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  #1  
Old 06-15-2018, 10:39 PM
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Default K 321 Broken Valve Stem

Any ideas on what may have caused this exhaust to break at the stem?
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File Type: jpg K321 Exh Valve (460x613).jpg (22.2 KB, 100 views)
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Old 06-16-2018, 12:06 AM
J-Mech J-Mech is offline
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I'd say mostly age, but looks like heat may have been a factor also. Probably an older stellite valve. Looks like the head popped off at the seam. Looks like the head gasket was leaking on the typical corner.

I'd probably just rebuild it, but if it wasn't an oil burner I suppose you could fix it. Need to do at least a valve job, but that's a pretty tough thing to do on an assembled engine without getting stone dust in the motor. I've done it..... but don't like to.
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Old 06-16-2018, 10:30 AM
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Originally Posted by J-Mech View Post
I'd say mostly age, but looks like heat may have been a factor also. Probably an older stellite valve. Looks like the head popped off at the seam. Looks like the head gasket was leaking on the typical corner.

I'd probably just rebuild it, but if it wasn't an oil burner I suppose you could fix it. Need to do at least a valve job, but that's a pretty tough thing to do on an assembled engine without getting stone dust in the motor. I've done it..... but don't like to.
I believe it's time for a rebuild. Doing some rough measurements the cylinder seems to be out of specs. With the piston still in at the bottom of the stroke I measured the cylinder with a telescope gauge and it's around 3.537.

If I'm reading the manual right the maximum wear should be 0.0030 over bore size?

So if my measurements are right the cylinder is .004 over maximum wear limit?

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Old 06-16-2018, 11:06 AM
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Don't get too hung up on maximum wear lmit. All that refers to is when doing an overhaul, the cylinder needs bored if above that limit. It does not mean it needs overhauled at that point. The cylinder will wear until it burn oil and won't hold compression anymore. A telescoping gauge isn't a very accurate way to measure bore anyway. If it isn't burning oil, and ran decent it's up to you what to do. Like I said, I'd probably just rebuild it. More for the reason of I know what it costs, and for the work involved in properly fixing it, I'd rather do a rebuild.
But.... if it isn't a bad motor, I suppose you could get a new valve, lap it to the old seat and run it until it's life is over. Up to you.
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Old 06-16-2018, 12:02 PM
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Don't get too hung up on maximum wear lmit. All that refers to is when doing an overhaul, the cylinder needs bored if above that limit. It does not mean it needs overhauled at that point. The cylinder will wear until it burn oil and won't hold compression anymore. A telescoping gauge isn't a very accurate way to measure bore anyway. If it isn't burning oil, and ran decent it's up to you what to do. Like I said, I'd probably just rebuild it. More for the reason of I know what it costs, and for the work involved in properly fixing it, I'd rather do a rebuild.
But.... if it isn't a bad motor, I suppose you could get a new valve, lap it to the old seat and run it until it's life is over. Up to you.
Thanks, it has been using oil so while it's tore down this far I'll take it to a machine shop and have them check the bore and then go from there.
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Old 06-16-2018, 01:06 PM
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If it's an oil burner, it will need bored.
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Old 06-16-2018, 05:16 PM
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So is .030 the most the K321 can be bored? This engine is already bored to .030, I see that there are .040 pistons available in aftermarket.
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Old 06-16-2018, 05:41 PM
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I have had 1, M12 Kohler that I thought sure would need bored, but I took it into the machinist and he said "I got lucky, looks like the piston took the abuse instead of the bore on this one". and on that particular motor overhaul I was able to buy std parts and everything was still within tolerance, but "don't count on it".
Don't remember which 12hp I did, either that one or the K301 before it, but when I took it to the machine shop, they called me and said it needed a new exhaust valve because it was "necked," it looed like someone got it red hot and pulled on the valve head and stem, it was definitely skinnier in that section than the rest of the stem.
I won't swear to it but I THOUGHT that the "kohler kit guy" in Ohio had advertised a 0.040 piston at one time.
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Old 06-16-2018, 08:02 PM
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So is .030 the most the K321 can be bored? This engine is already bored to .030, I see that there are .040 pistons available in aftermarket.
If the block can handle it, and .010" more will clean it up, you can. If not.... find another engine or sleeve it.
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