• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Lycoming exhaust oil leak

B

bearsnack

I have a 150 horse narrow deck that is putting oil out of the exhaust port, enough that it makes the pipe wet about 2 inches down from the cylinder attach flange. Comp check shows 75 over 80 and all looks normal when rocker cover is removed. I have not seen this before and need some input if anyone has previous experience with this problem.
 
How long since the cylinder was rebuilt? Did the cylinder have to be welded and where? I have seen them at overhaul need to have the guide holes welded back to to standard and when they do that they have to face the spring seat area and with all of the other welding that takes place that is typical with Lycoming cylinder cracks you get some porosity that can open a pin hole from under the spring seat to one of the ports. You could also have a worn out exhaust guide/valve stem that allowing oil to pass. A piece of dirt/crud blocking the rocker box drain tube and not allowing the oil to drain back as freely. Several different things can cause this do some more looking to see what you find.

Matt
 
My guesses would start with a worn-out valve guide.

A close second guess would be a crack encompassing both the exhaust port area and the inside of the rocker box.

Either of these issues would invite rocker box oil into the exhaust port of the cylinder. Plenty of Lycoming cylinders get some rework in the guide and exhaust port areas during cylinder overhauls, as Matt alluded to.

makes the pipe wet about 2 inches down

What exactly do you mean? On the inside of the "pipe" exhaust stack? On the outside of the stack?

I'm guessing you're talking the outside.

I guess a little clarification would help here also:

putting oil out of the exhaust port

Again I'm a bit confused that you know it's out of the exhaust port unless you've got the stack off and are looking inside.

Sorry that I don't get your whole drift, so to speak.

To really find the source of this leak, you oughtta thoroughly clean the area of oil and then run the engine for a short time, maybe a minute, then look for the leak. If it hasn't shown up in a minute, try for another couple of minutes, then maybe 5 more. Heck, maybe you'll have to fly it or run it up til it's hot before the oil shows. This is, of course, assuming that you're seeing the oil on the outside of the stack.

Sorry to sound like a jerk asking such specific questions. I swear I'm just trying to help. :wink:

Whatever you think, prepare yourself. You're likely to be looking for a new cylinder.

Hopefully you've got a super-leaky-cub rocker cover gasket. If you do, buy those new orange silicone gaskets next time. I love 'em. A 'real' time saver, and they work with beat-up old covers, too.

Good Luck. DAVE PS let us know what you find.
 
Geez Dave, your always picking at me! :D Just kidding.
It is on the outside of the exhaust, I have looked the fins over for cracks, thought for sure I would find some but haven't.
TSO is 1850 on engine, I beleive the cylinder has run this time also.
I fly the airplane daily back and forth to work, some days it does not put out as much . The most is a couple inches long, narrow dribble on the back of the exhaust pipe ( Just below exhaust flange)
Gotta go, I am at work. I will try to write more tonight.
Joe
 
OK I am back. It appears that the oil is coming from the exhaust port. It is burned onto the exhaust gasket and wet down the back of the pipe ( 2 inches max). It doesn't take much oil to make a mess and hot oil at that.
I have inspected and inspected it , all return lines and box covers are not leaking and I find no visual dicrepancies. I am hoping it is a guide and I can run it for another 50 hours or so.
Oil screen is clean and it is not consuming more than normal.
Let me know what you guys think.
 
Dear Bearsnack,

Most likely you have a cracked cylinder or a loose valve guide. A loose valve guide can be detected by applying a side load to the guide with a screwdriver or other prying tool. Take care not to use too much force. Often there is a crack between the walls of the exhaust port and the rocker box cavity. This information is only true if the oil is actually coming out of the exhaust pipe. If the oil leak indication is external to the exhaust system then there are numerous causes. What model powerplant are we talking about here?
 
Model is 150 horse A2B. Narrow deck.
I dropped the exhaust pipe down and inspected the guide and valve. All looked well. No cracks. It is dry in the port area downstream of the valve and seat and the seat looks fine. What I am thinking is that there is a crack or porous area that is letting oil out just behind the exhaust flange. I cleaned this area up and inspected it, I can't find anything.
I suppose if it is a crack it will open and show itself eventually.
What I need to do next is comp check when it is hot with soap bottle spray for leaks. I suspect it may be one of those.
Behindprop: I will troubleshoot more and possibly contact you for a cylinder.
Thanks for the continued input!
 
Just had this happen on my O-360. Pushrod tube o-ring at the cylinder head. It's right on top and drips through the head to the exhaust flange.
 
Just my 2c, check the push rod , if that's not it, pull the cylinder and have it rebuilt or a new one. We could make guess's but it's still got to come off and get fixed. Behind the prop made a great offer, using it for work you can't afford down time and flying it with a problem for 50 hour, that's on you.
 
I know it was from 13 years ago but the problem was never solved on here. lol So I thought I would add mine. Now I replaced the o-ring and it still leaked. Pulled the tube and looked it over again to find it had a 1/2 inch crack in it. Dripped right down to the oring and then through the fins.
 
Guys , We have an AEIO 360 in a 2004 Super Deke that was zero time overhauled (first life) recently with new Lyco cylinders. Front left cylinder has had oil appearing on the exhaust in the same place as detailed above.
I am sure I have checked all the likely places that are visible, silicon rocker gaskets , oil drain back tubes , push rod tubes etc .
Engine runs fine but has always run hotter oil temp since the overhaul. The same engine on its first life was always rock solid on 180-200c oil temp dependent on the day , now runs up to 20 degrees hotter.
Comps are good. The oil seems to appear from the exhaust gasket and runs down the outside of the pipe down onto the cowl and appears out of the left side as an dark brown/black streak on the outside of the lower cowl.
We are thinking the only way oil can get there is guides or cracks?? Is there a way to check before biting the bullet and pulling the cylinder?

Thanks in advance
 
One thought - - clean the engine thoroughly with solvent and let it dry. Spray suspect areas with dye penetrant developer powder, run engine until source appears. I've read a simpler way here, but can't remember at the moment.
 
Thanks Gordon , That would certainly highlight where it is coming out however I think we already know that as it appears from the exhaust gasket so I think the source may be buried a little deeper?
 
I had a leak that I would have sworn was oil cooler or case parting-line related, but turned out it was a tiny crack in the engine case. The powder test would at least confirm or refute an external leak vs a crack inside the head - maybe?? It will be interesting to learn what you find.
 
Back
Top