Tuesday, September 06, 2011

Exhaust Valve Deposits - Concentricity

Look for deposit concentricity. This pattern can only occur if the temperature across the valve face is the same at any distance along the radius. Even temperature can not occur if the valve is leaking hot exhaust at a spot on the circumference.


Concentric - deposits share same center axis shows that valve face temperature is the same at any distance from the center. If the valve face were leaking then the temperature at that spot would be hotter and the deposits would no longer be concentric.

Continental Exhaust Valve Concentric Deposits

Not Concentric

Not Concentric - valve face leakage

Not Concentric

Exhaust valve leakage

Not Concentric

Lycoming exhaust valve leakage


  1. Great photos! Thanks for posting.
    Nice article, thanks for the information.

    Exhaust Parts

  2. Anonymous8:58 AM

    Have you ever observed this kind of overheating leading to fatigue cracking and failure (crescent shaped pieces breaking off) in INLET valves in Lycoming engines?

  3. No, not that I recall. One sees many more leaking exhaust valves than intake valves so our attention was always on the hard-working exhaust.

    Intake seats are a little harder to grind properly so I would say typically a leaking intake on a low time engine is suspect for a seat issue.