something leaking from exhaust stud

[seagull]

I noticed this leak that appears to be coming out of the #1 cylinder lower exhaust stud. It appears to be oil. There are no drips on the lower cowling and it is not blown back on the engine. This tells me it is either evaporating, (not oil) or a very small leak. Everything was cleaned 50 hours ago. The # 3 exhaust is leaking from the same area but the stain is smaller. Cylinders 2 & 4 have no leak.

[RFSchaller]

Did you check the torque on your exhaust nuts? Might be soot blowing out from a rich cylinder.

[Tacco]

Just went through this, although my “leak” was much smaller than yours. First, there is no penetration of the exhaust stud hole into the crank case or oil channels. I convinced myself it was left over assembly lube leaking out of the hole. The lube then “collects” exhaust residue/soot that circulates inside your cowling. My thoughts for what they’re worth.

[printbr]

I had similar looking oil coming out the end of the exhaust and found that I had oiled the air filter way too much. Since it is happening only the one side of the engine I would suspect the oil is coming from the Carburetor air filter feeding that side. Clean the filters with cleaner and rinse them well, and then only put a very very light spray of oil on them. But it looks like that flange needs to have the torque checked as well.

[Speedpants]

I had a customer that had the same issue with 2 of his cylinders on his 912 RV-12 I called lockwood and apparently it is an issue with the exhaust valve guide oil seal being made of imperfect rubber(basic description). The seal when working correctly will keep engine oil from the head from making its way down to the face of the exhaust valve....but when it expands or comes off its seat it will allow oil to leak by, I filed the defect paperwork to lockwood and have been waiting to hear back since mid April. But having covid throw a wrench into things I have never heard back. On the positive side after about 50-60 hours the leak has subsided, my guess is the rubber seal finally set against the valve shaft. From everything me and the owner have seen there were no adverse effects on engine performance or maintenance, besides from having to wipe the cowling and heads clean. Not the best answer but hope it helps for understanding why and where the is leaking from.

Mitch AP/IA

[seagull]

Originally Posted by Speedpants

apparently it is an issue with the exhaust valve guide oil seal being made of imperfect rubber(basic description). The seal when working correctly will keep engine oil from the head from making its way down to the face of the exhaust valve....but when it expands or comes off its seat it will allow oil to leak by

This may be the cause of what I am seeing. In my case the engine has 600+ hours and in the last 100 hrs the amount that has leaked out isn't enough to drip on the cowl.
The assembly lube in the stud hole theory probable isn't it based on the hours.
I saw on the Rotax forum a possible explanation, an exhaust leak combined with a sinking float washing exhaust soot out. I thoroughly cleaned it and will be watching.
I did check the torque on the nuts and they all in excess of 100 in lb.

The right side of the engine, cylinders #1, #3 run hotter than the left by 50 degrees based on the EGT's. I am not sure if that is a clue.

[Jonathan Alvord]

I would say there is a microscopic crack in the weld for the exhaust flange under the cover. Just my own two cents, as that happened on my RV 7a.

Jon