Oil Fouled Spark Plugs

hamer

hamer

Pre-takeoff checklist
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hamer
I've got one plug (1B) on my O-290-D that is oil fouling. Is there anything I can do/inspect to help alleviate the issue?
 
Find out how the oil is getting in the cyl? There is only three ways. Past the rings, past the guides, or a crack. The solution is the same, pull the cyl.
 
unsafervguy said:
Find out how the oil is getting in the cyl? There is only three ways. Past the rings, past the guides, or a crack. The solution is the same, pull the cyl.
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Sounds easy enough to diagnose. If it's past the rings can just the rings be changed? Or does the entire cylinder need to go out?
 
The only thing you can actually check with out pulling the cylinder, is the valve guide, by doing a valve wobble check.
And then only the intake valve will introduce oil into the cylinder.
IMHO 99% of these gripes are the rings.
Do you know how much time is on the cylinder.
 
Tom-D said:
The only thing you can actually check with out pulling the cylinder, is the valve guide, by doing a valve wobble check.
And then only the intake valve will introduce oil into the cylinder.
IMHO 99% of these gripes are the rings.
Do you know how much time is on the cylinder.
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About 300 hrs. But the top overhaul was done years ago. I bought the airplane last year with 200 hrs on the top end. I put 100 hrs on it since November. Compressions were high 60s when I got it, I was hoping everything would come up as I flew it more, but I haven't re-checked yet. Annual is due in September.
 
hamer said:
Sounds easy enough to diagnose. If it's past the rings can just the rings be changed? Or does the entire cylinder need to go out?
Click to expand...
It should get rebuilt.
Honed .015" over, new piston, rings, valve guides, new valves, and piston pin.
and then it may crack :(
 
Tom-D said:
It should get rebuilt.
Honed .015" over, new piston, rings, valve guides, new valves, and piston pin.
and then it may crack :(
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What do you mean may crack?

Tom-D said:
Were these rebuilt cylinders at that time?
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That I'm not sure, I'll have to go back and look at the logs.
 
The Lycoming uses a 3/8" oil drain tube from the rocker box to the crankcase. If it sludges up it will tend to fill the rocker box and the oil will easily flow down the intake stem and foul that cylinder. I have found those sometimes bent so they have a low spot where crud will settle after shutdown

Be a shame to pull a cylinder only to find the new one doing the same thing because the drain is blocked.
 
Dan Thomas said:
The Lycoming uses a 3/8" oil drain tube from the rocker box to the crankcase. If it sludges up it will tend to fill the rocker box and the oil will easily flow down the intake stem and foul that cylinder. I have found those sometimes bent so they have a low spot where crud will settle after shutdown

Be a shame to pull a cylinder only to find the new one doing the same thing because the drain is blocked.
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Thanks for that suggestion, I noticed that tube when I was working in there and didn't know what it was for. I will inspect it.

I measured the resistance on that plug and it was 15 mega ohms. Way out of spec. That plug definitely wasn't firing and likely the reason it built up like that. I would not be surprised if the drain was blocked up.
 
I have no idea what MMO is.
 
Unit74 said:
You need some MMO..... It fixes anything, including poor stick and rudder skills.
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You laugh, but it could be an oil control ring stuck with carbon. If the guides weren't wobbly, I'd try a ring-wash procedure, yes with MMO, before I pulled a cylinder. Can't hurt, might help. Always try cheap and easy before expensive and difficult.
 
Chip Sylverne said:
You laugh, but it could be an oil control ring stuck with carbon. If the guides weren't wobbly, I'd try a ring-wash procedure, yes with MMO, before I pulled a cylinder. Can't hurt, might help. Always try cheap and easy before expensive and difficult.
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I'm privy to private conversation ,,,, it is not the cylinder, bad harness, plug not firing for over 100 hours.
 
Tom-D said:
I'm privy to private conversation ,,,, it is not the cylinder, bad harness, plug not firing for over 100 hours.
Click to expand...

That'll do 'er. No bad mag checks in 100hours though?
 
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