I have a Briggs Sprint 3.75 engine on my mower. I was mowing my lawn, hit a rock and the thing just started making this horific noise. I don't know anything about fixing a mower but follow instructions pretty well. Can someone help?

Umm, well take the mower, drain the gas, no need for that with the oil. Take the mower and put the handle to the ground so the mower is on its back wheels while holding the flywheel brake, make sure the plug wires disconnected and check and make sure the crank spins without any wobble, and I mean none!! And that it doesn't drag while holding the stop lever, now if the crank wobbles you'll have to get the crank professionally bent back or buy a new one. If it sounds like the flywheel brake doesn't let the flywheel rotate, the brake may have fallen off or screwed up somehow. Now how big of a rock was it?? Was it a metal like noise or engine noise?? Not saying but the blade could have also hit the rock just right to make the blade hit the deck.

Thanks Briggs, I'll check it out. The rock wasn't more then an inch in diam. The blades are hitting so I'll check the crank.

Yeah do check it out, may be the crank is bent, they can be bent back but get a pro to do it if you are not sure how too. But it may have bent the blade, I've seen it do that as well. What is it on, a murray, mtd etc. some blades are thinner or thicker depending