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Engine/RV-10 stuff I learned at Airventure 2021

I would like to remind folks of the advice from Don Rivera of AFP regarding setting idle mixture. Leaning on the ground is generally not necessary when idle is correctly set. See this educational thread from years back when Don was still on the forum:

https://vansairforce.net/community/showthread.php?t=94002

Erich

I also follow DOn's guidance. Both of my engines have FI with properly set idle mixtures. I never lean on the ground and have never fouled a plug and valve guides clean and on spec clearances (800 hours on one and 200 on the other). I do a 1800 RPM runup for 15 seconds before each shut down to burn off an deposits; Lycomings recommendation I believe. Not trying to start a debate. Just passing along a contrarian data point.

Larry
 
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I also follow DOn's guidance. Both of my engines have FI with properly set idle mixtures. I never lean on the ground and have never fouled a plug and valve guides clean and on spec clearances (800 hours on one and 200 on the other). I do a 1800 RPM runup for 15 seconds before each shut down to burn off an deposits; Lycomings recommendation I believe. Not trying to start a debate. Just passing along a contrarian data point.

Larry

Yes, absolutely agree with Don on this. However, I don't think we have ever seen one come in that was correctly set. It takes a lot of time to do it, requiring very fine adjustments, and unless done at sea level on a standard day, it doesn't seem right for all other days/temps/altitudes.

Just my experience.

Vic
 
I would NOT give bad advice to anyone.

Certainly not intentionally.

Everybody trying to get them below 380-400 in a climb, especially on hot days, is just wasting time. It's not necessary

The arguably true part of that statement is "It's not necessary", as strictly speaking, Lycoming allows 435 for max continuous. However, efforts at CHT reduction are well worth the time. It's about probability of failure, and we want to stack the odds. Consider...

1. All aluminum alloys lose significant strength at elevated temperatures. Here's an example, a chart of strength loss from DOT/FAA/AR-MMPDS-01. I just grabbed this one (7075 alloy) at random, but the trends will be similar for the 200 or 300 series casting alloy in a Lycoming head. I've plotted 150F, 300F, and 435F on the 1000 hr exposure line, 150 and 435 being the two ends of the Lycoming range. Take a moment to grasp the very steep slope. At 435F, UTS is about 20% of strength at 150F. 300F is more than twice as strong as 435F.

ScreenHunter_884%20Aug.%2007%2020.31.jpg


2. Detonation margin is improved at low CHT. And if an operator inadvertently pushes a cylinder into detonation, with low initial CHT the only result will be a sudden increase in temperature indication. It is unlikely to damage anything.

3. Thermal fatigue (repeated material stress due to differences in temperature between different sections of a component) is reduced at lower temperature. It's a key factor in head distortion and cracking.

4. Valve cooling is improved with low CHT. Heat transfer is a function deltaT. A cooler seat and guide means a cooler valve.

5. Ring sealing and ring land wear is improved at lower temperatures. Higher CHT means greater increase in cylinder diameter near the top of the bore, meaning more piston to wall clearance and less land support for the top ring.

6. Closely related is a greater risk of failure at the head-to-barrel screw joint. The aluminum head expands faster than the steel barrel, reducing friction clamp force, thus increasing stress at the topmost thread. Remember the ECI head separations?

https://resources.savvyaviation.com...ticles_eaa/EAA_2013-02_separation-anxiety.pdf

7. Not everyone believes in shock cooling, but if you do, lower CHT reduces the probability. Again, basic physics...heat transfer (here loss from head to air) is reduced due to lower deltaT.

Now, given the above, who at Lycoming believes high CHT is good, and what reason did they give?
 
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...

Now, given the above, who at Lycoming believes high CHT is good, and what reason did they give?
As a data point, not from Lycoming, here's what Mike Busch has to say:

MikeBushWebinarCHT350-400.png

MikeBuschYoutubeVideoQuote said:
To minimize valve sticking ... keep CHTs in the "sweet spot" between 350F and 400F ...

https://www.youtube.com/watch?v=7ohsVvYbAaQ&t=1298s

Since the reasoning is related to lead formation, I guess those running unleaded don't need to worry so much about keeping the CHTs in that range.
 
As a data point, not from Lycoming, here's what Mike Busch has to say:

View attachment 14456



https://www.youtube.com/watch?v=7ohsVvYbAaQ&t=1298s

Since the reasoning is related to lead formation, I guess those running unleaded don't need to worry so much about keeping the CHTs in that range.

You should ask mike for the rationale behind his opinion. All of the science that I have seen says that lead deposits form at cool temperatures, not hot. In fact, most of it is happening at idle. Also, valve stem deposits are not lead; They are jet black and lead is dull grey.

I do agree with both sides on heat. I believe that the cyl's can handle continuous 435, but also agree with all of Dan's points on why cooler is better if you can make it happen.

Larry
 
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You should ask mike for the rationale behind his opinion. All of the science that I have seen says that lead deposits form at cool temperatures, not hot. In fact, most of it is happening at idle. Also, valve stem deposits are not lead; They are jet black and lead is dull grey.

I do agree with both sides on heat. I believe that the cyl's can handle continuous 435, but also agree with all of Dan's points on why cooler is better if you can make it happen.

