[dtw_rv6]

<.>

 

[Dan 57]

consistent with a stuck exhaust valve

and those are? Your description does not really fit with a stuck valve, but who knows.
Do you have an engine monitor, data?
History, has this been a new occurrence or has it happened before?
From your text the shaking happens WOT, and then diminishes when the throttle is reduced, correct?
What lead you to look for a stuck valve in this cylinder in the first place?

Those are honest questions trying to analyse what's happening in your engine. Not sure about picture #2, is that the guide with the borescope going thru? The valve itself looks ok, no seizure marks on the stem, and the seat face and margin look ok considering the engine hours.
Regarding the observed taper on the guide, the proof of abnormality would be given by performing the wobble test, as this measures not only minimum but also maximum lateral play. Yes, I guess comparing it "manually" to one of the other cylinder would be a step in the right direction.

 

[Roadjunkie1]

and those are? Your description does not really fit with a stuck valve, but who knows.
Do you have an engine monitor, data?
History, has this been a new occurrence or has it happened before?
From your text the shaking happens WOT, and then diminishes when the throttle is reduced, correct?
What lead you to look for a stuck valve in this cylinder in the first place?

Those are honest questions trying to analyze what's happening in your engine. Not sure about picture #2, is that the guide with the borescope going thru? The valve itself looks ok, no seizure marks on the stem, and the seat face and margin look ok considering the engine hours.
Regarding the observed taper on the guide, the proof of abnormality would be given by performing the wobble test, as this measures not only minimum but also maximum lateral play. Yes, I guess comparing it "manually" to one of the other cylinder would be a step in the right direction.

All of the above except: the allowable tolerance of the wobble test is 0.013 and 0.035. I am not sure how sensitive your fingers are but would guess they are not that sensitive. When I was doing my wobble test, the loosest was 0.024 and the tightest was 0.017, Manually wiggling the stem: I could feel no difference in the two. You need to do a wobble test before you pull the cylinder. Time to do one anyway on all 4 cylinders. Do your cylinders have the "C" stamp? Coming from Superior they might not. The 400 hour wobble test SB is on Lycoming engines and might not apply to yours. But would still be good information.

AND: this might not be the issue. What DID prompt you to think it was a stuck valve and why that particular cylinder? What do your fuel injection nozzles look like? Could this be FI-related? Many other things to consider before taking the engine apart. IMHO; YMMV

 

[Dan 57]

I'm sure others will chime in, but it sounds like you either have a fuel, or an ignition problem (yep, that was an easy guess ).
Spark plugs, spark plug wires, ignition system, fuel pressure, etc, etc, all and more could be faulty.

I doubt it is an induction leak since the symptoms would be different and last.

 

[elev666]

That sound’s exactly like the symptoms I had on my first run over hauled Lycoming cylinders 3 years ago, it would act up and go away so when I dropped the oil and found all kinds of aluminum shavings in my filter , thinking it was a wrist pin Cap I was set to remove all my cylinders to find the issue , this is what I discovered under my # 2 Cylinder valve cover ,
what I’ve learned from this is I wish I hadn’t powder coated my Valve covers or I would have found this problem sooner , the cover was badly peened from the inside but I was busy overhauling my Carburetor & mags and didn’t notice the obvious, also very happy I didn’t open my wallet to buy alloy valve covers since my oil would have left my engine very quickly !