Exhaust valve failure!

[N201MKTurbo]

3 hours ago, GeeBee said:

It means you have no ring end gap. You may read it as 80/80 but it is not.

OK, it was probably 79.9/80....

I measured all the ring gaps. they were all exactly at the minimum gap.

Well, I did two pistons worth and then saw a pattern, so I quit taking them off and measuring them.

[Fly Boomer]

5 hours ago, N201MKTurbo said:

I have cylinders that are 80/80

Maybe a better prediction would be "no TSIO-360 cylinders are 80/80".
 

[A64Pilot]

 Having a cylinder at 80 does NOT mean no leakage, it means no leakage in excess of the “master orifice” that’s used to adjust the gauge to read 80. The orifice is actually quite a large leak, and if you happen to have the one meant for big radial motors it’s a really big leak, you shouldn’t of course but I have seen it done by mistake.

I believe the orifice we use is .040, so a 40 thou hole at 80 PSI is a decent leak, so your cylinder can leak that much and still show 80

I’ve got cylinders that on a good day will measure very close to 80 on my Lycoming, but I’ve not seen a Continental measure 80, but it’s possible I think, especially with some oil in the cylinder.

My SWAG is that valve was overheated which can happen from a sloppy valve guide and or poor seating in the valve seat, a valve is cooled of course by transferring heat to the head through those two contact points

Edited July 8, 2023 by A64Pilot

[EricJ]

2 hours ago, HeyChuck said:

A couple other mechanics I have shown this to had a similar thought. No signs of the classic asymmetric burn pattern that sometimes foretell a failure.

It looks like maybe the whole head got coated with something during the failur, so I'd see whether the current deposits will clean off easily to see the valve.   It may be green underneath, or at the edges of the fractures.    The inside of a head doesn't usually look like that.   I think that finish is the result of the failure.

[PT20J]

2 hours ago, EricJ said:

It looks like maybe the whole head got coated with something during the failur, so I'd see whether the current deposits will clean off easily to see the valve.   It may be green underneath, or at the edges of the fractures.    The inside of a head doesn't usually look like that.   I think that finish is the result of the failure.

Great observation. But, I can't see what material would be available to coat it. I looked at the picture again and it looks more like the carbon was scoured off and the head and valves eroded. When I had my short preignition event it scoured off the carbon. A longer event will cause erosion. It would be interesting to see what the piston crown looks like.

 

[EricJ]

4 minutes ago, PT20J said:

Great observation. But, I can't see what material would be available to coat it. I looked at the picture again and it looks more like the carbon was scoured off and the head and valves eroded. When I had my short preignition event it scoured off the carbon. A longer event will cause erosion. It would be interesting to see what the piston crown looks like.

 

Looks like it might just be oil splatter or something.   Hard to tell from the pic, but it may be worthwhile to try to see if there was some evidence of burning on that valve.   If not, something else caused it to fracture, perhaps FOD ingestion or something, but that doesn't usually look like that.

[PT20J]

I ran the picture past George Braly and he also thought it looked like detonation damage. If you zoom in, it appears that the exhaust valve is thinned and that may be why it broke. George suggested looking at all the engine monitor data since the last borescope inspection if its available.

[MB65E]

Valve defect. Change the Valve, guide, and lifter. Then Cyl if needed. 
Stuff brakes. Fix and move on. Take a look at the Turbo inlet too for damage.

-Matt

[alextstone]

On a Continental, I always change the lifters when I swap a cylinder. They are too cheap not to change out.

Please educate me as to why "on a Continental"? A history of known problems with Continentals vs Lycomings?

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[GeeBee]

Just now, alextstone said:

Please educate me as to why "on a Continental"? A history of known problems with Continentals vs Lycomings?

Sent from my Pixel 7 Pro using Tapatalk
 

A Continental does not require a case split to change the lifter. You can simply pull them out. Not so on a Lycoming. In addition for whatever reason, Continental lifters are cheap. No reason not to replace them just to be on the safe side. I keep two on the shelf just for such occasions.

[alextstone]

2 minutes ago, GeeBee said:

A Continental does not require a case split to change the lifter. You can simply pull them out. Not so on a Lycoming. In addition for whatever reason, Continental lifters are cheap. No reason not to replace them just to be on the safe side. I keep two on the shelf just for such occasions.

Thank you

[EricJ]

12 hours ago, PT20J said:

I ran the picture past George Braly and he also thought it looked like detonation damage. If you zoom in, it appears that the exhaust valve is thinned and that may be why it broke. George suggested looking at all the engine monitor data since the last borescope inspection if its available.

I think you're on to something here.   Detonation does scour the deposits in the head, and it looks like that may be what happened.    If the other cyls are okay it may have gotten a carbon deposit or something that led to preignition first.   I'd definitely check the other cylinders for detonation evidence in case it was due to an operating condition rather than a preignition site.

[HeyChuck]

Attached is a close-up picture of the extracted exhaust valve showing two through-going cracks on the valve head that are tangential to the stem.

