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  #1  
Old 09-14-2021, 08:33 PM
rv6n6r's Avatar
rv6n6r rv6n6r is offline
 
Join Date: May 2007
Location: Gearhart Oregon
Posts: 368
Default White checking on exhaust valve mating surfaces

O-360 A1A, ~1600 hrs. What's the white checking on the mating surfaces? I only see this on the exhaust valve on one cylinder. Everything else seems fine, no asymmetric pattern or green on the valve face. Some symmetrical yellow however. Thoughts?

As an aside, is there a good reference with photos that could help with evaluating what we see in borescope inspections? I've read articles such as this one from AOPA that show the basic exhaust failure modes but nothing showing things like valve seat wear etc.
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RV-6 / O-360 / CS, 1600+ hrs, 1st flight Sept. 1999
Outstanding Workmanship OSH 2000
Airport committee chair & AOPA ASNV for Seaside, OR Municipal (56S), www.seasideairport.org
Donated August 2021
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  #2  
Old 09-15-2021, 05:23 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,215
Default Looks terrible doesn't it . . .

I think it is created by two primary processes, one being the capture, deposit and crushing of tiny lead deposits and the other is high temperature corrosion. But since the seat is quite a bit cooler than the valve head, lead deposits is the winner.

Seat wear is controlled by the hardness of the materials, so you would not automatically see that. It is likely at WOT your carb is allowing a richer mixture (relatively) to this jug.

You ever find these tiny lead balls in the chamber or stuck in the spark plug?

This process is one reason that you don't want a valve job with those precision three angles and a narrow contact rim for an aircraft engine. At least not one you want to last 2-4000 hrs, it should have a wider contact rim.

Valve faces look considerably different in diesel, or non-leaded gasoline engines for this and other reasons. Longer hours (10,000) on a diesel with a duty cycle of an aircraft will look much smoother, but it too depends on fuel, oils, and operating temperatures.
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Last edited by BillL : 09-15-2021 at 05:26 AM.
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  #3  
Old 09-15-2021, 05:47 AM
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rocketbob rocketbob is offline
 
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Location: 8I3
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Default

Lead filling low spots eroded by microwelding. Yellow is sulfur which is a normal deposit to see.
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  #4  
Old 09-15-2021, 10:08 AM
rv6n6r's Avatar
rv6n6r rv6n6r is offline
 
Join Date: May 2007
Location: Gearhart Oregon
Posts: 368
Default

Thanks. Yes I usually have lead balls in some of the spark plugs which I clean out at annual or whenever they are out.

Is this something to be concerned about and addressed? I try to lean pretty aggressively including during ground ops. It's normally aspirated however so running lean of peak can be problematic.

I am currently in the process of swapping out my left magneto for a P-Mag (already have one on the right side). I imagine that will change things too.
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Randall Henderson
RV-6 / O-360 / CS, 1600+ hrs, 1st flight Sept. 1999
Outstanding Workmanship OSH 2000
Airport committee chair & AOPA ASNV for Seaside, OR Municipal (56S), www.seasideairport.org
Donated August 2021
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