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Cylinder #2 Stud/Nut Oil Leak

A

ambrosesquadronca

Member
I have a Lycoming YIO-360-M1B with 125 hours on it and have been keeping an eye on this leak or more like a seep on the #2 cylinder, lower, forward 1/2" stud.

It appears to me the nut is riding on the cylinder wall radius slightly not allowing it to sit down 100%. The nut has an integral washer flat with a sharp edge. Probably not good having a sharp edge ride the radius of a casting.

Not sure what to do with this:

Leave it and let it seep?
Goop it up with something?
Thin washer and radius the edge (only 2 thread protrude nominally though)?
Round off the edge of the nut?

Opinions?

Thanks.
Dave Ambrose
RV-8A

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I've noticed the same small weeping on the YIO-360-M1B in my -7. I think its normal for a Lycoming....from what I've been told.
 
Leaking stud

Assuming this stud is threaded into the case half and is not a thru stud. It usually comes from oil that wicks around the case threads & stud and seeps out just like in your photo. Most engines are dry in this area but it's not unheard of to have a little seepage here. I have dealt with this issue several times and the only real fix is to remove the stud, clean throughly & reinstall with loctite. Not a hard job but unfortunately the cylinder has to come off to be able to remove the stud. If it takes 15-20 hrs to make the amount of mess in the photo I would leave alone and monitor. I have never seen a cylinder base nut that did not sit flat on the cylinder base flange, but yours may be the first. A seated nut has no sealing function so even if you could get it to seal the oil would just seep out between the cyl flange & case.


Don Broussard A&P, IA

RV-9 Rebuild in Progress
 
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Stud leaking

Appears to be a narrow deck engine. Narrow deck engines that I have seen have socket nuts to clear cylinder. I agree that would not stop the leak. The engine assembler may have left out one of the "0" rings between the case halves that seal the case bolts. That would cause your problem.
 
The dribble has the appearance of oil running down the side of the barrel base flange. Just for clarification, the barrel is forged steel and the fins are machined from a solid blank. Still subject to stress concentrations, even more than if cast.

I thought the Vans YIO 360 M1B was a wide deck engine - how do you tell?
 
That looks like #2 cylinder, you can see the nearest thru stud in front, the one with the spacer on it. If so it's not a missing case o ring as suggested. So the one leaking is a threaded or "set" stud. These thread into an open hole in the case so the stud has to seal when it is installed.
I don't think you can do much without pulling the cylinder, which you'd have to do to re-set the stud and it's very possible maybe likely it's the cylinder o ring leaking anyway.
Major surgery to repair repair a minor leak... probably best to leave it alone.
You could try locktite 209, thats the wicking product used on assembled fastners. Getting it clean first and applied to the stud at the case would be a good trick without pulling the cylinder, but it may be worth a try.
Tim Andres
 
Leak

Would be good to clean it throughly and spray some dye penetrant developer powder on the suspected area and fly it for 30 min to start. You might need to adjust flight time to be able to see where it leaks first. Sometimes the first sign of oil will be on the threads where they come thru the nut. This certainly looks like a wide deck engine due to the thickness of the base flange. Narrow decks use the internal Allen nuts and the doubler plates.

Don Broussard

RV-9 Rebuild in Progress
 
replace the O ring

I just had to deal with this problem on the#4 cylnder. I had oil seeping from one of the large bolts on top. the O360 engine has about 1600 hours since new.

We removed the cylinder and replaced the O ring that goes around the base of the cylnder. I think if the o ring was missing you would have oil leaking from all of the bolts. I bought about $30 in new gaskets and seals.

My A&P friend Al and I took about 8 hours to do the work.

Besides being a relatively easy job I learned alot. Thanks Al

Alan
 
8 ball said:
Appears to be a narrow deck engine. Narrow deck engines that I have seen have socket nuts to clear cylinder. I agree that would not stop the leak. The engine assembler may have left out one of the "0" rings between the case halves that seal the case bolts. That would cause your problem.
Click to expand...

I hope it's not a narrow deck engine since there are no cylinder hold down plates...:eek:

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Stud oil leak

Gil is correct concerning the narrow deck engine, however all case studs should have "0" ring seals. See lyc repair manual.
 
Stud Oil Leak

Thank you everyone for your responses.

Lycoming confirmed I have a wide deck engine.

Lycoming suggested that Loctite 290 may work but it is not an approved repair by them. They mentioned it because I have the "experimental" Lycoming engine (YIO...) so it may be worth a try.

The repair for this is in Lycoming Service Instruction 1290F which Gil posted the link for (thanks Gil). This SI has a repair for assembled and disassembled engines.

Dave
 
The Old Joke

The old joke about lycomings is that if they isn't a small leak somewhere you should check to be sure that the engine has oil.
 
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