Larry

Larry you really should give the earlier part of the video a watch. He talks fairly in depth about it. At about the 13 min mark he talks about Ed Kollins and how he performs a laboratory chemical analysis on the deposits. Then talks about why the valves are cooler from being heat sinked with the head. He even talks about why Lycomings have more problems with it than Continentals.

Long story short I believe Mike on this one which is why I try and keep my CHTs in the sweet spot. He probably also has more engine data than just about anyone in the industry too. In the end though I'm not as old and wise as many of the other gents on here. :D
 
Here's the written version:

https://resources.savvyaviation.com...ticles_aopa/AOPA_2020-07_why-valves-stick.pdf

It's a rehash of Ed Kollin's work, although Kollin likes slightly lower CHT.

https://aslcamguard.com/wp-content/uploads/2019/08/Camguard-Parts-1-to-3.pdf

Kollin borrowed the valve illustration from TRW, then relabeled it. Here's the original:

TRW%20Valve%20Temp%20Illustration.jpg


Take a good look at the illustrations. Busch/Kollin argue that the valve stem must be kept above the condensation temperature of lead oxy-bromide, which Kollin identifies as being about 1300F. However, none of the illustrations show anything near that high at the part of the stem which peeks in and out of the valve guide.

Not that it really matters, because the original TRW illustration is generic. There is no evidence that the illustrated temperatures are actually those found in a Lycoming or Continental. They simply re-labeled the generic values in Fahrenheit, and placed "Lycoming" and "Continental" at the bottom. Frankly, that is made-up data.

TRW%20Kollin%20Busch%20Valve%20Temps.jpg


Although Busch/Kollin claim the Lycoming sodium filled valve is more prone to deposit formation because the stem is cooler, the illustrations actually show a higher stem temperature at the location of interest. For example, note the location of the yellow 600C zone for the sodium filled valve in the TRW illustration, vs the 600C location for the solid valve. It's no surprise. The whole point of the sodium filled valve is to move heat from the head of the valve to the stem.

Neither writer offers any sort of concrete connection between actual valve stem temperature and their favorite CHT range.

Kollin does stress maintaining higher combustion temperatures, and I agree. A lot of owners are pouring fuel into hot cylinders, or trying to run way LOP, in order to maintain a reasonable CHT. For a moment, forget about what to call reasonable. Instead, consider this. Very rich and very lean both lower combustion temperature. Put another way, they put less heat into the cylinder head. It works, but one is costly and the other makes less power, while neither expedite the chemical reactions Kollin described. Instead, work on taking more heat out of the head, i.e. a better cooling system. It allows cruise at peak EGT, which is precisely what Lycoming has recommended for decades....as does Kollin, if you think about it.

This afternoon, somewhere over southern Indiana. Peak EGT, with low CHT and low cooling drag. Results not worth the time?

IMG_20210808_155421931%20600w.jpg


So, why am I poking holes in the referenced Busch opinion? (Yes, it's an opinion column.) Because it illustrates a point.

We live in a society full of misinformation, often generated by good people. Followers spread the misinformation without giving it critical thought, or making an effort to find the underlying data. It's just human nature, and top to bottom their belief is often quite sincere.

It doesn't matter who says it...vendor, bystander, or industry expert. Nor does it matter where you heard it...Oshkosh, a magazine, an aviation forum, or God forbid, Facebook. Ask for the underlying "why", and think about it before passing it along. If someone presents a contrary opinion, and brings good data to the debate, be happy!
 
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At about the 13 min mark he talks about Ed Kollins and how he performs a laboratory chemical analysis on the deposits.

It is my opinion (just an opinion) that the guide deposits are coked or burned/oxidized oil. As you probably know, the AD oil that we use has additives that help to hold debris in suspension. An engine burning leaded gasoline will have a lot of lead particles in the blowby gasses and some of this ends up being held in suspension in the oil. If that oil is then brought to the valve guide and then burned/deposited onto the guide, it seems quite logical that a chemical analysis of the deposited material will include lead, in addition to the carbon rich coke. Meaningfull chemical analysis would need to include the percentage of the various elements found in the sample.

IMHO, the fact that lead is found in the valve guide deposits is not necessarily evidence that lead is being deposited there via exhaust gasses, because the oil is saturated with lead particles. I struggle to believe that lead is a majority component of the deposits. If they were, the deposits would be grey and soft, not hard/brittle and black.

It is my opinion that the continentals deliver more oil volume to the head and therefore cool the valve guides better than the Lyc's and this is the reason that Lyc's have more problems. Again, just my opinion. Like Dan, I believe we should bring all opinions to the table looking for facts. I refuse to believe something just because Mike B says it's so.

Larry
 
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“…I refuse to believe something just because Mike B says it's so…”


“…I refuse to believe something just because XXXX says it's so…”

There, I fixed it for you…
 
It is my opinion (just an opinion) that the guide deposits are coked or burned/oxidized oil. As you probably know, the AD oil that we use has additives that help to hold debris in suspension. An engine burning leaded gasoline will have a lot of lead particles in the blowby gasses and some of this ends up being held in suspension in the oil. If that oil is then brought to the valve guide and then burned/deposited onto the guide, it seems quite logical that a chemical analysis of the deposited material will include lead, in addition to the carbon rich coke. Meaningfull chemical analysis would need to include the percentage of the various elements found in the sample.

