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LOP Price to pay

N

N427EF

Well Known Member
The picture on the front page is a reminder of the price you pay for LOP operations.
Comments made by longtime engine overhaul expert clearly show a trend in engines run LOP, so much so that the experienced AP can tell how the engine was run just by looking at burned exhaust valves.
The LOP subject has been beat to death and I too run LOP but I am always bothered by the relatively high EGTs when operating LOP.
I have been assured not to pay attention to high EGTs as they "don't really matter".
I like the low fuel burn and clean engine but I am beginning to weigh the risk of running my engine in this fashion knowing full well that my exhaust valves will suffer premature wear and possibly failure if I don't do a top overhaul or catch a developing problem early on.
Maybe DR can tell us how many hours you have on that Cylinder and if you run LOP, I bet my saved gas money you do.
 
th_popcorncat.gif
 
Weasel said:
th_popcorncat.gif
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:D

A snippet from the savvy aviator #59 by Mike Busch:

"If I operate at peak EGT or LOP, don't I risk burning my exhaust valves?

This question belies a common misconception that burned exhaust valves are caused by high EGTs. This is not correct. Burned exhaust valves are caused by valve-guide wear and valve-stem wear, and the best way to keep that from happening is (1) to keep CHTs down, and (2) to run a lean mixture to minimize build-up of combustion byproducts on the valve stem. The leaner you operate (while keeping CHTs at prudent levels), the happier your exhaust valves will be."
 
Photo does look like the valve is over to the left side a bit------just what a worn guide could allow.

VAF_110%20Jan.%2009%2015.13.jpg


Or, then again it could be camera angle??
 
Mike, the arrows show where the valve got hotter and burned off the carbon deposits. These are the areas where it lost contact with the seat and now leaks. I make no other conclusions.
Burned%2520Valve.jpg
 
BillL said:
Mike, the arrows show where the valve got hotter and burned off the carbon deposits. These are the areas where it lost contact with the seat and now leaks.
Click to expand...

Exactly, ties in with what I was saying above, but I was actually addressing the quote from Mike Busch below.

DougJ said:
Burned exhaust valves are caused by valve-guide wear and valve-stem wear
Click to expand...

Looking at the photo, it appears that the entire valve is shifted to the left, and that the right side is away from the seat---------thus allowing gas leakage/flow and the resultant burning of the valve. The only way I can think of for the valve to shift sidewise is if the stem or guide or both is/are worn.
 
The irony of the argument from A&P's is that many valves in the same failure mode have been from ROP run engines. Explain that.

The issue is valve face to seat fit.

The issue of valve temp is directly related to CHT, not EGT and that has been known since Adam was a young boy working on the engines in Noah's ark.

It would be interesting to know more about that cylinder. So far we know very little.

I wonder if DR saw this coming on his engine monitor, he should have.
 
N256h has 1,300+ hours so far and most of that running LOP. Even if the cylinders were shot already, we probably have more than saved enough money in fuel to pay for 1/3rd or a set of cylinders. Our compressions are still in the 70's.
 
Seats are ground to be concentric with the guides. Sometimes the ream for an o.s. guide goes a little crooky and the seat gets ground off center. Usually guide slop happens ninety degrees to what we're seeing (if its not photo angle).
 
Mike S said:
Looking at the photo, it appears that the entire valve is shifted to the left, and that the right side is away from the seat---------thus allowing gas leakage/flow and the resultant burning of the valve. The only way I can think of for the valve to shift sidewise is if the stem or guide or both is/are worn.
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Yeah, I understand, but photos can be so misleading with shadow etc and the only thing for sure seemed to be the burned spots. There are a couple of other things that affect too many conclusions.

First, valve guides usually wear on an axis perpendicular to the rocker arm pivot axis. This appears to be a parallel valve, aren't the pins on the head parallel to the crankshaft? (or close to it?)

2nd, exhaust valves rotate in operation (or should or they burn), I don't know the design detail of this engine and whether it has positive rotators or depends on the rocker and valve stem grind and geometry for rotation.

Also, burning of a valve can be due to a tight valve guide as well as a worn beyond spec one. Just too many unknowns here to draw conclusions. Maybe the owner (not DR) will come back and tell us his findings from parts dimensional inspection.
 
