Exhaust valve leak

simtech

simtech

En-Route
Joined
Aug 15, 2012
Messages
3,089
Location
mississippi
Display Name
Display name:
Simtech
My last annual I had a low compression on cylinder #2 on my O-360. We did the compression test cold because I had already drained the oil the day before. So the compression was 64 and all other other mid 70's. Every annual before test was done hot and comps all in the mid 70's.

Well this annual the low compression, cold, was accompanied with air coming out the exhaust pipe. I flew for 20ish hours and we retested today. Still cold test BUT compression back up to 70 and still feel slight air from the exhaust.

Mechanic said its fine ( carbon stopping it maybe, keep flying) and Im still concerned and not wanting to fly much now. Im looking to have another mechanic look at it but im not sure I should be flying it at this point. Engine runs great, no issues at all. So until I can get anther mechanic out to look is there anything I can look at to get a head start? Do the test warm first before I get too upset? Keep flying it another 10 then retest?
 
Last edited:
Scope the cyl and look at the valve. I bought a very nice for price scope at $200. Priceless...
 
205489754

watch the first video on the left side of the screen.
 
64 and came up to 70. Keep flying it. I dont even look twice until I get a couple in a row in the 50s.
 
So the fact that the exhaust valved leaked during a cold compression test is nothing to get upset about? It wasn't so much the lower compression that got me but rather air I felt coming from the exhaust stack.
Tom-D said:
205489754
watch the first video on the left side of the screen.
Click to expand...

I have a harbor freight scope but the 90 degree mirror that I would need just slips on. Im afraid it would fall off. But having in recordable on the phone is pretty cool.

455 Bravo Uniform said:
Scope the cyl and look at the valve. I bought a very nice for price scope at $200. Priceless...
Click to expand...
link?
 
simtech said:
I have a harbor freight scope but the 90 degree mirror that I would need just slips on. Im afraid it would fall off. But having in recordable on the phone is pretty cool.
Click to expand...
my fear too, I superglued mine and am very careful
 
I had good comps, low comps shortly after, then it came back up after some running. Carbon happens. During the low test, you could hear the leak, but it sorted itself out.
 
I bought the one in this article:

https://www.aopa.org/news-and-media/all-news/2017/may/pilot/savvy-maintenance-borescope

There are also other web resources discussing visual valve assessment.

Not the be-all, end-all, but it can help ease your mind or confirm suspicions. Worst case it does nothing, you got a cool tool. Use it to monitor cylinder corrosion. I also used mine to inspect a couple cam lobes thru the oil fill (TCM IO-470).
 
Back when I was working at NAS building engines Uncle Sam bought us a $80,000 Olympus multifunction bore scope that could measure to .001"
The first time it was use on a J-52 the jet crew lost the mirror attachment.
MISSING TOOL,, shut down the entire division.
two weeks later we got a package from Olympus, the back ordered mirror attachment..
 
simtech said:
My last annual I had a low compression on cylinder #2 on my O-360. We did the compression test cold because I had already drained the oil the day before. So the compression was 64 and all other other mid 70's. Every annual before test was done hot and comps all in the mid 70's.

Well this annual the low compression, cold, was accompanied with air coming out the exhaust pipe. I flew for 20ish hours and we retested today. Still cold test BUT compression back up to 70 and still feel slight air from the exhaust.

Mechanic said its fine ( carbon stopping it maybe, keep flying) and Im still concerned and not wanting to fly much now. Im looking to have another mechanic look at it but im not sure I should be flying it at this point. Engine runs great, no issues at all. So until I can get anther mechanic out to look is there anything I can look at to get a head start? Do the test warm first before I get too upset? Keep flying it another 10 then retest?
Click to expand...

I’d put MMO in the fuel and go fly it hard for a few hours. Your mechanic gave you the green light to fly it. Go blow the carbon out of it.
 
When I got leaking exhaust valves during a test I'd take the rocker cover off, put the pressure in the cylinder, and tap the rocker over the exhaust valve with a soft-faced hammer. It would usually pop the bit of carbon loose that was causing the leak, and the compression would come up. If it didn't, it needed work. Doing this saved having to put things back together and pushing it outside to run it again.
 
