Changing the spark plug on a self-propelled mower is a relative easy repair to make, but few people know how to do it. This means that they wind up hauling the entire mower into a repair shop and paying around $100 for a relatively simple repair.
To start, find out what type of spark plug your mower needs. This is usually listed in the mower’s operation manual. If you do not have the owner’s manual for your model, then look up the make and model number online. Many spark plug manufacturers keep databases of what spark plugs match up to which models of mower. If you cannot figure out what type of mower you own, remove the spark plug and take it in to your local hardware store or large plant nursery. They should be able to identify the part for you.
Once you have purchased a new spark plug, it’s time to get started. Make sure that the mower’s engine is completely cool before starting. A hot engine can severely burn you. Some people prefer to take the added precaution of draining all of the gasoline, but this is largely unnecessary. As long as the engine is cool, working on the mower is safe.
If you have not done so already, disconnect the old spark plug from the mower. To do this, use a spark plug wrench. Turn the wrench counter-clockwise in order to remove the old spark plug. You can dispose of the old plug in the regular trash, it does not need any kind of special disposal.
Next, check the gap of the new spark plug. This means to check the space between the wires of the spark plug. Spark plugs usually need to be adjusted to match the exact spacing required by the mower. You may need to use a specialized gap tool, a pair of pliers, or a set of feeler gauges to make adjustments to this gap.
There are several ways to find the right space. The owner’s manual will usually specify the right spacing. It is also possible to use the old spark plug as a guide.
After making the proper adjustments, go ahead and install the new spark plug. While you are doing this, be very careful not to cross-thread the plug. If everything has been done right, you should be able to smoothly thread it in by hand for a few turns. Once the spark plug can no longer be placed into the socket by hand, use the spark plug wrench to continue tightening it. Once you make sure the plug is in firmly, make sure that you do NOT over-tighten it.
As a final step, reconnect the spark plug wire. After this is done, check over all of the work. If you drained the oil or the gasoline before beginning the repair, make sure you replace it before starting the mower. Otherwise, go ahead and start the mower.
If possible, allow the motor on the mower to run for at least ten minutes. You can use the mower while the engine is running. By letting the motor run, you will give the mower enough time to determine if there are any problems with the new spark plug.
It’s a good idea to make sure that everything else on the mower is working properly, since you will already have most of the tools you need readily available. Be sure to check the gas and oil as well. Making a habit of conducting regular maintenance on your mower is a good way to get the longest possible life out of your machine.