Did I kill it?

[thx712517]

I took out the lawn mower (Craftsman push mower with B&S 550e motor) to mulch some leaves this afternoon. Got it started and after two feet of happy mowing, I struck a hidden stone. The stone was about one inch by two inches and the mower immediately shot out a cloud of black smoke and began making a horrifying metal clanking sound. I shut it off and took a look.

The blade has a notch in it but is otherwise okay. I don't feel any play in the blade. I took the cylinder head off and the bore looks clean for the full stroke of the piston with no sign of gouging. I buttoned it back up and started it again. Clanking that quieted down a bit but never fully went away. Did I blow up a bearing? Trash the crank? Time to tell wifey we need a new mower?

 

[pugaltitude]

You have possibly bent the crankshaft or the blade is hitting against a part of the deck.

You might also have sheared the flywheel key and the timing of the engine is knocked out which is still allowing starting but rough running.

 

[primerbulb120]

I also have had this happen to me. While mowing a tangle of vines (I should have used my wheeled string trimmer) I hit a stump. Black smoke issued from the muffler. After pulling my mower off of the stump, I attempted to restart it and could not turn it over. I inspected the underside of the deck and found that the blade was bent and could not turn, so I took it off and could not start the engine without the blade installed because of kickback. I installed a new blade and successfully started the engine, but the whole mower shook violently as it ran, for the crankshaft was bent. I took the blade and the self- propel adaptor off, turned the crankshaft until the bend was slanting up, slid a large piece of pipe over the crankshaft and hit it with a sledgehammer until it was mostly straightened. After starting the engine, I proceeded to mow the lawn with it, although the slightly bent crankshaft still caused the mower to vibrate. The vibrations caused a front wheel and the muffler to fall off. :laughing: After putting them back on, I straightened the crankshaft even more until it appeared straight. After having the other front wheel fall off, there have been no problems and the mower runs like it did before I hit the stump.
Like pugaltitude said, check the blade to see if it is hitting the mower deck. If it turns out that you have a bent crankshaft, hopefully you will be able to straighten it like I did with mine.