IMHO, the fact that lead is found in the valve guide deposits is not necessarily evidence that lead is being deposited there via exhaust gasses, because the oil is saturated with lead particles. I struggle to believe that lead is a majority component of the deposits. If they were, the deposits would be grey and soft, not hard/brittle and black.

It is my opinion that the continentals deliver more oil volume to the head and therefore cool the valve guides better than the Lyc's and this is the reason that Lyc's have more problems. Again, just my opinion. Like Dan, I believe we should bring all opinions to the table looking for facts. I refuse to believe something just because Mike B says it's so.

Larry

Ed doesn’t simply say it’s lead but lead oxybromide that has crystalized. I agree though that it sure would be nice to see percentages of everything.

I don’t blindly believe Mike but he has data that seems to show that if our engines are run too cool there is an associated uptick of sticking valves. Of course I have not seen the data myself though…

So I’ll keep running my engine around peak and keep my CHTs around 325-380 as he suggests. My personal ideal is 350 but that is just my feeling. Haha

Certainly a subject where there appears to be some mystery still.
 
Like Dan, I believe we should bring all opinions to the table looking for facts.

Actually, I believe we should make fact available when we state an opinion.

“…I refuse to believe something just because XXXX says it's so…”

Absolutely agree...you, me, Vic, Larry, Busch, Kollin, anyone. In God we trust, all others should bring data for peer review.
 
Actually, I believe we should make fact available when we state an opinion.



Absolutely agree...you, me, Vic, Larry, Busch, Kollin, anyone. In God we trust, all others should bring data for peer review.

Is experience considered data, I have lots of the former very little of the latter.... just saying :eek:
 
Is experience considered data, I have lots of the former very little of the latter.... just saying :eek:

Agreed. Unless one of the VAF members has a mass spectrometer in their basement, we are kind of left piecing together speculations based upon other knowledge and experience. I agree that data is king, but what do we do in the absence of data?

Larry
 
Ed doesn’t simply say it’s lead but lead oxybromide that has crystalized. I agree though that it sure would be nice to see percentages of everything.

I don’t blindly believe Mike but he has data that seems to show that if our engines are run too cool there is an associated uptick of sticking valves. Of course I have not seen the data myself though…

So I’ll keep running my engine around peak and keep my CHTs around 325-380 as he suggests. My personal ideal is 350 but that is just my feeling. Haha

Certainly a subject where there appears to be some mystery still.

I believe that crystallized lead oxybromide is also what forms on your sparkplugs and it looks like little grey beads and is soft. Not a chemist, but what my research bore out. This looks / appears VERY different than what comes out of the guides.

I fly a LOT in the winter with CHTs less than 300* (LOP). At 750 hours I did a wobble test. All valve clearances were at the loose end of the range (i.e. no deposits). If Mike's theory were accurate and low CHTs cause deposits in the guides, why don't I have build up in my guides? It would seem that some other variables are in play, as I probably fly more than most with CHTs below 300 and have no deposits in the guides.

A sample size of 1 doesn't mean much, but it still raises questions on the validity of his theory, as I should be considered a "worse case scenario."

Larry
 
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I believe that crystallized lead oxybromide is also what forms on your sparkplugs and it looks like little grey beads and is soft. Not a chemist, but what my research bore out. This looks / appears VERY different than what comes out of the guides.

I fly a LOT in the winter with CHTs less than 300* (LOP). At 750 hours I did a wobble test. All valve clearances were at the loose end of the range (i.e. no deposits). If Mike's theory were accurate and low CHTs cause deposits in the guides, why don't I have build up in my guides? It would seem that some other variables are in play, as I probably fly more than most with CHTs below 300 and have no deposits in the guides.

A sample size of 1 doesn't mean much, but it still raises questions on the validity of his theory, as I should be considered a "worse case scenario."

Larry

This confirms that there is still some mystery to this topic. On a fleet wide basis Mike and Ed both have found that colder beyond a point they see more sticking valves. Again I have not seen the data myself but I also don’t know why they would lie about it either.

I have always been fascinated by this topic. In the end I guess all we can do is take our guess and monitor for a sticking valve/ do wobble tests since there doesn’t appear to be readily available data to look at.

I don’t pretend to have the answers but Walt brings up a good point about experience. It’s the reason I put so much weight in what you, Dan, Vic, Walt, Bob and many others say, including Mike B.
 
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Is experience considered data?

Sure. For example, we might have "I've seen this many times", "I've seen this 10 times in the last 100 airplanes", or "I've seen this 10% of the time, and here are detailed records for the last ten cases". All are valid, the difference being precision, and how much weight a thinking reader might give to them.

A I agree that data is king, but what do we do in the absence of data?

Indicate it's an opinion without much basis.

Let's not get too far into semantics. Most people have a reason for their opinion, and will share it if asked...logic, physics, a reference, math, something.

On a fleet wide basis Mike and Ed both have found that colder beyond a point they see more sticking valves. Again I have not seen the data myself but I also don’t know why they would lie about it either.

First, I'd bet neither man has any fleet data on the subject. Kollin is basically a chemist, and naturally he would tend toward a chemist's theory. Busch just played the role of mouthpiece, reporting what Kollin thinks. Second, although the doctored illustration is BS, there is no reason to think either of them lied about about the theory.
 
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I wonder what role mixture plays. I would imagine cooler CHTs LOP would be less conducive to buildup than ROP simply because there is less gas being burned more efficiently.
 
