If you have a lawnmower that has a bent deck, you can straighten it back into shape. The procedure will be very similar to taking a dent out of an auto body door or fender, and will require the same tools. You'll need to use a considerable amount of elbow grease to take the dent out of your lawnmower deck. If you don't straighten the deck, the blades won't be able to turn properly, rendering the machine useless.
Place the lawnmower on a sturdy, level surface. Put a drop cloth next to the mower.
Find the motor mount that secures the engine to the deck. There are generally four to six motor mounts that are held in place by retaining bolts.
Unfasten the motor mount retaining bolts. Put on gloves, and carefully lift the motor off the deck, placing it on the drop cloth. Remember to lift with your legs and not your back. This will protect the engine from accidental damage and keep fuel from flooding it as well.
Turn the mower over and remove the cutting blade, using a wrench. Some models will have a cotter pin to pull out with pliers and then a retaining nut you'll need to loosen with a wrench. Set the blade aside as well.
Place a folded cloth over the dent. Pound the dent out of the lawnmower deck with a ball peen hammer; hammer on the peak or obtruding side of the dent to make it flush with the deck again.
Sand the dent and surrounding area as necessary to get rid of any chipped paint and/or hammer marks in the deck. Apply one coat of primer and paint to conceal the repair.
Replace the cutting blade once the paint has dried, and then remount the motor on the deck. Use the lawnmower normally thereafter.