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The problem is guide wear, NOT LOP.

Once the guides wear, the valves do not rotate and then there is a tendency for hot spots to develop where the valves do not contact the seat. This is clearly evidenced in the photo by the stains on the cylinder and seat.
 
The problem in the picture wasn't caused by LOP operations but instead by lack of proper priming. A coat or two of zinc chromate would have prevented this from happening. ;)
 
If Bob's right and it quit rotating your going to see a stripe on the valve tip from the rocker arm.
 
I knew this was not going to be a one answer thread and my reason for posting was rooted in a comment made by an AP who claimed to notice the ever increasing number of burnt exhaust valves on engines barely half way to TBO noting an especially sharp increase in the last 10 years or so.

As always both entertaining and educational.
The problem in the picture wasn't caused by LOP operations but instead by lack of proper priming. A coat or two of zinc chromate would have prevented this from happening.
Click to expand...

This question belies a common misconception that burned exhaust valves are caused by high EGTs. This is not correct. Burned exhaust valves are caused by valve-guide wear and valve-stem wear, and the best way to keep that from happening is (1) to keep CHTs down, and (2) to run a lean mixture to minimize build-up of combustion byproducts on the valve stem. The leaner you operate (while keeping CHTs at prudent levels), the happier your exhaust valves will be."
Quote
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I am not expert enough to question Mike Bush but based on the assertions by the aforementioned AP, can I assume that all of a sudden airplanes are running
with overly rich mixtures gunking up their valve stems and burning exhaust valves as a result? Have engine compartments become so tightly cowled that everyone is running excessively high CHTs and toasting their exhaust valves in the process and thereby beginning the accumulation of lead deposits and or erosion on the valve guides and stems?
Is it possible that the excessively high EGTs (about 1350F in my engine) begin to erode the valve/seat geometry allowing combustion gases to escape into the valve guide area at maximum temperature before the time of the exhaust stroke?

What I do know is that in the last 10 years or more just about everyone has climbed on the LOP bandwagon including me.
If my argument is invalid, tell me why overhaul shops find so many burnt exhaust valves.
 
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N427EF said:
What I do know is that in the last 10 years or more just about everyone has climbed on the LOP bandwagon including me.
If my argument is invalid, tell me why overhaul shops find so many burnt exhaust valves.
Click to expand...

I would guess that 'just about everyone' are not equipped to operate LOP. Unless you have fuel injection and have balanced the injectors, then attempting to run LOP probably leaves one or more cylinders a little rich of peak, exactly where you do not want them. It's easy to forget how many aircraft in the certified world are still running without all-cylinder engine monitors. My guess is the price of avgas has caused many pilots to attempt to run leaner than before, but not really getting all cylinders LOP.
 
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Seems like the price of rice in China amounted to a hill of beans and my wife bought a new pair of shoes! Dang I'm out more gas money again!
 
60av8tor said:
David, please expound on this - erratic EGT on that cylinder..? Thanks in advance; always enjoy your insight.
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Trend monitoring. In the APS class we have some great traces (shown in the online course too) with early detection and then progression over a long period of time. You either need to be very familiar with the EMS or graph the downloads, then pick what is noise and natural variation from tell-tale spikes.

Very rare is a valve failure instantaneous (i.e.breaking the head off the stem) which I have seen, in a C340. The pilot found full power and full rich the only option for the other engine, and boy did it work hard.

The typical failure as depicted is usually seen over 20-50 hours and trend monitoring will pick it up.

Leak down checks were once all we had. Today with an engine monitor and borescope checking you can get a much better measure of valve health.

A leak down test showing 30/80 can actually be a non event provided you monitor the EMS and borescope it. We have record of one that was known not to be a leaking valve yet in a static leak test in the shop it was 20-30 over 80. That cylinder had something like 1500+ hours on it and was run another 300+ at 90% power all LOP......an I mean ALL.

If my guess was good, and it might not be but that picture is probably a valve that started to deteriorate about 20ish hours ago. Very hard to tell as they are all their own little lab experiments.
 
N427EF said:
I knew this was not going to be a one answer thread and my reason for posting was rooted in a comment made by an AP who claimed to notice the ever increasing number of burnt exhaust valves on engines barely half way to TBO noting an especially sharp increase in the last 10 years or so.

