Small Engines (Lawn Mowers, etc.): A treet killed my lawn mower, repair options, tree root

Question
Hello Marc,

Today while mowing the lawn I ran over a tree root that I didn't
see.  The lawnmower immediately died and now will not start.  
the blade seems to turn, but it just makes a rattling noise.  I only
bought this mower 6 months ago!  Please help.

thanks so much

Answer
The reason it won't start is likely due to a sheared flywheel key, however, further inspection is required.  You need to make sure the crankshaft isn't bent first.  If it is still straight, the blade hub and blade mounting assembly needs to be thoroughly inspected for damage and the appropriate parts replaced.  Then the flyhweel key can be replaced.  If you are taking it to a shop for repair and the crank isn't bent, the repair won't be too costly.  If the crank is bent, it is better to have a good shop give you some repair options (short block, crankshaft replacement, etc.)  Hope this helps.