LOP Price to pay

[BobTurner]

Originally Posted by N427EF

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.

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.

[crabandy]

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!

[RV10inOz]

Originally Posted by 60av8tor

David, please expound on this - erratic EGT on that cylinder..? Thanks in advance; always enjoy your insight.

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.

[David-aviator]

Originally Posted by N427EF

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.

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.

[rocketbob]

Originally Posted by aerhed

If Bob's right and it quit rotating your going to see a stripe on the valve tip from the rocker arm.

No because the exhaust valve has a stellite-coated rotator cap.

Hence the name!

[aerhed]

Oops, wrong valve. Thanks Bob.

[johnny stick]

Originally Posted by N427EF

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.

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

[airguy]

Originally Posted by BobTurner

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.

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.

[Toobuilder]

If Lycoming endorses running at peak EGT (factory endorsed = "good"), then how can running cooler (LOP) be "bad"?

[N395V]

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.

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.