Maybe more than just the temperature effect of mixture.

I wonder what role mixture plays. I would imagine cooler CHTs LOP would be less conducive to buildup than ROP simply because there is less gas being burned more efficiently.

Well, if the mixture is really rich there is some raw fuel in the exhaust, either as an aerosol or gas. An aerosol is likely to something akin to a "particulate" which could stick to an exposed valve stem, also gasses can/will condense on something cooler, like an exhaust valve stem. They are all rich on cold starts.

I have seen a diesel run at low idle is a cold room (-20C) and unburned fuel condensed in the exhaust pipe. It was a catalyst test and we thought it was over. Then as it warmed up liquid began to drop out of the exhaust - something like tar with a heavy syrup consistency. In the real world it would either plug the catalyst or heat slowly until it flaked off and eventually burned away. This kind of explained how this engine was getting enough carbon in the turbine to lock the turbine wheel (mostly in Canada).

The point is . . . . weird things happen in engines. Logic does not always lead to understanding, but understanding is usually advanced by the unexpected.
 
I wonder what role mixture plays. I would imagine cooler CHTs LOP would be less conducive to buildup than ROP simply because there is less gas being burned more efficiently.

I would expect mixture plays a slightly different role.

The lead scavenging agent comes with the fuel, so more fuel = more lead scavenger at a constant ratio. The important thing is enough temperature for the scavenging reaction to complete.

A scarcity of oxygen at richer mixtures might also encourage the lead oxybromide compounds to release their oxygen and convert to lead bromide.

I would hypothesize that the least deposits would occur at temperatures close to peak EGT on the rich side because you have the highest temperatures and least oxygen.

It's probably not a coincidence that this is your "red box" where detonation is most likely because that is also a chemical reaction dependent on temperature and time. But at recommended power settings (RPM and manifold pressure) for that mixture setting you should not be at risk of detonation.
 
First, I'd bet neither man has any fleet data on the subject. Kollin is basically a chemist, and naturally he would tend toward a chemist's theory. Busch just played the role of mouthpiece, reporting what Kollin thinks. Second, although the doctored illustration is BS, there is no reason to think either of them lied about about the theory.

Man I sure hope not, Mike's company has a lot of data at their disposal and helps many people work through problems, even developed an exhaust valve analytic (which I have never used, and also somewhat unrelated). I suppose you could be correct but Mike has gone on record saying that too low of CHTs results in higher occurrences of sticking valves, I sure hope this is based on some Savvy data. My usage of the word fleet was probably not correct though.

Edit: I see that Ed's articles say the same thing and it is quite possible that Mike just put it into his own words. Again, I hope he has some Savvy data to back it up...
 
Man I sure hope not, Mike's company has a lot of data at their disposal and helps many people work through problems, even developed an exhaust valve analytic (which I have never used, and also somewhat unrelated). I suppose you could be correct but Mike has gone on record saying that too low of CHTs results in higher occurrences of sticking valves, I sure hope this is based on some Savvy data. My usage of the word fleet was probably not correct though.

Edit: I see that Ed's articles say the same thing and it is quite possible that Mike just put it into his own words. Again, I hope he has some Savvy data to back it up...

His computer data cannot positively confirm a stuck valve. The only way he could have meaningful data is if he was handed a plane that he then confirmed had a stuck valve. He would then need some way to analyze how that engine was run for the last several hundred hours, along with copious amounts of instrumentation data. He would need to repeat this 10's or 100's of times before being able to say his theory was based upon data. It typically takes 500+ hours for enough build up in the guide to create a stuck valve. Therefore you need 100's of hours of instrumentation data before you can start making assumptions like low CHT's definitively cause stuck valves. You would also need to disprove all other possible scenarios that could be causing the issue, many of which are related to oil. You would also need to find engines with stuck valves that routinely ran inside his CHT range and compare the occurrence rates, as they disprove his theory.

You get the point. It seems quite unlikely to me that he has meaningful data to backup his theory. Some experts become experts via pontification and not necessarily expertise. Not intending to throw stones, as he is an experienced guy with a lot of knowledge, only questioning that he has real data on THIS subject. I agree with Dan that he likely borrowed someone's theory and added it to his own. I do believe he has emperical data like stuck valves being more prevalent on Lyc's vs Conti's, but unfortunately that is not definitive as MANY things are different between these engines.

If you really want data, VAF is a great source. Start a thread and ask each member that has experienced a stuck valve to answer a series of questions about how their engine was run over hundreds of hours. The community can even help to develop a set of questions that would help to find a common theme. This community has MUCH greater reach than Mike does. It would be interesting to see if anyone here running mogas had a stuck valve as that COMPLETELY trashes the theory.

I remain convinced that the stuck valve issue is not a simple as just running outside of mikes recommended CHT range. Kind of like saying I wore a mask and didn't get covid, therefore masks prevent the spread of covid. Science is just not that simple.

Larry
 
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Wow

Wow, there are so many “experts” on these boards…

…many of which have no issues bashing other “experts”…some of whom actually have a business troubleshooting and engines…
 
Edit: I see that Ed's articles say the same thing and it is quite possible that Mike just put it into his own words. Again, I hope he has some Savvy data to back it up...

One of the best ways to consider a claim or theory is to divorce the claimant from the claim. Put another way, if someone whose name you did not recognize made the claim, or if the claim was published anonymously, you would examine the data on its own merit.

