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Failing exhaust valve, I think

rv6n6r

Well Known Member
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Thoughts?
Worth trying to lap in place? I've never lapped a valve but reading about it, doesn't seem like too big a deal.
 

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Lapping‘s done to restore compression.
Your valve looks more not to rotate… if valve is tight, valve guide to be reamed (or honed), valve stem to be cleaned, rotator cap replaced, all in situ.
Reinstall, fly say 10 hours, borescope check.
 
That is carbon build up/deposits. certainly worth a try, but may be difficult to remove via lapping compound. You will likely need to do it multiple times until you are at the point of a smooth steel surface with all of the raised carbon deposits gone. Looks like the deposits are almost .010" in height. I would start with the coarse compound and finish off with fine once the deposits have been removed. The compound breaks down pretty quickly, so will need to keep applying fresh paste. Lapping is normally done just to make parts mate. Here you are using it to remove a good amount of hard material. Carbon deposits like that are very hard and stick better than glue. Think about a diamond. Take carbon, add a lot of heat and pressure and you get a diamond. Here you have 1500+ degrees and at least 200 PSI. What it produces won't be a diamond, but will be darn hard.
 
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Worth a Try

Sure, I’d try lapping it. Only costs some time and if it doesn’t work you were pulling the cylinder anyway.
 
I would run a can of TPC through your fuel system and then re-look. If the build-up is still there then I would 100% attempt to lap this, but first I would want to understand the failure. -
What is the Leak-down, and did it change suddenly or slowly? What are your operating conditions? Do you have an engine monitor, and has the data changed?
 
That engine/valve is perfect candidate for lapping. Figure out the procedure, Find a buddy, watch utube videos.
Then go for it, you have nothing to loose but get some experience doin it.
Art
 
I would 100% attempt to lap this, but first I would want to understand the failure. -
What is the Leak-down, and did it change suddenly or slowly? What are your operating conditions? Do you have an engine monitor, and has the data changed?
The first and only indication of an issue was the look of the thing from borescoping during condition inspection, particularly the classic asymmetric heat pattern and perhaps a hint of green.

Other than that, compression is good, high -70s and hasn't changed over time. No apparent change to EGT or CHT. Engine monitor data shows no change and no rhythmic oscillation in the EGTs. Wobble test came out fine at .018, right between Lycoming's published limits. The carbon buildups look similar to varying degrees on all cylinders.

And it runs great. I figure this won't go away but I also wonder of it's critical to do something before putting any more hours on it.
 
Been there, done that

Seat looks about like mine did when I successfully lapped in situ last year when I noted the compression was a bit down on #4. A year later and things are still good. I think it's lead deposits, not carbon.

I didn't have the off-color face though. I'd lap it, and then re-borescope in 10 hours. Hopefully the colors will look better then.
 
I think it's lead deposits, not carbon.

.

Lead is essentially a lubricant. While it can leave a microscopic coating on a valve or seat, it cannot leave large chunks, as it has no grip. Beyond the microscopic layer, it can't really stick to anything due to it's lubricity.
 
That is carbon build up/deposits. certainly worth a try, but may be difficult to remove via lapping compound. You will likely need to do it multiple times until you are at the point of a smooth steel surface with all of the raised carbon deposits gone. Looks like the deposits are almost .010" in height. I would start with the coarse compound and finish off with fine once the deposits have been removed. The compound breaks down pretty quickly, so will need to keep applying fresh paste. Lapping is normally done just to make parts mate. Here you are using it to remove a good amount of hard material. Carbon deposits like that are very hard and stick better than glue. Think about a diamond. Take carbon, add a lot of heat and pressure and you get a diamond. Here you have 1500+ degrees and at least 200 PSI. What it produces won't be a diamond, but will be darn hard.

What causes these carbon deposits?
 
