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Preventing sticking exhaust valves

charrois

Member
Hi there.

A little while ago, I had a flight with my IO-540 where one of my EGTs (#3) fluctuated significantly, between "normal" and a hundred degrees or more hotter than normal (CHTs were rock solid stable at the same temperatures they normally are). Hoping it might just be a EGT probe sensor problem, I swapped sensors between #1 and #3 to see if the problem followed the probe or the cylinder, but the result was inconclusive in that a subsequent test flight didn't see any temperature fluctuations at all. I since brought the sensors back to where they belong, in the process replacing the #3 sensor altogether with a new one. In the 4-5 hours of flying I've done since, I haven't seen any more fluctuations, so perhaps it was a sensor acting up after all; it's certainly what I am hoping it was.

But of course, I have to also consider the possibility it was a real issue, and it seems if it was, a sticking exhaust valve might have been the culprit. But I've seen very conflicting information on how to reduce the likelihood of a sticking exhaust valve. On the one hand, Lycoming recommends (in addition to frequent oil changes, air filter cleaning, etc., which I do) that the engine be operated at cooler temperatures, since excessive heat and hot spots may cause the formation of deposits:

https://www.lycoming.com/content/operational-and-maintenance-procedures-avoid-sticking-valves

Yet, Mike Busch, a well-respected engine expert seems to recommend exactly the opposite - that combustion temperatures be kept high (ideally with CHTs between 350-400):

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

Whose advice should I follow? I should also mention that traditionally, I have been running lean of peak (also on the advice of Mike Busch) and normally my CHTs are in the 320 range while in cruise flight. I'm not sure how I would actually increase CHT temperatures other than operating rich of peak or adding baffling... but on climb out in the summer, it's already a struggle to keep them below 400 unless I'm in quite a shallow climb.

Any advice?

Dan
 
I too am a “Mike Busch guy”.

This is what I do:
- Lean on the ground until just before the engine stops. If you add throttle and the engine bogs down, you are just lean enough. I suspect this is the leading issue for stuck valves.
- I know of RV drivers that rarely touch the red knob - always full rich. Great way to mess up an engine.
- I also run LOP 95% of the time. On high altitude cross country my CHTS were also below Mike’s 350 target. I’ve since changed how I run the engine. For LOP I go just LOP, perhaps 15-20 degrees. I find going any leaner power (speed) drops off faster than fuel flow. If CHTs are low I run at peak (peak still means I’m getting everything out or each drop of fuel).

So try peak when CHTs are below the 350 target.

Carl
 
So try peak when CHTs are below the 350 target.

Great suggestion - until I read Mike's article about sticking valves, I generally thought "the lower the CHTs the better". But it makes sense to try leaning to peak EGT to raise the CHTs if that might help, especially considering I tend to do my cross countries >10,000' so keeping below 65% power is a given whether I intend to or not.
 
I have 750 hours on the 320 in my 6a. I do not lean on the ground (though idle mixture is properly set) and have done MANY x-ctry flights in the winter with cht’s around 300* or less. I am lop 95% of the time and cht’s rarely go above 400. Recently did the wobble test and each exh valve is in the middle of the recommended range, indicating no build up inthe guides.

Many different opinions on the cause of build up in the guides and most are just speculation. I am in the camp that heat is the cause. But that is just another unresearched opinion. My experience does not parallel mikes opinion.
 
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Many different opinions on the cause of build up in the guides and most are just speculation

+1, I’m with Larry on this one.

And almost the same data, though mine is a O-360. Loitering thru the Alps and across EU at my usual 19/20 (or 20/20 if I’m in a hurry) = about 43% power, lo EGTs and CHTs, running mostly MOGAS. No lead in fuel sure helps, not only the environment nobody cares about, but also leads to a cleaner engine overall.

Had my share of stuck exhaust valves, a few of them on the smaller Contis, and 1 on a 320 where I found the guides extremely tight. Reamed them all up resolved the problem. Plenty of threads on VAF and other sites on the subject.
Used and still use Camguard on all my engines, though more for corrosion protection than anything else...
 
There are two ways valves get stuck:

1. Imperfect seal on either exhaust or intake valves and seat interfaces causes exhaust gases to work up between the valve and the guide. The gas is hot with lead and carbon particles in suspension, while vaporizing oil in guide, which causes deposits to form. Easily seen by discoloration of exhaust spring and retainer components.

2. Dark oil with high levels of lead and carbon in suspension. Valve gets drip lubricated with dirty oil, thus leaving deposits in the guide, due to localized temperatures being high enough to cook the oil.

None of this has to do with how you lean or whose advice you follow. The degree to which deposits form depend on the mechanical condition of the valves and keeping the oil clean.

One can run LOP all day long but if you're valves aren't seating optimally or your oil is dirty then your valves will stick.
 
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Keep on keeping on and do the wobble test when indicated.

Hi there.
<snip>
Whose advice should I follow? I should also mention that traditionally, I have been running lean of peak (also on the advice of Mike Busch) and normally my CHTs are in the 320 range while in cruise flight. I'm not sure how I would actually increase CHT temperatures other than operating rich of peak or adding baffling... but on climb out in the summer, it's already a struggle to keep them below 400 unless I'm in quite a shallow climb.

Any advice?