Wow, there are so many “experts” on these boards……many of which have no issues bashing other “experts”…some of whom actually have a business troubleshooting and engines…

For example, if Bob offered any meaningful input, I would consider it without regard for persona ;)

Seriously, when considering a theory, why should we conflate the offered facts with the claimant's business?
 
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Wow, there are so many “experts” on these boards…

…many of which have no issues bashing other “experts”…some of whom actually have a business troubleshooting and engines…

Never claimed to be an expert (though I have read a lot on the subject) and certainly not bashing Mike, as he has seen much more than I have. I simply questioned one of his theories and included detail on why I don't accept it. Sorry, but just because someone has a business doing something doesn't, IMO, mean that EVERYTHING they say is accurate. That, I feel that I am an expert on, as I have seen it countless times in my career. Often, extensive experience can lead to over confidence and draw conclusions that aren't supported by evidence or data.

Larry
 
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I am sorry I made this post, I meant to share information in hopes that it might help other people on this board. Instead it turned into bashing and reminded me why I don't post on social media platforms. Moderator, can you please delete or at least lock this post?
 
I am sorry I made this post, I meant to share information in hopes that it might help other people on this board. Instead it turned into bashing ...
For me this is just guys talking, exchanging ideas, and learning - not bashing. It's all in good spirit, and I for one am learning stuff.
 
Challenging theories and asking for data is how facts are derived.

Suspect a phenomenon, let's call it a theory. Collect data, analyze data, re-examine theory. Repeat. Nothing personal it's how science works.

I see nothing wrong with challenging this theory and asking for data. A publisher of a theory should invite critique in the interest of advancement.
 
Don't be sorry. Thank you for starting the most informative thread in a while.

If every time someone tries to set the record straight by presenting facts instead of beliefs and the thread gets deleted we'll never learn anything.

Lenny

I am sorry I made this post, I meant to share information in hopes that it might help other people on this board. Instead it turned into bashing and reminded me why I don't post on social media platforms. Moderator, can you please delete or at least lock this post?
 
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It’s too bad that the guys being bashed are not on this board to defend their positions…

Which guys would that be Bob? As an aerospace engineer, perhaps you could focus on the claims and logically argue why they are correct. Would not proving them correct be better than demanding they not be questioned?

I am sorry I made this post, I meant to share information in hopes that it might help other people on this board.

Chris, the point is that hearing it at Oshkosh does not guarantee truth, a good lesson for anyone entering EAB. The same can be said for publications and vendors, an unholy marriage despite the sincerity of many responsible for publishing.

It's not a modern problem. Allow me to recommend an entertaining read, a 1969 Flying Magazine article. It's an EAA Rockford-in-retrospective piece written by a young Peter Garrison, which includes this memorable turn of phrase...

"...the poop sheet in which a lot of questionable poop gets aired."

Starts on page 53:

https://books.google.com/books?id=Y...ce=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
 
...
It's not a modern problem. Allow me to recommend an entertaining read, a 1969 Flying Magazine article. It's an EAA Rockford-in-retrospective piece written by a young Peter Garrison, which includes this memorable turn of phrase...

"...the poop sheet in which a lot of questionable poop gets aired."

Starts on page 53:

https://books.google.com/books?id=Y...ce=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Thanks for that Dan! Much of that article that could have been written almost every year about "the show".

Frank Smith, the boss at one of my part time jobs when I was a kid, and the guy that taught me to fly in his piper tripacer and introduced me to homebuilding in the 70s was building a KR-2 with a VW engine. He was always amazed when he bought something mail-order he found in sport aviation or another magazine and actually got something useful. Homebuilding was harder then, that's for sure.

When it was knocking off time, he'd jokingly say "let's go get high!" and we went flying. His tripacer had to be hand propped, and he didn't like doing it alone.
 
Actually...

"...Which guys would that be Bob? As an aerospace engineer, perhaps you could focus on the claims and logically argue why they are correct. Would not proving them correct be better than demanding they not be questioned?..."

Actually, Dan, I choose NOT to argue the points presented.

Why?...because my engineering focus was not even close to the chemistry involved in lead deposits, or the thermodynamics of heat transfer on exhaust valves.

I, therefore, am NOT an expert in this discussion, and I am fine with that.

My issue is with people here who claim to be "experts", bashing people that are NOT here to defend their position.

In other words, it's a one sided argument...or, as is seen here frequently, XXX says it's so, so it must be true...

As you are apparently an "expert" in these things, it would be interesting to get Mike B to debate you and defend HIS position...
 
Actually, Dan, I choose NOT to argue the points presented. Why?...because my engineering focus was not even close to the chemistry involved in lead deposits, or the thermodynamics of heat transfer on exhaust valves.

No one argued those points. In the case of Busch and valve sticking, the assertions were (1) the illustration was generic, borrowed from TRW, and re-labeled as Lycoming or Continental without factual basis, (2) the borrowed illustration actually showed higher stem temperature for the asserted "Lycoming" valve, the opposite of the text, and (3) the authors made no factual connection between valve stem temperature and their recommended CHT range.

My issue is with people here who claim to be "experts" bashing people that are NOT here to defend their position.

Point out the claim. If you can't, kindly admit it's a straw man argument.
 
