Annualing a Cessna 310 this week, doing compression check and found just 20psi/80psi on a cylinder.
Broke-out the new borescope (check the thread on this) and here’s what I found :
So, student A&Ps, please tell the class what’s going on here ? 
Exercise:
- Identify the exhaust valve
- What does the reddish color tell us ?
- How can you tell that the exhaust valve is “burnt” ?
- What is the remedial course of action in this case ?
All you have ever want to know about valves but never dared to ask!
The red are normal deposits?
The burn is the green spot on the right side?
Remove the valve, redo the valve seat, put in a new valve and inspect the rocker arm?
The colour distribution pattern seems a little funny with that black band down the middle in between two red bands. Is it caused by the valve not turning properly?
O zen master of engines, enlighten us!
Very interesting – I have next to no idea what these things look like, I found the photos on dye testing in the other thread fascinating, so am genuinely curious!
In general, you want to see a circular pattern. Anything that is different indicates hot spots which lead to failure. In this photo it’s obvious.
What about that crack goig down the cyl half? 
My interpretation: Warm up your credit card
C210_Flyer wrote:
What about that crack goig down the cyl half?
Isn’t that a stain from a drip of oil or something like that?
You forgot there was a smiley at the end of that sentence.
