I have a Craftsman mower, 6hp, B&S overhead valve engine. This engine has always started on the first or second pull. Open throttle, close the manual choke, give one or two lazy pulls and it fires right up. It is the easiest starting mower I have ever had!
I ran over a stump that stuck up a few inches - it was in tall grass, I didn't see it, and the blade hit it hard, immediately stopping the engine. Thunk, engine stopped. The plastic cover over the pull starter popped off, it hit so hard.
Now the engine won't start. It pops and sputters and backfires out the carb, but absolutely will not start. Thinking a timing gear (or whatever valve timing mechanism it has) had skipped a gear/notch, I pulled the valve cover, pulled the spark plug, and watched to see if the rockers arms would both rock at TDC, and as far as I can tell they do, though I'm not sure how accurate or reliable of a test that is.
The engine turns over easily, but it always has - if anything it turns over easier than it should, which is what made me think the valve timing was off, though it's hard to tell.
Anyone have enough experience with this engine or type of engine to comment on what might have happened, and availability/cost of parts should I decide to tear the engine down? I don't know if sheared a key, skipped a tooth/cog, bent a valve in the process or what I'll find when I tear it open. It's been a good mower, and it's worth a bit of time and effort to me to fix it.