LOP potential problem

[Tommy]

Today I popped into my mechanic's hangar just to say hi and saw three Cessna's all had at least one cylinder taken out due to low compression and waiting for a replacement! I casually asked what would've been the cause of a bad cylinder, my mechanic said, without hesitation, LOP operation. 

 

What worries me is that he wasn't the first mechanics that said the same thing.

 

So just exactly what sort of damage can LOP do to your engine? The one I heard most of the time was burnt exhaust valve because there is no extra fuel to cool it. Anything else? And how can one prevent them?

 

Now let the WAR begins! 

 

[Marauder]

There are mechanics who steadfastly maintain that LOP operations cause issues, including mine. I don't run LOP primarily because I want to get from Point A to B as fastest as possible.

I'm sure like everything else we will find out over time if running LOP can be associated with premature wear or failure. I'm not sure if there is documented evidence anywhere that running lean of peak over a period of time causes issues.

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[Shadrach]

Why didn't you ask your mechanic to explain how LOP operations destroy cylinders? A credentialed individual that you know has made a declarative statement. Why would you come here to have forum member explain his statement? You should go ask your mechanic or hit the search function here. I'm 99% sure that nothing new will be said about LOP operations in this thread.

[ArtVandelay]

I hope he wasn't changing cylinders just because of a low compression reading?! They are notorious for being inconsistent and not a good indicator of cylinder health, Mike Busch has gone into this in great detail.

[Shadrach]

I once had a self proclaimed 10,000hr CFII sarcastically tell a group of us that he just wasn't "smart enough" to run LOP. I asked him why and he told me all about melted pistons and burnt valves. After he finished, I agreed with his initial assessment.

[Tommy]

If you read my topic title closely, I am hoping to find out what are the theoretical problems that can arise from LOP operation partly because I want to give myself a specific pattern to look out for when I analyse my engine monitor data. Partly because I am certain that burnt exhaust valve aren't the only theoretical risks of running LOP. 

 

So you think you know everything about LOP, Ross? 

 

Perhaps you can shed some light on my original question please? Preferably with reference rather than anecdotal evidence that you just quoted...

 

Thanks! 

[Shadrach]

I've never said that I knew everything about anything. The topic has been covered so many time that there are likely pages and pages of threads to choose from. Then there are john Deakin's engine columns here:

http://www.avweb.com/news/pelican/182544-1.html

 

Specifically the  "Where should I run my engine" series at the bottom.

What I know about LOP is from research and personal experience. I am not credentialed, however your mechanic is! Why didn't you ask him to explain the specifics of why it is detrimental?

To my knowledge there are no theoretical problems with LOP. There are occasional application problems (poor A/F distribution, turbo bootstrapping etc). I can't speak to your mechanics opinion without knowing the "why" behind the opinion.

My comment about the CFI was only meant to illustrate that it's not uncommon for people regardless of their credentials to make statements without really knowing. If the CFI had given some sound reasoning for his opinion, I'd not be using him as an example. However, he clearly knew nothing about combustion science, and was all too clear that, at least on that particular day, he was not interested in learning.

[Tommy]

I am interested in learning that's why I ask! I know LOP has been covered but it is still very much a new way of operating an engine and I am hoping to see if there is anything new pops up!

 

One question I do have is that what happens if you have a spread of 80F in EGTs when operating LOP? (for e.g. two cylinders at 1460 and two at 1380? Peak 1510) 

[PTK]

Today I popped into my mechanic's hangar just to say hi and saw three Cessna's all had at least one cylinder taken out due to low compression and waiting for a replacement! I casually asked what would've been the cause of a bad cylinder, my mechanic said, without hesitation, LOP operation. 

 

What worries me is that he wasn't the first mechanics that said the same thing.

 

So just exactly what sort of damage can LOP do to your engine? The one I heard most of the time was burnt exhaust valve because there is no extra fuel to cool it. Anything else? And how can one prevent them?

 

Now let the WAR begins! 

 

 

Could very well be that cylinders needed to be pulled. But it's way too easy sometimes to jump to that extreme.

 

Questions that come to mind:

 

What engines are these out of?

 

What were the borescope results? How did cylinders and exhaust valves look?

 

What is the oil changing history and condition?

 

Are there engine monitor data and have they been looked at?

 

Was SB 03-3 consulted?  http://www.tcmlink.com/pdf2/SB03-3.pdf

 

Is he saying lop caused burnt exhaust valves?

