Kawasaki 17hp twin cylinder liquid cooled, FD501V smoking bad

I just picked up a 2000 model LX279 with a twin cylinder 17hp liquid cooled Kawasaki model FD501V. The guy selling it said it was smoking like a freight train and he "was told that the rings were burnt up". I removed the cylinder heads and the head gaskets looked rough. Both cylinders looked great, smooth, no scratches at all. The piston heads were much better than I expected, not much carbon or buildup at all. The only problem I saw anywhere was the exhaust valve on the left hand side looked pretty bad and I suspected the valve stem seal or guide might be bad. I replaced both head gaskets and all four valve stem seals. I filled it with Rotella 15W40 and cranked it up and it was still smoking really bad. Obviously not the head gaskets. I warmed the engine and did a compression test. Both cylinders were right at 120 psi compression. I drained the coolant to access the flywheel and then I did a leak down test. The engine was cool by this time. I tested at 120 psi. Both cylinders showed a leak down to 116 psi. I could hear air passing into the crankcase when testing each cylinder but I could not hear any air passing through the exhaust or intake valves.

So....what does this mean? Is 120 psi acceptable compression? The results of the leak down test lead me to believe the rings are good. If that exhaust valve stem guide on the left hand side is bad, would that show up in the leak down test?

Also, after running the engine and removing both spark plugs, the right side plug looked dry and pretty clean, just as I would expect it to but the left side plug was black and oily.

Valve stem guide or piston rings or something else?

On the last engine I rebuilt I ignored the acceptable results of the leakdown test and tore the engine down and replaced the rings only to find out that wasn't the problem, it was a bad valve stem guide. I'm trying to learn from my mistakes. I want to make sure I haven't overlooked something here.

http://www.mymowerparts.com/pdf/Kawasaki-Service-and-Repair-Manuals/

engine repair manual is five down FD501V

disassemble, inspect everything carefully, pistons, rods, crankshaft, cylinder walls for scoring, replace piston rings, let us know how it goes, thanks.

Thank you for the link to those manuals. I realize that worn piston rings are the usual culprit, but the leak down test here would indicate that the rings are good. I have seen experts here time and time again recommending a compression test and a leak down test. I ignored the results of the last leak down test I did which indicated that the rings were okay and I tore that engine down anyway only to find it wasn't the rings.

Before I remove the engine from the mower, split the case and remove everything to put new rings on I want to make sure I rule out everything else. In this case I am curious about that one exhaust valve guide that may be bad. That's why I wanted to know if a bad exhaust valve guide would show up on the leak down test. If it is the valve guide I can replace that one cylinder head without much trouble or effort, I certainly wouldn't have to the remove the PTO, pulley and then take the engine off the mower, what a hassle!

Just to recap, the compression test indicated 120 psi on both cylinders and the leak down test indicated a drop from 120 psi to 116 psi on both cylinders. What should those number tell me about the condition of the piston rings?

Leak down test does not test the valve guides as the valves are closed and no pressure at guides. Test your valve guides and see if they are worn out.

That's actually good, that what I was hoping to hear. I would much rather replace the cylinder head than tear the engine apart to replace the rings. I've replaced the seals already. Is there a test I can do to check the guides? It may be a moot point, I found a used LH cylinder head on Ebay for $35.00 shipped. I sure hope that's the problem! I would like to check the guides anyway, or know how to for future reference.

So valves go up and down. Lift valve and see if you have any left or right movement. If you do the the guides are bad.

Lol, I was hoping for something a little more technical! I had done that, I could detect the slightest of movement, I mean barely noticeable at all. So slight that I questioned whether I was really feeling movement or not.

Im betting you do not have worn valve guides.
https://www.youtube.com/watch?v=0w2BRxAiUKw

If you have the guides & valve stems clean & dry, that is when you will detect most movement (if any), oil has viscosity & will give false feel for looseness.

Unless you have mics & etc to actually measure the clearances.

If the cylinders look good and you have decent compression, I would bet that it is the oil rings. I had similar issues with two automotive engines in the past that smoked like crazy and burned a quart of oil every 50 miles or so. They both had good compression, and the culprit ended up being bad / stuck oil rings. Just my two cents and worth every penny...:laughing:
Bruce