Rotary lawn mowers, like the MTD lawn mower, use a rapidly rotating lawn mower blade to cut the grass. After many uses, the blade slowly dulls until it no longer cuts the grass cleanly. It instead rips and tears at the grass which leaves rough edges that are vulnerable to fungus and disease. If the lawn mower blade comes in contact with stones or twigs, the blade will dull even quicker. To maintain the health of your grass, it is imperative to change an MTD lawn mower blade yearly.
Turn the lawn mower off and disconnect the spark plug cable from the spark plug.
Remove all gas from the gas tank by either siphoning it into a gas can using a siphon hose or by letting the lawn mower run until it's out of gas. Letting it run out of gas is much easier and can be a lot less messy.
Lay the lawn mower on its side. Wedge a small board between the lawn mower blade and the mower housing to prevent the blade from spinning when you remove the bolt.
Position your adjustable wrench on the bolt and turn counterclockwise to loosen it completely and remove it. Remove the old blade. Set the bell washer and the blade adapter aside to reinstall with the new blade.
Lubricate the engine crankshaft and inside surface of the blade adapter with engine oil. Also lubricate the bolt and bolt hole.
Install the blade adapter. The "star" side should face away from the engine. Position the blade over the blade adapter with the side marked "bottom" facing away from the engine. Put the bell washer over the blade with the tabs in the holes of the blade. Insert the bolt and tighten it with the wrench.
Position the lawn mower upright and reattach the spark plug wire.