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Discussion Starter #1
The tractor started burning oil so I replaced the head gaskets on both cylinders. I changed the oil and filter. I started it up and no problem with some oil burning but thought it was the residue from before. Now it is burning oil again and oil is dirty. Heads were torque to spec .
Is it bad head gaskets?
I took one exhaust pipe off to see if it is one cylinder or the other. It looks like both are burning oil.
Any help is appreciated...
 

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It could also be the piston rings, or even worn valve guides (or leaking valve guide seals if they have them), or possibly the crankcase vent going to the intake is putting oil into the engine.
 

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Sounds like that engine is due for a rebuild, or at least a thorough top-end refresh... any idea how many hours are on it?
 

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You can check the qualtiy of ring sealing by checking compression 'dry', and then squirting a t Tsp of oil into the cylinder and checking again. If the pressure developed increases significantly, likely you have ring leakage.
Remember also that the crankcase has a hurricane of oil being blown around by the crankshaft, and a pulsating pressure developed by the pistons motion. As they reciprocate, the pressure increases on the down stroke, and drops on the upstroke. If your ventilation is clogged or the tube plugged, you may be pushing oil out and into the intake as mentioned. One last thought is if you check the level and get too much lube into the crankcase, you can flood the piston rings with excessive oil and no ring can control that. Excess oil will raise the level in the sump, and cause oil to be whirled around even more by the crankshaft, counter weights, and connecting rod throws. Make sure you have the level correct and are checking it properly. There are two methods, given you are on level ground, and I don't know which applies. One is to remove and clean the dipstick, and screw it back in place, remove and read. The second method is to just place the dipstick on the filler without screwing it down, and then remove and check. If the first method is used on a machine that needs the second method, oil level will likely be too high if oil is added based on the dipstick reading.
tom
 

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Does your engine have the flat style air filter? The engines that had those and were used in dusty environments had dirt ingestion issues that led to excessive bore wear and oil burning issues.
 

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Discussion Starter #6
The engine has 266 hours on it with a oval type air filter. I checked the pvc valve and it was working fine. It did not have a gasket. It looked like just sealer was used during motor build.
I need to get a compression test so may have to wait. Will work on it more today.
 

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Well that's awful low hours for the thing to be shot... hmm.

What's the history on this machine... are you the original owner or did you get it used?
 

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Discussion Starter #8
I got it from a neighbor. They said it was burning some oil so they parked it and sat for a year. When I got it a cleaned it up as it did have grass under the cover. I went ahead and replaced both head gaskets adjusted valves. Cleaning all as I went along the usual built up on head and spark plugs. I did not think the rings were bad but think they are now but will try the compression test next.
 

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The engine has 266 hours on it with a oval type air filter. I checked the pvc valve and it was working fine. It did not have a gasket. It looked like just sealer was used during motor build.
I need to get a compression test so may have to wait. Will work on it more today.
That air filter works just fine, so I doubt you have a dirt ingestion issue. A leakdown test is the best but if you do not have a tester the compression test should show if rings are worn, make sure valves are adjusted the same on both sides and that the carb is open when you are cranking it. . If the rings are worn there should be increased blowby and you may see oil in the intake. You could pull the breather hose off the back of the air cleaner elbow and watch it when you start it to see if a lot of blowby is coming out of it.
 

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You likely will get inaccurate readings from a compression test,as most small engines have a built in compression release mechanism that bleeds off some compression at cranking speeds ..

I'd suspect the rings are stuck from the engine sitting so long,I have had a few engines that took as long as an hour of running to get the smoking to stop (and I had to top off the oil level several times) before it finally became less and eventually stopped..

It could be the cylinder bores are scratched up too though,or pitted from rust -or the piston skirts have collapsed enough to let excess oil pass up to the rings..

Do not overlook the crankcase breather possibly being the culprit also..they can make an otherwise "good" engine smoke ,foul spark plugs and carbon up the intake valve & cylinder head in short order..
 

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DSC01168.JPG This was my bore after 180 hours of dirt ingesting use, never saw wear like this in my many years of engine work. Had to go .020 over to clean it up.
 

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Discussion Starter #12
Does anyone know what the compression numbers should be for a 24hp b&s model 44m777 1091 b1?
 

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Because of the ez spin it can vary with the exhaust lash setting. There is a small bump on the bottom of the exhaust lobe that bleeds off compression to allow easier starting. A loose lash will cause more compression. Just check that both cylinders are similar.
 

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A compression test may not be significant as far as oil consumption as the compression is built by the sealing of the compression rings, not the oil control rings. IOW, it may not tell you much you already don't know.
Essentially, if it starts readily and runs well, except for the blue smoke and oil consumption, it is doubtful the compression rings will be bad. If the compression rings were bad, it would be more difficult to start and not develop as much power as it would normally. If bad, you would also get a lot of blowby, forcing combustion gas into the crankcase, through the breather, and of course, some to the intake manifold to make a second trip through the combustion chamber.
Have you checked the valve stem for sloppy fit in the valve guide? I don't know if it should have valve stem seals, but they could also be a cause for oil consumption if they are missing or have broken up.
When you had the cylinder heads off, did you inspect the cylinder bore for scratching or a ridge at the top? Did you try to move the pistons in the bore to see if they could be wobbled around? There should be a little motion when pushed side to side or up and down, but not a lot. Perceptible by feel, but not real visible, more or less. If you look real close you can see it, but it's not real obvious.
Head gaskets generally do not cause oil consumption except in the case where the leak is into the crankcase, as happens with the B&S OHV engines, where compression gases will push oil out the breather.
tom
 

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Discussion Starter #15
It does start easy and run well with plenty of power. The cylinder walls looked good with no scratches. I did not check the valve stem guides. I did get two with the gasket kit and the kit says they are for the intake valves. From the parts manual it looks like the exhaust valves do not have seals. Do they have exhaust valve seals? Just wanted to do more checks before pulling the heads.
 

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Discussion Starter #16
When I changed the head gaskets in the beginning i also clanged the oil/filter. After running it for 15 minutes and checking the new clean oil it was starting to get black but did not smell like gas.
 

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A head gasket when blown out to the crankcase will overpressurize the crankcase and force oil thru the breather tube into the carburetor. This can be checked by removing or observing the breather tube were it enter the intake. Some of those briggs had air filter sealing issues this can be checked by using a light and looking at the after air filter side of the air intake or possibly running a finger or rag into the housing. Any signs of dirt there indicate the air filter was not sealed and dirt has passed thru the engine causing premature wear. Also recommend a leak down test more than a compression test. Remove the oil fill, air cleaner, then hook up the tester with engine at TDC. Listen for any leaks at the oil fill, air inlet and muffler outlet. To test the rings further remove the valve covers and push rods and again test at BDC. Just a note on valve seals The intake valve are usually under vacuum and can draw oil if the seals are bad or missing, exhaust is under pressure and does not usually need a seal, they need all the lubrication they can get.
 
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