After every 25 hours of use, you should change the blade on your Yard-Man lawn mower. You might need to do that even sooner if you hit a hard object when you are cutting your lawn. Either way, you'll know when it's time for a change because newly-cut areas of your lawn will exhibit a ragged or uneven appearance.
Things You'll Need
Heavy work gloves
2-by-4 block of wood
Wait to change your mower blade until you have nearly drained the fuel tank of gasoline and the engine has cooled. Remove the spark plug wire to safeguard against accidental starting while you're working on the mower. Put on work gloves to protect your hands from being cut while handling the old and replacement blades.
Tilt the mower on its side with the carburetor and air filter facing up. Put a block of wood between the blade and the mower deck to prevent the blade from rotating while you're attempting to remove it.
Use an adjustable wrench to unloosen the blade bolt by turning counterclockwise. Take off the blade bolt and blade bell support and set aside. Slide the blade and blade adaptor off of the engine crankshaft.
Drizzle some oil on the crankshaft and blade adapter's inner surface before reassembling. Reinstall the blade adapter with the star away fro the engine. Place the newly sharpened replacement blade on the crankshaft next, being sure to position the blade so the side with the word "bottom" is located away from the blade adapter..
Put the blade bell support over the blade and tighten the blade bolt in a clockwise manner until snug. Use a torque wrench so that the torque on the blade bolt measures between 450 and 600 ft. lbs. Tilt the mower back upright.
Purchase a Yard-Man replacement blade from an authorized retailer or have existing blades re-sharpened by a professional to ensure they are properly balanced.