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SmilinSam

Smokin 8hp Kohler

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SmilinSam
Got a 8hp Kohler I stuck in this Case 220 to make it go. Starts easy, has lots of power, seems to have great compression. Smokes real bad though. Nice thick puffy white smoke, cough cough, gag, gag..:p puts out smoke real bad when first started and every time you quickly run the throttle ahead. Seems to smoke less when you are running it under a heavy load and get the engin hot. Perplexes me as what to diagnose since there does not seem to be power loss anywhere at any time like usually experienced with worn rings. Case in point I broke the axle off on my heavy homade plate steel dump cart tonight out by the road picking up garbage cans. So I just drug the broke wagaon all the way down the gravel 400 fot lane. Didnt lack any power at all.8D What say you? Broke or worn ring(s) plugged breather? Outside there is no visible signs. Going to pull the engine and put another on and try. I have two more to use up yet. Wouldnt mind fixing this if its not too involved.

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ZippoVarga
White smoke.....does it have a distinct odor? Like un burned gas? The only thing I can figure is the possibility of the valves being worn only to the point where you are getting some blow by in the exhaust valve. This would present it self in the way of a fuel dump/aka white smoke yet maintain most of the power.Perhaps you can pull the head and check for carbon build up in the valve. That would be a perfect world scenereo. Just sounds like a valve not seating correctly to me. Hope it gets figured out. I'm sure others will also present their ideas and we'll all get it worked out as a well oiled machine. Sean

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MrSteele
Is it..White smoke is oil smoke and black smoke is fuel? Or is it the other way around? What does the smoke smell like? Not knowing a lot more than you say here, I'd lean toward rings, or, as you say, possibly a choked crankcase breather. I think I'd check the breather first. If you can pull the head without pulling the engine, look down the bore and see if your ring gap is more than about .010" If so, how much more? The Briggs I tore down because of basically the same symptom, a bit over a quart of oil per tank of gas, had nearly a 1/8" ring gap on the top ring, and still ran fine.

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BLT
I had a 10 HP Briggs with the same scenario. I would run fine no power problem, then load up blow white smoke all other neighborhood and then run fine again. Turns out air baffle around eshaust side was really plugged and when it got real hot, it would spew white smoke. It took out the rings and scratched the bore around exhaust side. Salvaged bore in time, cost me a piston and chrome ring set. I think it now six years running and fine. It is just relegated to mowing.

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HubbardRA
Sam, I am guessing a stuck oil ring. Would still have good power if compression rings are working, but would smoke because of oil rings. By-the-way, I have two Kohlers that do the same thing. Both make great power. Neither has a scored cylinder. I'm guessing that the rings need replacing. I had a Briggs that acted that way because it had been overheated and rings had lost their tension. New rings fixed it.

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ZippoVarga
Un-burned gas will most times be white with a distinct fuel smell. Which is why I questioned the smell. If it's blue/white and doesnt smell like gas then I agree with every one else that it's the rings. I had a heavily gummed up exhaust valve that was letting un-burned fuel to escape causing white smoke. When it would warm up the condition was a little better and there was never a loss of power. When Sam mentioned that when the engine was under load and the governor kicked in that the smoke was less is why I leaned towards a valve and not the rings. Oil burns blue/white and burned gas in a rich condition will produce black smoke. What wasnt making sense to me was that when under load, the smoke didnt get worse....it got better. This pointed me in the direction of fuel blow by. Not an oil ring problem. Higher pressure and more fuel to the engine should have produced more oil smoke, not less. Unless i'm mistaken that is. Just going by my experiences here.