Dan Thomas said:
When I got leaking exhaust valves during a test I'd take the rocker cover off, put the pressure in the cylinder, and tap the rocker over the exhaust valve with a soft-faced hammer. It would usually pop the bit of carbon loose that was causing the leak, and the compression would come up. If it didn't, it needed work. Doing this saved having to put things back together and pushing it outside to run it again.
Click to expand...
The carbon probably wasn't between the valve and seat, it most likely was on the stem of the valve holding it open. when you hit it with hammer it simply slammed the valve closed and it sealed.
one must remember when we pull the prop thru to move the piston to TDC the valves move slowly, if they are not free to close, they may stay open a little. hitting them with a hammer simply avoids finding a cylinder with morning sickness.
Finding a valve that will not close, isn't the time to force it to close just to see higher pressures, it is time to prevent further damage to the valve guide, it's time to fix the problem that is holding the valve open.
 
Last edited:
Tom-D said:
Back when I was working at NAS building engines Uncle Sam bought us a $80,000 Olympus multifunction bore scope that could measure to .001"
The first time it was use on a J-52 the jet crew lost the mirror attachment.
MISSING TOOL,, shut down the entire division.
two weeks later we got a package from Olympus, the back ordered mirror attachment..
Click to expand...
Oh no! Hahaha
 
Tom-D said:
The carbon probably wasn't between the valve and seat, it most likely was on the stem of the valve holding it open. when you hit it with hammer it simply slammed the valve closed and it sealed.
one must remember when we pull the prop thru to move the piston to TDC the valves move slowly, if they are not free to close, they may stay open a little. hitting them with a hammer simply avoids finding a cylinder with morning sickness.
Finding a valve that will not close, isn't the time to force it to close just to see higher pressures, it is time to prevent further damage to the valve guide, it's time to fix the problem that is holding the valve open.
Click to expand...
When I did that, the airplane would go back to work and stay that way. No more problems. Taking sparkplugs out often dislodges bits of carbon, and they can fall into the valve and sit there and cause a very temporary leak that causes the mechanic to take the cylinder off and spend a bunch of money on it.
 
Dan Thomas said:
When I did that, the airplane would go back to work and stay that way. No more problems. Taking sparkplugs out often dislodges bits of carbon, and they can fall into the valve and sit there and cause a very temporary leak that causes the mechanic to take the cylinder off and spend a bunch of money on it.
Click to expand...
It's far fetched idea the a speck of carbon falling off a spark plug is going to land and stay in a valve seat.
 
A couple of years ago Santa gave me a vividia bore scope with an articulating head. I believe it was around $200. It connects to your I phone or iPad and take pretty nice pictures or video.
I definitely would want to know why any exhaust valve is leaking.
 
This is the scope I have $350 from AS. You can take pictures or video. I'm still learning what is viewed. So far I have used to inspect cylinders, vertical stabilizer spar, wing spar and look for a missing socket I dropped under the floor. Not a bad tool I have it hooked up to my lap top, a little cumbersome. I do like the full screen view vs a small screen on my I phone.

The only down fall I can see is the camera tip is delicate and I think you need to send to manufacture for replacement.

12-04892a.jpg
 
1RTK1 said:
A couple of years ago Santa gave me a vividia bore scope with an articulating head. I believe it was around $200. It connects to your I phone or iPad and take pretty nice pictures or video.
I definitely would want to know why any exhaust valve is leaking.
Click to expand...
That's what I posted VA-800, the VA-400 is $200 I think
 
I use a plain 'Ol Android inspection cam. Make a nice loop in the cord and zip tie the cam head back to it so it's pointing back 180 degrees. Make a nice little safety wire handle, and you can see your valves and cyl walls just fine. Takes a nice pic, and cost me all of $10. Works great for fishing down the wing root, up behind the panel and under the floors too.
 
Tom-D said:
It's far fetched idea the a speck of carbon falling off a spark plug is going to land and stay in a valve seat.
Click to expand...
But it can and does. And turning the prop sucks air into and out of the cylinders, moving that carbon dust around. It sometimes finds its way into the valve/seat interface.
 
Tom-D said:
It's far fetched idea the a speck of carbon falling off a spark plug is going to land and stay in a valve seat.
Click to expand...
We had a piece of the orange rubber gasket on an air filter flake off and get under an intake valve. You'd think for sure that it would melt away, or be pounded into submission, but ... no. It was stuck on the valve seat, and the engine backfired until it was cleaned off. Engines have a way of surprising you with their failure modes. (I spent the first eleven years of my working life as a motorcycle, automobile, and marine mechanic.)
 
