The flywheel on a John Deere mower serves as a timing device for the electrical spark flowing to the engine's cylinder. There are two magnets in the flywheel. As the flywheel spins on top of the engine, it passes by the prongs on the ignition coil that is bolted to the engine block. This creates the spark for the engine. If the shaft key of the flywheel shears, the engine timing will be off, causing the mower to run erratically. You will then have to remove the flywheel, which should take you about 15 minutes.
Park the lawnmower on a hard, level surface and set the parking brake. Turn the key to the Off position.
Open the bonnet of the mower. Remove the three screws holding down the rotating screen directly on top of the engine, using a Phillips screwdriver. Remove the five bolts holding the plastic blower housing that covers the top of the engine, using a 10mm wrench. This will expose the flywheel.
Place the flywheel strap wrench around the entire flywheel. Place the 1/2-inch breaker bar with a 30mm socket on the top nut in the middle of the flywheel. Tighten the flywheel strap wrench by winding it clockwise to take out any slack. Turn the breaker bar counterclockwise to remove the nut.
Attach the flywheel puller. Turn the two screws on the flywheel puller evenly into the two holes in the flywheel until hand-tight. Tighten the middle puller screw until the flywheel loosens off the tapered shaft. Remove the flywheel.