 

What exactly was his decision to change cylinders based on?

If somebody wants to remove cylinders they better have specific reasons with appropriate documentation to back up their decision.

[Marauder]

Why didn't you ask your mechanic to explain how LOP operations destroy cylinders? A credentialed individual that you know has made a declarative statement. Why would you come here to have forum member explain his statement? You should go ask your mechanic or hit the search function here. I'm 99% sure that nothing new will be said about LOP operations in this thread.

I have. His explanation was that part of what fuel does is to act as a lubricant. Is he right or wrong? Don't know, don't care...

Alls I knows, is that running ROP of peak got me beyond TBO on the first run of this engine and I got another 1,000 trouble free hours on this rebuild -- wish I could say the same for my exhaust or my KX-170B or my ADF or my prop governor or my KT-76 or my boost pump or my

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[chrisk]

Lean of peak should not be a problem.  But, if you are at peak, instead of lean of peak, temperatures and cylinder pressures are going to be higher.  Perhaps the  mechanic meant something along the lines of:  Some pilots are idiots.  They think they are LOP and are really Peak.  This is due to the lack of instrumentation, or lack of monitoring.  Eventually they over heat the engine and the failure rate goes up. 

[Bob - S50]

I'm not an expert but I may be a know-it-all.  With that in mind...

 

1.  I agree.  Ask the mechanic why LOP ruined the cylinder.  I'll bet he can't explain it, that's just what he believed.

 

2.  Here is a link to a John Deakin article on what causes burnt valves (hint, it isn't LOP):  http://www.avweb.com/news/pelican/182155-1.html

 

3.  Here is a link to a Mike Busch webinar about cylinder failure (hint, it isn't LOP):  http://www.eaavideo.org/video.aspx?v=1204537102001

 

From what I've learned, LOP will not cause cylinder or exhaust valve failure unless you do so improperly at high power settings.  That is, power settings above about 75%.  Even then, you can run LOP if you know what you are doing.  In high power situations (takeoff and initial climb), running not rich enough or not lean enough (in between) can cause detonation or even worse, pre-ignition.  But that won't cause early cylinder failure, that will cause engine destruction.  I prefer to reserve LOP for ground and cruise operations.

 

According to what I've read, running ROP can cause burnt valves, and here is a summary of why.  Again, this is what I remember, learn for yourself.

 

Exhaust valves get burnt because they do not seat properly or because they cannot transfer heat from the valve to the head adequately.  Normally, hot exhaust gases flow past the valve only 25% of a 4 stroke cycle.  The other 75% is spent getting rid of most of the built up heat through contact with the head.  If a valve does not seat properly, hot gases will leak past it which not only prevents it from cooling properly, but may actually be adding to the heat at the location of the leak.  Why to valves not seat properly?

 

• Improper manufacturing in which the valve guide is not quite aligned with the seat.
• Warped head from too much heat
• Warped valve from too much heat
• Carbon build up on the valve or seat.  This can only occur when running ROP since there are not unburnt fuel molecules when running LOP.
• Carbon build up in the valve guide.  Again, can only happen ROP.  During the exhaust cycle, carbon gets deposited on the valve stem.  After the exhaust cycle, when the valve retracts to close the port, some of the carbon on the stem gets transferred to the valve guide.  Over time, deposits cause misalignment of the valve and a leak develops (and your plane probably has morning sickness too).
• Exhaust valve manufacturing defect.
• Carbon build up causes insufficient heat transfer from the valve to the head.

As for LOP causing cylinder failure, I cannot think of a reason why LOP could be a problem except as mentioned earlier.  The main reason would be improper management which lets the cylinder head get too hot causing warping.  But 1480 EGT ROP is the same temperature as 1480 LOP.  Its up to you to manage your power/mixture/airspeed to keep CHT's within reasonable limits.

 

On the other hand ROP can cause deposits in the cylinder and on the piston which can provide sources for hotspots if you are trying to destroy your engine by pre-ignition.

 

As for the specific engines you mentioned, if the plane only had a single cylinder EGT/CHT indicator, it is entirely possible the owner was running LOP on the one cylinder they could monitor and really running 50 ROP on others.  They could have had excess CHT's on the cylinders they could not monitor.  In my opinion, it is asking for trouble to try and run LOP unless you can monitor all cylinders.  It was done for years, but with the equipment available today, it seems like cheap insurance to monitor all cylinders.  Spend $3000 now to extend the life of your engine by 500 hours.  That will more than save the $3000.  As the old Fram commercial used to go:  You can pay me now or you can pay me later.

