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Troubleshooting Quiz. Now Solved


Al

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Hi, I will describe an actual problem and give some clues to its solution. Every day or two I will add clues until it is solved. Problem: KT17 Kohler engine, tired, has been completely disassembled, crank ground, new main bearings, new rods, cylinders bored 020, new pistons and rings. Valves ground, new front seals, points, condensor, plugs etc. Customer uses tractor and it uses some oil. Not abnormal. Customer continues to use tractor and oil consumption gets worse. Use continues and tractor starts to smoke some. We look at the tractor and check the compression, normal, check the crankcase vacuum, normal. Do a cylinder leakdown test. Leakdown excellent, high in the green, both cylinders. Engine runs good but sucks a lot of oil. Timing is right on. Air cleaner is NOT soaked with oil. Here is a riddle for you: Oil, Oil who is drinking my oil. This is in a Cub Cadet 682, and it is not Mr Mc Cormick from Mc Cormick Deering- Farmall. Al Eden
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Interesting, Are the valve guides wore so much that the engine sucks oil through them on the intake stroke?
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Well Levi, that would have been my quess. Second a bad crankcase breather but unlikely because air filter not soaked (but I don't know where the breather is attached on that engine).
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Not using straight 30 weight oil. Instead using 10w30. started with straight 30 weight oil added 10-30 oil as replacement oil to top off completely changed oil using only 10-30 weight oil
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Cyl. over bored perhaps. My guese would be the rings have turned and alligned themselves. What do the 2 plugs look like?
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I'd imagine if the gaps on the rings had alligned, it would have shown on a leakdown test. From the description, I'm hearing that the motor smokes worse as it warms up. This makes me think the motor may be running hot due to clogged fins or a lean fuel mixture that could be as simple as a fuel filter or tank screen. Incorrect oil as mentioned before could be a possibility.
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I am not completely familiar with this engine, but. You have given a clue, true, but you have not given the whole scenario. Is the engine perhaps leaking the oil, and the smoke simply a new set of rings breaking in? Did you tighten all oilpan bolts, or miss a couple of inches of gasket when assembling? If it were valve guides in that bad of shape, you would have noticed when you were rebuilding and replaced them, if possible. I would have. Crankcase breather would be next on my list of things to look at, though I do not know exactly how that one is arranged. I need to know more about the overall engine to make any decision
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Hi, Clue 2 Crankcase vacuum is normal indicating the breather is OK. Leakdown test is normal, indicating there is not excessive blow by into the crankcase. Ring alignment is not the problem. Note that it is normal due to torsional action for rings to rotate and they do as the engine runs, unless the rings are stuck with carbon. I used to belive that when building a racing engine you put the top compression ring in with the gap on the thrust side of the cylinder, so the least gap was exposed. Later I read some articles on the rotation of rings in the cylinder and when I pulled engines down for refressh rings found they had their own mind on this. Since I have seen several articles that demonstrate that they rotate in the cylinder. Compression is equal and normal in both cylinders. Oil is correct SAE 30, and the fuel pump holds pressure indicating the diaphram is OK. Oil is clean and fins are clean. Engine has probably less than 75 hours on it. What I expected to find I found. The problem is something that when the engine was assembled the mechanic doing the job should have caught. Cylinder bores are true and the crosshatch in the cylinders is still good. There are no external leaks. Here I gave you 3 or 4 clues, I can't keep a secret well. But will add some more soon. One question, are you interested in this type of thing or would you rather not have any more? Al Eden
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Al, One more thing, this is a used tractor that we sold. The customer has had it about a year. It has always used oil. We never ran it over 15 minutes after the overhaul. The persone that did the job no longer works for me. We had it in and put a new breather in it and it didn't help. I went out and got it, took the customer a tractor to use and told him we would fix it because we sold it with an overhauled engine and IT WILL BE RIGHT. This fix is on our nickel and we are fixing it no charge. When we sell a used tractor most of the time we do a warranty on it. Even if not if the customer gets it and it is not right we fix it no charge, unless it is sold as is. Then we are very open about any problems it might have. I would have caught the problem when assembling the engine. My mechanic missed it. It doesn't matter, WE SCREWED UP and wE ARE STANDING BEHIND IT! When I tell you what the problem is you will understand. Now it will use a half a quart in an hour and smokes.
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Wouldn't be sometime as simple as a maladjusted choke? And I do like the quizz !!!
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I remember Al posting this problem a while back but can't remember the cause. I tend to make mental notes on his posts. Seems like it was something simple Ike
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HI, Bob,I am going to give it to you. One plug was fouled with oil worse than the other and one exhaust port was oily. The oil ring expander was bad. The oil ring is composed of 2 thin steel rails and a spring type expander. The ends of the expander butt together and it compresses length wise. When I pulled the jug off, the oil rails were flush with the piston wall and provided no oil control in that cylinder. It appears that the expander was defective new and one little wavy segment short. When putting the expander in the cylinder it lacks about 3/16" of butting together. When the mechanic put the rails on the expander they should stick out of the piston and slide back and forth about 1/8" and the end gap uncompressed be about 1/4". When I do an engine I always put each ring in the cylinder it fits in and check the end gap to be sure it fits correctly to assure the ring is good. Next when I put the oil rails on the expander I put each rail on with the end gap 1/3 turn the butt in the expander. The rails do not rotate on the expander, but the assembly may rotate in the cylinder. Next I check the butt match up on the expander and slide the assembly around in the ring groove to be sure the rails are setting properly on the expander and not binding on the sides of the groove. This would not have happened on this piston and had he done this I wouldn't be paying for a come back. I had a 58 Chevy 348 that had a similar problem. It would foul the #7 plug and everything checked OK. Compression was same as other cylinders etc. Would still run 99 to 100 in the quarter mile and in the low 14s and high 13s with standard 58 vintage street tires and about 142 top end but would foul the #7 plug. Pulled it open and the expander in the oil ring had broken. This was with Perfect Circle rings, who pioneered the 3 piece oil control ring. There is no way to measure this problem. (that I am aware of) The oil rings fit in the lower ring groove that always has holes or slots in the bottom of the groove. Anymore the oil rings usually have a thin steel rail and then a cast iron back up ring with slots in it and a flat spring expander under it, or a 2 thin steel rail ring with a spring expander under them. The piston comes down and the first ring or rail squeegees a lot of the oil ahead of it. Then the second wipes the rest and it goes through the holes or slots in the ring groove back into the crankcase. If the grooves or holes are plugged the same effect as a broken expander will result. The compression rings will not wipe the oil as there is no hole or path for the oil to excape. The oil rings have practically no effect on the compression because the holes in the piston and the compression rings usually seal well enough that that far down the chain the effect is negligible. Regarding compression, the 2nd compression rings often have a bevel or step on the inside. Some designs have a step on the outside. The ones with the step or bevel on the inside, the bevel provides a larger surface on the inside and the compression that goes between the piston and ring on the top presses on the ring outward and downward to press the ring against the cylinder harder or a better seal. Rings with the step in the outside of the ring the inside of the ring being thicker also has more square inches of surface than the outside area that is against the cylinder wall this gives an outward "hydraulic" pressure gain from the combustion pressure to increase the outward pressure on the rings against the cylinder wall. These processes increase the compression sealing of the compression rings yet allow the rings to not have as much residual pressure on the walls through the other 2 cycles for longer wear. The principle works just like an O-ring works in a hydraulic application except the piston rings are solid. Hope you enjoyed this. If you like I may do a few more of this type thing. Al Eden
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