Dan Thomas said:
But it can and does. And turning the prop sucks air into and out of the cylinders, moving that carbon dust around. It sometimes finds its way into the valve/seat interface.
Click to expand...

With what frequency does it happen though? In the 10ish years I’ve been working on airplanes I’ve yet to see it happen, despite being warned about it. I’ve never seen it happen in the 25ish years I’ve been working on all sorts of other engines either.

So far, every aircraft cylinder that I’ve seen that could be revived by staking the valve had more serious problems, usually with the valve/guide. I think the procedure is worth trying but it should be treated as simply another tool to use in the troubleshooting process, not a repair.
 
A big engine shop owner told me to diagnose a valve issue you add some MMO to the fuel and run it hard to blow out carbon on the seat and add MMO to the oil if you suspect morning sickness. I’ve done the former a few times and it worked. When the run it hard thing hasn’t helped it was a valve guide problem. I’ve never had morning sickness in an airplane engine.
 
Stewartb said:
A big engine shop owner told me to diagnose a valve issue you add some MMO to the fuel and run it hard to blow out carbon on the seat and add MMO to the oil if you suspect morning sickness. I’ve done the former a few times and it worked. When the run it hard thing hasn’t helped it was a valve guide problem. I’ve never had morning sickness in an airplane engine.
Click to expand...
sounds like you weren't pregnant.....it's all good. :D
 
It doesn’t have morning sickness so not thinking it a stuck valve and in fact the engine runs smooth and without a hitch. My mechanic pretty much says no worries fly it like normal. And since we didn’t do it warm everything wasn’t expanded by heat and seated fully. But like I say all other cylinders were fine. He said go fly. I trust him but the last thing I want is the valve to come from together in IMC with family on board.

I will for sure look in the cylinder and I have flight today planned. What is considered fly it hard? Full rich WOT down low?

The compression improved up to 70 without doing anything but flying and I’m not worried about compression but more worried about the slight air coming from the exhaust. My oil samples show a history of a few years of nickel (valve guide) above the universal average but no one seems to mention anything about it. Filter is always void of metal.

Ill fly it normally for another 10 hours and retest on a hot engine and then see what happens. If still leaking then ill have him investigate further.
 
Dan Thomas said:
But it can and does. And turning the prop sucks air into and out of the cylinders, moving that carbon dust around. It sometimes finds its way into the valve/seat interface.
Click to expand...
The type of carbon you speak of will not do what you say it does, the carbon in the combustion chamber is crystal in nature and will crush under the force of the valve spring. the carbon formed on the valve stem is much different it is hard glass like material, it will and often does hold the valve open. that is what morning sickness is all about.
 
simtech said:
It doesn’t have morning sickness so not thinking it a stuck valve and in fact the engine runs smooth and without a hitch. My mechanic pretty much says no worries fly it like normal. And since we didn’t do it warm everything wasn’t expanded by heat and seated fully. But like I say all other cylinders were fine. He said go fly. I trust him but the last thing I want is the valve to come from together in IMC with family on board.

I will for sure look in the cylinder and I have flight today planned. What is considered fly it hard? Full rich WOT down low?

The compression improved up to 70 without doing anything but flying and I’m not worried about compression but more worried about the slight air coming from the exhaust. My oil samples show a history of a few years of nickel (valve guide) above the universal average but no one seems to mention anything about it. Filter is always void of metal.

Ill fly it normally for another 10 hours and retest on a hot engine and then see what happens. If still leaking then ill have him investigate further.
Click to expand...

when the valve guide got hot and expanded the carbon that was holding the valve open now fits and allows the valve to close..

Just because the engine runs well when hot, does not mean the carbon went away. It is still there wearing the guide. Some day the guide will wear to the point the valve will no longer set square with seat, at that time the guide must be replaced.
 
simtech said:
It doesn’t have morning sickness so not thinking it a stuck valve and in fact the engine runs smooth and without a hitch. My mechanic pretty much says no worries fly it like normal. And since we didn’t do it warm everything wasn’t expanded by heat and seated fully. But like I say all other cylinders were fine. He said go fly. I trust him but the last thing I want is the valve to come from together in IMC with family on board.

I will for sure look in the cylinder and I have flight today planned. What is considered fly it hard? Full rich WOT down low?

The compression improved up to 70 without doing anything but flying and I’m not worried about compression but more worried about the slight air coming from the exhaust. My oil samples show a history of a few years of nickel (valve guide) above the universal average but no one seems to mention anything about it. Filter is always void of metal.

