What causes exhaust valve failure

[Shadrach]

On 6/23/2021 at 5:16 PM, kortopates said:

Sure, here is an article from one of our guys on valve lapping in situ:

https://www.tennesseeaircraft.net/2011/11/13/exhaust-valve-lapping/

It has some limited pictures, yet explains the process in detail. But the article is very conservative and just shows lapping the valve by hand - which os safest. But most of us need mechanical assistance to fully clean up the valve to seat junction, so here is an additional article that has more pictures and shows how one can safely and carefully attached the valve stem to an electric drill without attaching the drill chuck to the valve stem directly which would definetly cause damage. You'll notice he uses vinyl tubing, while most of us use rubber tubing - rubber should be a bit beefier - but the concept is the same. He also gives a good tip on cleaning the valve & seat after. Scroll down to article 131 on this page:  https://airplaneownermaintenance.com/tag/borescoping/

I thought this was a common process? I helped rope trick, ream and lap an exhaust valve in the O200 that powered the C150 I trained in. That was 23 years ago.

[cliffy]

55 minutes ago, Shadrach said:

I thought this was a common process? I helped rope trick, ream and lap an exhaust valve in the O200 that powered the C150 I trained in. That was 23 years ago.

Heck I did it on a 172 with morning sickness 40 years ago!  Old as the hills and twice as dusty. 

"Those who forget history are bound to repeat it!"

[Gary0747]

Valuable thread here   I am steep on the learning curve on this.  Can I get an opinion on this exhaust valve from #4 cylinder Lycoming IO360a1a 1300 hours  compressions good but concerned about the asymmetry here.

[201Steve]

Curious the other feedback coming but it’s a nice circle, no discoloration of the green variety, just not dead in the center.  

[carusoam]

Uneven cooling causes asymmetric pizza formation…

valves rotate to improve their cooling symmetry…

 

valves that don’t rotate show a hot spot that interrupts the pizza, out to the edge of the valve…

there is a valve chart that shows the different symptoms with their explanations…

 

Got any JPI data to go with that?

PP thoughts only, not a mechanic…

Best regards,

-a-

[Gary0747]

Yes JPI data looks good with around 15 degrees delta in EGT at 75 pct power  between all cylinders and no saw toothing.  It did look like the valve is not rotating.  Apparently Lycoming uses what are called passive rotators where Continental uses a more positive rotator cap?  The Lycoming parts manual for the IO360 A-B series calls out an exhaust valve part number LW-16740 that they label “ Valve Exhaust (rotator type) “  that makes me wonder if there is a non rotator type?

I also wonder if the sodium internal cooling of the Lycoming valves might distort the pie pattern if the valve contents were not entirely full.  But this is just likely a wild thought  

I am trying to decide if I should just closely monitor this or take some corrective action now  

[carusoam]

Let’s see if @M20Doc is cruising by…. (IO360 exhaust valve, with non-centered pizza)

Best regards,

-a-

 

[BDPetersen]

Excellent Mike Busch article on exhaust valves in latest AOPA Pilot.

[buckfever06]

Mike Busch and SAVVY Aviation have a treasure trove of information! Here is a good video that talks about cylinders, including valves...Pic is just a screenshot. Click the link to watch the video.

https://youtu.be/CEI3UfkFWX8

[Fly Boomer]

13 hours ago, buckfever06 said:

Click the link to watch the video.

I have collected bunches of Busch stuff, but this is one of the most blurry videos I have seen.  Might be intentional, or might just be attributable to uploading/downloading through one of the cloud services that has helpfully reduced the resolution in order to reduce the file size.  I just spent some time looking for a different, better version of this, but all I can find is the YouTube CEI3UfkFWX8 version.  Anyone got a better version, or a link to one?

This is from a screenshot during the video:

 

[hammdo]

EAA presentation was good when I took it live. I have a chart too, I'll see if I can find it...

Screenshots/pics:

[hammdo]

Link to a good review...

(Dean Showalter)

 

-Don

Exhaust-Valve-Borescope-Inspections.pdf

[buckfever06]

On 5/4/2022 at 11:22 AM, Fly Boomer said:

I have collected bunches of Busch stuff, but this is one of the most blurry videos I have seen.  Might be intentional, or might just be attributable to uploading/downloading through one of the cloud services that has helpfully reduced the resolution in order to reduce the file size.  I just spent some time looking for a different, better version of this, but all I can find is the YouTube CEI3UfkFWX8 version.  Anyone got a better version, or a link to one?

This is from a screenshot during the video:

 

If you are an EAA member you can access many of Mike Busch's webinars on the EAA web site. I am not a member yet, but I think this is the same video via EAA... https://www.eaa.org/videos/1204537102001

[Fly Boomer]

32 minutes ago, buckfever06 said:

I think this is the same video via EAA...

I think so.  Didn't watch much, but still blurry.  Maybe it's my eyes.

[Shadrach]

On 6/13/2021 at 5:23 PM, DXB said:

I'm pretty skeptical that an exhaust valve can reach the point of failure without showing clear visual evidence of a hot spot at a rim well in advance. That cannot be said of the SAVVY FEVA signature on the EGT trace, which is often a very late event when failure is imminent [also I believe they check for it for free when you upload data to their site, though they don't publicize this.]

I suppose the hours you fly between annuals makes a big difference - if it's a lot, getting your own borescope and checking every 50-75 hours is a quick, easy, cheap do-it-yourself option that most any owner can avail.

Maybe not so much  today with all of the tech most have for monitoring. Without that tech or an understanding of how to read it, it is entirely possible to be enjoying smooth operations with everything seeming healthy and have it all go pear shaped in an instant. It happened to my dad in S Dakota. He landed in a little town called Winner. The engine didn’t quite in the air but the vibration even at idle was significant. Engine quit on roll out. One of the cylinders swallowed a valve. 
 

