What causes exhaust valve failure

[buckfever06]

On my last annual, (October 2022), Mooney M20C with IO-360-AB36D, 200 HP, the number four cylinder failed the compression check. It turned out to be a burnt/stuck exhaust valve. The A&P recommended replacing the cylinder. The part is hard to find and I had quotes of about $3000 from one place, and $4000 from another supplier. I am a member of SAVVY Aviation (I highly recommend them.) So I contacted Savvy and asked for advice. They suggested I contact Western Skyways and see if they could overhaul the can. A few phone calls and emails later, the A&P had pulled the cylinder and I shipped it off to Western Skyways. A month later, my freshly overhauled cylinder, with a new valve and associated parts arrived in the mail. The whole thing cost me just over $800 with shipping. I think the actual overhaul was about $780, and shipping was about $40-$50 each way (insured.) Overhaul included cleaning, inspection, resurfacing the cylinder wall, painting, new set of rings, the works! It looked like new. If you run into this problem, I recommend looking into an overhaul instead of replacement.

The only downside was that one of the rings was found to be cracked. For some reason they installed the new rings in the cylinder for shipping. The piston was at the hangar with the airplane. Either during the install into the cylinder, or during removal, one of the rings must have been damaged. They quickly agreed to replace the cracked ring...no big deal.

My annual membership to Savvy was $350 I think. I got a return of $3650 from them on just one ticket. Those guys are awesome! Sorry, I was going to post pics and I can't find them on my phone ):

Edited April 2, 2023 by buckfever06

[carusoam]

27 minutes ago, buckfever06 said:

On my last annual, (October 2022), Mooney M20C with IO-360-AB36D, 200 HP, the number four cylinder failed the compression check. It turned out to be a burnt/stuck exhaust valve. The A&P recommended replacing the cylinder. The part is hard to find and I had quotes of about $3000 from one place, and $4000 from another supplier. I am a member of SAVVY Aviation (I highly recommend them.) So I contacted Savvy and asked for advice. They suggested I contact Western Skyways and see if they could overhaul the can. A few phone calls and emails later, the A&P had pulled the cylinder and I shipped it off to Western Skyways. A month later, my freshly overhauled cylinder, with a new valve and associated parts arrived in the mail. The whole thing cost me just over $800 with shipping. I think the actual overhaul was about $780, and shipping was about $40-$50 each way (insured.) Overhaul included cleaning, inspection, resurfacing the cylinder wall, painting, new set of rings, the works! It looked like new. If you run into this problem, I recommend looking into an overhaul instead of replacement.

The only downside was that one of the rings was found to be cracked. For some reason they installed the new rings in the cylinder for shipping. The piston was at the hangar with the airplane. Either during the install into the cylinder, or during removal, one of the rings must have been damaged. They quickly agreed to replace the cracked ring...no big deal.

My annual membership to Savvy was $350 I think. I got a return of $3650 from them on just one ticket. Those guys are awesome! Sorry, I was going to post pics and I can't find them on my phone ):

great pirep on the value of Savvy membership!

Thanks for sharing the details.

Invite @kortopates to stop by… 

Best regards,

-a-

[carusoam]

Around here…

We see a bunch of exhaust valves that stop turning, before they fail…

and, at least one valve that tulip’d…. Literally looked like a tulip after it got damaged…

and one, that got jammed… valve guide packed with carbon…. Valve stuck in the down position and met the piston crown moving upwards… causing a small bend in the valve’s rod…

 

our best defense is an engine monitor and the ability to review the data… or recognize an EGT that is higher than the rest…

The minor failure, the valve stops working properly, long before it fails completely…

We want to get good enough to recognize the minor failure before it gets worse….

We probably get many flights and several hours before things get bad…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[Brandt]

On 6/9/2021 at 8:51 PM, EricJ said:

People keep making that comparison, but for people who race regularly, including racing junkyard cars in endurance races, it doesn't seem like a supportable argument.   Most aircraft engines don't make 100% power for extended periods, and often cruise for long periods at medium power in thermally and mechanically stable conditions.    Come flog random old, janky auto engines on repeating 100%/0% cycles including frequent trips to redline rpm and hop curbs around a road course for long periods or just regularly, especially with custom tunes to make sure you're really getting that 100% or more, and you get a better feel for where the reliabilities really are.   And usually this is done with engines that are >10 and up to 30+ years old.

Usually if a near-stock auto engine fails in a race it is because of a very few common causes:  a) it got overheated for a significant time period, b) it got significantly over-revved,  c) it lost sufficient oil pressure (sometimes because of (a), sometimes because of repeated loss of scavenging on hard corners).    If you keep those things under control, the likelihood of reliability under conditions of long periods or frequent aggressive use is quite high.   Bad tunes can kill engines, too, but that's not the fault of the engine design, imho.

I can't think of the last time I saw a valve fail in a race car that wasn't the result of a piston hitting it due to a bottom end or timing chain/belt failure.