What causes these carbon deposits?

several sources. Gasoline is a hydro carbon and can leave carbon deposits, though not common to get them this large unless the engine is run excessively rich for long periods. The other is oil, which is carbon based. If oil gets on a hot part, it can oxidize and become coke. That is a very hard substance that is mostly carbon and sticks tenaciously. Most likely is an issue with the guide allowing oil to drip down to the seat area or a limited occurrence of a blocked oil return line. In the pic you can see the oxidized oil on the lower part of the stem, below the guide. You dont get them on the intake, as there is not enough heat to oxidize it.
 
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Any results from lapping in place??

I’d love to hear how you made out! The exhaust valve seats on my O320-E2D look exactly like yours. A white, alligator skin-like deposit. What is the stuff?? I can’t seem to find a definitive explanation. Some BeechTalk guys think its lead bromide but I run unleaded auto fuel. The RV guys think it’s carbon. But isn’t carbon black in colour??
 
Lapping seemed to go fine without anything too unexpected. This MB video was invaluable.

The white stuff seemed to mostly come off - or at least smoodge out, hard to tell for sure. Here's the "after" photo.

Now I'm just putting a few more hours on it before I take another look. I'll post a follow-up then.
 

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I’d love to hear how you made out! The exhaust valve seats on my O320-E2D look exactly like yours. A white, alligator skin-like deposit. What is the stuff?? I can’t seem to find a definitive explanation. Some BeechTalk guys think its lead bromide but I run unleaded auto fuel. The RV guys think it’s carbon. But isn’t carbon black in colour??

The white stuff is deposits from the fuel additives and it typically forms in greater thicknesses in cooler areas, like the intake valve. It is soft and and comes off without much effort. It is NOT carbon. You can almost get the deposits off with your finger nail. The black carbon almost needs a hammer and chisel to remove.
 
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Follow-up

It's been 15 hrs since lapping and I borescoped it again.
Looks maybe better, at least not worse. Specifically, that narrow edge of yellow / green around one edge seems to be gone. I'll keep an eye on it but expert opinions welcome.

As an aside, I also realized (d'oh!) that the "economy cruise" that I've been flying a lot also keeps CHTs way down and not hot enough to properly scavenge lead and other buildups. So the "bad" news is I really should start going faster :D
 

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How Low is CHT?

As an aside, I also realized (d'oh!) that the "economy cruise" that I've been flying a lot also keeps CHTs way down and not hot enough to properly scavenge lead and other buildups. So the "bad" news is I really should start going faster :D

What CHT's do you see in economy cruise, and what RPM, MAP and at what altitude?
Just curious, thanks.
 
What CHT's do you see in economy cruise, and what RPM, MAP and at what altitude?
Just curious, thanks.
19.5"MP / 2350 RPM / 5500' / OAT 57. Coolest (#1) 300, hottest (#4) 340.
I added an air dam in front of #1, and started running higher power:
22" MP, 2330 RPM / 5500' / OAT 43. Coolest (#2) 364, hottest (#4) 390.
 
Rotator Valve Stem Cap

What about valve rotation - or lack thereof? Does this engine have the Rotator Valve Stem Caps installed? As I understand it, they are meant to cause the valve to rotate in service - keeping the valve/seat interface cleaner.
How they actually cause rotation is a mystery to me....and everyone I ask. Does anyone know?
The Continental rotator cap is a whole different animal...and I can understand how they work, but the Lyc just looks like a simple cap that fits over the end of the valve stem to protect the stem from wear! So how does it make the valve rotate...or does it!
 
... the Lyc just looks like a simple cap that fits over the end of the valve stem to protect the stem from wear! So how does it make the valve rotate...or does it!

A WAG: I surmise that because of a slight eccentricity or spring lean, a valve may favor some position. The stem in direct contact with the rocker arm may then begin wearing a slight grove across the stem end. Then the valve is more or less locked in position by this matched wear pattern. No Rotation. However, with the cap, rotation could continue between the cap and the stem.

I had given this some thought previously. I have a Franklin engine from a wreck likely caused by a dropped valve. The engine has no special valve rotation devices. The valves of the wiped out cylinder were not rotating for a long time as evidenced by stem end wear. A stem cap, if it could be applied might do a lot of good.
 
the exhaust valves normally do rotate... here's Mike Busch's take:
The rate of valve rotation varies with engine rpm and rotator cap construction. For most TCM engines, it's about one revolution per minute at typical cruise rpm and a bit faster for most Lycoming engines.

