment to identify the correct socket size, so it is worth the effort to avoid damage or the need to drill out a seized spark plug later on. Be sure to use the proper wrench or ratchet for the socket size as well.
Types of Lawn Mower Spark Plug Sockets
In addition to the standard spark plug socket sizes mentioned earlier, there are some other socket variations useful for working in the tight confines around a lawn mower engine:
Spark plug socket with rubber insert
The rubber insert helps provide a snug fit on the spark plug’s hex shape. This allows the socket to grip better when removing tight or corroded plugs.
Deep well spark plug socket
A deep well or extended spark plug socket has a longer body to reach plugs that are down in deep recesses. Many overhead valve engines have plugs that require around a 2 inch depth to access.
Flex head spark plug socket
The flex head has a pivoting head on a u-joint to fit into hard to reach plug locations. Very useful when changing the plug on a small engine without removing the whole blower housing or muffler.
Universal spark plug socket
A universal spark plug socket uses spring-loaded jaws that automatically resize to fit different plug diameters. Handy to have as a single tool that works on all engine plugs, but less durable than a dedicated sized socket.
Magnetic spark plug socket
The magnet helps retrieve dropped plugs in hard to reach areas around the engine. It also provides a better grip on the plug when working upside down.
Using Socket Extensions for More Access
In some lawn mower engines, the spark plug location is difficult to access with just a socket alone. In these cases, adding extensions between the socket and ratchet/wrench handle can provide the extra reach needed. Common extension sizes are 2 inch, 4 inch, and 6 inch lengths. Avoid too many extensions in a row, as it can lead to excessive leverage and damage.
Socket Accessories for Easier Plug Changes
Along with the correct sized spark plug socket, some other handy tools can make lawn mower plug service quicker and simpler:
- Universal joint – Allows angling the socket on hard to reach plugs.
- Plug wire remover tool – Simplifies detaching the plug wire boot.
- Plug gap gauge – For checking and adjusting the spark plug electrode gap.
- Ratcheting wrench/ratchet – Gives better leverage for unscrewing stubborn plugs.
- Anti-seize compound – Prevents corrosion when installing the new plug.
- Torque wrench – For tightening a new plug precisely to specs.
Conclusion
Identifying and using the proper socket size is imperative when changing your lawn mower’s spark plug. The most common sizes are 13/16″, 5/8″, and 3/4″ drive, with variations like deep well and rubber insert sockets available for easier access. Refer to your mower’s manual or measure the plug itself to determine the correct socket. Using the wrong size can damage the plug or cylinder head. Equipping yourself with the right socket and accessories makes routine small engine spark plug service much simpler.