We get engines that fail from time to time, but usually because of the a-c reasons or because it was highly built with some highly stressed parts or had a bad tune.   I have some friends making >1000 hp out of an early Ford Taurus SHO (with the stock Yamaha block and crank) that got a ton of use of out it and set some records before an aftermarket rod failed last year.   That's more than 4.5x the stock output.    It's not apples-apples, but modern (i.e., less than 30 years old) automotive engines I find to be basically far more reliable and better engineered than our ancient air-beaters under stressful use.

https://www.dragzine.com/features/blue-turd-zach-wrights-one-of-a-kind-1000-hp-ford-taurus-sho/

There have been some metallurgy/material changes in our aircraft engines for the better (e.g., lifters), but for the most part they're still ancient designs and we still see engines getting failures in normal use cycles, which really aren't that stressful, imho.   If Lycoming/Continental had been able to invest and adapt our engines with the sorts of economy scales that automotive engines have enjoyed, I think there'd have been a lot of important and useful improvements made over what we actually have.   I think it's notable that when they need to adapt a new aviation application, they make an entirely different engine that looks nothing like what we're using:

https://www.lycoming.com/engines/del-120

Just my dos centavos.    Opinions clearly vary on this topic.

How many of those race engines were air cooled?

[philiplane]

Lycoming engines burn valves once the guides are worn far enough that the valve no longer seats concentrically.

Continental engines burn valves once the rotators stop rotating. 

[Shadrach]

1 hour ago, Brandt said:

How many of those race engines were air cooled?

There are plenty air cooled Porsche flat 6’s that have gone 200k+ without overhaul.  I personally know of a 1997 Porsche 993 with an aftermarket supercharger running NA stock compression ratios. Pulls as strong as ever with 165k on the odometer.

[Pinecone]

And track/race cars are typically full throttle open or full throttle closed, and nothing in between.

[Gary0747]

On 4/2/2023 at 9:42 PM, philiplane said:

Lycoming engines burn valves once the guides are worn far enough that the valve no longer seats concentrically.

Continental engines burn valves once the rotators stop rotating. 

I have been closely monitoring the exhaust valves in my Lycoming IO 360A1A for a couple of years (which is only about the last 100 hours).  I have 1400 hours on the engine and it is running fine.  I am tracking the data closely on my JPI900. I have two exhaust valves that have the non symmetrical pizza pattern that are likely not rotating.  There does not appear to be any signs of burning and they have had this distorted pattern for the whole time.  Is there a way to get them rotating or should I just keep monitoring?  I understand the Lycoming rotator caps are passive and only allow the valve to rotate if they want to so changing them may not do much?

[N201MKTurbo]

2 hours ago, Gary0747 said:

I have been closely monitoring the exhaust valves in my Lycoming IO 360A1A for a couple of years (which is only about the last 100 hours).  I have 1400 hours on the engine and it is running fine.  I am tracking the data closely on my JPI900. I have two exhaust valves that have the non symmetrical pizza pattern that are likely not rotating.  There does not appear to be any signs of burning and they have had this distorted pattern for the whole time.  Is there a way to get them rotating or should I just keep monitoring?  I understand the Lycoming rotator caps are passive and only allow the valve to rotate if they want to so changing them may not do much?

Pull the valve springs using the rope trick and spin them around. If you are real ambitious, pull the exhaust riser so you can spray some carb cleaner on the stems and clean some of the deposits off it.

[Yetti]

9 hours ago, Gary0747 said:

I have been closely monitoring the exhaust valves in my Lycoming IO 360A1A for a couple of years (which is only about the last 100 hours).  I have 1400 hours on the engine and it is running fine.  I am tracking the data closely on my JPI900. I have two exhaust valves that have the non symmetrical pizza pattern that are likely not rotating.  There does not appear to be any signs of burning and they have had this distorted pattern for the whole time.  Is there a way to get them rotating or should I just keep monitoring?  I understand the Lycoming rotator caps are passive and only allow the valve to rotate if they want to so changing them may not do much?

I would say Marvel Mystery Oil is the same vintage as the design of our engines.   Most likely you have a bit of coking going on.   MMO may get you a few more hours before you have to ream them.     We had to ream mine twice.   The Grumpy IA uses air pressure to remove and reinstall the keepers.     I got pretty good at using the prop and top of cylinder and one of these https://www.zoro.com/craftsman-flexclawr-pickup-tool-cmmt14112/i/G604105016/?utm_source=google&utm_medium=surfaces&utm_campaign=shopping feed&utm_content=free google shopping clicks&campaignid=17303393492&productid=G604105016&v=&gad_source=1&gclid=CjwKCAjwydSzBhBOEiwAj0XN4Hnaulkf2ZGlLkrzzh_QnNrmhDLUePjXyRs7LLe2KaClopkqrfjbPxoCwSwQAvD_BwE&gclsrc=aw.ds

 

The trick my other IA did was cut off two apposing claws.   I can get the valve back in with just pulling the spark plug going in the bottom hole with the grabber and a flashlight in the top hole. 

[jetdriven]

On 6/12/2021 at 1:31 PM, Cruiser said:

Has anyone had a failed burnt exhaust valve operating LOP and CHT below 380°F  ?

I did, on my own personal plane. These cylinders had something like 400 hours since new, and I sent the cylinder to Poplar Grove and he said the exhaust guide was totally shot and the valve was setting to burn.  It had a large asymmetrical green area. So they replaced  the valve guide and valve  and then lapped it all properly and it’s fine for another 300 hours.