 

Let us know what the mechanic says.

 

Bob

[Shadrach]

I am interested in learning that's why I ask! I know LOP has been covered but it is still very much a new way of operating an engine and I am hoping to see if there is anything new pops up!

 

One question I do have is that what happens if you have a spread of 80F in EGTs when operating LOP? (for e.g. two cylinders at 1460 and two at 1380? Peak 1510) 

 

Those numbers are no more important LOP than they are ROP.  This is to say that the actual digits are not important. What is important is how far lean or rich of peak they are.  Think of them as 4 individual engines running in unison. you want them all to be as close to whatever setting you're using as possible. Let's say you have set your engine at peak EGT and you have the world's most perfect fuel/air distribution. You find that every cylinder peaks at 10.1gph at the following numbers:

 

#1 1375

#2 1455

#3 1510

#4 1420

 

The spread from highest to lowest EGT is 135 degrees.  However, every one of your 4 little engines is running at the setting you've chosen which is Peak EGT.  The takeway is that you need to know if all of your little engine are working closely together. They may peak at totally different numbers, but the will all be putting out about the same amount of power. This equals a smooth running engine. The raw numbers don't matter much (except in isolated instances but those are for more advanced discussion).  Please do study the Deakin columns, he is a damn fine writer that has great way of simplifying complex concepts.  Each column builds on the last in way that really facilitates a quick understanding by the reader.  

[Shadrach]

Bob has put up some solid information. I will say that an engine monitor is a smart investment no matter how you run your engine.  After using mine for 100s of hours, I am pretty sure I could easily set power LOP  in most 4 Cyl lycs with no analyzer purely from airspeed changes and engine smoothness.  I have no confidence that I could set the engine ROP.

[Marauder]

Am I the only one who feels this is the movie "Groundhog Day"? Or perhaps just a little Déjà vu?

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[MB65E]

I think the reason things get hot running LOP is that people spend too much time trying to find LOP and end up at Peak for longer than they should. I recently learned that Proper LOP is obtained by watching the LAST cylinder to peak and not the first. Someone on MS mentioned that. Our common tendency to lean to the first cylinder would mean that all the others could be much closer to peak.

As a technician, I'm interested in the science of LOP due to the fact I don't understand some of it. I don't think many techs really know either. I don't know a single old timer tech that will tell me he thinks it's OK. They all say, well "good luck with your exhaust valves."

I don't think its harmful if it's done properly, but it's hard to do. On my fuel servo peak and 50 LOP is probably around 1 turn on the mixture setting. (And about a 8kts-10kts off the ICA. A power change, air density, climb or decent will change the EGT's.

When I operate my engine I try to stay below 380 and 1450. Hopefully keeping the heat out of it will make it last.

-Matt

[aaronk25]

Ok I'll throw a twist on this topic. Given we are running a super stable 100ll fuel, on our planes detonation is zero factor. Even at a hot temp of 450cht in a properly functioning cylinder detonation is zero issue.

So if it isn't detonation/preignition that is creating havoc what is left? Pressure and temperature, right?

Sure running 30lop will create a higher egt than 100rop, but the exhaust valve is cooled by the seat everytime it closes. Think about how hot it is on the face of the valve during the combustion process. 30,50 or 150 degrees difference in air temp flowing past the exhaust valve isn't going to make a difference vs the temp it sees when the charge is lit off.

So that leaves CHTs and pressure. I've ran 2000 hours on my cylinders with most of the time in the "scary red box at peak or 15rop 24"-27" 2400-2700rpm with the limiting factor being never ever exceed 380 CHTs. And cruise at no more than 360chts, mostly 330-350chts.,,.guess what? At 2000 hour overhaul the cylinder barrels still met new specs! Not service limits new specs!

My guess is those cessnas you saw were torn apart due to stuck rings from running excessively rich (low compression), got the Cylinder hot and "potato chipped" the rings (low compression) or the sat for a few months without use got a slight rust fill on the cylinder barrels which when scrapped off left small pits and in turn wore the rings out (low compression) or continental did a crappy job machining the seat to exhaust valve interface and resulted in a burnt valve.

[M20S Driver]

Today I popped into my mechanic's hangar just to say hi and saw three Cessna's all had at least one cylinder taken out due to low compression and waiting for a replacement! I casually asked what would've been the cause of a bad cylinder, my mechanic said, without hesitation, LOP operation. 

