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Oil Leaking from Lower Exhaust Stud

Tacco

Well Known Member
I have a very small amount if oil, a couple drops, leaking from the lower exhaust studs on two cylinders. Why?
 
Unlikely, it would have to be a crack in two heads. Weird thing is, how does oil get into a stud hole? Are they drilled all the way into an oil pathway?
 
I have a very small amount if oil, a couple drops, leaking from the lower exhaust studs on two cylinders. Why?

Tacco -

Is this issue with a new engine???

If so, I had the exact same thing happen to me. After my initial flight around the field, taxied back to the hangar and removed the cowlings for an inspection ... noticed the lower cowl had a couple of oil drips on it.

Interestingly, the oil seemed dirty and brownish. I got to thinking and decided that it could not be any of the fresh oil I placed in the engine. Further examination showed evidence of oil coming from one of the #1 cylinder's exhaust studs.

Cleaned off the oil and went for another run ... far less oil the next run .... then nothing.

I attribute this oil to be machining oil left over from manufacturing. Below is a photo showing the area I had the oil ... as can be seen in the inspection mirror.
https://2.bp.blogspot.com/-kt_AZA3Saaw/WCHVz5o-WEI/AAAAAAAAMe8/Y-w6RHrB04YIm63FkEcOcf1e9GTYdFDTQCLcB/s1600/DSC02404.JPG

Happy flying,
 
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Thanks John! Exactly my problem. Yes, new engine. I suspected assembly lube but the stud is supposed to be inserted with locktite. I’ll keep an eye on it.
 
No, it's pretty obviously the stud. Hopefully it will go away as John said. It's supposed to be secured with Locktite 648, which is green and cures. I guess I'm surprised the stud goes all the way into the valve chamber - if what we're seeing is oil and not assembly lube.
 
Keep an eye on it, and report back. I'd think it's assembly lube.

I just can's see a stud going clear through to the valve assembly area inside the head, with access to motor oil and or crankcase blow by pressures from that area that pump the motor oil back into the oil sump canister.
 
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I also have a leak at the #2 cylinder exhaust screw. By the oil residue on the bottom cowl, I would say about eight drops of oil. If I can ever figure out how to post a picture I would. This is at 60 hours on the engine.
 
I had the same problem 4 years ago. It drove me crazy. The oil source is not from the stud. It is blown there from another source. For me it turned out to be a very small valve cover leak after doing the Rotax oil purge. I fixed the leak and throughly cleaned the valve covers, but I still kept getting visible oil around the exhaust stud after engine runs. When the stud got hot from the exhaust it would drip. This occurred until I used mineral spirits on Q-tips to completely clean the stud and the oil coating on the underside of the exhaust pipe retaining rings. This solution worked for me.
 
The studs are in the head not the barrel. And it is not from a leaky valve cover either. It is most definitely from the stud, which is totally illogical.
 
Actually, it is logical.

8 of the 16 studs screw into inserts in the crankcase where the holes are drilled through. O-rings on the inserts keep oil away from the studs. If O-rings are bad, oil can travel up the studs and leak at the bottom of the cylinder head. Below are a couple of photos showing the result on my airplane last year.

I've attached the Rotax Service Instruction that RFSchaller referred to above. This was the solution to my leaks.

The same leak was happening at several studs. We think the reason was because the cylinder barrels had been loosened from the crankcase for a previous repair that involved removing the cylinder heads (at about 88 hours). Our theory was that the O-rings had hardened a bit in use and wouldn't completely seal when the heads were retorqued.
 

Attachments

  • Oil Leak.JPG
    Oil Leak.JPG
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  • Leak at Cylinder Stud.JPG
    Leak at Cylinder Stud.JPG
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  • SI-912 i-006.pdf
    2.4 MB · Views: 271
Actually, it is logical.

8 of the 16 studs screw into inserts in the crankcase where the holes are drilled through. O-rings on the inserts keep oil away from the studs. If O-rings are bad, oil can travel up the studs and leak at the bottom of the cylinder head. Below are a couple of photos showing the result on my airplane last year.

I've attached the Rotax Service Instruction that RFSchaller referred to above. This was the solution to my leaks.

The same leak was happening at several studs. We think the reason was because the cylinder barrels had been loosened from the crankcase for a previous repair that involved removing the cylinder heads (at about 88 hours). Our theory was that the O-rings had hardened a bit in use and wouldn't completely seal when the heads were retorqued.


Germans, and Austrians, have a lot of one time use bolts, and one time use O-Rings, due to the tightness of tolerances they tend to run.

I wouldn't be the slightest bit surprised that the Rotax heavy manual recommends replacing all the O-Rings when a cylinder or head or stud gets loosened or comes out.


It's my belief it's some sort of Teutonic mindset, use once and dispose of. It's been that way on my VW's and Audi's since my first VW jetta diesel in 1981, later my 1983 Audi 5000 turbodiesel. One time, stretch to use head bolts, head gaskets, and on, and on and on. American designed engines tend to reuse things several times on engines, transmissions and such.
 
Actually, it is logical.

8 of the 16 studs screw into inserts in the crankcase where the holes are drilled through. O-rings on the inserts keep oil away from the studs. If O-rings are bad, oil can travel up the studs and leak at the bottom of the cylinder head. Below are a couple of photos showing the result on my airplane last year.

I've attached the Rotax Service Instruction that RFSchaller referred to above. This was the solution to my leaks.

The same leak was happening at several studs. We think the reason was because the cylinder barrels had been loosened from the crankcase for a previous repair that involved removing the cylinder heads (at about 88 hours). Our theory was that the O-rings had hardened a bit in use and wouldn't completely seal when the heads were retorqued.

All well and good, but we’re talking about the exhaust flange studs here. This SI is not applicable.
 
Pretty sure I've figured this out. There was indeed some residual assembly lube or anti seize that seeped out of the stud, or was always there. New engine remember. A minuscule exhaust leak at the cylinder head resulted in this residual fluid "collecting" soot from the blow-by. How did I arrive at this conclusion? Re-torqued all my exhaust nuts. The only two that were not near the required torque were the two where the "leak" had occurred.

That's my theory anyway.
 
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