Well to know what engine you have we need the model number since there are more than one B&S engine in this size range.

I suggest you remove the spark plug and see if there is any compression on that cylinder.

Walt Conner

***"I assume this is a flathead engine, w/ a side cover for getting to the valve springs ? Any pushrods or lifters involved ?"***
Please allow us to delve into this issue by posting the critical engine numbers (from the engine). We need Model #, and Type #.
"Thanks for any info."
Also....compression tested: By thumb, or by gauge?

Sorry for lack of info,....thought they were basically the same.
Model #42E777 Yardman
Type 1280 01
Both plugs out, No sign of any compression (thumb tested)
I have a gauge, but not needed here for sure.

Just looking at it, mite it be easier to remove the hood-cowl assy, than to remove the engine ?

Note: I am a retired mechanic, just not familiar w/ this small stuff.
Thanks for any info.

Rich

Yes, opposed twin flat head engine. Click the link below to view the Briggs IPL for this engine. Find item # 551 in the IPL. This is the cover for the valve compartment (one on each bank). Remove the cover on the cylinder that lost compression. How difficult this will be I can't tell you because I don't know what you will need to remove from your tractor to gain good access to the engine. The valve compartment cover is behind the intake manifold (see image I have posted for an idea of what you are looking for). Inside the compartment, you might find a broken valve spring, broken collet, or both, along with valve keepers. If you do not find anything obvious inside this compartment, turn the engine by hand (spark plugs removed) while you watch the movements of the valves and tappets. You should see both valves move up and down freely at different times while you are turning the crankshaft/flywheel. It takes 2 turns of the crank to turn the camshaft once, so it will require 2 turns of crank to observe all the movements of both valves, ONE time.

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Here is a link that might be useful: 42E777 IPL

"Sorry for lack of info,....thought they were basically the same. "

You're kidding.

I still am not clear on what is going on. Are you saying no compression on the one cylinder? You say you removed both plugs and no compression.

The most common cause would be throwing a rod but you said there was no noise which there would be if that happened. Next most common cause with this engine is a valve seat coming loose, out, so valve doesn't seat.

These engine will start and run happily on one cylinder, just no power.

Walt Conner

A "cylinder leak down" test (or reasonable facsimile) using compressed air can be done to identify the route by which the compression is escaping. To do a "bona fide" leak down test requires a "percent of leakage gauge" but a close approximation of the test can still be done if you have (1)Compressed air available, and (2) a threaded adapter fitting that will screw into the spark plug hole and also receive an air hose, (3) a means of securely locking the crankshaft/flywheel in the "TDC of compression stroke" for the cylinder to be tested. Actual testing is simple and amounts to listening to determine where the air is escaping when compressed air is applied to the cylinder through the spark plug hole adapter fitting. As follows: Turn the crankshaft/flywheel to position the piston of the testable cylinder to TDC of the compression stroke. Here's a hint, the valve train for both valves of that cylinder will place the valves in the closed position. you determine this by watching the tappets through the open valve compartment. When both TAPPETS or lifters, are retracted toward the camshaft, and you can detect clearance between the end of valve and the tappet.....lock the flywheel in place so the crankshaft can't turn when air pressure is applied to the cylinder. Failure to securely lock the flywheel against moving could result in personal injury if the crankshaft rotates. In addition to the locking of flywheel, keep your hands away from the flywheel and crankshaft until air pressure is disconnected from cylinder. With the flywheel locked securely, thread the adapter fitting into the spark plug hole (threads are 14mm dia. X 1.25 pitch when you ask for the adapter fitting) and tighten it so it can't leak air. Connect the air hose from a source of compressed air (60psi to 90 psi recommended). You will hear air leaking from somewhere. Carefully determine where the air is escaping by using a 2 foot length of hose or tubing. Place one end of the hose or tube close to an ear (but not inside your ear) and then move the other end of hose to the exit portal of the exhaust system. If air is heard loudly escaping here, the defect is in the exhaust valve or seat. Check the intake valve condition by moving the end of the hose to the throat of the carb (throttle must be held wide open, choke butterfly open, and any crankcase breather hose must be disconnected from the carb, if carb is mounted to the intake manifold). If air is heard loudly here, the defect is in the intake valve or seat. If you do not detect air escaping from either of those places, check to see if you can hear air escaping from the crankcase breather hose (or pulse hose if impulse fuel pump is present). If you hear air escaping from the crankcase breather hose, or pulse hose, the defect is in the piston or cylinder wall. Always remove the compressed air supply from the cylinder before unlocking the flywheel. A leaking head gasket serious enough to cause loss of compression would be obvious without any test equipment, and you know it right away when the engine is running.

Thanks all. The engine is exactly like the illustration shown. Thru the spark plug hole I could see the intake valve staying open. I was able to remove the LS cowling, and get at the head and the valve spring cover. Nothing wrong w/ the spring, so I removed the head. By tapping lightly, I drove the intake valve back closed, then turned the engine to open it, but it stayed open. I then w-d'd it, and tapped asgain, and it snapped closed. A few more times and it now open and closes normally.

I was wrong, a valve can stick while it is running. But my new question is why ? And what are my chances of it happening again ? The cylinder shows no sign of overheating.
I'm thinking of running some top oil in the gas for a while ? What do you think ?

