Exhaust Valve Seat out of Round

[gov98]

Recently was noticing some odd behavior on cylinder #3 on the engine monitor, so took it in to the shop, and low an behold the #3 cylinder had 0 compression, and whistling about the exhaust valve.

Cylinder was removed and red tagged because the valve seat was .005 out of round. My question is for those who know… How did that happen? Please brain trust help!

 

[Grum.Man]

What engine? I’m not sure how they were able to measure the valve seat, if they did I doubt .005” would result in zero compression. Most likely the valve was stuck open or had carbon buildup on the back side.

 

[455 Bravo Uniform]

Your question on finding root cause is spot on.

Only automotive experience here, the real A&Ps will be along shortly. Seat burnt, loose or misalignment? Not concentric/never “lapped” to begin with? Valve not rotating? Bent valve? Overheating? Some of these are chicken vs egg as to causes. If you can’t find an intra-head cause, go to fueling, cooling, maybe even cam/lifter/pushrod causing overheating. Maybe pull and compare historic monitor data to look for a step change or gradual change in some parameter.

 

[Bell206]

Cylinder was removed and red tagged because the valve seat was .005 out of round.

Red tagged? What type "shop" is this? Don't quite follow this. Are you saying: they found 0 compression then removed and scrapped/discarded the cylinder? What did they replace it with? FYI: valve seats can usually be repaired/replaced.

 

[gov98]

Engine is a Lycoming IO-540. The cylinder was pulled and sent to Lycon in Visalia, who I trust. They examined the cylinder and stated that the cost to repair made it more practicable to obtain a new cylinder rather than repair. I’m not terrible worried about doing that. I’m just more curious what happened, or why that would happen. I trust my shop/mechanic. I just want to know if I did something wrong and what to avoid in future.

Symptoms were a dead cylinder at low idle, at increased rpm’s the cylinder would run properly.

 

[Dan Thomas]

Worn valve guide. Lycoming had problems with that up until 1999 when they started using a high-chromium-content bronze guide. There was an SB that demanded a valve stem wobble check every 300 hours to detect that. When the guide wears, the valve starts striking the seat off-center, wearing the area that gets struck first.

The rocker, as it moves the valve, also puts some side-force on it, wearing the guide.

https://www.lycoming.com/sites/defa...termine Exhaust Value and Guide Condition.pdf

 

[Bell206]

They examined the cylinder and stated that the cost to repair made it more practicable to obtain a new cylinder rather than repair.

That is not how you described at first. Sounds more like there was an issue with the cylinder head vs just the valve seat if uneconomical to repair. As to why... without more info tough to pin point. Could be anything from a mfg'r defect to a one-off operational issue. Did you have the remaining cylinders borescoped to see if there were any similarities between them?

 

[gov98]

That is not how you described at first. Sounds more like there was an issue with the cylinder head vs just the valve seat if uneconomical to repair. As to why... without more info tough to pin point. Could be anything from a mfg'r defect to a one-off operational issue. Did you have the remaining cylinders borescoped to see if there were any similarities between them?

Everything else is working fine. I really didn't mean to create confusion.

 

[gov98]

Worn valve guide. Lycoming had problems with that up until 1999 when they started using a high-chromium-content bronze guide. There was an SB that demanded a valve stem wobble check every 300 hours to detect that. When the guide wears, the valve starts striking the seat off-center, wearing the area that gets struck first.

The rocker, as it moves the valve, also puts some side-force on it, wearing the guide.

https://www.lycoming.com/sites/default/files/Procedure to Determine Exhaust Value and Guide Condition.pdf

Thank you! Odds are that's probably exactly it. Thank you so much!

 

[Bell206]

I really didn't mean to create confusion.

What I can't understand is why the new cylinder. Regardless if it was a valve seat or even the valve guide mentioned above, both are a standard repair at a cost point well below a new cylinder. Does your shop have to outsource the repairs?

 

[gov98]

What I can't understand is why the new cylinder. Regardless if it was a valve seat or even the valve guide mentioned above, both are a standard repair at a cost point well below a new cylinder. Does your shop have to outsource the repairs?

So, my shop sends the cylinder out to Lycon. The way it's described to me, is that it is repairable, but not inexpensively and that given the overall age and condition of the cylinder it is better to just get a new cylinder. I don't really have a way of knowing, perhaps I should be more suspicious that Lycon is trying to grab my cylinder and add it to the shelf for someone else...but I guess I have no way of knowing this and really it's beyond mine ability to know.

 

[gov98]

Hey Bell,

So based upon your post I called Lycon and spoke to them directly, and apparently, it wasn't the exhaust valve guide that was out of round, it was the entire cylinder bore, so the shaft had worn unevenly and was out of round. Now I'm even more lost as to what was happening on that cylinder.

