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Discussion Starter #1
Hey all!
Ive got a decent GT2550 with 419 hours on the clock that has been using oil a bit this summer. I went to clean up leaves this morning and its been back-firing a lot, and seemed to be running on one cylinder. So, I pulled the plugs and the right one was plugged up with carbon and sludge. I cleaned the plug up and reinstalled it, and it runs great now. Would the rings be going bad in that cylinder? If so, what for specialty tools would I need? I'm very mechanically inclined, have done head gaskets on a few cars, so I'm pretty good around motors and whatnot. I'd tear it down this winter with my son and rebuild it, if its the rings that are bad. If thats what it is, what else should I replace?
 

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I'd start by doing a compression check to help identify where the problem actually is before I tore anything apart.

Rings shouldn't be worn out at 400 hours.
 

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Yeah, I would do more diagnosis first. Compression test, cylinder leakdown test, if you have an inspection camera, maybe poke it in the spark plug holes to check out the cylinder wall & piston top to see how they look (moving the piston to the bottom of it's stroke).
 

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For starters Cub have the full repair manual on line as a free download, good place to start .
Kohler also have their full service manuals on line as a free download

A blown head gasket can also cause a plug to oil up quite bad although the Command series are not known for doing this , it does happen.
Because it is a PIA to remove the blower housing and air cowlings on these engines , owners get a bit slack about cleaning out the debris from around the engine and in particular around the heads .
I have done a couple that have overheated and loosened the valve guides which also leads to oil leakage into the cylinder .
A leak down would be the best way to go as the decompressors tend to give funny readings on most mower engines
Although 60 one side & 0 the other does tell a tale .
 

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Discussion Starter #5 (Edited)
So I used my homemade leakdown tester without a gauge, and dont know what to make of the results.
No air leaked through exhaust or intake when the valves were closed. When they were closed, nothing leaked from the oil fill until enough pressure built up in the cylinder. Then a little air was coming out of the oil fill.
I know a little leak is expected, but not sure how much? Being it only has 400 hrs, rings wouldn't be my guess, but what do I know? Any advice?
 

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If you're going to have it down that far you might as well do a complete rebuild and then you should have a strong and reliable motor. When one thing goes out there's usually a succession of problem where things wear out. Why not do it once and done.

Sent from my motorola edge plus using Tapatalk
 

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The leak points: intake, exhaust, rings, and head gasket. Occasionally a crack will occur in the cylinder walls, head or piston crown, but not likely.
When you pulled the plug that was fouled, was it 'wet' foul? or was it dry, like black 'ashes', or a black coating? Were the electrodes coated and almost touching?
If it was black with ash-looking, that is generally fuel, Wet and oily indicated what you expect. If the valve guide is loose, you can pull oil down past the valve stem, and if the valve stem seal is baked and hardened, it may no longer prevent oil intrusion, especially with the vacuum of the intake manifold helping.
When you checked using the leakdown, did you have any sort of gauge on it at all? Did you use a compression test gauge and crank it over? Do that to have a better idea of compression, but in general, with the verbiage, it seems you don't have compression leakage of severe nature.
I think I would do a comparison between cylinders using the leakdown test. If they both sound about the same, it is likely they are working within range, and you should look elsewhere.
One last thing, where does the crankcase vent unload the vapors? If it is nearer or biased towards the cylinder that had plugs that were fouled, it could be crankcase vapors that caused the fouling. Be sure also that the crankcase is more or less completely sealed, as it will pump air through if there is an opening, and carry lube around with it and sometimes overpower the ability of the oil separator to grab the droplets from the vapor and redirect them back to the sump.
tom
 

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Ejl in Pa.
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Hey all!
Ive got a decent GT2550 with 419 hours on the clock that has been using oil a bit this summer. I went to clean up leaves this morning and its been back-firing a lot, and seemed to be running on one cylinder. So, I pulled the plugs and the right one was plugged up with carbon and sludge. I cleaned the plug up and reinstalled it, and it runs great now. Would the rings be going bad in that cylinder? If so, what for specialty tools would I need? I'm very mechanically inclined, have done head gaskets on a few cars, so I'm pretty good around motors and whatnot. I'd tear it down this winter with my son and rebuild it, if its the rings that are bad. If thats what it is, what else should I replace?
419 hrs is not a lot of hours for a Kohler V Twin unless it was seriously abused with oil changes. I have a 25 hp Kohler V Twin in a CC 3235 with 1200 hrs on it that still runs strong and has never been rebuilt. I would perform a compression test on both cylinders and if you have one that has low compression do a leak down test to let you know where the problem lies.
 

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Discussion Starter #9
When you pulled the plug that was fouled, was it 'wet' foul? or was it dry, like black 'ashes', or a black coating? Were the electrodes coated and almost touching?
It wasn't wet, I had to use a pick to break off the coating. The gap was fully filled with hardened sludge or whatever it was.
When you checked using the leakdown, did you have any sort of gauge on it at all? Did you use a compression test gauge and crank it over? Do that to have a better idea of compression, but in general, with the verbiage, it seems you don't have compression leakage of severe nature.
I didn't have a gauge at all. Can't find anyone that has one, and don't feel buying a good one would get used often enough. I didn't do a compression test, but I can borrow a tester from a buddy (will post results later).
I think I would do a comparison between cylinders using the leakdown test. If they both sound about the same, it is likely they are working within range, and you should look elsewhere.
One last thing, where does the crankcase vent unload the vapors? If it is nearer or biased towards the cylinder that had plugs that were fouled, it could be crankcase vapors that caused the fouling. Be sure also that the crankcase is more or less completely sealed, as it will pump air through if there is an opening, and carry lube around with it and sometimes overpower the ability of the oil separator to grab the droplets from the vapor and redirect them back to the sump.
I gave the tool back, so I'll have to borrow it again. Crankcase vent? Ill have to do some digging to figure that out.
 

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Discussion Starter #11
419 hrs is not a lot of hours for a Kohler V Twin unless it was seriously abused with oil changes. I have a 25 hp Kohler V Twin in a CC 3235 with 1200 hrs on it that still runs strong and has never been rebuilt. I would perform a compression test on both cylinders and if you have one that has low compression do a leak down test to let you know where the problem lies.
So I used my homemade leakdown tester without a gauge, and dont know what to make of the results.
No air leaked through exhaust or intake when the valves were closed. When they were closed, nothing leaked from the oil fill until enough pressure built up in the cylinder. Then a little air was coming out of the oil fill.
I know a little leak is expected, but not sure how much?
 

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Discussion Starter #12
Ran a compression test, weird... 160 in suspect cylinder, 140 in the other...
20psi difference not good?
Why would the bad cylinder have higher compression?
 

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Discussion Starter #13
Ran a compression test, weird... 160 in suspect cylinder, 140 in the other... 20psi difference not good?
 

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guyina4x4
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you're over thinking it
it just needs head gaskets
I bet I changed 100 Kohler command head gaskets this summer
 

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BEcause there is a 1/4 " of burned up crud in the head reducing the squish band .
Add to that gum & gunk build up around the piston & rings
 

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Money Pit
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I think your fine. Once a plug gets carbon fouled it's going to get oily nasty. I highly recommend using non ethanol fuel. Check your oil drain and see if it's loose in the engine block.
 
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