As always both entertaining and educational.




I am not expert enough to question Mike Bush but based on the assertions by the aforementioned AP, can I assume that all of a sudden airplanes are running
with overly rich mixtures gunking up their valve stems and burning exhaust valves as a result? Have engine compartments become so tightly cowled that everyone is running excessively high CHTs and toasting their exhaust valves in the process and thereby beginning the accumulation of lead deposits and or erosion on the valve guides and stems?
Is it possible that the excessively high EGTs (about 1350F in my engine) begin to erode the valve/seat geometry allowing combustion gases to escape into the valve guide area at maximum temperature before the time of the exhaust stroke?

What I do know is that in the last 10 years or more just about everyone has climbed on the LOP bandwagon including me.
If my argument is invalid, tell me why overhaul shops find so many burnt exhaust valves.
Click to expand...

The valve was leaking, your conclusion re the cause is speculation based on "so many engine shops" etc.
Mike Bush is an competent source of information on this subject,his aircraft has been flown over 4000 hours LOP. That is reliable data, engine shop talk is not.
 
N427EF said:
I knew this was not going to be a one answer thread and my reason for posting was rooted in a comment made by an AP who claimed to notice the ever increasing number of burnt exhaust valves on engines barely half way to TBO noting an especially sharp increase in the last 10 years or so.
Click to expand...

I think you have to consider that fewer hours are being flown, so engines are sitting longer between use. We all know that airplanes engines do not like to sit. I would rather have an engine running LOP, than one that runs only once a month. ... And that's because it means I am flying more:)
 
BobTurner said:
I would guess that 'just about everyone' are not equipped to operate LOP. Unless you have fuel injection and have balanced the injectors, then attempting to run LOP probably leaves one or more cylinders a little rich of peak, exactly where you do not want them. It's easy to forget how many aircraft in the certified world are still running without all-cylinder engine monitors. My guess is the price of avgas has caused many pilots to attempt to run leaner than before, but not really getting all cylinders LOP.
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Precisely correct. It's not enough just run LOP - you have be equipped properly for it, and then know enough about your equipment to do it correctly. Joe Blow in his carbed 172 with only a single EGT sensor running LOP because the guys at the airport say it's a good idea - he's the one that is going to burn valves and trash cylinders, and he won't have a clue why. Then he'll join the masses preaching against LOP because he had a bad experience with it.

If you have balanced injectors, and full engine monitoring, there is no better way to treat your engine. If you don't have those things, then you don't know what exactly you are doing to your engine. It might be good, it might be horrible - but you don't have a clue and in the end it's likely to bite you.
 
If Lycoming endorses running at peak EGT (factory endorsed = "good"), then how can running cooler (LOP) be "bad"?
 
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What I do know is that in the last 10 years or more just about everyone has climbed on the LOP bandwagon including me.
If my argument is invalid, tell me why overhaul shops find so many burnt exhaust valves.
Click to expand...

What never seems to get mentioned in these ROP/LOP conversations is why do so many engines make it to and past TBO without burnt valves, worn cams etc. whether run LOP or ROP.

I would submit that there are a hundreds if not thousands times as many engines without problems as there are engines with burnt valves not matter how they are run relative to mixture.

The reason so many mechanics talk about broken stuff is that nobody brings them a normally operating engine without problems.

Methinks the key is to run the engine correctly and frequently.

So far the only thing missing from this conversation is MMO.

The answer to dilemma is simple. If you think LOP damages your engine just don't do it. Run ROP and be happy.

Now if I can just keep low sulfur diesel from destroying my Superduty Powerstroke by adding ATF to every tank of fuel. Several mechanics have told me this is the problem and the cure.
 
Toobuilder said:
If Lycoming endorses running at peak EGT (factory endorsed = "good"), then how can running cooler (LOP) be "bad"?
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Not saying there is a problem, but . . .

There is more to the discussion that just temperatures. Oxygen content of the exhaust goes up with leaning. Cars are limited to 3% due to keep the catalytic converters functioning properly. We can run higher (oxygen and much cooler) if the lean combustion stability remains good. IF and IF there were an exhaust valve material that was sensitive to oxidation at those temps then it could be worse.

