LOP Price to pay

N427EF said:

I probably got it all backwards but it's hard to ignore prallel trends.
One, everyone flying LOP and two,an onslaught of burned valves showing up at overhaul shops.

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You have just defined 'correlation' with this statement (the link is from a business dictionary but the principle is still the same). One must always be cognizant of the fact that events that correlate do not mean that one causes the other. Too many times one looks at a correlation of events that happen in conjunction with each other and then makes the leap of deduction that one event MUST BE CAUSING the other event. BE VERY CAREFUL in making that kind of assumption. It most definitely will come back to prove you wrong time and again.

Kind of reminds me of certain FAA discussions of late concerning obesity and sleep apnea.

EGT Upper Limit?

I understand Lycoming does not publish an upper limit for EGT. However, there has to be a "normal range".

I have an IO-360. AFS 4500 EGT redline kicks in at 1450 degrees. I usually see cylinders one and two at or below that, but 2 and 4 will cycle below 1450 to 1525 depending on power/rpm/mixture settings.

Should I be concerned?

I'll admit - in racking and stacking my skillset of skills necessary yo build an operate an RV-8A, engine knowledge was pretty far down the list.

There is no limit to EGT, you need to move the "red alarm state" away from a normal number, otherwise your brain will treat all alarms with contempt.
Set it at 1650. Unlikley you will ever see that unless a spark plug or magneto fails.

And that would be an appropriate alert, although it should be a yellow advisory not an alarm.

While I have your attention, set your RED ALARM status for CHT at 400dF. Do not set it anywhere else, especially lower for the above mentioned reason. Do not set it at 500dF or 450dF because one day in the remote chance you have a genuine run away CHT by the time you see it and deal with it damage may well be done.

CHT alarm = 400dF and nothing else. I hope I have not stressed that too hard

Valves

Lycoming valve problems are not necessarily related to mixture/EGT. When Cessna resumed single production the oil pressure pickup point was moved to the front of the engine. This allows approximately 10 pounds more oil pressure while retaining the same approximate reading as before on the gauge. Experts seem to believe that this was done to improve valve oiling and cooling.
EGT readings on normally aspirated Lycoming engines are irrevalent. All you care about is where the instrument reading peaks and then set the mixture rich or lean of that peak a predetermined amount. Many EGT gauges do not even have numbers. Many of the steam gauges can be adjusted to put the peak reading at a predetermined point. Peak reading will vary considerably depending on where the probe is located.
Read the Mike Busch articles on EGT and google the info on the Cessna modifications and you will have an entirely different opinion on EGT.
My experience with Lycomings predates the era when EGT gauges became common on light aircraft. We just leaned until the engine ran rough and richened until it ran smooth. Some of these engines ran past TBO, I don't EVER recall any cylinder problems in that era.
There are some who believe that 50(or two small marks) rich of peak is the most damaging EGT.
Turbocharged airplanes in some cases have limits. The Piper Navajo is a turbocharger limit and in this case there are actual numbers on the instrument.
Years ago a Lycoming tech rep told me that you cannot hurt a normally aspirated Lycoming with mixture when operating below 65 % power. I don't know the current factory opinion on this.

jrs14855 said:

Years ago a Lycoming tech rep told me that you cannot hurt a normally aspirated Lycoming with mixture when operating below 65 % power. I don't know the current factory opinion on this.

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I didn't know this "trivia tidbit". I like to fly long distances at around 8-10,000ft so my engine stays around the 65% or lower mark. Its good to know I am doing the right thing, even if it was unintended.

RV10inOz said:

While I have your attention, set your RED ALARM status for CHT at 400dF. Do not set it anywhere else, especially lower for the above mentioned reason. Do not set it at 500dF or 450dF because one day in the remote chance you have a genuine run away CHT by the time you see it and deal with it damage may well be done.

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Makes sense to me.

So,
now that we all agree that burned valves have nothing to do with LOP operations and we have established that there are no upper limits on EGTs

There is no limit to EGT, you need to move the "red alarm state"

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Someone like to explain where the burned valves come from?
I am not demanding an answer rather hoping that someone would shed some light on a disturbing trend.
I realise it's not a trend for everyone but there can be no harm in finding out the cause for those who do show up with burned valves at the overhaul shop.

I am sure the smart folks from APS will have a ready answer for it.
How about it David?
Simply explain what sort of operating procedure will cause valves to burn up
like the one depicted on the front page over the weekend, keeping the above quote in mind.

I admit it is probably silly to take the account of a single AP seriously and no cause for alarm.

I'll try a spitball. Years back valves were all hand lapped. Couple decades ago I noticed lots of shops and evens OEM's making statements like "valves blue checked to fit". Last few years some shops have made a point to mention they lap valves. Could there be more valve leakage than years past? I've seen quite a few new cylinders that really needed lapping.

N427EF said:

So,
now that we all agree that burned valves have nothing to do with LOP operations and we have established that there are no upper limits on EGTs

Someone like to explain where the burned valves come from?
I am not demanding an answer rather hoping that someone would shed some light on a disturbing trend.
I realise it's not a trend for everyone but there can be no harm in finding out the cause for those who do show up with burned valves at the overhaul shop.

