Hank wrote:
On Jul 28, 7:00 pm, Zootal wrote:
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.

Since you hit a stump, I agree that the flywheel key should be
replaced whether it is bad or not. But! FIRST check the blade to see
if it is bent and also the crankshaft to see if it is bent. If the
crank (shaft) is bent, throw out the mower and go no further.


Exactly what I was going to say.