 

[Jdm]

I don't really have a way of knowing, perhaps I should be more suspicious that Lycon is trying to grab my cylinder and add it to the shelf for someone else...but I guess I have no way of knowing this and really it's beyond mine ability to know.

I wouldn’t overthink it. If their job is overhauling cylinders they’re probably steering you straight.

Back in the old days it wasn’t uncommon for us to yank a cylinder and do a grind & lap, assuming the valve stem looked ok (not burnt or elongated etc.) We’d grind the seat until smooth. We’d turn the valve until true and smooth. Ream the guide. Then put the valve in it’s place and lap it to mate. We would inspect the pattern and see how well it was centered, etc. If the contact look good we would plop the valves in place, pour avgas into cylinder with the valves just sitting there (no springs). If it didn’t leak, it was good. I’m just going off memory, but that was the basic process many years ago in a 135/FBO shop. Once the cylinder was on the bench the work took only about an hour. I can’t imagine it taking much longer these days. Cylinder work seems way too expensive now, and I can’t tell that they are any more reliable.

My guess is that your shop is way ahead of our old school practices and have pre-determined that your cyl was going to be out of bounds by the time they got everything trued up. Therefore they probably decided to grab another to start with.

 

[Bell206]

Now I'm even more lost as to what was happening on that cylinder.

No need to be lost. The key is to learn from this as everything is now very plausible. So, yes, if the cylinder barrel is out-of-round then a new cylinder can be your best route especially on older or over-sized cylinders. As to the why, one cause of an out-of round cylinder bore is a valve problem as mentioned in Dan's post. And to take his post one step further, this is a good example of where some OEM recommendations can be proactive/preventative in finding issues early. Wobble checks, 500 hr mag checks, alternator brush checks, fuel injection line checks, etc. that while not mandatory for Part 91 aircraft are items recommended for a reason. Would a wobble check have prevented your cylinder replacement? Maybe or maybe not. But as with everything aviation you as owner get to make those calls based on the information or experience you attain over time. And now you have a bit more knowledge to make those calls.

 

[Chip Sylverne]

The only fly in the replacement ointment is the lack of new jugs available from Lycoming. I hear the wait list isn't pretty.

 

[flyingbrit]

one cause of an out-of round cylinder bore is a valve problem as mentioned in Dan's post.

Huh? The way I read it Dan's post mentioned only guides, valves, and rocker arms. Please explain how a valve problem can cause an out-of-round cylinder bore.

 

[Checkout_my_Six]

Something must be lost in the communications.....

Huh? The way I read it Dan's post mentioned only guides, valves, and rocker arms. Please explain how a valve problem can cause an out-of-round cylinder bore.

 

[Bell206]

Huh? The way I read it Dan's post mentioned only guides, valves, and rocker arms.

Dan's post explains one version how the valve will fail and give the OPs 0 compression reading. N'est-ce pas?

Please explain how a valve problem can cause an out-of-round cylinder bore.

The leaking valve will cause unbalanced combustion resulting in one side of the cylinder becoming hotter than the other. This temperature difference can tweak the bore out of round depending on severity.

 

[Dan Thomas]

Hey Bell,

So based upon your post I called Lycon and spoke to them directly, and apparently, it wasn't the exhaust valve guide that was out of round, it was the entire cylinder bore, so the shaft had worn unevenly and was out of round. Now I'm even more lost as to what was happening on that cylinder.

Re: the out-of-round bore and "unevenly worn shaft." The only shaft in there is the rocker pin, so I think what they might be getting at is that the valve guide bore in the head was out-of-round, and a new guide wouldn't fit properly, and maybe it was bad enough that an oversize guide, if they're still available, wouldn't be big enough to allow reaming of that hole for it. The "shaft" might be the valve stem. Clear as mud.

For those that are wondering what we're talking about, here's a simplified diagram of the valve, valve guide and valve seat relationship in the head:



That guide is a press fit in the head, to keep it rigidly in place. The bore for it in the head needs to be accurately made, and it it gets pounded out, or someone makes a bad job of replacing the guide and chews the bore up, it's a bad deal.

 

[Bell206]

Clear as mud.

Agree. I took it has they found a secondary issue with the "cylinder bore" out-of-round in addition to the valve guide wear during Lycon's prelim inspection. Perhaps the OP can post a copy of that report to see the terms used?

 

[Magman]

My belief is loose / missing baffles may cause a permanent out of round condition.

Also a brief ground run ( as opposed to cold or after flight) creates

uneven heating of the cylinders that does the same temporarily.

This can present as a lower compression reading than the other 2 options.

Commennts?

 

[gov98]

So, to clarify as best I can.

