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Discussion Starter #1
One of the reasons I decided to tear into this engine was because in addition to blowing a lot of smoke and using lots of oil, when I put some STP and some 40 weight in, the crankcase pressures built up so high it blew the oil filler cap right off the top and sprayed engine oil all over the place. After pulling the jugs, the pistons and rings were definitely worn beyond limits so they're getting replaced with 0.010 oversized. By the way, I DID find the Mahle pistons on eBay for about 66 bucks each. Much better than the 200+ for the old styles!

I'm trying to limit the teardown so I didn't remove the components on the front of the engine: the PTO assembly and the cover plate. But, I got to thinking about the condition of the oil pressure relief valve, which is basically just a spring and ball arrangement. So, my question is this: Would it be worth removing the PTO and cover plate in order to check out the oil pressure relief valve considering that the engine oil pressures were high enough to blow oil out the oil filler neck? And, if so, is it necessary to remove both the PTO assembly and the cover plate separately? Or, can they be removed as one unit?

Thanks! -Swede
 

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First off, high oil pressure will never blow off the Oil cap or dipstick. The pressure is built up between the bearing surfaces. It does not pressurize the crankcase. That is caused by something like piston rings, bad breather assembly etc. These engines seem to have a lot of these issues. Hi crankcase pressure. Some is normal and in some version of this engine the fuel pump is actually operated off these pressure pulses. Not yours though.

While your working on the cylinders pay attention to the breather assembly located on the top of one of the cylinders. It's a rather flimsy contraption and resembles a feeler gauge and usually has some sort of rubber seal all attached to a plate beneath the tappet cover. And you should find a stiff Styrofoam sponge. I would assume this is installed to stop oil from being sucked into the air cleaner. (Depending on what type of air cleaner you have.) Check out the parts manual for details.

Also, many times overlooked is the intake valve seal. If you engine smokes excessively right after startup or acceleration then slacks off, look there. Most have been removed long ago in some previous overhaul. This coupled with a bad breather assembly allows oil into the cylinders through the intake valve. Excessive valve stem wear can also do this. Oil can also enter the cylinder through the exhaust valve but only after the engine is shut down. Rather then the oil bleeding down into the crankcase it runs thru the loose valve guide and cylinder. The next time you start the engine it will smoke until the oil is burned out. It seems the oil drains very poorly from the tappet area back to the sump. Which leads to the last suggestion I have. When you reinstall the cylinders, pay very close attention to seal material (gasket maker). The drain holes I mentioned above can be plugged by this which may be the issue all along. Some older Kohler engines use gaskets, some don't. They just call for gasket material. Make sure which you need. And if so, make sure the correct gasket is installed.

Sorry to drag this out. It's hard to explain. And hopefully I didn't confuse you too much.
 

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Swede, you need to be a little more informative about what you are working on. I assume is it KT17 Kohler engine in a Deere 317 tractor. Series I or Series II?

I have a 1979 317 with KT17 Series II engine that did not smoke when I purchased it but did blow the fill plug from the tube. Also engine was covered in oil.

Two fixes:
These two improvements corrected situation on my 317.
 

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Discussion Starter #4
Hello Kelvin and JetJoe, the motor is a Series II, 24301, from the early 80s, off a JD 317. I suspected the crankcase breather the first time this happened but it all checked out fine (it's the new one) and the breather tube that vents overboard is fine, too. I suspect the higher than normal crankcase pressures were caused by blow-by back into the crankcase by a combination of worn rings and pistons, and possibly through the valve stems, though less likely given their condition when I pulled the jugs. The incident happened twice, each time after I added a small amount of STP and maybe a half a quart or slightly more of 40 wt, rather than the 30. I was chasing a tapping noise, which turned out to be the fuel pump attachment screws were loose so that the fuel pump lever was not in proper alignment to the cam lug, thus causing a tapping that definitely didn't sound like metal-to-metal (the pump lever is a hard plastic, I believe). Anyway, I suspect the top end rebuild will cure the problem, unless maybe the oil pressure relief valve is somehow stuck, gummed up, or whatever. The inside of the case looks real good, but you never know.