 

What worries me is that he wasn't the first mechanics that said the same thing.

 

So just exactly what sort of damage can LOP do to your engine? The one I heard most of the time was burnt exhaust valve because there is no extra fuel to cool it. Anything else? And how can one prevent them?

 

Now let the WAR begins! 

 

 

My mechanic encourages me to run LOP since he says that he could use the additional business

LOP in red zone is fine if you watch out for any changes and watch the EGT and there is no roughness of the engine.  At 65% or less, my mechanic is fine with LOP, Peak, or ROP to go faster.  I do mostly flights less than one hour and go 75+ deg ROP.

[kerry]

Were the Cessna carburated.  I was talk with a mechanic last weekend pulling a cylinder off a 182 because of running LOP.  He mentioned he doesn't see problems of running LOP on fuel injected engines.

[cujet]

I'm not a big fan of LOP operations on underpowered aircraft. The speed loss and additional mechanical expense don't make much sense to me. I could, for example, add nearly an hour to my typical 700 mile trip by using reduced power/LOP to save fuel. My time and engine/prop/airframe expense do count against the fuel savings. It's not my goal to build hours. My time is precious, I'd like to arrive prior to lunch! 

 

As a professional A+P mechanic, I cannot provide any mechanical reason for avoiding proper LOP operations with healthy equipment. It's simply that my 200HP engine, operated at 100-125HP, is not enough to make me happy. 

[DaV8or]

Why to valves not seat properly?

 

• Improper manufacturing in which the valve guide is not quite aligned with the seat.
• Warped head from too much heat
• Warped valve from too much heat
• Carbon build up on the valve or seat.  This can only occur when running ROP since there are not unburnt fuel molecules when running LOP.
• Carbon build up in the valve guide.  Again, can only happen ROP.  During the exhaust cycle, carbon gets deposited on the valve stem.  After the exhaust cycle, when the valve retracts to close the port, some of the carbon on the stem gets transferred to the valve guide.  Over time, deposits cause misalignment of the valve and a leak develops (and your plane probably has morning sickness too).
• Exhaust valve manufacturing defect.
• Carbon build up causes insufficient heat transfer from the valve to the head.

 

Well, there is another cause for valves not seating properly and that can be lead deposits. One of the benefits of LOP ops is the cylinders run colder. However, if they run too cold, the additives in AVGAS that is intended to scavenge the lead in the fuel doesn't get hot enough to do a complete job and you get lead deposits. For some of us where I guess the baffling is to good in our planes and the cylinders run cold anyhow, this might be a problem.

 

I run LOP all the time and this is a possibly a problem for me. Inspection of my pistons through the spark plug hole shows lots of lead build up. In addition, I have lead fouling problems with my lower plugs. I have also experienced a sticking valve in the past. What caused my sticking valve? Nobody knows, but fortunately it was remedied by "staking the valve" in other words, beating on it with a hammer.

 

I have toyed with the idea of running some TCP in my fuel to see if I can reduce, or eliminate the lead deposits in my cylinders. I have read that some of the Cirrus drivers have to do this as running LOP in those planes is actually mandated in their POH and some have experienced lead deposit problems. Did lead build up cause my valve to stick? Don't know. Could a chunk of lead get stuck between the valve and the valve seat and cause the valve to eventually burn? Don't know, but sounds plausible, but it would seem that the lead would either melt, or pound out before there was any real damage done.

 

 

As for LOP causing cylinder failure, I cannot think of a reason why LOP could be a problem except as mentioned earlier.

 

Well, I will repeat what Mark Rouch of Top Gun told me about LOP ops. [This is his theory, not mine. I am only the messanger.] He says that Lycoming cylinders and pistons are machined and designed to operate at a particular temperature and if they don't get hot enough, they don't expand enough and this causes blow by that eventually leads to glazed cylinders that will result in lower compression high oil consumption and need honing. I personally don't buy this story, but I'll throw it out there as one man's opinion on how LOP can hurt cylinders.

 

Lastly, I think it is possible (this is my theory now) that it is possible that LOP ops might cause exhaust systems to prematurely fail. Corrosion is one of the leading causes of exhaust system failures and when you run LOP, there is an excess of oxygen. Oxygen is what causes corrosion, so hot oxygen rich air would suggest a possible higher rate of corrosion. I have no proof of evidence of this and neither does anyone else. It's just a theory that no one has ever run any lab tests on and likely never will. 

