Advice on exhaust leak

[frtrkap]

Hi,

During preflight not long ago I found an exhaust leak from #3. The exhaust was about 1/16" from the cylinder which was enough for exhaust to shoot all over the spark plug and the intake.




My mechanic think this is a crack in the exhaust port, so I assisted on removing the exhaust and spark plugs and this is what I found.






Some background info: coincidentally, this cylinder has a leak down of about 68 compared to the other cylinders at 72+. When looking in the spark plug holes, I could see some oil at the bottom of the cylinder, piston face is oily and spark plug had some oil too, mostly carbon (maybe from the combustion burning the oil). Looking at the valve from the rocker box, the exhaust valve seems to have more carbon deposits.

I am mostly trying to understand what I am looking at in the exhaust port. Is all this carbon normal? Is it normal that the valve stem is this dirty?

Exhaust pipe is white in color inside, so not burning stupid amounts of oil.

Has anyone seen anything similar?

(Yes, of course it's going to get looked at. The cylinder will probably be removed and sent to an engine shop. Just wanted to hear from people that might've seen this before.)

Thanks!

 

[Dan Thomas]

Looks like the exhaust valve has been pretty hot, possibly because it was leaking and causing the low compression reading.

Both of those studs will need replacing. The exhaust port face will need refacing, otherwise a new gasket will just leak. The leaking exhaust has eroded the studs and port face. Annual/100 hour inspections are supposed to catch stuff like this before it gets this far gone.

 

[Der Fliegermeister]

Frankly, I wouldn't be comfortable just throwing a new gasket on there and cleaning the valve guide. If you were one of my preferred customers, I'd have you exchange that core cylinder for a new one and be done with it. Glad this didn't end up worse for you and I applaud you really focusing on on it because this is a serious issue. Keep us posted on what course you take with your mechanic's guidance!

 

[Doc Holliday]

How did this get missed for so long that it’s now in this condition?

 

[JAWS]

Besides fixing/replacing the cylinder, I'd also be looking at the exhaust flange for erosion and a true flat surface. And if the cylinder is repaired, the exhaust will fit differently compared to the others. Shimming might be in order for a leak free fit.

 

[Dan Thomas]

The actual leak happened during a flight.

I'm having trouble believing that. There's just way too much carbon, way too much erosion for that to happen on one flight.

There was a LOT of leakage. Look at the warped, half-melted baffling:

 

[Gary Ward]

It wasn’t like this at annual in January and I check that spark plug wiring is tight before each flight. The actual leak happened during a flight.

Sorry but that amount leakage went on for many hours and months. Good luck with it.

 

[Jdm]

This engine has been neglected for a long time. At a minimum, that cylinder needs to be yanked and properly repaired. While it’s off you should have good A&P look at the airplane and see what else has been missed.

 

[Magman]

Oddly enough I’ve just encountered 2 cylinders with exhaust port leakage.

Since only the port a comp check will not show it.

Owner confirmed stains via pressuring exhaust system with Exhaust Valve closed

by means of a leaf blower / soapy water.

After removing stack an air gun was used externally and you can see bubbles in the

cracked port.

I can send a short video to someone but posting is above my pay grade.

 

[Dan Thomas]

This engine has been neglected for a long time. At a minimum, that cylinder needs to be yanked and properly repaired. While it’s off you should have good A&P look at the airplane and see what else has been missed.

I'd be inspecting every inch of that exhaust system. If it got past the mechanic that easily, who knows what might be lurking somewhere else? All the exhaust risers need thorough checking with a flashlight and mirror, especially up near the cylinder flanges. They're famous for cracking there. The other ends of the risers need checking where they enter the collector or muffler, and the muffler needs a real close check for cracks. Anything under the cabin heat muff needs a real good look, since any leakage there sends carbon monoxide into the cabin. That'll kill you dead. In Canada we have an AD that applies to any aircraft using the exhaust system for cabin heating, demanding an annual/150-hour inspection for just that reason. Using a vacuum cleaner to inject low pressure air and soaping everything to look for bubbles is advised. Any more pressure than that and you blow the soap off and don't see bubbles.

 

[Jdm]

Excellent advice! Also, get a portable electronic carbon monoxide detector for the cockpit. They are extremely accurate these days. I have one in every piston engine that I fly.
There’s honestly no telling what I could find on this airplane. With something like this getting past inspection it’d be no problem for a good mechanic to find a laundry list of airworthiness items. I’d get a good inspection done ASAP (by a reputable shop). Then start whittling your way to safety, one discrepancy at a time.
Btw, what part of the world are you located? Surly we can find a qualified person in your area to help.