I don't know what exhaust head materials are being used, but Continental always recommended the leaner the better, as long as the engine remained running smooth.

Large natural gas engines greatly extended their life by going very lean and getting near diesel exhaust temps. Valve materials last much much longer with cooler operation.

Just for the record. I plan on running LOP, as much as I can get it.
 
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.

Of course with no cats on aircraft, I'd like to hear if there is any composition of the exhaust gasses that is harmful to exhaust valves. If it is something other than simply a matter of temperature and contaminants, I'd like to know. Both of which are lower at LOP than the peak setting endorsed by Lycoming.
 
My pea brain has accumulated some facts over the years and here's what I believe to be true concerning LOP:

1) Lycoming does not list an upper limit for EGT on non-turbo engines (turbo is 1600, but that is limited to keep the turbo alive)

2) Lycoming allows running continuously (in cruise) at "peak" EGT (in other words, as hot as your engine will make the EGT go)

3) lead, carbon, trash in the fuel and poor machining will prevent the exhaust valve from seating fully and limit the transfer of thermal load to the head, causing local overheating of the valve and failure.

4) LOP EGT is by definition cooler than allowed by the factory, results in less fuel (and by default, less lead, carbon and trash in the exhaust), and because of the lower energy of combustion, lower CHT.

If the above 4 factors are true, what additional factors make LOP ops "bad" or "damaging"? I'm not talking about poor engine management skills, I'm talking specifically "LOP causes damage because of..."
 
Toobuilder said:
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.
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Probably more so to keep the pistons alive. Usually over rich mixtures cause higher Cat temps as the fuel lights off inside. There is a tricky balancing act between piston and Cat life with regards to WOT AFRs.
 
What else has changed?

My sincerest apologies to Mr. Freitag. While trying to post a reply, watch NFL TV and type on an iPad, I somehow deleted most of his post. Would Mr. Freitag please re-post as best as he can remember? Again, my apologies to Mr. Freitag, Sincerely and feeling like a dunce, Don Hull
 
Toobuilder said:
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.

Of course with no cats on aircraft, I'd like to hear if there is any composition of the exhaust gasses that is harmful to exhaust valves. If it is something other than simply a matter of temperature and contaminants, I'd like to know. Both of which are lower at LOP than the peak setting endorsed by Lycoming.
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Sorry not to be crystal clear - it is OXYGEN OXYGEN OXYGEN is the difference as the hot mixture goes LOP. The fuel burn goes from a carburizing flame to oxidizing flame.

Full load enrichment on the Vett is for power. More fuel across the catalyst will not BURN because there is NO OXYGEN. Many cars have this. It is not to "protect" the catalyst. Lets not get off track.
 
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So, does the gaseous makeup of the exhaust contribute to valve distress, or is it simply temperature (and/or the impurities which prevent the physically prevent the valve from transferring its heat load to the head/fins/air)?
 
Misssing information

What engine is this valve from?

What engine monitoring device do you use? Does it have a LOP leaning mode?

What power setting do you normally run in cruise?

What was your last GAMI spread and when did you run it?

This information may help the discussion.
 
Don Hull,
No problem and no appologies necessary.

The answer to dilemma is simple. If you think LOP damages your engine just don't do it. Run ROP and be happy.
Click to expand...

That would be simple but not an answer.

I certainly agree that flying frequently is both good for the engine as well as the pilot. I have no plans to abandon my LOP flying habits, in fact, since my last post I went out and burned 25 gallons of gas and 4 of us enjoyed a beautiful flight and an ok hamburger. LOP all the way CHT all less than 300F, granted the OAT was 50ish.

What bothers me is when an AP who has overhauled engines for 40 years tells me that burned valves show up in his shop with alarming frequency and those observations are fact not shop talk.

2) Lycoming allows running continuously (in cruise) at "peak" EGT (in other words, as hot as your engine will make the EGT go)

3) lead, carbon, trash in the fuel and poor machining will prevent the exhaust valve from seating fully and limit the transfer of thermal load to the head, causing local overheating of the valve and failure.
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I understand the heat exchange dynamics playing out in the valve/stem, valve guide and cylinder head assembly.

If running the engine almost anywhere is approved by Lycoming then what causes all those burned valves?

