So you want to know what a burned exhaust valve looks like? One that will give you about 15/80 compression? Well here you go!

Take a look at the BeechTalk Thread contributed by Mike F. on three of his IO-550 jugs that were giving him 15/80, 15/80 and 55/80 compressions. The valve on the left and middle were at 15/80 and the one on the right was 55/80.

Here's what Walter Atkinson of Advanced Pilot Seminars had to say:

"...the one on the right doesn't look like it was leaking (if any, hardly) while the engine was running... only during the static compression check. I'd love to see an engine monitor download on it. That one looks very much like a normal heat pattern on a healthy LOP-run valve with VERY minor edge changes. The other two look like they were leaking significantly while the engine was running."

Note the uneven burn patterns of the first and middle valves as opposed to the valve on the far right.

Here is a close up of the first valve, the one on the left:

Hopefully this will give you and your mechanic an idea of what you might see in a Borescope when exhaust valve problems are suspected.

Visit the CSOBeech engine ops narrative HERE to learn more about Advanced Pilot Seminars and my experiences with LOP/GOP operations on my IO-470Ls.