One really dead cylinder

Tom-D said:
I'm not asking, I'm trying to point out that Lycoming does not want you to clean all the lead out of the guide nor do they want you to clean it off the valve, Why Not.
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From Lycoming's SB388C:

EXAMPLE
.019 = Total thickness of gage required to measure valve movement.
.010 = Thickness of gage used to establish a starting point.
.009 = Actual amount the valve stem has moved: This indicates insufficient clearance between the valve stem and valve guide which can be corrected by reaming the valve guide I.D. to remove a build up of carbon deposits. (Refer to the latest revision of Service Instruction No. 1425 for valve guide reaming.)

SI1425 speaks or reaming the guide. Pretty hard to leave any lead deposits in there doing that.

Dan
 
Dan Thomas said:
SI1425 speaks or reaming the guide. Pretty hard to leave any lead deposits in there doing that. Dan
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No it's not, the reamer will return it to standard, that leaves the diference between wear, and standard as lead.

Lycoming does not want you removing any more than the reamer will because if you clean it all out, and clean the valve, the cylinder will fail the wobble test.

you only ream when the standard won't fit, you ream back to standard,
 
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Tom-D said:
I'm not asking, I'm trying to point out that Lycoming does not want you to clean all the lead out of the guide nor do they want you to clean it off the valve, Why Not.
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The lead lubricates the valve in the guide.
 
NC Pilot said:
The lead lubricates the valve in the guide.
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OWT, Proven wrong many times.

Lycomig wants you stay at standard, because removing all the lead form the guide and valve will cause the cylinder to fail the wobble test. and burn oil like crazy then the lead carried to the guide by the excess oil, makes it stick again.
 
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kmead said:
A Malibu had a rough engine and a big loss of power yesterday. I sent our Malibu and a Mechanic out to find the problem and he found it. The valve head snapped off and imbedded itself into the #3 cylinder piston. I haven't seen anything like this for 20 years.

Kevin
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How hot did that aluminum piston have to be to allow the steel valve to embed itself to that extent? What do the rings and the grooves look like? Valves sometimes break along the stem, but the usual resulting carnage doesn't manifest itself with like the picture. The piston would have to be approaching liquidus temperature for that to happen. Aluminum pistons frequently operate at a face temperature of 650 F, but with good lubrication cooling, there's a steep downward gradient away from the face. I'm guessing that the whole depth of the piston would have to be around 700 F for that to happen. Hope you can share the factory's post-mortem, but I'd guess a lubrication failure and operating ROP enough to really heat things up, plus a fluke valve stem failure.
 
Trapper John said:
How hot did that aluminum piston have to be to allow the steel valve to embed itself to that extent? What do the rings and the grooves look like? Valves sometimes break along the stem, but the usual resulting carnage doesn't manifest itself with like the picture. The piston would have to be approaching liquidus temperature for that to happen. Aluminum pistons frequently operate at a face temperature of 650 F, but with good lubrication cooling, there's a steep downward gradient away from the face. I'm guessing that the whole depth of the piston would have to be around 700 F for that to happen. Hope you can share the factory's post-mortem, but I'd guess a lubrication failure and operating ROP enough to really heat things up, plus a fluke valve stem failure.
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It would have been at operating temp, with the forces at or near the top of the stroke will forge that valve in to the piston with one hit.

There are two types of valves, the angle valve that runs at an angle to the cylinder bore, when these stick open the piston will bend the stem as it drives the valve closed, that sticks it closed and the rocker and cam action will force it open and then the piston hits again, usually this will break off the head of the valve.

the other type is the parallel valve these will usually survive a little longer because the valve doesn't get bent when its driven close.
 
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I had one pretty much the same way. Ok, my kid did, but I opened it up, this is what I found on two pistons - said he was just driving normally up the mountains when it lost power.

95 Saturn
 

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gkainz said:
I had one pretty much the same way. Ok, my kid did, but I opened it up, this is what I found on two pistons - said he was just driving normally up the mountains when it lost power.

95 Saturn
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Melted ring lands is a sign of detonation. Driving up the mountains in too high of a gear will do that. Low RPM, high MP. That car should have had knock sensors, but maybe even with the timing fully retarded it might have been detonating.

Cheap low-octane fuel, too, maybe.

Dan
 
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