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  #1  
Old 06-04-2019, 06:07 PM
MiserBird's Avatar
MiserBird MiserBird is offline
 
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Location: Cornelia, GA
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Default Green color in center of exhaust valve

Doing a borescope inspection on my O320E2A with 188 hour low compression ECI cylinders and found the exhaust valves to be almost too
clean with a green dot in the center of some.









I have read that green is not good, but the location seems strange to me. I cruise at around 50% power, 325 CHT, 50deg ROP, 5.5 GPH ( by tach
time) 18in hg around 2200 RPM. One PMag 32 deg max on NGK BR8EIX's , one Slick on Tempest UREM37BY's. The plugs were white, with heavier light color deposits in the UREM37BY's than the very clean NGK's.

It has been said that it's difficult to damage a Lycoming at less than 65% power, but I'm beginning to wonder if I need to change any settings.

FWIW, the engine runs perfectly, and will idle down to 600 RPM on the EMag alone, with a Catto prop.

Thanks in advance for any insight, and advice.
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KAJR - Cornelia, GA

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1980 RV-3 N3VR Bought flying Sept 2017

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Last edited by MiserBird : 06-04-2019 at 08:36 PM. Reason: trying to get pics full size
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  #2  
Old 06-04-2019, 11:01 PM
lr172 lr172 is online now
 
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exhaust valve stem is sodium filled and acts as a heat sink. Therefore the area with the green dot (center, where the sodium filled cavity ends) will be cooler than the balance of the valve face. Not surprising that this could account for different deposit types or rates. Deposit type and color is often dictated by temperature at the deposited surface. Notice different deposits on exh valve vs intake valve vs cyl crown, etc. All are at different temps.

The green color wouldn't concern me in the slightest. Different fuel additives also account for different colored deposits.

Larry
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Last edited by lr172 : 06-04-2019 at 11:11 PM.
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  #3  
Old 06-05-2019, 06:45 AM
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Sulfur deposits...normal.
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  #4  
Old 06-05-2019, 07:43 AM
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The bright white color and super clean valves generally means high combustion temps.
If the plugs are bright white instead of the normal tan color I would be looking at low fuel flow.
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Last edited by Walt : 06-05-2019 at 08:27 AM.
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  #5  
Old 06-05-2019, 08:02 AM
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Great borescope. What brand and model is it?
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  #6  
Old 06-05-2019, 11:58 AM
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Thanks for your responses. I'm going to enrich the mixture to around 100 deg ROP and take a look again.

The borescope used is a Vividia VA-400.
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  #7  
Old 06-06-2019, 07:55 AM
Boyd Birchler Boyd Birchler is offline
 
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At such a low power setting I would go to peak on the leanest cylinder. The engine is running too cold! The higher EGT would help to keep from sticking a valve caused by combustion deposits. Lycoming says you can run peak EGT at any power setting below 75%. My personal preference would be below 65%.
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Old 06-07-2019, 01:22 AM
Yen Yen is offline
 
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Why are you running rich of peak. I thought the object would be to get max power from min fuel and to do that you run lean of peak.
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  #9  
Old 06-07-2019, 02:33 AM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by MiserBird View Post
Thanks for your responses. I'm going to enrich the mixture to around 100 deg ROP and take a look again.

The borescope used is a Vividia VA-400.
100 degrees ROP corresponds to max power, max CHT?s, max stress and strain, max wear and tear, min economy, min longevity. Not a good place to spend much time!
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  #10  
Old 06-07-2019, 05:55 AM
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Quote:
Originally Posted by Yen View Post
Why are you running rich of peak. I thought the object would be to get max power from min fuel and to do that you run lean of peak.
Max power is ROP. Cannot make power without fuel. As fuel flow is lowered, the engine will start running lean of peak (LOP) producing less power. Less food (fuel), less horsepower.
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