I do not know if there was any issue with the valve seats at all. The cylinder was getting 0 compression. My shop took the cylinder off and sent to LyCon. LyCon examined the cylinder. The cylinder bore was out of round. Information was communicated to my shop, that was in turn communicated to me, and in the game of telephone I believed it was the exhaust valve seat that was out of round. In fact it was the cylinder bore. As a result, I need a new cylinder. Fortunately, it appears that Aircraft Spruce had a cylinder for my engine in stock.

Unfortunately, this will be yet another maintenance expense related to the plane, but I guess it just comes with the possessing something 54 years old territory.

 

[Bell206]

Unfortunately, this will be yet another maintenance expense related to the plane, but I guess it just comes with the possessing something 54 years old territory.

Perhaps to spot any future issues at bay based on this episode, have your AP look over the remaining cylinders for any similarities as the failed cylinder. For example, as mentioned above check all the baffling is installed and seals properly. Given your original issue was a compression leak out the exhaust valve have them perform of review of your valve health via existing OEM guidance along with a borescope. While shEit breaking is a pain there are preventative measures to take that can reduce that pain. The old adage "pay me now or pay me later" always seems appropriate with these discussions.

 

[Dan Thomas]

So, to clarify as best I can.

I do not know if there was any issue with the valve seats at all. The cylinder was getting 0 compression. My shop took the cylinder off and sent to LyCon. LyCon examined the cylinder. The cylinder bore was out of round. Information was communicated to my shop, that was in turn communicated to me, and in the game of telephone I believed it was the exhaust valve seat that was out of round. In fact it was the cylinder bore. As a result, I need a new cylinder. Fortunately, it appears that Aircraft Spruce had a cylinder for my engine in stock.

Unfortunately, this will be yet another maintenance expense related to the plane, but I guess it just comes with the possessing something 54 years old territory.

The cylinder bore would have to be massively out-of-round to take the compression to zero. Massively. Broken rings too, maybe.

 

[flyingbrit]

Remember the OP said: "the #3 cylinder had 0 compression, and whistling about the exhaust valve."

My take is that a leaky valve caused the zero "compression", but LyCon checked everything out before doing any work and ended up condemning the cylinder due to an out-of-round bore.

 

[Snowmass]

The only fly in the replacement ointment is the lack of new jugs available from Lycoming. I hear the wait list isn't pretty.

Why not from Superior? Usually cheaper better.

 

[Chip Sylverne]

Why not from Superior? Usually cheaper better.

I had occasion to do some looking for a parallel valve Lyc jug recently. It seems all flavors are on back order. Fortunately my problem worked out, but pity the guy looking for a new one.

 

[Dan Thomas]

Why not from Superior? Usually cheaper better.

Superior has had ADs on cylinders, pistons and piston pins. They've had teething problems. They're not necessarily Superior, especially when you have to pull off low-time cylinders and throw them away.

They now have an AD against some of their Lycoming O/IO-360 crankshafts.

 

[Checkout_my_Six]

You know what….that just may have jinxed you. lol

I had occasion to do some looking for a parallel valve Lyc jug recently. It seems all flavors are on back order. Fortunately my problem worked out, but pity the guy looking for a new one.

 

[Snowmass]

Superior has had ADs on cylinders, pistons and piston pins. They've had teething problems. They're not necessarily Superior, especially when you have to pull off low-time cylinders and throw them away.

They now have an AD against some of their Lycoming O/IO-360 crankshafts.

That pulling off low time, perfectly good cylinders on my Conti is more an example FAA arrogance and stupidity than anything else. Why did I need to junk cylinders due to a calendar time limit? What does calendar time have to do with potential fatigue problems. I have a pile of IO-520 cylinders scrapped at 1000 hours even though they are barely worn.

 

[Jdm]

Is this a new cylinder AD for Superior? I did a quick search and see the crankshaft AD being the more recent. In reading the AD I saw nothing about a “teething” issue.

 

[Dan Thomas]

Is this a new cylinder AD for Superior? I did a quick search and see the crankshaft AD being the more recent. In reading the AD I saw nothing about a “teething” issue.

"Teething issues," like the painful time small kids have when their teeth are breaking through the gums, imply the problems that arise in products made by young companies, problems that have to be sorted out. Stuff that arises from engineering or manufacturing errors. For instance, ECi had three cylinder ADs in their short life, and a con rod AD. That's bad. Many of those cylinders failed, not just one or two. Improper machining, bad heat-treating, casting defects, whatever: they're all "teething" problems you can encounter in a new company trying to figure out out to build stuff to undercut the OEM, who has been doing this for a long time. Continental and Lycoming figured out how to build cylinders right a long time ago, and the problems they've had with some components are usually associated with contracted-out stuff like the Lycoming crankshaft failures of 20 years ago. The contractors messed up, perhaps taking shortcuts of some sort. Or cheaping out on a process.

Continental bought ECI in 2015, perhaps for their manufacturing facilities. Continental' engineering would fix ECi's quality problems.