Small Engines (Lawn Mowers, etc.): toro lawnower shudder/stall, tree root, crankshaft

Question
After hitting a tree root that loosened my blade,I re-tightened the blade and proceeded mowing for some 5 minutes when the machine started to shudder ,like when the blade came loose.It was fine, so I tried to re-start but each time I pull the cord,it yanks it back out of my hand. Bent impeller maybe?  

Answer
You have a sheared flywheel key, that is causing the rope to pull out of your hand.  The shudder and vibration is from a bent crankshaft.

Have a helper pull the rope when the mower is on it's side, remove the plug wire to avoid accidental starting.  Watch the bolt in the end of the crank.  does it turn "true" or does it seem to run "out of round".  I'm guessing out of round.  If it is you have a bent crankshaft and the mower is scrap. Repair cost 275.00