I would actually ask that a moderate NOT close the thread. I like others above am learning a great deal about this topic (and decision making in general) that is very valuable. Although there is a difference of opinion by some I feel like it is pretty civil with no bashing of each other. I will reach out to Mike B and see if he could express any more thoughts on the matter. I hear he is good about email, we shall see.

Rocketman I agree that it would be nice to have Mike be able to defend his argument. I do however now see that Dan pointed out a troubling fact about the valve comparison picture. Hence, something was learned.
 
As promised I reached out to Mike B. He is either too busy or doesn't really care to defend his position with much else than can be heard in one of his webinars.

He initially referred me to Ed (who I am still waiting to hear from). I pressed Mike a little bit more on whether Savvy has seen a correlation between too cold of CHTs and increased reports of sticking exhaust valves to which he replied "Yes, we have. Especially on Lycomings." So yet again we have no real data to back up that statement or any elaboration of it. Sure would be nice to see the data but apparently I don't have enough street cred to get it out of him. :p Will report back if Ed emails me.

P.S. I specifically asked him if he has any data or any research that confirms the theory.
 
I did some searches for more of Ed's stuff.

The original paper posted earlier is interesting, he is more focused on combustion temperature than CHT, but the CHT reflects the combustion temperature, and i guess targeting a low CHT is a frequent cause of low combustion temperatures

lower combustion temperatures don’t permit this conversion of lead oxy-bromide to lead bromide and the valves run cool enough to allow this lead oxy bromide to form on the stem and this leads to (Hot Side) valve sticking.

Running either too LOP or ROP lowers peak combustion temperatures enough to cause this deposit problem. The low combustion temperatures are reflected in lower cylinder head and valve temperatures. Low combustion temperatures reduces both the conversion of lead oxy-bromide to lead bromide and the exhaust valve temperature, which allows the lead oxybromide to crystalize on it.



Some other stuff I found (quoted from BeechTalk on DiamondAviators.net, so 3rd hand here):

Some additional detail, I've had numerous reports of big bore Continentals (Bonanza's, Mooney's, Cirrus's, Cessnas's and Lancair's) with intermittent roughness and exhaust valve sticking. They seem to be associated with running a normally aspirated engine high (low manifold pressure) AND deeply LOP. This sets up the conditions for lead oxybromide deposits formation on the exhaust valve stem and potential valve sticking. This is usually accompanied by low CHTs
...
You can reduce these deposits by periodically running the engine very hard and sufficiently ROP (red box) for a few hours.
...
I flew my 210 with a IO 520 for 10 hours at 55% power and 30 degrees LOP.
The exhaust valve stems had deposits on them. I then flew it at 75% ROP for 10 hours, and the deposits were essentially gone.

Basically, if you run a 65% power or less, run at peak EGT so the scavenger chemistry can function as intended. It is the combustion temperature that is important, determined by manifold pressure and mixture, and CHT is an imperfect approximation of it.
 
I find it interesting to see both Busch and Kollin insist the best proxy for a high combustion temperature is CHT, not EGT.

Is EGT a reasonable indicator of combustion temperature? Consider these plots from the Lycoming dyno, where we see peak EGT and peak CHT are quite close.

Detonation%20Survey%20360%20WOT-2700.jpg


Detonation%202400%20RPM.jpg


Next up, from C.F. Taylor's classic Internal Combustion, plots of head temperature and exhaust valve temperature, showing both to peak at stoichiometric mixture (F/Fc), i.e. very near peak EGT.

Mean%20Gas%20Temp.jpg


Spin the dial on the wayback machine all the way to the 1930's, and we find NACA data plotting actual valve temperature against EGT, at essentially the same mixture, 0.066 F/A, again stoich.

Exhaust%20Valve%20Temp%20vs%20Mixture.jpg


EGT looks like a pretty good indicator to me.

As Andrew relates, apparently Kollin at least once wrote...

Basically, if you run a 65% power or less, run at peak EGT so the scavenger chemistry can function as intended. It is the combustion temperature that is important, determined by manifold pressure and mixture, and CHT is an imperfect approximation of it.

Peak EGT at cruise power has long been Lycoming policy. Are we now to burn our hymnals from the Church of LOP, and abandon its promise of low CHT salvation? Has the Sheridan Road sect split with the Ada faithful? Stay tuned for another episode of "As The Propeller Turns".
 
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I find it interesting to see both Busch and Kollin insist the best proxy for a high combustion temperature is CHT, not EGT.

I don't see where Ed Kollin says the best proxy for combustion temperature is CHT. He is regularly referencing EGT/LOP/ROP. The closes he gets is saying the quest for lower CHT is causing people to run combustion temperatures too low.

One additional point is that if the combustion temperature is high enough for the scavenging reaction to work properly, the valve stem temperature doesn't really matter because there will be minimal lead oxy-bromide compounds present in the exhaust.
 
Interesting Read

Is there any way the "experts" can give there experience and background on the subject? If X is a used car salesman I'd like to know. If Y is a professional pilot with thousands of hours flying I'd like to know. Why do we read these and know nothing of the writers background? To me this is just a waste of time reading authors that have limited education or experience.
 
...

Peak EGT at cruise power has long been Lycoming policy. Are we now to burn our hymnals from the Church of LOP, and abandon its promise of low CHT salvation? Has the Sheridan Road sect split with the Ada faithful? Stay tuned for another episode of "As The Propeller Turns".
:D Don't forget - there's a new "troublemaker" coming to the show soon - unleaded fuel.
 