Dan

Hi Dan, Honestly it seems like Lyc says the lead in the oil is the main culprit and Mike says it comes from exhaust gas. Likely some from both, as we know oil gets down there.

The valve/guide/head design geometry is complicated, very complicated, and to reduce it a single parameter is not realistic for a well developed engine with decades of field experience. The Lyc document hints at some of the engineering challenges and tradeoffs making it hard to read after edited by marketing. Finding the lead deposits on the stem (assuming it is in the proper axial location) via analysis does not tell us where the lead came from, exhaust or oil.

Recommendation? Run lean as much is practical, nothing extreme, and allow CHT to become what they are - low is not a bad thing IMO. Low is a relative term, but your numbers sure sound happy.

Data Point: The oil change is another variable from Lyc that makes sense. I looked at my oil analyses and for 34, 40, 45 hrs on the changes, Pb PPM was 1640, 3000, 3300 for the three. 34 hr sample was during Phase I break-in and run a full power a lot. The 45 hr sample had lots of rich running for instrument training. It will be interesting to see if the next sample yields any jewels of wisdom, meanwhile I will be following my own recommendation.

I like "keep your oil clean" from rocketbob!!! I bet Bob could "name that tune" in the fewest notes.

BLane_3 Clip.jpg
 
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what about the opposite problem?

While we are on the subject of sticking exhaust valves how about the opposite problem where the valve guides are too loose and worn.

This is my reality, with a 350hr engine that started leaking exhaust valves, when we finally pulled the cylinders we found 3 of them with the guides very worn and loose. The only thoughts from the engine shop was possibly running too hot at some point?

Are there other operational things to watch out for that would increase guide wear?
 
Hi there.

A little while ago, I had a flight with my IO-540 where one of my EGTs (#3) fluctuated significantly, between "normal" and a hundred degrees or more hotter than normal (CHTs were rock solid stable at the same temperatures they normally are).

Any advice?

Dan

Also consider the possibility that one plug was temporarily fouled, which would result in higher EGT (but likely slightly lower CHT, over time). Another possibility is a temporarily restricted injector. If it happens again, do a 50° LOP mag check and see what it shows.
 
oil pressure/cooling

search Marvel/Scott-what Lycoming won't tell you. Since resuming production of 172 and 182 if you read 70# on the gage in either airplane the real pressure is 80#. This is achieved by measuring oil pressure at the front of the oil gallery as opposed to the rear.
I ran my 0 360A4A powered Pitts with fixed pitch prop for 1000 hours with no problems. Oil pressure was set near the high end of the green arc. Every aerobatic flight was frequent operations at 3300 r/m. At 1000 hours when I sold the airplane the compression was near perfect.
I am an absolute believer that high oil pressure on Lycomings keeps the valves lubricated.
 
good, albeit dated, find jrs14855
The driving sentence of that article: Thus comes the missing hint for engine longevity. Crank up the oil pressure to the maximum you can, subject to the red line limitation on your engine installation.

On the other hand my guess is that most guides have now been replaced by the better ones and should therefore also lessen the sticking valve problem. Service bulletin pertaining to the “new” guide material: https://www.lycoming.com/sites/default/files/Exhaust%20Valve%20and%20Guide%20Identification%20Procedure.pdf
 
While we are on the subject of sticking exhaust valves how about the opposite problem where the valve guides are too loose and worn.

This is my reality, with a 350hr engine that started leaking exhaust valves, when we finally pulled the cylinders we found 3 of them with the guides very worn and loose. The only thoughts from the engine shop was possibly running too hot at some point?

Are there other operational things to watch out for that would increase guide wear?

Andy, I'll comment via obvious theory . . . lubrication ( how much oil actually gets to the valve stem), valve guide materials, then EGT would be the major parameters affecting wear and sticking. Lyc says they have "improved guides" after 1996. It is likely that several guide materials are available in aftermarket.

The hands-on experienced builders here can give more helpful detail.

I would guess in your case it is lubrication and guide material as the leading suspects.
 
While we are on the subject of sticking exhaust valves how about the opposite problem where the valve guides are too loose and worn.

This is my reality, with a 350hr engine that started leaking exhaust valves, when we finally pulled the cylinders we found 3 of them with the guides very worn and loose. The only thoughts from the engine shop was possibly running too hot at some point?

Are there other operational things to watch out for that would increase guide wear?

In my opinion, excessive valve guide wear typically stems from poor geometry during any of the several machining processes involved with valve setup. Even poor rocker arm geometry can create it, if excessive.

Heat alone should not generate valve guide wear, though starving them of oil can.

Larry
 
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Sticking valves due to a build-up inside of the valve guide is a common problem on Lycoming and Continental engines. McFarlane sells special reamers for cleaning out those valve guides and it can be done without removing the cylinder from the engine. I suggest looking at their web site for more information or calling/emailing their tech support folks.

A comment for akarmy: Just a guess, but if valve guides are wore slap out at 350 hours I suggest they were improperly reamed or they forgot to change them out at overhaul. I always measure the guide I.D. after reaming to ensure it's in spec. It is quite possible to go oversize if you're not careful and make sure everything is right.
 
McFarlane?

Skyjunkie, it looks like you have a total of 16 posts and have mentioned McFarlane in 9 of them. Just curious, any affiliation?
 
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