Power off the John Deere lawnmower and open the hood. Remove the oil drain plug from the side of the Briggs & Stratton engine. The plug is at the base of the oil dipstick. Allow the oil to drain into a pan.
Reset the oil drain plug in its housing.
Find the distinctively circular flywheel near the rear of the Briggs & Stratton engine assembly. It will have a cover. Remove the bolts with a socket wrench and pry off the cover.
Tell an assistant to place a flywheel holder over the John Deere lawnmower's flywheel as you take out the center flywheel nut with the socket wrench.
Lower the flywheel holder's dual arms over each side of the flywheel. The center bolt of the holder should be aligned over the top of the PTO shaft on the center of the flywheel. Use a socket wrench to tighten the holder's bolt until the pressure causes the flywheel to be released. Set the flywheel aside.
Find the revealed John Deere lawnmower's flywheel key now that the flywheel is out of the way. This small, metal "key" is upright and can be pulled straight out.
Look at the bottom base of the Briggs & Stratton engine and remove the bolts you see, using a socket wrench to remove the oil pan.
Remove both the bolts from the revealed rectangular PTO shaft with a wrench.
Return to the top of the engine and strike the center with a rubber mallet to dislodge the John Deere lawnmower's PTO shaft.
Slide a replacement PTO shaft into the engine assembly's center in the space vacated by the old shaft.
Follow the previous procedures in reverse to reassemble the various engine parts.