Small Engines (Lawn Mowers, etc.): blade will turn, but then hang, briggs stratton, air hammer

Question
My best friend and I are roomates.  We live in her house.  We purchased a self-propelled push lawn mower.  She hit something in the yard with it and now it won't start.  I tilted the lawnmower over and looked at the blade.  I turned the blade and found that it would rotate, but only to a certain point, then it would "stick".  I cleaned out all of the grass, and it did the same.  I can actually "force" it past the point where it "sticks", but it is very hard.  Some people are saying that it is a simple fix by replacing the bearing.  Not knowing much about lawn mowers themselves, I can deduce that something appears to be "bent" inside (it doesn't appear to be the blade).  I imagine I am going to have to take the blade off.  Can you please give me some things to look for?  The lawn mower is a Bolens, engine is Briggs & Stratton, and we purchased it only a month and a half ago...

Answer
Hi Nellie,

If 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, twisted crankshaft or more serious damage depending on the severity of the impact but usually the key just shears.  

Let me know how you make out.
Michael