Lawn mower blades are connected to your lawn mower with a single bolt into the engine shaft. Over time it's possible that they can become loose. If you are mowing your grass and you hear a rattling sound coming from where the blade is, chances are your lawn mower blade could be loose. In order to save your lawn mower from possible damage, it is crucial to turn the lawn mower off and tighten the mower blades. Doing this is much easier and less expensive than possibly having to replace the lawn mower because it was damaged from a loose blade.
Disconnect the spark plug from the lawn mower. You can either remove the spark plug connection alone or remove the spark plug entirely with a spark plug wrench.
Remove the gasoline from the tank. This can be done by either running the lawn mower until it's out of gas. You can also siphon the gas out of the gas tank back into a gas can.
Turn the lawn mower over on its side and wedge a 2-by-4 board in between the lawn mower blade and the mower deck. This will prevent the blade from turning when you tighten the bolt that holds the blade to the engine shaft.
Take an adjustable wrench or the correct size box wrench and tighten the bolt that holds the blade to the engine shaft. To tighten it, turn it clockwise.
Set the mower back up straight and reconnect the spark plug to the lawn mower.