As to how and why that happens, is kind of mysterious. To me... but eager to learn ;)

Here's the view of the inside face of one of the rotator caps on my engine. This clearly depicts the rotary motion of the valve.
 

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What about valve rotation - or lack thereof? Does this engine have the Rotator Valve Stem Caps installed? As I understand it, they are meant to cause the valve to rotate in service - keeping the valve/seat interface cleaner.
How they actually cause rotation is a mystery to me....and everyone I ask. Does anyone know?
The Continental rotator cap is a whole different animal...and I can understand how they work, but the Lyc just looks like a simple cap that fits over the end of the valve stem to protect the stem from wear! So how does it make the valve rotate...or does it!

OK, I'm quoting myself...but everyone is missing the point of the question:
Does the valve rotator cap on a Lycoming do what the name implies - that is, does it CAUSE the valve to rotate, or does it simply ALLOW the valve to rotate.
 
OK, I'm quoting myself...but everyone is missing the point of the question:
Does the valve rotator cap on a Lycoming do what the name implies - that is, does it CAUSE the valve to rotate, or does it simply ALLOW the valve to rotate.


My vote -- it allows it to rotate.

I don't see how the force applied to the valve stem by the rocker is translated into rotation by anything other than sheer luck...

Edit: Lycoming specific statement
 
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yes, it rotates

I have checked the valve it is rotating.

I too have wondered how the rotator works - don't really know but I've verified that it does, just by bonking the valve stem repeatedly with a plastic mallet and seeing that it incrementally rotates.

It's about 25 hours since I lapped this valve and borescope inspections indicate that it's improving or at least not getting worse. I'll keep checking and reporting back.
 
Update and response from Savvy

Update: Latest borescope image, about 30 hrs after lapping. I also sent this to Savvy (with whom I have a QA subscription) and their response was:
I think the valve looks great. It can take up to 50 hours for the face to even out, so I'm not worried at all. Rotation + good compression will keep this valve happy. (posted here with permission)​
 

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Update: Latest borescope image, about 30 hrs after lapping. I also sent this to Savvy (with whom I have a QA subscription) and their response was:
I think the valve looks great. It can take up to 50 hours for the face to even out, so I'm not worried at all. Rotation + good compression will keep this valve happy. (posted here with permission)​

The lapping compound wasn't cleaned off very well looking at the photo. It ends up turning into crusty material that stays on the edge of the valve like it did here. Use a big Q-tip soaked in solvent to clean while spinning the valve.
 
Exhaust valve rotation

[QUOTE Does the valve rotator cap on a Lycoming do what the name implies - that is, does it CAUSE the valve to rotate, or does it simply ALLOW the valve to rotate.[/QUOTE]

It only allows rotation. A careful look at dimensions shows that the rotator cap sits on the valve keepers, not on the top of the valve stem. I recall the nominal spacing between rotator cap and the top of the stem is about .004 inches.

When the rocker arm actuates the valve, the first movement is the rotator cap slightly releasing the keepers, thus allowing rotation. Only then does it start to move the valve itself. What causes rotation? The rotating exhaust stream passing by the valve. Why does it rotate? For the same reason that water flowing out of a sink rotates -- Coriolis force is my guess.
 
great thread

I must say that this thread is hitting a lot of very important topics for our lycoming engines, comps, wobble specs, exhaust valve pics and rotation. spread the word to all your friends that this is crucial for a healthy running engine! beside this info 'morning sickness' is a tell that a stuck valve is coming soon. I know of a rv that went down recently and the pilot was unaware of this stuff. I'm sure this is probably what happen. thanks for this post . I would also include yearly oil change, coarse screen check, oil filter cut open for inspection, oil analysis and proper leaning below %75 power and flying the *rap out of it on a regular basis. ;)
 
