What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

White checking on exhaust valve mating surfaces

rv6n6r

Well Known Member
Patron
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.
 

Attachments

  • cyl1_06.jpg
    cyl1_06.jpg
    56 KB · Views: 213
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.
 
Last edited:
Lead filling low spots eroded by microwelding. Yellow is sulfur which is a normal deposit to see.
 
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.
 
Back
Top