So, does the gaseous makeup of the exhaust contribute to valve distress, or is it simply temperature (and/or the impurities which prevent the physically prevent the valve from transferring its heat load to the head/fins/air)?
Click to expand...

The last quote is touching on my suspicions specifically concerning the chemical make up of exhaust gases resulting from an extremely lean mixture,
possibly contributing to valve/seat erosion before the onset of any valve stem/valve guide contamination. Simply put, I think the valve/seat gets ruined a little before the onset of lead and other byproduct deposits begin to deteriorate the valve stem/valve guide interface.
Once the heat exchange mechanism is ruined a quick deterioration of the valve face will follow.

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.
 
BillL said:
...Full load enrichment on the Vett is for power. More fuel across the catalyst will not BURN because there is NO OXYGEN. Many cars have this. It is not to "protect" the catalyst. Lets not get off track.
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WARNING! Going off track for a second

Bill and Ross-

Here's what a well known GM tuner says about COTP:

...There are two safety protocols that GM has to save the cats. One is the COTP or cat over temp protection. When the exhaust temp reaches 1616F the first of three tables kicks in to add fuel and cool the exhaust temp. When the O2s reach a second threshold, you get another load of fuel, and finally as much as 20.5% more fuel in the third tier....


Since you guys called me out on that one, I figured I'd cite a supporting source. You can Google it if you'd like to know more.

...back to airplane stuff!
 
Toobuilder said:
WARNING! Going off track for a second

Bill and Ross-

Here's what a well known GM tuner says about COTP:

...There are two safety protocols that GM has to save the cats. One is the COTP or cat over temp protection. When the exhaust temp reaches 1616F the first of three tables kicks in to add fuel and cool the exhaust temp. When the O2s reach a second threshold, you get another load of fuel, and finally as much as 20.5% more fuel in the third tier....


Since you guys called me out on that one, I figured I'd cite a supporting source. You can Google it if you'd like to know more.

...back to airplane stuff!
Click to expand...

Thanks for the update, sorry, my information is obviously lacking in all the details of current controls systems. I spent some years developing catalysts, but for diesels. I learned the auto techniques from my GM contacts in Detroit, and they probably did not use these algorithms back before OBDII. My main point was that automotive does not go high in oxygen content, A/F perturbation typically goes from 0-3% O2 (or so) and back due to the functioning of the catalyst for NOx CO and HC reduction. None of which is relevant to our LOP discussion.

OK, back to airplane stuff !
 
N427EF said:
What bothers me is when an AP who has overhauled engines for 40 years tells me that burned valves show up in his shop with alarming frequency and those observations are fact not shop talk.
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BUt you counter that single A&P with 40 years of experience with Mike Busch - also an A&P - that says he's wrong. Observation by itself proves nothing - it just raises questions that need to be explained.

I've been running LOP with my carbureted engine on my -8 for 1700 hours now. We swapped jugs a couple of hundred hours ago due to a problem with defective rings, and the valves were pristine. Does that PROVE anything? Not really - except that those who say you can't run LOP with a carb need to re-think their statements.

I have been playing with flying machines for over forty years, and I can tell you that among pilots and owners I hear far fewer stories of engine problems today then thirty or twenty years ago. Again - observation of a small sample size (well, I watch a pretty broad spectrum of GA) that needs to be examined for truth.
 
Ironflight said:
BUt you counter that single A&P with 40 years of experience with Mike Busch - also an A&P - that says he's wrong. Observation by itself proves nothing - it just raises questions that need to be explained.

I've been running LOP with my carbureted engine on my -8 for 1700 hours now. We swapped jugs a couple of hundred hours ago due to a problem with defective rings, and the valves were pristine. Does that PROVE anything? Not really - except that those who say you can't run LOP with a carb need to re-think their statements.

I have been playing with flying machines for over forty years, and I can tell you that among pilots and owners I hear far fewer stories of engine problems today then thirty or twenty years ago. Again - observation of a small sample size (well, I watch a pretty broad spectrum of GA) that needs to be examined for truth.
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Which follows the route of my question. On my Rv7a we are going with a 0-320 . and someone on page 3 of this thread said those with carbs don't need to try LOP, and i understand the theory, but then the same person(sorry forgot the name) says that Rich of peak is not were you want to be. So if you can't run LOP "safely" with a carbed engine and you don't want to be ROP, then were to you run it ????? full rich, Im not agreeing or disagreeing, I am realitivly new to flying (250hrs in cessnas and 150 in my Decathlon),, so Im just trying to get educated. We're about to finish our RV7A with 0-320 and I don't know whether we need a mixture knob or not after reading this thread lolol..
 