Thanks again

Rich

Some say due to the gasoline of today. I suggest using some Marvel Mystery Oil per instructions on the can. Seafoam MIGHT do it, I don't know.

Walt Conner

***"But my new question is why ?"***
Can't say for sure but I recommend that you get back to the tractor and do a very thorough inspection of the air filtration set up, carb mounting gaskets, intake manifold gaskets, carb throttle shafts.......any place or location where dirt, dust, grit might possibly enter the induction stream. I recommend doing that because, as you said, "valves don't stick while the engine is running"!!!
I'm sure there have been some exceptions to this "rule", but largely, for a valve to stick open, it had to have been open at the moment the engine stopped when last shut down.
...........................................................
Now, to speculate about YOUR stuck valve, and the future of your engine.
What you experienced may be due to a combination of varnish and possibly dust/dirt on the intake valve stem. That is why I say you want to really check all the places fine particulates can enter the induction stream. But, even if dust were PART of the problem, I feel that varnish is the bigger problem.
***"I'm thinking of running some top oil in the gas for a while ? What do you think ?"***
I highly recommend that, not just for a while, FOR-EVER more! I also recommend using gasoline stabilizer in all your fuel cans/jugs all the time, so that your fuel is stabilized while it's waiting to be used. Storing unstabilized fuel, and then adding stabilizer to the tank is pretty much a waste of time and product. I like to add Stabil or Seafoam, along with 1 oz. per gallon of Marvel Mystery Oil, to my gas cans BEFORE I fill them at the gas pump. I have simply made this "my ritual". The benefits of adding "top oil" (a.k.a. "upper cylinder lubricant") are: The oil leaves a very light film of lubricant on all surfaces of the entire fuel system, this means that all the things that are exposed to the fuel, also receive a light dose of lubrication, where they formerly got none (using "plain pump gas"). This light film may offer some protection against wear and corrosion to the "innards" of carburetors (float hinge pin, needle valve retainer clip, fuel solenoid plunger, etc.) The "top oil" in the induction stream will also afford a bit of lube to the choke shaft and throttle shaft pivot points that would otherwise also never know what oil is. The intake valve stem is situated squarely in the induction stream. This means that the valve stem is constantly "washed down" by the liquid fuel droplets in the stream. This "wash down" amounts to a solvent bath to the valve stem, removing the light film of engine lube oil that was on the valve stem. Some of this solvent gets into the valve guide and that is where a valve "sticks". By adding "top oil" to your fuel supply, you assure that the liquid fuel droplets being fed to the cylinder contain a bit of lubricant. The gasoline portion of the fuel will evaporate from the valve stem but the oil will remain. This oil coat helps prevent solid varnish from forming on the valve stem and that reduces the chance of a valve becoming "stuck" (I sometimes say the valve "gets mired up in varnish").
I will also advise that frequent oil changes are beneficial to help remove some of the "bad stuff" in the oil that can also contribute to the formation of varnish.
You might consider changing the oil in that engine twice as often as you have been doing it (now that you have "looked the devil in the eye").

That all makes good sense,.....I'll do good search for dirt ingestion, and add top oil. W/ the "used" head gasket, the engine is back running fine for now. I'll probably change the gasket before putting it all together.

Thanks for all the information.

Rich

Just a followup,...
Mowed about 2 hrs this morning,.....engine runs beautiful,..even w/ a used head gasket :))

I couldn't find any sign of dirt injestion anywhere.
I put 10 ozs of "Marvel Mystery Oil" w/ about 1.5-2.0 gals gas, and it runs great. I bought a large bottle, and will keep running it after this.
I'll always wonder what caused that intake valve to stick open.... while running, and hope it don't happen again.

Thanks to all,

Rich

What is Top Oil? Is Marvel Mystery Oil also called top oil or am I missing something?

***"What is Top Oil? Is Marvel Mystery Oil also called top oil or am I missing something?"***
"Top Oil", or "Upper Cylinder Lubricant" is an "ancient automotive term". The terms "Top" and "Upper" refer to the "top end" or "upper end" of the engine. The terms apply to the areas of the engine that are normally exposed to the fuel/air mixture that the induction system feeds the engine. The beginning of the "upper cylinder area" is usually defined as the intake valve stem that is exposed to the induction stream of fuel/air in the intake port of the cylinder head. The next area is the piston and upper piston rings, and the cylinder walls. The last area in this section is the exhaust valve stem that is exposed to the exhaust stream in the exhaust port of the cylinder head. Marvel Mystery Oil is just one of many products that can be rightly called top oil, or upper cylinder lube, and it might be the most popular of the "old standards" of automotive marketing. Some of the other name brands that offered their own versions/formulae, STP brands, Wynn's, Bardahl, Casite, Siloo, Motor-Medic, to name some. Besides these "independent" brands, nearly every major oil company had their own branded version to sell. As I have said, I feel that it is beneficial to have some lubricant in the fuel supply to help prevent "valve stem sticking" and to give parts of the fuel system some protection from corrosion as well as a bit of lubrication to moving parts of the fuel system that do not normally receive any lube at all.