I'm not real sure what the oil pressure relief valve even does, or how important it is, actually. I presume the spring keeps the check ball in position until crankcase pressures build too high, but then what? Where does that pressure go once the ball valve opens? Does this valve control pressures inside the crankcase, or inside the closed lubrication system itself?

If the darn thing were easier to get to, I'd definitely check it and replace if necessary. I can see only two possibilities: either the spring is compressed, allowing the valve to remain open all the time; or the ball/passage is gummed up so that the ball can't move. Not sure which condition would cause what. Either way, to check it I'd have to remove both the PTO assembly and the coverplate, which I'd prefer not to do unless necessary. Hence my original question: Can I pull the cover plate off with the PTO assembly still attached or must I remove the pulley, PTO unit, etc. first?

I didn't see anything in the service manual about the PTO assembly. It seems straight forward to remove it, but if I can get away with not doing so and just pulling the coverplate, I'd definitely do that.

Thanks for the help! Semper Fi, Swede
 

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I really think you can forget the oil pressure relief. But to answer your question, the ball and spring controls the pressure by simply opening a passage that returns some of the oil back to the pump itself. The spring tension is calibrated to a specific pressure. Most hydraulic systems do exactly the same thing. But I cannot see a condition where high oil pressure would cause high crankcase pressure. As I said, this is really not unusual in these Kohler engines. I have seen bungee holding these caps on for the same reason. The newer Kohler's did away with the plug type cap and installed a threaded cap on the oil fill. I would guess for this very reason. Not saying you shouldn't address it but it seems you're on the right track with reconditioning the cylinders.

One more thing, I have several different Kohler KT manuals and the oldest makes no mention of an oil pressure relief in the overhaul and reassembly instructions. I never seen one, but who knows. Maybe some early KT's never even had one. When paging through the Series 2 or Magnum manuals the reference is inserted right at front cover assembly instructions. No mention of Serial Number where these manuals applied. Nice of them to do that.
 

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Discussion Starter #6
Hey, JetJoe, Thanks. That's a big help. I noticed somewhere that the Kohler Series I motors didn't have the oil pressure relief valve. The manual I have discusses it but the photos are so poor it's hard to see. Plus, I still can't figure out whether or not I can remove the coverplate with the PTO assembly still on it. Probably have to remove the pulley, but it looks like there rest of the PTO can stay. Anyway, I don't think I'm going to bother with it. Your explanation cleared things up well. Crankcase pressure and oil system pressure are really two different things and the oil pressure relief valve is in the oil system. Therefore, it has nothing, really, to do with high crankcase pressures. Makes senses

Would you happen to know what lives behind this small cover on the right side of the engine? The one with the two hexhead allen bolts? Semper Fi, Swede

cover with hexheads.JPG
 

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Given the oil burning/crankcase pressure problem you are trying to solve, the only reason to remove the front closure plate would be to fix an oil leak at the plate gasket or shaft seal (the PTO clutch would be removed first if this were the case). As you and jetjoe conclude, the oil pressure relief has nothing to do with crankcase pressure. In fact, the relief is set at such a high pressure, that it probably never opens in a well-used engine. I have not encountered a problem with the simple spring/ball relief assembly in doing many KT17 series II rebuilds.

Maybe you discussed servicing valves in another post. At the minimum they should be cleaned, lapped, and have the valve/tappet lash set. Presumably a shop is boring the jugs 0.01", so it would not add much cost to have the valve seats ground and the valves faced. Setting the lash is a bit of work, as the valve stems have to be ground down (flat) a tiny bit, re-installed, and measured. This usually takes several passes for each valve.

The small cover is a blank for an oil filter adapter.
Harold
 

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That's where an oil filter is mounted. Or a attachment to install a remote oil filter. There is nothing behind it but passages.
 

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Discussion Starter #9
Thanks to you both for responding, JDALCHEMIST and JETJOE. You've both helped a lot. We have a good snowmachine repair shop down in Willow that's going to bore the cylinders and I can take care of the valves here at home, with help from a friend. I appreciate all the insight you and others have given me over the course of this project. Semper Fi, Swede
 
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