Is there any way the "experts" can give there experience and background on the subject? If X is a used car salesman I'd like to know. If Y is a professional pilot with thousands of hours flying I'd like to know. Why do we read these and know nothing of the writers background? To me this is just a waste of time reading authors that have limited education or experience.

Dwight,
I think you missed the point of DanH when he talks about providing supporting documentation.
We are better Experimental aircraft builders and owners if we do not take the spoken word as fact no matter who provides the word. We are much better off finding or having been provided supporting documentation.
I learn a lot more from the used car salesman when he provides me proof than I do from an "expert" when it is merely opinion or there is not proof.

Example,
Having a two stroke motorcycle engine background from my youth and even a class on club plane operation from our head instructor taught 75 degrees ROP. I was scared to death of LOP operation. Coming into the experimental world and VAF I was hearing a lot about LOP.
It took a lot to convince me. I did a lot of research and fortunately was even provided a lot of back up support. I now fly 90% of my time LOP with a complete (well maybe not so complete after this thread) understanding of LOP and how I operate my engine.

Take care.

Oh and I know many professionals that don't fully understand their own profession . Mostly because they have been listening to "Experts without support".
 
I did some searches for more of Ed's stuff.

The original paper posted earlier is interesting, he is more focused on combustion temperature than CHT, but the CHT reflects the combustion temperature, and i guess targeting a low CHT is a frequent cause of low combustion temperatures

lower combustion temperatures don’t permit this conversion of lead oxy-bromide to lead bromide and the valves run cool enough to allow this lead oxy bromide to form on the stem and this leads to (Hot Side) valve sticking.

Running either too LOP or ROP lowers peak combustion temperatures enough to cause this deposit problem. The low combustion temperatures are reflected in lower cylinder head and valve temperatures. Low combustion temperatures reduces both the conversion of lead oxy-bromide to lead bromide and the exhaust valve temperature, which allows the lead oxybromide to crystalize on it.



Some other stuff I found (quoted from BeechTalk on DiamondAviators.net, so 3rd hand here):

Some additional detail, I've had numerous reports of big bore Continentals (Bonanza's, Mooney's, Cirrus's, Cessnas's and Lancair's) with intermittent roughness and exhaust valve sticking. They seem to be associated with running a normally aspirated engine high (low manifold pressure) AND deeply LOP. This sets up the conditions for lead oxybromide deposits formation on the exhaust valve stem and potential valve sticking. This is usually accompanied by low CHTs
...
You can reduce these deposits by periodically running the engine very hard and sufficiently ROP (red box) for a few hours.
...
I flew my 210 with a IO 520 for 10 hours at 55% power and 30 degrees LOP.
The exhaust valve stems had deposits on them. I then flew it at 75% ROP for 10 hours, and the deposits were essentially gone.

Basically, if you run a 65% power or less, run at peak EGT so the scavenger chemistry can function as intended. It is the combustion temperature that is important, determined by manifold pressure and mixture, and CHT is an imperfect approximation of it.

So, I will add a little more about my experience, as it seems a lot of this supposed data is really experiential. I did the wobble test at 750 hours on my 320 and found no meaningful deposits in the guides (loose clearances). Pretty much ALL cruise flight is WOT and 50-60*+ LOP and CHTs vary from 280-360 depending upon the ambient temps at cruise altitudes (-10 - 75F). Even when puttering around locally, which I do a lot of, I fly 80* LOP, though rarely observe the CHTs in those cases, but speculate they are around 300-325. I almost never get above 405 in climb and, as mentioned, I do a lot of winter flying with CHTs below 300. Also, my idle mixture is properly set and never lean on the ground.

While there may be some validity to the rationale and science behind their positions, it seems clear from my experience that there is more to it than they speculate and possibly completely unrelated. My unscientific opinion remains that the build up in the guides is coked oil and the reason one plane has an issue and one doesn't is based more upon the clearances in the plunger and the resulting differences in oil flow rate to the rocker box. Unlike Hyd lifters in cars, the Lyc lifters do not have an oil bypass circuit, that sends a stream of oil up the pushrod. Therefore, the only oil that gets to the rocker box is that which leaks through the plungers clearance with it's shell. Some are tighter than others and they will flow less. Exh valves can be cooled with splash oil and any starvation will raise temps. Just Larry's opinion here.

In my case, I have a very strong understanding of how the engine was run. In Mike's case, I have to question how much understanding he can have about how the engine was run when he sees a stuck valve on an engine flown by one of his customers. If Mike only has one plane, then a detailed evaluation, like mine, will result in a sample size of one.

Just a data point for consideration.

Larry
 
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I don't see where Ed Kollin says the best proxy for combustion temperature is CHT.

Page two of the previously linked document:

Combustion temperature is reflected in both the Cylinder Head Temperature (CHT) and directionally,
the exhaust valve temperature, which we do not measure directly. (Exhaust valve temperature follows cylinder
head temperature because the valve guide is located in the cylinder head, to which it transfers heat from the valve.)
Valve temperatures do not follow Exhaust Gas Temperature (EGT).


