bruiser

Another possibility, besides bent crank, or bad shear pin/key, is the blade adapter. I have a Honda mower, but haven't checked to see if it has the adapter. However, the mower I had before the Honda had one. One day I was using it, and the engine started shaking, and I hadn't hit anything. I shut it down, turned the mower on it's side, and the blade was crooked. I could wobble the blade. Got to looking, and noticed the adapter had a crack in it. Replaced the adapter and the mower ran fine. You might check and see if the Honda has something like an adapter that bolts to the end of the crank.