It would help if you tell us which engine you have.

-Deerslayer

I'd pull the valve cover and look for something obviously wrong. If it "appears" OK, check the valve lash.

Short of hoping telepathy would work--its a OHV 18.5 briggs & Stratton ELS 500

Hmmm! 18.5 hp B&S OHV just like my LA100.Does it just click when you just try to start?If so then try to turn the engine by hand!See if its stuck!like mine was.

It may be a stuck valve. Here's a link to B&S engine manuals.

B&S Engine Manuals

-Deerslayer

All I could find on that site was the owners manual and parts list. I guess in a pinch the parts manual would work. Stuck valve sounds like a good diagnosis. It stopped when I told it too and wouldn't start back--I didn't hear a clink--like a broken valve but I'm deaf. Like my daughter sez--my ears are old. Good diagnosis--sounds right to me-- How would you un-stick a valve without breaking it down? I'm assuming the cover on the front of the engine with OHV stamped on is the valve cover? Take it off and tap the stems? Is there an engine manual anywhere? how to disassembe and reassemble?

thanks for responding--

fl

"How would you un-stick a valve without breaking it down?"
Like Bill said,"pull the valve cover and look for something obviously wrong".

"I'm assuming the cover on the front of the engine with OHV stamped on is the valve cover?"
Correct

"Is there an engine manual anywhere?"
It appears that B&S charges for their service manuals. I'm more familiar with Kohler engines. Here is a link to a Kohler service manual.
Kohler Service Manual
Section 9 describes disassembly. Keep in mind that your B&S will look a bit different.

Please let us know the outcome.

Good Luck!

-Deerslayer

It sounds like the key in the fly wheel is sheared off the crank shaft, Not too big a job to fix, you will have to remove the engine shrould and may need a gear puller to get the fly wheel off and the key is probably 1/4" or 3/8" square stock. It should not cost more then $75.00 to get fixed at a service shop. Let us know how you make out.

That would take some doin to shear a 1/4" or 3/8' key.I simply check to see if the keyway in the F/W and the C/S are aligned,after removeing the nut.I am for checking the valves first though.tbk JMHO

And just HOW does a sheared flywheel key result in NO COMPRESSION?

I had a Kohler 301AS do the same thing years ago. I shut it down for a few minutes, and it would not start again. It cranked real fast, then coasted to a stop because there was no compression. The intake valve was stuck open. I squirted some Marvel Mystery Oil on the valve stems and the stuck valve freed up. Then, the engine started fine. I put a couple of ounces of Mystery Oil with each tankfull of gas for a month, and never saw the problem again. This happened on a very hot day. Good luck with your problem. Charles Ranhheim

Bill, if the flywheel key is sheared off the crank won't rotate while cranking the engine, only the flywheel will rotate and not the crankshaft.

OK- Got ya!

"Pulled the choke and got a couple of small backfires only."

Backfires wouldn't be possible with a sheared flywheel key.

-Deerslayer

Deerslayer, Back fires are possible if the the key sheared diagonally and not straight accross, The key may catch the crankshaft once and a while cranking and the timing now being off 180 deg. will cause the back fire.
What do you say to that !

Stuck valve or valve seat came loose holding the valve open. Flywheel key while possible is unlikely. Valve stuck on my Honda generater while it was running, caused by old gas in the tank. Unstuck the valve and put in fresh fuel, still runs fine today.

"Back fires are possible if the the key sheared diagonally and not straight accross"
"What do you say to that!"

I suppose that's a possibility. And, if pigs could fly out of my butt, we'd all be eating bacon! 8^)*

-Deerslayer

* From Two and a Half Men

Update--No bacon this morning but I did pull the valve cover. laying in the valve cover was the exhaust valve shim. It didn't look like the adjuster was backed out or anything else was wrong. I put the shim back on top of the valve stem and adjusted both valves---still no compression. I rotated to TDC and blew compressed air in the spark plug hole. Air came out the muffler. I tried rotating the engine all the way through while putting in air, and air always came out of the exhaust--only out of the intake when it was open. I pulled the head and found the problem--the exhaust valve seat had come out. I figure at the factory they superheat the head and cool the seat to press it in--so why did mine come out--only 2 1/2 years old, not abused, change the oil etc. Anyway I went to the B&S site and looked up the head p/n using my parts manual that came with the cub. That part has been replaced by a newer p/n, along with a different gasket. Think they are having head problems? must be--the new head is out of stock and no backorder date. This seems to be a common theme--putting out products without fully testing or just putting them out as quickly as possible. I have a honda min-tiller that after 2 years of light use, the transmission gears went out. Could not buy a replacement gear, only a new transmission. The transmission was a different part number and the old one was no longer available. Maybe I'm just paranoid but I'm beginning to think that the manufacturers are happy with their design guys if the product will only last a little past the warranty.

Thanks for the help

fl in alabama

Great work!!! I bet you can buy a new valve seat...there's no need to buy a new head.

Replace Valve Seat

-Deerslayer

"Could not buy a replacement gear, only a new transmission."
See-Link You can get the gear and it is a maintenance issue.

Supposedly, a new valve seat can be peened into place.

Here is a link that might be useful: Link

After reading about the difficulties and potential problems with replacing valve seats, I wonder what the cost difference is between paying a professional shop labor charge and the cost of a new head. I have a power equipment dealer near me who once said, in some cases, it is cheaper to replace a small engine than to pay $75.00 an hour rebuilding one where there has been internal dmage to expensive parts. At that rate, if it took 4 hours to rebuild the engine plus parts, replacing the entire unit may be less costly, and have a more reliable ontcome. Charles Ranheim

In this case a new head may not be available for weeks if not months. What's the harm in calling a machine shop and getting a quote to install a new valve seat?

I can get a Kohler M12 rebuilt at a local machine shop to like new condition for $625, a new short block costs about $900, and a complete new engine about $1,400.

-Deerslayer

I had the same thing happen on my old snapper ride on mower. I mixed up some JB Weld and with a small screwdriver smeared some on the area where the valve seat sits into the head or block, if not OHV. I then tapped the seat ever so gently into place and wiped off any excess JB Weld. This was done 2 years ago and has been fine ever since. Worth a try...you can always pay someone to fix it if it doesn't work.

I also waited a day before reassembly to give the JB a chance to set-up properly.

Peen the seat,reassemble and test ,while waiting for new head,if peen'd seat works alright return new head :o) Jim