Kollin is not as specific as Busch (AOPA, July 2020, page 88, also previously linked):

The best proxy we have in the cockpit for exhaust valve temperature is cylinder head temperature (Note it isn't EGT)

I really would like to know why they say valve temperatures do not follow EGT, when multiple references suggest it does. I do realize a cooler head means a cooler valve, but it's a relationship seriously in need of quantification. If the CHT is 50F less, does it result in a valve stem temp 50F less, or 30, or 10? If it was 50 less, would it make a real difference in the context of lead compound condensation...in particular if we operate at higher gas temperature?

One additional point is that if the combustion temperature is high enough for the scavenging reaction to work properly, the valve stem temperature doesn't really matter because there will be minimal lead oxy-bromide compounds present in the exhaust.

Agree. And make no mistake, I do not question Kollin's lead chemistry, and I like the general theory of how it may relate to valve sticking . It's just that there are loose ends, which is why it's a theory.
 
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Page two of the previously linked document:

Combustion temperature is reflected in both the Cylinder Head Temperature (CHT) and directionally,
the exhaust valve temperature, which we do not measure directly. (Exhaust valve temperature follows cylinder
head temperature because the valve guide is located in the cylinder head, to which it transfers heat from the valve.)
Valve temperatures do not follow Exhaust Gas Temperature (EGT).

To me, that just says that increased combustion temperature gives increased CHT and valve temperatures, not that CHT is a useful measure of combustion temperature.

Kollin is not as specific as Busch (AOPA, July 2020, page 88, also previously linked):

The best proxy we have in the cockpit for exhaust valve temperature is cylinder head temperature (Note it isn't EGT)

I really would like to know why they say valve temperatures do not follow EGT, when multiple references suggest it does.

I think you are correct valve temperatures follow EGT. I don't think it affects Kollin's assertion that decreased combustion temperature gives decreased valve temperature.

Ed Kollin and Mike Busch seem to be saying slightly different things.

Kollin is saying peak EGT gives highest combustion temperatures which help the scavenging reaction and results in higher valve temperatures which reduce deposits. This sounds correct.

Busch is saying higher CHTs result in higher valve temperatures which reduces deposits. This seems over simplified at best.

I suspect Mike Busch has reinterpreted the Kollin article (or maybe it was edited by AOPA) to avoid direct conflict with LOP operations. However that misses Ed Kollin's key point, that high combustion temperatures at peak EGT reduce deposits.
 
Kollin is saying peak EGT gives highest combustion temperatures which help the scavenging reaction and results in higher valve temperatures which reduce deposits. This sounds correct.

Certainly true in the Beech Talk quote...

Basically, if you run a 65% power or less, run at peak EGT so the scavenger chemistry can function as intended. It is the combustion temperature that is important, determined by manifold pressure and mixture, and CHT is an imperfect approximation of it.

Hopefully Jereme will get a response from Ed. Given he participates in forums, perhaps he will respond directly, which would be terrific.

Busch is saying higher CHTs result in higher valve temperatures which reduces deposits. This seems over simplified at best.

Agree. And it's entirely possible to run 300~350F CHT at peak EGT.
 
Alrighty everyone, here is Ed's response. It also appears we have somewhat of an open book so if you reply with specific questions or drop me a PM I will get back to him with them. I did link the forum in the email but it sounds like he isn't responding directly here.

Hello Jereme,

I propose two different mechanisms for valve sticking hot side and cold side. The hot side involves the formation of lead oxy-bromide condensing on the valve stem and the cool side is due to blow-by fuel forming varnish, capturing lead bromide particles in the guide.

I state it is the lower combustion temperatures from lean mixtures at lower power that is the cause of the lead oxy-bromide formation.

Mike simplified my conclusion and just claimed it was just low CHTs, which is not correct.

I used many sources from 1940 – 1995 for this work that were in library at Exxon Research where I used to work running the engine laboratory in the Advanced Fuels and Lubricants Group for 20 years. The publisher did not have room for this (I think she didn’t believe anyone would be interest in it).

FYI I did reference TRW for the valve temperature data. I don’t know if Mike did.

What specific questions do you have about my article, not Mikes.

I will see what data or references I can offer you as time allows.

Regards,
Ed



Dan, in a previous post you mention EGT being a good proxy for combustion temperature. If that is true then why does the "data we are yet to see" indicate more sticking valves on the LOP side? Even if an engine is run fairly deeply LOP the EGT's are still notably higher than a typical ROP cruise. Of course the mixture during LOP burns slower which accounts for some. Also, I dind't see your post 97 until after the email was already sent. I will try and see if I can get anything out of him pertaining to why valve temps do or don't follow EGT.
 
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Alrighty everyone, here is Ed's response.

And an excellent response it is.

Dan, in a previous post you mention EGT being a good proxy for combustion temperature. If that is true then why does the "data we are yet to see" indicate more sticking valves on the LOP side? Even if an engine is run fairly deeply LOP the EGT's are still notably higher than a typical ROP cruise.

Ask Ed. Might get a better answer if you're specific, as "notably higher" is not a number.

will try and see if I can get anything out of him pertaining to why valve temps do or don't follow EGT.

Go for it. Only question I would add relates to the TRW illustration. Ed responded to you with "FYI I did reference TRW for the valve temperature data." Ask him to confirm those are generic "comparison" temperatures for sodium vs solid valves, not temperatures specific to Lycoming and Continental at some stated power setting, peak EGT for example.
 
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