Ironflight said:
BUt you counter that single A&P with 40 years of experience with Mike Busch - also an A&P - that says he's wrong. Observation by itself proves nothing - it just raises questions that need to be explained.

I've been running LOP with my carbureted engine on my -8 for 1700 hours now. We swapped jugs a couple of hundred hours ago due to a problem with defective rings, and the valves were pristine. Does that PROVE anything? Not really - except that those who say you can't run LOP with a carb need to re-think their statements.

I have been playing with flying machines for over forty years, and I can tell you that among pilots and owners I hear far fewer stories of engine problems today then thirty or twenty years ago. Again - observation of a small sample size (well, I watch a pretty broad spectrum of GA) that needs to be examined for truth.
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PD is on the money. :)

There is too much BS being spread in this thread (not a lot compared to years ago) but the Old Wives Tales seem to persist even if in reduced numbers.


jongurley said:
Which follows the route of my question. On my Rv7a we are going with a 0-320 . and someone on page 3 of this thread said those with carbs don't need to try LOP, and i understand the theory, but then the same person(sorry forgot the name) says that Rich of peak is not were you want to be. So if you can't run LOP "safely" with a carbed engine and you don't want to be ROP, then were to you run it ????? full rich, Im not agreeing or disagreeing, I am realitivly new to flying (250hrs in cessnas and 150 in my Decathlon),, so Im just trying to get educated. We're about to finish our RV7A with 0-320 and I don't know whether we need a mixture knob or not after reading this thread lolol..
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Jon,

Take a look at the interactive red box graphic we have on the APS website. If you want to educate yourself this is about the best if not only one stop source of education.

By the way a good O-320 runs LOP no problem at all.

I have seen some comments about you can't run LOP with Carby's you can only do it with an engine monitor blah blah....... all of which is complete nonsense. Some things are better however with the above mentioned. In fact we believe the ROP pilot needs an EMS more than a LOP pilot does, and some have trouble getting their mind around that.

Hope that helps.
 
RV10inOz said:
I have seen some comments about you can't run LOP with Carby's you can only do it with an engine monitor blah blah....... all of which is complete nonsense.
Click to expand...

Pull it back until it runs rough and push it in a bit? :)

That eons old Lycoming mantra seems to echo the Big Mixture Pull.
 
rzbill said:
Pull it back until it runs rough and push it in a bit? :)

That eons old Lycoming mantra seems to echo the Big Mixture Pull.
Click to expand...

Even with the "fancy" EMS in my airplane, I still use the "pull it back until it runs rough and push it in a bit" method for engine leaning. Has been working for me for over 30yrs and the engine just loves it.

The "fancy" EMS lets me know if something is not where it should be and gives me good numbers to compare.

:cool:
 
RV10inOz said:
PD is on the money. :)

There is too much BS being spread in this thread (not a lot compared to years ago) but the Old Wives Tales seem to persist even if in reduced numbers.




Jon,

Take a look at the interactive red box graphic we have on the APS website. If you want to educate yourself this is about the best if not only one stop source of education.

By the way a good O-320 runs LOP no problem at all.

I have seen some comments about you can't run LOP with Carby's you can only do it with an engine monitor blah blah....... all of which is complete nonsense. Some things are better however with the above mentioned. In fact we believe the ROP pilot needs an EMS more than a LOP pilot does, and some have trouble getting their mind around that.

Hope that helps.
Click to expand...
Many times, carbureted engines have inconsistent fuel distribution effectiveness. In this case, attempting to run LOP may put a cylinder or two in the wrong place attempting to "get there". Seen it many times. If you're fortunate enough to have a carb'd arrangement that provides good fuel distribution, then by all means, run LOP. But you need to be sure you know how each cylinder is responding (at least once, during the leaning process to know how the fuel distribution is occurring). And I've even seen a jet in a carb fail, throwing off the distribution radically. Been there, done that.
 
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