This data shows nine 7-second sample intervals, post-start, after which the engine was shut down due to vibration, and EDM not showing EGT on #4. But actually there was some EGT
Too much data can result in too much thinking about it. If you need the engine for safe continued flight, leave it running. If you’ve got an extra, consider shutting it down. Yes, exhaust valves stick – sometimes for moments, sometimes hard locked. Gently handled, the plane will continue moderately safe flight on the remaining cylinders. I once ferried home a C-150 with a stuck exhaust valve, which could not be repaired where it was. 4000 foot runway, and shaky flight, but it flew home on three adequately, and was properly repaired at a maintenance base.
A lesser known cause of sticking exhaust valves is a leak between the cylinder exhaust flange, and the exhaust pipe. Combustion heat is not carried away as intended, and the exhaust area of the cylinder will run unusually hot (EGT will show a little cool, as heat did not make it to the probe). When you close the throttle at top of descent, that part of the cylinder will cool faster than it should, and the guide can grab the valve – and it can take heat and hammering to drop the valve into the cylinder for guide reaming (which is a task anywhere, and more of a task on a floatplane in central Quebec!) A floatplane will not get off the water on 3 cylinders :(
Just do good maintenance, and run the engine with respect, and it should be fine. If it does stick a valve, consider the relative value of a shaky flight to maintenance, or calling for assistance from a farmer’s field, from which takeoff will surely not be possible!
To me both pictures look ok.
I think it is difficult to diagnose stuck valve from that kind of picture as the problem is within guide valve contaminated by combustion products. That you cannot see with borescope.
Your valve looks nicely symmetrically marked.
No green color on one side which would indicate burning.
That red color on second picture is not relevant.
Raven wrote:
I think it is difficult to diagnose stuck valve from that kind of picture as the problem is within guide valve contaminated by combustion products. That you cannot see with borescope.
It is true that most of the time the problem is the guide/valve stem clearance, or lack of. But a valve having a tendency to stick will most probably stop rotating first. And then this will be shown by asymmetric discolouration, and not necessarily green. Yes, green is no good, but the hot spot of the valve is usually part moon shaped, and of a different color than the rest. The last one I’ve seen was just reddish, against yellow for the rest of the circumference.
And yep, these 2 pictures show healthy valves.
The lower photo above was a seriously overheated valve, so
That red color on second picture is not relevant.
is not my understanding.
However, the cylinder repair shop (UK) cleaned it up and put it back in. When I found out, I told them to put in a new one!
The 8 o clock on the upper pic is hotter than the rest. Possibly not rotating and consistent with guide-valve clearance sticky
Do you mean this pic?
Yes. Was there any EGT symptom on the prior flight? Did the roughness go away after a min or two of ground running?
Looking at the EDM data, there was very low (~50% of normal) EGT for 1 minute post start. The engine was then stopped and restarted and all was ok. 2 more flights were done after that, with no evident issues.
My view is that it could have been a sticky valve, or dirt in the injector. The latter more possible because ~8 hours earlier I had flown through a cloud of probably volcanic ash N of Sicily and the top of the engine has still got brown dust on it. The Lyco injectors suck in air from the outside so something could get in there.
If a sticky valve, does one remove the cylinder for that? It’s a lot of work. #2 is not too hard but #4 would need more dismantling (of baffles etc). Then one burns 1-2k £ of extra avgas bedding it in, as well as no IFR flights due to the need for high power. There is also the “old rope trick” but good luck finding somebody who wants to risk it.
Could a valve free itself up?
