Hmmm; interesting. Is there a current contact address for him? I’d imagine his inbox must be busy…
I did a google on “green spot on exhaust valve” and found this.
All other hits point to either nothing (usually followed by a fight and a lecture on LOP 
) or “this is normal”, or the green needing to be assymetrical – like the above.
The suggestion is that green means high temperature, but the centre of the valve is attached to its stem which (on Lycos) is sodium filled and conducts heat away into the valve guide.
In traditional metallurgy, different colours during heat treatment mean different temperatures
but that’s a specific context. As with the amount of soot on spark plugs, it most likely depends on what the engine was doing in the last few minutes before shutdown.
I think a useful investigative avenue would be to run the engine LOP for say 5 mins (on the ground) and borescope the particular valve, and then repeat having run it for 5 mins say 150F ROP. It would be relatively easy to do during a service. If I remember, I will do that.
If the exhaust valve is axially simmetrical (round looking) then it is OK, there are no hot spots regardless of actual colour. The issue is always when a particular sector is different from the rest. This measn that sector is not seating, and thus transferring heat, properly .
Hello, today we had a friends RR O-240 boroscoped… What we found was kind of inconsistent and difficult to judge. Two cylinders had been replaced about a year ago, the other two are still old stock. Please let me upload the photos we have taken, open for your comments and suggestions. To prevent any bias i wont label which photo shows which zylinder. Question is if immediate action is required? thanks for your help!
Picture nr 4 shows a green valve. That might be worth looking at.
Re the valve pics, some are very oily, but that’s a different issue. The 1st one shows a heating pattern which is not concentric to the valve face, which is not right.
I think MSE disappeared but does anyone have an opinion on the valves?
Here’s a couple of mine. One exhaust, one intake. Both from the recently repaired #2 cylinder.
The odd pattern of blue on the intake one can’t be overheating; not on an intake valve. It’s probably a lead deposit; you can see some of it next to the valve.
It’s odd that the deposit is not axial-symmetrical. The valve should be rotating. Check back in 50 hrs and see if it evens out
Does a valve have to rotate all the way round? I can see non-rotation is indicative of assymetry, but does it actually matter?
Peter wrote:
non-rotation is indicative of assymetry
I think it is the other way around.
Yes valves are supposed to rotate in one direction all the time (CW or CCW) , not there and back. If not leaking and not seizing, I would not worry about that inlet valve, though.
Here is another lot:
and, no, I don’t know what happened to the 6th one, but the engine definitely has 6 cylinders
