Small Engines (Lawn Mowers, etc.): Cranking a 4 hp Briggs and Stratton engine, briggs and stratton, hp briggs

Question
I have trouble cranking a 4 hp Briggs and Stratton  engine on a Troy-Bilt Sickle mower. The motor starts and runs very well.  The problem is as I pull on the  starting cord, it is hard to pull, and after pulling it out a little bit, it pulls back very strongly (I
guess as the motor starts). I am afraid that it could hurt my arm as it pulls back so strongly.
I had never experienced this situation in starting many other small engines.

Answer
Hi George,

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 or twisted crankshaft depending on the severity of the impact but usually the key just shears.  

Let me know how you make out.
Michael