The picture of the piston shows more deposits on the top; I was told  it is fairly common to see more deposits where the fuel comes into the cylinder as it is cooler there.

Not sure about detonation because the intake valve and piston don't appear damaged, and the CHT stayed below 400 F.

[EricJ]

32 minutes ago, HeyChuck said:

Attached is a close-up picture of the extracted exhaust valve showing two through-going cracks on the valve head that are tangential to the stem.

The picture of the piston shows more deposits on the top; I was told  it is fairly common to see more deposits where the fuel comes into the cylinder as it is cooler there.

Not sure about detonation because the intake valve and piston don't appear damaged, and the CHT stayed below 400 F.

Thanks for the update.   Something happened to that poor valve.   I hope you get a good resolution on this.    The other cylinders look good?

And also, kudos for getting it all on the ground safely.    Gladdest to hear that part. 

[N201MKTurbo]

There may be something to this detonation thing. Look at the intake valve. It may be deformed downward too. I can’t seem to find a picture of what the valve should look like. 

[kortopates]

That sure looks like detonation damage to the piston at the 10-noon position. where you able to put a finger around the piston crown in that area to feel it? Could be wrong, but that looks like the crown is eroded there and melted. Would need to see the profile and feel it it be sure. Deposits can be misleading.


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[Pinecone]

17 hours ago, PT20J said:

I ran the picture past George Braly and he also thought it looked like detonation damage. If you zoom in, it appears that the exhaust valve is thinned and that may be why it broke. George suggested looking at all the engine monitor data since the last borescope inspection if its available.

That blasted look is the same as the cylinder and piston looked on a CAP 182 after detonation.

 

 

[HeyChuck]

32 minutes ago, kortopates said:

That sure looks like detonation damage to the piston at the 10-noon position. where you able to put a finger around the piston crown in that area to feel it? Could be wrong, but that looks like the crown is eroded there and melted. Would need to see the profile and feel it it be sure. Deposits can be misleading.


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Picture of the piston in profile from "10 to noon" aspect. Doesn't feel like melting or erosion around the piston crown to me, but I don't have a lot of experience with this.

 

 

[HeyChuck]

This is a close-up of the top of the piston in the 10-noon area. The rough spots are built up deposits, not erosion features.

[kortopates]

sure looks to me like the crown in the area mentioned is gone. Note the slope profile of the crown at the right edge in your pict. But head on, it appears perfectly flat 90 angle between top and side along with scrapes on the piston side which the rings normally prevent. Doesn’t look like severe detonation damage but light damage - at least to my eyes.


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[EricJ]

23 minutes ago, HeyChuck said:

Picture of the piston in profile from "10 to noon" aspect. Doesn't feel like melting or erosion around the piston crown to me, but I don't have a lot of experience with this.

 

 

The crown edge looks normal.    If it's like that all the way around then that's good.   

[A64Pilot]

I’ve never seen detonation get a valve, ever. especially not without destroying the piston.

As this is a turbo, I’d very carefully inspect the hot end of the turbo, those pieces of valve had to go through it and may have caused FOD

Attached photos are of an IO-540 that has detonation damage, they tried cleaning up the cylinder then gave up, this was a N/A IO for those that say you can’t detonate an N/A Lycoming by the way.

I can attach full size pics, but downsized these to save the forum space

Cant see the piston well in the photo but it’s full of pits like the head is

Detonation almost always “sandblasts” the piston and head like the photo @Pinecone posted, I’m sure this 540 woukd have gone just like the one he posted in a short time, but they quit flying pretty quickly after hearing it

Detonation rarely manifests itself like we think, that is rattling like it did in 1970’s cars. One case I’m familiar with was my Brother calling me on the radio and saying he thought the gear were thumping the belly and wanted me to come over and look, soon after he lost a cylinder, had a hole in the center of it. N/A IO-520. 

 

Edited July 8, 2023 by A64Pilot

[PT20J]

I sent the latest photos to George Braly. He replied:

The piston appears to evidence pre-ignition or fairly heavy detonation damage.

The fact that the valve is “clean” of deposits goes along with it having suffered the scrubbing effect from pre-ignition.

THAT is why having routine ongoing engine monitor data stored can “tell the whole story”.

I would check the timing and would consider changing both spark plugs in that cylinder if you just replace/overhaul  that cylinder.

[PT20J]

Good point about checking the spark plugs. A preignition source can be a cracked nose insulator. Happened to me. It only showed up at takeoff power, so the preignition could be separated from e valve failure by quite some time. It takes hours for the deposits to build back up on the head and piston.

[HeyChuck]

On 7/8/2023 at 5:44 PM, PT20J said:

Good point about checking the spark plugs. A preignition source can be a cracked nose insulator. Happened to me. It only showed up at takeoff power, so the preignition could be separated from e valve failure by quite some time. It takes hours for the deposits to build back up on the head and piston.

Thank you for your suggestions and getting input from George Braly. I will take the plane to a shop Wednesday to check the plugs, other cylinders, etc.