I must say that this thread is hitting a lot of very important topics for our lycoming engines, comps, wobble specs, exhaust valve pics and rotation. spread the word to all your friends that this is crucial for a healthy running engine! beside this info 'morning sickness' is a tell that a stuck valve is coming soon. I know of a rv that went down recently and the pilot was unaware of this stuff. I'm sure this is probably what happen. thanks for this post . I would also include yearly oil change, coarse screen check, oil filter cut open for inspection, oil analysis and proper leaning below %75 power and flying the *rap out of it on a regular basis. ;)

All good tips. A couple of others I'd recommend - based advice from people far smarter and more experienced than me - engine dryer and unleaded fuel.
 
The lapping compound wasn't cleaned off very well looking at the photo. It ends up turning into crusty material that stays on the edge of the valve like it did here. Use a big Q-tip soaked in solvent to clean while spinning the valve.
Thanks. Did my best with a long Q-tip and solvent.
 
Does the valve rotator cap on a Lycoming do what the name implies - that is, does it CAUSE the valve to rotate, or does it simply ALLOW the valve to rotate.


It only allows rotation. A careful look at dimensions shows that the rotator cap sits on the valve keepers, not on the top of the valve stem. I recall the nominal spacing between rotator cap and the top of the stem is about .004 inches.

When the rocker arm actuates the valve, the first movement is the rotator cap slightly releasing the keepers, thus allowing rotation. Only then does it start to move the valve itself. What causes rotation? The rotating exhaust stream passing by the valve. Why does it rotate? For the same reason that water flowing out of a sink rotates -- Coriolis force is my guess.



I have serious doubts this is the case. Seems pretty dangerous to partially release the keepers on every valve movement. This would likely create some pretty significant wear on a VERY key component. Look at the pics above; no wear on the cap where it would be hitting the keepers millions of times and compare to the significant wear where it contacts the valve stem. Valves WILL rotate without the keepers being released. Typically valves rotate from the geometery of the stem vs rocker angle, NOT from swirling air.

FYI, it is not called a rotator cap. It is called a "valve stem cap." Seems everyone here calls it a rotator cap, leading everyone to believe that it's purpose is to cause rotation. But Lyc doesn't call it that.
 
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Just to be clear - in my case the valve is rotating (verified by bonking the valve stem repeatedly with a plastic mallet with the rocker off). Just a tiny bit each time but measured over many bonks it incrementally rotates in one direction. I don't know the mechanism myself but I suspect it's a designed-in side-effect of the spring.
 
FYI, it is not called a rotator cap. It is called a "valve stem cap." Seems everyone here calls it a rotator cap, leading everyone to believe that its purpose is to cause rotation. But Lyc doesn't call it that.

This what Lycoming calls it on the IO-360-M1B, from the Parts Catalog:

"CAP, Valve stem, exhaust (rotator type)"
 
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Why does it rotate? For the same reason that water flowing out of a sink rotates -- Coriolis force is my guess.

Are the valves rotating the otherway down under? Coriolis affecting valve rotating direction?
I do believe in Santa and the 7 dwarfs, but this is a big one to swallow ;)
 
Just a tiny bit each time but measured over many bonks it incrementally rotates in one direction. I don't know the mechanism myself but I suspect it's a designed-in side-effect of the spring.

Same experience, same belief :)
 
This what Lycoming calls it on the IO-360-M1B, from the Parts Catalog:

"CAP, Valve stem, exhaust (rotator type)"

It is quite possible that there are different caps in use. Possibly some use the cap to create rotation and some do not. The 320 parts catalog that I referenced for that post did NOT state rotator type.
 
It is quite possible that there are different caps in use. Possibly some use the cap to create rotation and some do not. The 320 parts catalog that I referenced for that post did NOT state rotator type.

Possibly. I note that the OP has an O-360. The Lycoming Parts Catalog also shows 'CAP, Valve stem, exhaust (rotator type)' for all variants of the O-360-A engines (WD). Maybe the O-320s are different, or possibly a ND vs WD thing.
 
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