Low power settings and engine (valve) damage?

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Johnbo

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Johnbo
I’ve been hearing a lot lately of how low power settings can cause damage to an engine particularly by creating issues with the values but I’m having trouble finding out how mixture plays in and what exactly is the definition of “lower power setting”.

If your headed out for a local flight and at lower alt (3000’ and below) would careful leaning to get hotter gas temps prevent these issues? How about establishing a limit of sustained minim manifold pressure...any ideas where that threshold would be?

thx
 
John Deakin of Gami in Ada Ok has written a number of very good engine management articles in Pelican’s Perch. I believe it can be found on Avweb. Not sure about the veracity of the the low power setting causing problems claims. You want to avoid high power settings where mixture is set for best power, around 75 degrees Rich of Peak. This is typically “ Best power.” Ironically this is where many older POHs suggested you run your engine. At 65% power or so, the red box goes away and you can set the red knob anywhere you want without fear of engine damage. Advanced Pilots Seminar has a great online course. Not cheap but worth it.
 
Anecdotally I have experienced total loss of compression on cylinder number 4 during this sort of flight.
My EGT's run hot even at full rich when low. I can't run full throttle when low or I will be well into the yellow arc. So, I try to avoid prolonged flight at low altitude now for fear of valve damage.
 
FORANE said:
Anecdotally I have experienced total loss of compression on cylinder number 4 during this sort of flight.
My EGT's run hot even at full rich when low. I can't run full throttle when low or I will be well into the yellow arc. So, I try to avoid prolonged flight at low altitude now for fear of valve damage.
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Is that a 4-cyl Lycoming? Carb or injected?
 
No way to crank up the full throttle fuel on that carb?
Maybe it's the comp ratio that is doing it.
No doubt you have the baffles in great shape.
 
Fly per the POH, be conservative with your CHTs and dont be ham fisted or shock cool the heck out of it (flashing CLD if you are rocking a JPI).
 
James331 said:
Fly per the POH, be conservative with your CHTs and dont be ham fisted or shock cool the heck out of it (flashing CLD if you are rocking a JPI).
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My POH has me at 1650 TIT and 435* CHT. No way I am running those numbers.
 
That would be the conservative CHT part
 
Johnbo said:
I’ve been hearing a lot lately of how low power settings can cause damage to an engine particularly by creating issues with the values but I’m having trouble finding out how mixture plays in and what exactly is the definition of “lower power setting”.

If your headed out for a local flight and at lower alt (3000’ and below) would careful leaning to get hotter gas temps prevent these issues? How about establishing a limit of sustained minim manifold pressure...any ideas where that threshold would be?

thx
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valves or values?

https://aslcamguard.com/sticking-exhaust-valves/
 
FORANE said:
Anecdotally I have experienced total loss of compression on cylinder number 4 during this sort of flight.
My EGT's run hot even at full rich when low. I can't run full throttle when low or I will be well into the yellow arc. So, I try to avoid prolonged flight at low altitude now for fear of valve damage.
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no offense but I would be looking to figure out the problem instead of finding ways to fly around it.
 
Grumman

Can you run at 1000 for a couple hours without issue?
Do your EGT's run higher at 1000 ?
 
FORANE said:
Grumman

Can you run at 1000 for a couple hours without issue?
Do your EGT's run higher at 1000 ?
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Yea, don't think I've ever seen more than 1300 WOT at any altitude. The venture has exceptional cooling though so I wouldn't use it as a benchmark.
 
Johnbo said:
hearing a lot lately of how low power settings can cause damage to an engine particularly by creating issues with the valves
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If you fly by POH figures I don't really see how you would be causing an unreasonable amount of damage to an otherwise healthy engine.. the POH's I've seen have several power (manifold, fuel flow, RPM) setting going down as low as 2K feet.. on top of that CHT and EGT monitoring is your friend..

..it's honestly ludicrous that these engines need this much babying.. FADEC engine management would basically nullify most of this. But I digress.

GRANTED:
-I make an effort to fly around 65-75% power whenever possible, sustain at least 12-15 manifold pressure, etc. I have heard (in other forums) that sustained operation at low power settings (35%-45% power) aren't the best for an engine. I don't enjoy receiving ATC speed restrictions and long delay vectors when on an approach procedure (no greater than 110 knots and maintain heading X at 2,500 for traffic).. you get very crafty with power, flap, and mixture settings to keep the engine "happy"
 
If running at low power settings is damaging, how come the engine in your car (which runs at, like, 10% all the time) doesn't grenade?

What is the mechanism that causes this damage?

Note: I can see that if you are running pig rich (default mixture setting from the days when gas was cheap and the solution to problems was "more fuel"), that you could build carbon deposits on exhaust valves if there is not enough heat to keep the carbon from depositing.
 
Grum.Man said:
Yea, don't think I've ever seen more than 1300 WOT at any altitude. The venture has exceptional cooling though so I wouldn't use it as a benchmark.
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CHT’s are predicated on cooling. EGT’s don’t have anything to do with cooling airflow. EGT’s will be determined by mixture, ignition timing and probe placement. Actual EGT readings can be several hundred degrees different between aircraft but completely normal. EGT’s are a diagnostic tool as well as useful for mixture adjustments. What you look for in EGT’s are trends on a specific aircraft. As a simple example 1 EGT increasing 100 degrees above its norm with no increase in other EGT’s likely means you have one plug not firing in that cylinder.
 
Capt. Geoffrey Thorpe said:
doesn't grenade
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trust me, I as much as anyone else, if not more, appreciate the car engine analogies to aviation but our car engines are also laser-cut efficient works of engineering with electronic fuel control, variable timing, and a host of other features.. and not sand-cast 1940s relics we see in our aircraft engines..
 
If CHT’s are good and mixtures are set correct, I don’t see how lower power operations can damage valves...
 
Thx folks. Seems more to do with mixture than power setting.
 
Tantalum said:
If you fly by POH figures I don't really see how you would be causing an unreasonable amount of damage to an otherwise healthy engine.. the POH's I've seen have several power (manifold, fuel flow, RPM) setting going down as low as 2K feet
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I have an experimental so the POH is not this detailed but I should probably find a POH for a certified plane with the same motor to use as guidance.
 
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