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HubbardRA
I still think that the problem is with the rings. Gasoline smoke is a dark bluish to black looking color. A white to light blue color is oil. The oil ring does most of the smoke prevention during light throttle conditions. The compression rings are designed to seal better with increased pressure. As the load increases, the pressure differential across the compression ring increases, thus causing it to seal better(if the compression rings are in good condition). Compression rings themselves will wipe the oil off the cylinder and prevent smoking under heavy loading when cylinder pressures are high (if they are in good condition). I have seen engines for high performance(racing) use that had no oil rings at all. They had been removed to reduce friction. These engines would produce some smoke at lower rpms, but at WOT there was no hint of smoke. The compression rings prevented any oil leakage at the high cylinder pressures. If the compression rings are bad, they will allow compression to leak by them at all speeds and that pressure will cause the oil rings to stop working. Oil rings are only wipers to remove oil from the cylinder. They are not designed to be pressurized, and high pressures will push them away from the cylinder wall and cause oil burning. This is why we are all more familiar with major oil smoke under load when the compression rings are bad. Valves can only cause oil smoke if the oil is being sucked thru the area between the valve stem and the guide. This means that either the valve stem, the guide or both are worn. This smoking usually happens when the engine has been revving and then the throttle is suddenly closed. This makes a very high vacuum in the cylinder and causes the oil to be sucked past the valve stem when the valve opens. On an overhead valve engine, such as an automobile, bad valve seals and guides will also cause a lot of startup smoke, because the oil leaks into the cylinder past the seals and guides after the engine is turned off. There is significant oil lying on the top of the head because the engine has been running, and it leaks by any open valve into the cylinder. This normally doesn't happen on a single cylinder flathead because the drainage path is toward the crankcase, not toward the cylinder. Also, partially worn compression rings will cause startup smoke. They allow blowby that affects the oil ring, until the warm up and expand enough to work properly. All of the workings of the compression rings in an engine are relative to the pressure in the cylinder, the pressure/vacuum in the crankcase (backside of ring), and the tension in the ring which pushes it against the cylinder. This ring tension is usually the primary factor. It will be reduced as the ring and cylinder sizes change from wear, and it can also be affected by overheating the engine which anneals or stress relieves the ring and thus removes part of the spring tension. I hope this may help people to understand why I think it is basically the rings that are causing the problem. Two of my current tractors got "rings only" rebuilds and both are running great.

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portuncia
Somewhat related my 12 hp Briggs, blows black smoke which decreases when under load, driving/mowing. I just put a new plug in and pulled it out and the end of it is black, I figured oil. The guy who had it before me, last week, cleaned the carburetor and it had a stuck float, would my condition be caused by this issue?

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UCD
Black plug is also caused by a vacuum leak i.e. bad carb base and manifold gasket, warn throttle plate shaft etc. My immediate guess wold be the gaskets seeing that the carb has been worked on.

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SmilinSam
I pulled the head this morning and the bore looks great. No scoring and little to no lip at the top edge. Some carbon buildup around the valves but they seem to be seating tight. It did appaer to have wet oil around the valves especially in and under the exaust valve. I am going to remove the breather tonight and check that out.

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HubbardRA
Sam, I agree with your analysis, if there is oil under the exhaust valve then, in all likelihood, the crankcase is being pressurized. This can be either from a bad crankcase vent or from leaky compression rings.

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SmilinSam
Well nothing wrong with the breather, so I'd agree I'm looking at doing new rings. I did toss another K181 on the stand and found it works well without smoking so I will put it in the tractor and put some rings in this one when I'm on vacation and set it back for a spare. If the cylinder is in good shape, Do you have to hone the cylinder if you use chrome rings?

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BLT
quote:
Originally posted by SmilinSam
Well nothing wrong with the breather, so I'd agree I'm looking at doing new rings. I did toss another K181 on the stand and found it works well without smoking so I will put it in the tractor and put some rings in this one when I'm on vacation and set it back for a spare. If the cylinder is in good shape, Do you have to hone the cylinder if you use chrome rings?
Briggs says if bore is glazed, no and I have had good luck. Can't say about Kohler.

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HubbardRA
Sam, I have put rings into two B/S engines in recent years. The first, I just used sandpaper to break the glaze. The second got a light honing because it had been sitting in a shed without a head and had some light surface rust in the top of the cylinder. I don't use chrome rings unless I can't get the others. It is more difficult to get them to seat properly, and they tend to produce more cylinder wear than regular rings.

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BrianP
Sam, I agree with what Rod said. I always use standard rings, my thinking is, I'd rather have wear on the rings than on the block itself. Not certain about Kohler though, all my experience has been with Briggs.

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Bonaro
I have a green tractor with a kohler that smokes like yours..really thick stuff that fogs out the neighbors. I tore it down and found the ring end gap was about 3/8 inch when it should be about .020. I would say your rings are shot and since it is probably from high hours, your valve seals are likely gone also. Time for a complete rebuild with oversize piston.

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portuncia
By the way UCD thanks you were right finally started to fiddle with the carb on this thing and one of the mounting bolts has a screwed up tread and wasn't comepletly tight, i.e air leak. Runs much better now.

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