Small Engines (Lawn Mowers, etc.): craftsman lawn mower hit a stump wont start, dirt pile, air hammer

Question
i have a eager-1 craftsman 5.0hp mower i hit a couple stumps and a dirt pile and it stalled .the blade was loose .the bolt that holds the blade on had somehow unscrewed about an inch.i tightened up the blade . i have checked for spark , cleaned the plug,pulled the cord with the plug out motor sounds fine but with the plug in it wont start and sometimes pulls back when i pull the starter cord.

Answer
Hi John,

Since it quit right after striking an object, I could almost guarantee that the flywheel key is sheared.  The timing would then be off.  The flywheel is located under the recoil/cooling shroud. Its' bore is tapered and mates with the tapered crankshaft. The keyway in the flywheel and shaft keeps it from spinning on the shaft.  A nut secures it.  Use an impact wrench on the nut or a strap on the flywheel.  Don't put force on the cooling fins or they will break.  The recommended way to remove a flywheel is to use a puller.   An alternative, is to tap on the crankshaft top, with a brass hammer or use a punch tip on an air hammer.   The flywheel will need to be held up and supported or upward pressure applied with 2 large prybars. (A 2 person job.) Care is needed so the flywheel doesn't crack or bend.  Also be careful to not mushroom over
the crankshaft top.  Replace the key.  Install the flywheel after cleaning the tapers and re-tighten the nut to 65 ft/lbs.
There is also the possibility of a bent or twisted crankshaft depending on the severity of the impact but usually the key just shears.  

Let me know how you make out.
Michael