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  #1  
Old 04-26-2018, 06:07 PM
YellowJacket RV9 YellowJacket RV9 is offline
 
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Location: Clearwater, FL KCLW
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Default Borescope Pics - yellow deposits

Working on my condition inspection today, and borescoped all cylinders. All the exhaust valves look excellent (2 years, 200ish hours on the cylinders). Compressions 74,76,78,78

Only odd thing is the yellowish deposits around (not on) the valve face in in cylinder #4. Does not occur in any other cylinders. Any comments?


If the pic doesn't work: https://photos.app.goo.gl/KRN8ysdBQqb54amx7

Chris
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  #2  
Old 04-26-2018, 06:54 PM
BillL BillL is offline
 
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I don't trust the color rendering from my Vividia-400 unit, don't know about yours.
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  #3  
Old 04-26-2018, 07:11 PM
YellowJacket RV9 YellowJacket RV9 is offline
 
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Quote:
Originally Posted by BillL View Post
I don't trust the color rendering from my Vividia-400 unit, don't know about yours.
I had the same thought, just odd that I only see it on #4. Here is #1 for reference:


https://photos.app.goo.gl/7klqTOYS19uiYoxs1

Chris
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  #4  
Old 04-26-2018, 09:42 PM
VA Maule VA Maule is offline
 
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What kind of EGT is that cylinder running compared to the others is it cooler? The deposits look similar to the stuff that accumulates in spark plugs. Any way that cylinder could be running richer? Is the engine injected?
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  #5  
Old 04-26-2018, 09:51 PM
YellowJacket RV9 YellowJacket RV9 is offline
 
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I just reviewed the logs and #4 doesn't appear to be hotter or cooler than the others. It is carbureted, not injected, so mixture could certainly be different in that cylinder though. It did strike me as looking similar to the stuff I pulled out of the plugs.

Chris
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  #6  
Old 04-26-2018, 11:41 PM
Kyle Boatright Kyle Boatright is offline
 
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Is that oil? Any chance you could touch it with your camera, remove the camera, and check for residue on the camera? That, or cobble something up to rub that area with a Q-tip?
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  #7  
Old 04-30-2018, 07:54 AM
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storm_pilot storm_pilot is offline
 
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What kind of fuel are you running?
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  #8  
Old 04-30-2018, 08:40 AM
DavidBurton DavidBurton is offline
 
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Good call on the fuel. Alcohol in mogas can contribute to this. So can detonation. Look at spark plugs in that cylinder, especially too high heat range. Exhaust restriction in that cylinder, timing to far advanced.

We used to blame this on lead but I'm not convinced that's the issue. Maybe lead in conjunction with lean running for some reason.
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  #9  
Old 04-30-2018, 09:05 AM
YellowJacket RV9 YellowJacket RV9 is offline
 
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Quote:
Originally Posted by storm_pilot View Post
What kind of fuel are you running?
Quote:
Originally Posted by DavidBurton View Post
Good call on the fuel. Alcohol in mogas can contribute to this. So can detonation. Look at spark plugs in that cylinder, especially too high heat range. Exhaust restriction in that cylinder, timing to far advanced.

We used to blame this on lead but I'm not convinced that's the issue. Maybe lead in conjunction with lean running for some reason.
I run 100LL exclusively, and for the last 10 hours or so have also started Decalin, although I have never had any lead fouling issues. I generally am pretty religious about leaning, both on the ground and in flight. I run REM40E plugs, and the #4 plugs looked similar to all the other cylinders when I removed and cleaned them. Should I consider plugs with a lower heat range?

I just checked the timing, and it is still dead on at 25*. How would I check for an exhaust restriction?

Given the poor mixture distribution I suppose it could be too lean, although the in-flight EGT's don't seem to suggest that. Engine runs like a top.

Thanks for the input

Chris
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  #10  
Old 04-30-2018, 09:16 AM
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Default Good read

https://www.aopa.org/training-and-sa...e/valve-safety read and download the poster at the bottom of the page.
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