Cutting grass is made so simple by lawn mowers, we often forget that the grass that doesn't end up spit back out on the yard has to go somewhere. Wet, clumped grass often gets stuck underneath the mower deck. This grass, because of heat and moisture, becomes a thick mass of hard debris that is difficult to remove. If enough builds up under the deck, the mower will not perform as it should. Cleaning the underside of the mower deck regularly should be part of your regular mower maintenance.
Remove the wire from the mower's spark plug, and empty the oil and gasoline tanks. This prevents the mower from accidentally starting and keeps the fluids from leaking when mower is turned over.
Turn the mower onto its side, with the gas tank underneath the carburetor so any remaining gas doesn't leak into the carburetor.
Secure the mower blade by placing a block of wood at the bottom of the deck and pushing the blade into it. Remove the bolt from the middle of the blade, using the wrench, and remove the blade from the deck.
Fill the bucket with warm, soapy water, and apply it to the underside of the mower deck to soften the grass.
Scrape away the grass build-up, using the putty knife to remove hard chunks.
Spray the bottom of the deck with a garden hose after the grass has been removed to clear away the soap and any lingering grass particles. Allow the deck to dry.
Spread vegetable oil along the underside of the mower deck to coat and protect it against future grass build-up.