Push lawn mowers and riding lawn mowers use spark plugs to run the engine just like a car. Though they do not need replacing often, there will come a time when the mower will not start and you will have to replace the plug. Replacement spark plugs are available at hardware stores and some auto parts stores. Once you change the push mower spark plug, your mower will be running again.
Locate the spark plug on your lawn mower engine. The spark plug is typically at the front of the engine under the spark plug wire. Pull the spark plug wire off of the spark plug. Grab the boot of the wire, the part covering the spark plug, and wiggle the boot off with your fingers.
Remove the spark plug from the mower engine, using the socket wrench. Most spark plugs will need a ¾-inch socket to remove the spark plug.
Take the old spark plug to the hardware store or even an auto parts store when you buy a replacement. The sales clerks will be able to match your plug with a new plug. Many big-box hardware stores have single plugs specifically for lawn mowers in their garden section.
Thread the new spark plug into the spark plug hole in the engine by hand. Tighten the spark plug using the socket wrench. Do not overtighten the plug because you could damage the ceramic insulator. The insulator is the white, visible portion of the spark plug.
Slide the spark plug wire boot over the spark plug and push the boot in with your fingers until it locks over the plug.