Small Engines (Lawn Mowers, etc.): flywheel key, crank case, head gasket

Question
I have a craftsman mulcher mower 6.75hp ~1997.  I replaced the lower crank case gasket and head gasket.  Now it runs about 10 sec then dies (three times now). Each time it splits the flywheel key and looses time.  Any ideas as to why it keeps loosing the key?  

Dan

Answer
Hi Dan,

This a tough one!  The only things that I can think of, that would cause immediate key shearing are:  A loose blade or flywheel.  A timing gear that was thrown off when you replaced the crankcase gasket.  

Let me know how you make out.
Michael