Small Engines (Lawn Mowers, etc.): Hit Rock & Engine Died, impact gun, key hole

Question
Eric, I tried to do a nice thing & mow the yard for my husband.  Unfortunately, I hit one of the edging rocks (yes, I lifted the mower & tried to use it as a weedeater...doh!).  When the blade hit the rock, the engine immediately died and now the engine won't restart.  It's a Craftsman 6 hp push mower, model 917-388300.  What is the likely damage?  Is this something I can quickly fix before hubby gets home?  Or will I have to explain the half-mowed yard and plead for mercy?

Answer
Start by checking the crankshaft.  Remove the spark plug.  Have a friend tilt the mower up so you can see under the mower...you need to see the blade.  Have your friend pull the starter string while you watch the blade.  If the blade appears to wobble then the shaft is bent...not good.

If the crankshaft is not bent, then you need to check the flywheel key.  The key is intended to shear when you hit solid objects like large rocks.  To check the key you need to remove the starter assembly and flywheel nut.  The flywheel nut takes a 3/4 inch socket.  The flywheel nut will be very tight.  You have have a friend try to hold the blade, but we use an impact gun at the shop.  

Once you see the flywheel key make sure the flywheel key hole and the crankshaft key hole are lined up.   If the key holes are not lined up then the key is sheared.

Let me know what you find.
Eric