I am sure the smart folks from APS will have a ready answer for it.
How about it David?

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Ernst, it is my comprehension when reading every post to this point on this thread that several individuals have already answered this question. The burned valve came from the valve stem seating improperly for some, as yet, undetermined reason that the owner of the offending valve has yet to come on here and post about. Perhaps he will come on here and do so but in the meantime the general consensus is a bad valve seat causing this condition.

N427EF said:

Simply explain what sort of operating procedure will cause valves to burn up
like the one depicted on the front page over the weekend, keeping the above quote in mind.

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It sounds to me like you are convinced there is some type of operational procedure you can perform as pilot that will prevent this from occurring. I think, other than following the already recommended mixture procedures, there is no super duper procedure that will cure this. Causation is more likely to be an issue with engine manufacture, engine construction or perhaps even metallurgy rather than operational error. In my opinion (keeping in mind it is only worth what you payed for it), you are thinking in terms of trying to validate your A/P's opinion that it is indeed Operator Error that is causing this issue.

If there is any pilot induced engine operation that could potentially be a cause for this type of failure it would be most likely a result of allowing very rich operations that would allow for deposit build up on valve stems or valve guides. Or perhaps utilization of substandard fuel that could allow for some type of fuel contaminant to be introduced into the valve stem area. I think your A/P is jumping to some very large erroneous conclusions by his staunch belief that a pilot's flawed operations are the root cause of such problems.

N427EF said:

So,
now that we all agree that burned valves have nothing to do with LOP operations and we have established that there are no upper limits on EGTs



Someone like to explain where the burned valves come from?
I am not demanding an answer rather hoping that someone would shed some light on a disturbing trend.
I realise it's not a trend for everyone but there can be no harm in finding out the cause for those who do show up with burned valves at the overhaul shop.

I am sure the smart folks from APS will have a ready answer for it.
How about it David?
Simply explain what sort of operating procedure will cause valves to burn up
like the one depicted on the front page over the weekend, keeping the above quote in mind.

I admit it is probably silly to take the account of a single AP seriously and no cause for alarm.

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Ernst.....

Skype me mate, it has been a while. we should catch up again and it is so much easier to do that way. Pity we can't make a webinar but .....at the risk of alarming some people, we do a big session on this at the APS course. The next one is Ada OK in March and for those down under in May.

RVbySDI,

You are right, burned valves have been explained and I understand and have no concerns with an occasional burned valve among other cylinder head issues.

My original post was based on the observation of a lone AP who reported an "alarming" increase in burned valves. It can't be that all Cylinder head shops have become sloppy machinists.

You are also exactly right about my attempt to make surer I can avoid such an occurrence in my engine. Your second paragraph explaines it better that I can.

Well, maybe I will attend an APS course and find more answers.

Thank you all for posting, I'll leave it alone now.

onslaught of burned valves

I keep seeing claims of increasing rates of burned valves viz the changing aircraft population and number of hours of operation.

Does the claimant actually have any data to support these claims? Actual quantifiable data such as, for example, work orders dating back for 10 or 20 years than can be analyzed?

Is the claimant familiar with the term "confirmation bias"?

Valves

Read: Lycomings latest-increasing oil pressure in the new Cessna 172 and 182 by Bill Marvel and Bill Scott.
My take form this is increased oil pressure equals improved valve cooling and lubrication which in turn helps reduce burned valves.

jrs14855 said:

Read: Lycomings latest-increasing oil pressure in the new Cessna 172 and 182 by Bill Marvel and Bill Scott.
My take form this is increased oil pressure equals improved valve cooling and lubrication which in turn helps reduce burned valves.

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Good Reading: - note that it was talking about 320H models but extended slightly. They did not seem to make a sweeping claim to me, but did point out that it was design weakness. Not surprising.

http://egaa.home.mindspring.com/valves.html

“the observation of a lone AP who reported an "alarming" increase in burned valves”
“shed some light on a disturbing trend.”

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I do not believe the observations of a single mechanic rise to the level of "an alarming increase, or a disturbing trend."

In the last 2 days I have asked 3 mechanics( AP IAs) with many decades of experience if they have seen a disturbing or alarming trend of increasing numbers of burnt exhaust valves. After several seconds of perplexed looks their answers were all uh no.

I believe Weasels initial thought on this was dead on when he posted:

Lycoming

The Marvel/Scott article was not talking about H engines. The H engine was replaced by the 0 320D2J on 172's in 1881. When production was resumed in 1996 the engine was changed to the Lycoming IO 360-L2A. Some of these installations are derated to 160 hp.

Kahuna,

Did you get any feedback from your engine builder?

Combustion fun fact:

In case anyone needed an excuse to go get more popcorn, check this out:

The combustion temperature of a mixture of gasoline and air are somewhere in the 4000 to 5000*F, perhaps higher. Of course, this rapidly diminishes through radiative and convective heat transfer, as well as via the large expansion that goes on during the power stroke.

See, the 1500*F egt is quite cool