Small Engines (Lawn Mowers, etc.): Lawn Mower Vibrations, safety reasons, crankshaft

Question
Hey Mike,

  I was just wondering about a problem with my lawnmower it seems like ever since i ran over a piece of rock, my mower has been shaking alot more than it ever use to

 I just bought a brand new blade and i thought that would fix it but it still shakes a ton. All i know that it is a craftsman 21 inch cut with power drive.

Answer
Hi Dave,

I suspect a bent crankshaft.  Remove the spark plug for safety reasons and for easier cranking.  Have a helper pull it over while you watch the center of the blade hub.  It should spin concentrically and not out of round.

Let me know what you find.
Michael