Exhaust valve sticking on young engine

[sbalmos]

Having gone to enough of Mike Busch's talks at Oshkosh over the years, I finally invested in a better borescope this past season, one that articulates. This was the first time I've been able to see the exhaust valves. My #3 exhaust is apparently sticking. Since this is the first time seeing the valves, I don't know to what extent this has progressed over the 4 years and 220 hours of time I have on the plane and engine.

There's isn't any telltale green (yet), and all other metrics of the engine show it to be very healthy. I /really/ would rather not have to pull the jug. If it's something I can just keep in the back of my mind, monitor, and see if/how bad it progresses next winter at the next annual, even better. But clearly the burn pattern shows the valve is sticking. I tried to take some pictures around the valve seat. But the hotspot is in the one area of the valve seat that I can't really get the borescope camera around to. Regardless, I'm not seeing anything sticking out (pun intended).

I run EFII, definitely lean, and my CHTs usually stay in the mid 360s to 370s in cruise, so most of the too-lean/too-rich/too-cold/too-hot ideas I wouldn't think would apply at first blush.

Thoughts, comments, ? It's surprising me that it's showing up after only 220 hours.

 

[N427EF]

I am sure others with more experience will have an explanation of what you are looking at but this does not look like a burned "sticking" valve to me.
What I see is carbon deposit missing on that discolored part of the valve, hence the bare metal exposure and different color.
Hi resolution pictures can scare the 'ell out of you when in fact things look quite normal.
Have you done a compression check to confirm a leaky valve?
If your valve was in fact "sticking" as you point out, you would definitely notice it in flight. Sticking valves make a shuddering noise and are very noticeable in flight.
Wait for the more replies and see what they have to say.

 

[rocketbob]

If the springs can't rotate then the valve can't either. The spring seat washer and springs can get carboned up, requiring cleaning. Pull the valve cover, remove the rockers and springs and try to rotate the valve by hand. If wont spin freely then in-situ valve lapping is necessary.

 

[Mconner7]

Sticking?

I agree that you will know when a valve sticks. I had one begin to stick at around 550 hours since new. It only occurred twice about 50 hours apart and manifested itself as a serious shudder from the motor that only lasted a couple of seconds. I wrote it off as water in the fuel.

Fast forward 100 hours and almost a year and with no warning #3 stuck hard and lasted almost 2 minutes. When I scoped the cylinders, no sign of unusual color and the seats on #3 felt right once the spring was off.

I dropped all of the valves and reamed the guides, cylinders 2 and 4 were very tight.

I would not assume sticking based on color but would definitely do a wobble test as it is easy and will let you know if the guides need reaming.

I am NOT an engine guru but have learned a lot….

 

[sbalmos]

Fair enough. There's an engine shop on field, and the owner knows most of us. I'll see if he's around tomorrow and has a free few seconds. For the record, if a stuck valve is as noticeable in-flight as you're saying, then it's not sticking. I haven't noticed anything like a nasty shudder or any type of loss of power, CHTs and EGTs are all fairly balanced between all 4 cylinders, etc. The compression today on the cylinder was 74 cold, which is right about where it's been all along.

 

[wcalvert]

My IO-360 stuck a valve at about 200 hrs. The only evidence was the morning sickness and a dead EGT, clearly no combustion in that cylinder for a minute until it warmed up. No sign of any discoloration on the valve. When I pulled the cover to do the reaming it needed to be tapped out with a drift.

If you're concerned about the discoloration, you may have something other than a stuck valve. Like one of the previous posters said, maybe there's an issue with valve rotation or a precursor to a burned valve.

Good idea to talk to an engine expert, my experience doesn't go that far.

Best of luck

 

[Dan 57]

Hi Scott
Guess we’re talking Lycoming 320 or 360. Zooming in on the picture in the lower left, some yellowish discoloration can be spotted. The rest of the discoloration shape is rather atypical, like broken deposit.
In addition of Bob’advice, I would:
- replace the rotator cap
- check for enough of a bypass gap between the cylinder’s head and rear baffle. If none, make one. Few threads on here about the subject

 

[sbalmos]

Showed our engine guy the pics, he immediately said nothing to worry about. It's definitely not sticking, else I'd know it in-flight (as you all said), and there'd be much more obvious greening. He agreed it looked like broken off deposit. I asked about pulling the springs and turning the valve. He didn't think so, otherwise there'd be more extensive burning. So, yeah, freaked out by the first "good borescope" pictures. It'll be something I'll keep a watch on in years to come. I've already got a washer to gap the rear baffle. Time to move on with other annual stuff. Thanks all!

 

[lr172]

But clearly the burn pattern shows the valve is sticking. I tried to take some pictures around the valve seat. But the hotspot is in the one area of the valve seat that I can't really get the borescope camera around to. Regardless, I'm not seeing anything sticking out (pun intended).

You don't get isolated burns or hot spots from the valve sticking open. Burns or hot spots appear when that area of the valve is not making contact with the seat. Exh valves get very hot and they transfer their heat away to the seat via direct contact. When something prevents a portion of the valve face from touching the seat it creates that hot spot in the immediate area where there is no contact with the seat. This is heat damage. This can be from debris preventing the contact or can be from warpage. Problem is that the hot spot often creates its own warpage.

You can try lapping it in place and then put prussian blue on the valve face and determine if it was effective in creating full contact. A leak down test can also be used to check for contact. It is also possible that there is no warpage and the debris preventing the contact has cleared itself.

Larry

 

[Canadian_JOY]

Showed our engine guy the pics, he immediately said nothing to worry about. It's definitely not sticking, else I'd know it in-flight (as you all said), and there'd be much more obvious greening. He agreed it looked like broken off deposit. I asked about pulling the springs and turning the valve. He didn't think so, otherwise there'd be more extensive burning. So, yeah, freaked out by the first "good borescope" pictures. It'll be something I'll keep a watch on in years to come. I've already got a washer to gap the rear baffle. Time to move on with other annual stuff. Thanks all!

I stuck a valve at almost the same number of engine hours. The valve showed NO greening whatsoever so, from my sample size of one, I would suggest relying on colour as a single indicator of a sticking valve to be unreliable.

BTW my engine sat pickled, FULL inhibiting oil for a decade. I suspect this inhibiting oil crudded up the valve stem and that crud started to coke the first time I started the engine. That's the only reason I can come up with for sticking a valve so early in an engine's life (it was a factory new O-360).

 

[rocketbob]

You know the position of the burnt spot. If you check in a few hours and its in the same spot the valve isnt rotating. The appearance is not normal and I look at a lot of them....several hundred this year.