Saddest part of the story is that the MX pro did not thoroughly clean the air box after installing the new cylinder. When my dad test flew it after the cylinder was replaced, a different cylinder ingested debris from the previous failure. Another 3 cylinder approach into Winner and another $3500 and he was on his way.

[DXB]

This very recent Mike Busch article sheds further light on the valve failure issue and also calls into question some of my impressions articulated previously in this thread:

https://www.aopa.org/news-and-media/all-news/2022/may/pilot/savvy-maintenance-failure-to-rotate

It also raises more questions in my mind than it answers...

-He seems to think that valve failures are far more likely to originate from subtle defects at the time of manufacture and/or IRAN/overhaul than anything the pilot did.

-Another striking point is his belief that a valve with early signs of a hot spot on its face can reasonably be lapped in place and the rotator cap replaced without pulling the cylinder.  This impression runs contrary to my assumption that by the time you see asymmetry on a valve face, the guide must already be trashed.  Maybe next time I see early signs of a burned valve on borescope I will insist on a formal wobble test before deciding to pull the cylinder.

-He does do a nice job highlighting the differences between Lycoming and Continental valve design but leaves me confused regarding their implications.  The rotator coils on Continentals seem to fail commonly but the same issue with the Lycoming rotator cap is rare.  But in my experience the burnt valve issue in Lycomings is not rare at all.  And does it really make sense often to simply lap a Lycoming valve in place and replace the rotator cap given that difference between the two designs?

 

[Raymond J1]

When the IO 360 A1A engine used the PNr 73111 valve (1/2 inch outer diameter rod, sodium forged nimonic), Superior created an alternative part which is SL 12720, same technology. Does anyone of you have any experience with this model of exhaust valve, now replaced by 16740 ?

[skykrawler]

On 5/8/2022 at 11:45 AM, DXB said:

 

-He seems to think that valve failures are far more likely to originate from subtle defects at the time of manufacture and/or IRAN/overhaul than anything the pilot did.

 

Assuming any reasonable operation management and maintenance this seems to be the most likely basis.  But there are plenty engines that aren't run and don't get oil changes when they should.

[A64Pilot]

On 8/6/2021 at 9:19 PM, Shadrach said:

I thought this was a common process? I helped rope trick, ream and lap an exhaust valve in the O200 that powered the C150 I trained in. That was 23 years ago.

it is, personally I prefer air pressure, just use a soft nylon rope not some old hemp rope of course

Lycoming legitimized it with their SB of course, and that’s important to a professional mechanic

I am NOT a fan of valve lapping as it’s just a patch at best, it’s not a repair. It’s ONLY use in my opinion is after valves have been replaced or seats reground, lapping validates a concentric seat that the valve seals on, Seats have been imperfect before and even guides have not been perfectly aligned before, lapping gives visual evidence of a good fit and if a multi angle valve job was done it’s shows where the valve seals, if a multi angle job you want it sealing at the outside angle of course.

If you chose to lap a burnt valve, find out what caused it and correct the problem, just lapping it isn’t going to fix anything, if for example the rotator is bad it will burn again probably pretty quickly if you don’t get it rotating again.

[RLCarter]

1 hour ago, A64Pilot said:

it is, personally I prefer air pressure, just use a soft nylon rope not some old hemp rope of course

Lycoming legitimized it with their ……..

3’ of 3/8” cotton rope lives in a ziploc bag in the spare parts cabinet ….. I’ve had 2 stick in 1500+ hrs…. Seen several others, generally I can get them free by pushing with my thumbs and twisting with rocker arm removed….. the rope never pushes straight on the valve and bending a valve is very possible ….

[Shadrach]

On 4/9/2022 at 3:46 PM, Gary0747 said:

Valuable thread here   I am steep on the learning curve on this.  Can I get an opinion on this exhaust valve from #4 cylinder Lycoming IO360a1a 1300 hours  compressions good but concerned about the asymmetry here.

Gary, 

How is your engine doing 8 months later? That valve does not look worrisome to me. I can’t speak to why it’s has asymmetric deposits on the face but it does not appear to be burning.

[Pinecone]

2 hours ago, A64Pilot said:

If you chose to lap a burnt valve, find out what caused it and correct the problem, just lapping it isn’t going to fix anything, if for example the rotator is bad it will burn again probably pretty quickly if you don’t get it rotating again.

Mike Busch recommends replacing the rotator if you have to lap a valve.

 

[A64Pilot]

47 minutes ago, Pinecone said:

Mike Busch recommends replacing the rotator if you have to lap a valve.

 

I threw that out there as an example, but the key isn’t just replacing a rotator, but determining if it’s defective, and if any damage has occurred. I’ve never seen a Lycoming rotator fail, Conti’s yes.

Point is just like the “ring flush” if you don’t determine the cause and fix the cause then the “fix” isn’t going to work for long and it’s as likely as not that the problem when it re-occurs will be worse.

I’ve never seen rings gummed up in a properly functioning cylinder, it’s not a normal operating condition like say a carboned up plug is, a plug you clean because it’s normal to be fouled, rings you don’t just clean because that isn’t normal. You need to determine why they gummed up and fix that.

You need to determine what has occurred with the valve and correct it, then lap if you think that fixes anything.

 

[A64Pilot]

What causes exhaust valve failure?

Overheating.

But the causes of overheating are many, rotation failure is just one

[Gary0747]

6 hours ago, Shadrach said:

Gary, 

How is your engine doing 8 months later? That valve does not look worrisome to me. I can’t speak to why it’s has asymmetric deposits on the face but it does not appear to be burning.

Still running fine from the data logging on that cylinder  I plan to recheck next oil change with a scope.