Ill fly it normally for another 10 hours and retest on a hot engine and then see what happens. If still leaking then ill have him investigate further.
Click to expand...

Go out solo and run it at high MP and higher than normal cruise RPM for a couple of hours. Run it like a hotrod and enjoy that you’re doing it a favor, not a disservice. At least that’s what I was was advised to do. It won’t hurt it and it may help it. Or do nothing at all. 70# cold is not reason for concern. Me? I’d just like the chance to make it better.
 
Unnecessary for what he’s describing. You and Dan have wandered off from the OP’s situation. If the guides are starting to go? It’ll be a slow developing trend. I assume that’s why his hands-on mechanic told him it was good to fly.
 
This is the cause of 99% of sticking valves that leak when cold.
"morning sickness"
 

Attachments

  • P1010005.JPG
    P1010005.JPG
    69.5 KB · Views: 56
Stewartb said:
Unnecessary for what he’s describing. You and Dan have wandered off from the OP’s situation. If the guides are starting to go? It’ll be a slow developing trend. I assume that’s why his hands-on mechanic told him it was good to fly.
Click to expand...
Most mechanics will advise to keep flying a cylinder with 70/80 when hot.

but he also said he still has air coming out the exhaust, that IAW the FAA's recommendation is not acceptable.

and that in my opinion should be fixed then when done should add life to the cylinder.
 
Last edited:
simtech said:
It doesn’t have morning sickness so not thinking it a stuck valve and in fact the engine runs smooth and without a hitch. My mechanic pretty much says no worries fly it like normal. And since we didn’t do it warm everything wasn’t expanded by heat and seated fully. But like I say all other cylinders were fine. He said go fly. I trust him but the last thing I want is the valve to come from together in IMC with family on board.

I will for sure look in the cylinder and I have flight today planned. What is considered fly it hard? Full rich WOT down low?

The compression improved up to 70 without doing anything but flying and I’m not worried about compression but more worried about the slight air coming from the exhaust. My oil samples show a history of a few years of nickel (valve guide) above the universal average but no one seems to mention anything about it. Filter is always void of metal.

Ill fly it normally for another 10 hours and retest on a hot engine and then see what happens. If still leaking then ill have him investigate further.
Click to expand...

Installed a factory reman TSIO 360 a few years back, and initial oil analysis through 300 hrs showed higher than normal Nickel. Sure enough an exhaust valve was burning. My borescope picture looked suspiciously like the OP's second picture. Yea, Continental repaired the cylinder on their dime, but I had to pay labor. Now oil analysis shows normal nickel for the last 150 hrs.
 
Tom-D said:
Most mechanics will advise to keep flying a cylinder with 70/80 when hot.

but he also said he still has air coming out the exhaust, that IAW the FAA's recommendation is not acceptable.

and that in my opinion should be fixed then when done should add life to the cylinder.
Click to expand...

And per Lycoming instructions test it hot. There is no cold compression test standard that I’ve seen.
Operate the engine until normal cylinder head and oil temperatures are attained; then shut down the engine making sure that magneto switches and fuel supply valves are shut off. Proceed with the test as soon as possible after shut down.
Click to expand...

https://www.lycoming.com/sites/default/files/Cylinder Compression.pdf
 
Your motor runs like crap at first start of the day? That's how my friends describe it. I have no experience with that but I do have experience with carbon in the seats and worn guides.

The OP reported his compression cold. I'd expect it to improve considerably tested warm. I'm guessing his mechanic would agree.
 
JAWS said:
Isn't that what the operator is for? To communicate when things aren't right?
Click to expand...
hopefully but not always.

in for annual, then you get told "it's been doing tat for about 6 months".
 
My engine fires up and smooth. No morning sickness. That's why I believe my mechanic said fly it ain't no problem yet. No morning sickness and have had no other issues other than leaky exhaust valve on a cold soaked engine. He agreed if it's decent now it will be better when hot. That's why he said he is not worried yet.
 
Tom-D said:
hopefully but not always.

in for annual, then you get told "it's been doing tat for about 6 months".
Click to expand...

Not my problem until I see or hear about an issue. If Mr Owner wants to sit on it for six months, that is his choice. Want me to fix it? Authorize me to troubleshoot and repair.
 
You must log in or register to reply here.
Back
Top