 

Anecdotal evidence from owners shows that some have exhaust system failures and blame LOP and others do not and go to TBO. Is there a higher failure rate of exhaust systems LOP vs. ROP? Nobody knows because these stats are not easy to document and are not kept.

 

Anyhow, since I am rarely in a big hurry to get anywhere and I need to save money where ever I can to be able to afford this ridiculous hobby, I run LOP pretty much all the time.

[carusoam]

There are Mooney pilots that like to fly fast.

There are Mooney pilots that prefer to fly efficiently, to some extent.

There is a right way to run LOP.

There is a wrong way to run LOP.

There are people that simply don't know they are improperly running LOP.

There is an organization (Gami) that teaches the right way based on science and experience.

They (Gami) have a guy that teaches how to operate your engine LOP properly, in Australia. He shows up on MS often, but I have not seen him lately...

Know your Gami spread. You will need FF and EGT (for all cylinders).

Know that some engines run LOP better than others because of tight Gamis spread at cruise conditions.

Try to be nice to the people on the Internet. After all, they may have information that you may want to know. Keep in mind, MS is not an infinite number of faceless people here...

Best regards,

-a-

[Shadrach]

Am I the only one who feels this is the movie "Groundhog Day"? Or perhaps just a little Déjà vu?

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They say we're young and we don't know

We won't find out until we grow

Well I don't know if all that's true

'Cause you got me, and baby I got you

 

 

I told myself I would not get drawn in...  There are multiple threads, articles and columns on the subject and yet it always boils down to these types of threads.  When I started learning about this stuff 12 years ago, it was not mainstream nor was there a huge amount of info on the subject.  Where are we now?

 

• Continental and Lycoming both say it's fine (though Lycoming stands by its notion that most of us are too stupid and or lack the instrumentation to do it...or both).

 

• The POH for the SR22T and the M20TN have published LOP settings.

 

• The early Malibu POH recommended LOP power settings but the smart pilots "babied" them on the rich side just to be safe and contributed to an abyssal record for cylinder replacement. 

 

• TCM is making "tuned injectors" now (still can't compete with GAMI) as opposed to the "untuned injectors" its engines must come with stock.  

 

• Engine monitors are mainstream and any pilot with even a basic set up can plainly see what occurs as an engine is leaned past ~80 ROP through peak and beyond.  (speed, FF and CHT all decline but FF and CHT do so to a much larger degree)

 

• Anyone can see many of the published graphs both by TCM, Textron Lycoming, P&W, Curtiss-Wright or Gami to see what happens to Internal Cylinder Pressure (ICP), Fuel Flow, Brake Specific Fuel Consumption (BSFC), Horsepower and CHTs as one leans from full rich to fuel starvation.

 

And yet...we still have credentialed professionals saying that LOP operations will burn valves and can destroy cylinders.  That is piss poor.  I don't care what anyone does. I am not an evangelist. I use a broad range of power settings depending on my goals. However, I find it really sad that pilots are still having experiences like Tommy's.  90% of the A&Ps that say this stuff do not hold a PPL and have never "flown an engine" (FYI, I do make up 95% of my statistics on the spot). 

[Shadrach]

I have. His explanation was that part of what fuel does is to act as a lubricant. Is he right or wrong? Don't know, don't care...

Alls I knows, is that running ROP of peak got me beyond TBO on the first run of this engine and I got another 1,000 trouble free hours on this rebuild -- wish I could say the same for my exhaust or my KX-170B or my ADF or my prop governor or my KT-76 or my boost pump or my

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How does he feel about peak?  Is there enough fuel at peak to "lubricate" whatever it is he believes is in need of said excess fuel?

[Shadrach]

My mechanic encourages me to run LOP since he says that he could use the additional business

LOP in red zone is fine if you watch out for any changes and watch the EGT and there is no roughness of the engine.  At 65% or less, my mechanic is fine with LOP, Peak, or ROP to go faster.  I do mostly flights less than one hour and go 75+ deg ROP.

 

Are you for real or just just stirring the pot?  You say "My mechanic encourages me to run LOP since he says that he could use the additional business" and then proceed to tell us that you run your engine at the hottest, highest pressure mixture setting (75ROP) for trips under an hour.  Most any NA continental or Lyc engines will tolerate it just fine, but it is the most abusive setting you can set.