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My experience is similar to Jon Jay. My #2 exhaust would stick open randomly/periodically. But it only ever lasted a few seconds, so anything I did seemed to cure it. Cut power, cured. Richen mixture, cured. But always accompanied by loss of EGT. This went on for a long time because it was so intermittent. When I removed the valve cover, it was clearly a valve tight in its valve guide. Reamed it out and no more symptoms. In retrospect, I could hear the valve occasionally not closing fully when at high rpms. Just an almost imperceptible miss.
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The End of The Story!
So, to circle back to the beginning of this thread and wind things up...while the aircraft was at Saint Aviation for an avionics upgrade, I asked Jesse if he would mind adding popping the #2 cylinder head cover off and checking the exhaust valve for freedom of movement after the way it had been running and the info learned on this thread.
He agreed, and we added it to the bill of work. I arrived today (as the project is reaching its end) and Jesse informed me that the mechanic he'd brought over to check this out for him opened things up, and they discovered a verrrry difficult to move exhaust valve-so much so, that it took a socket extension and a bit of persuasion with a hammer to move it at all. The mechanic disassembled the associated valve train and then cleaned out the guide with a hone (removing a fair amount of gunk) and the valve moves silky smooth now. Test flight tomorrow, but I gotta believe this is going to resolve the engine stumble. Wouldn't have guessed an exhaust valve issue without this website! Thanks to all who contributed, and I'll PIREP how she runs (especially lean of peak) after the flight home. Thanks again, all! Rob |
As noted above, it's not injection nozzle or similar since I have a carburetor.
I would like to persue the intake tube theory. Is there a test for an individual intake tube? As for the sticking valve, I'll ask my mechanic. I do occasionally run 100LL but as noted, I burn very little of it and a recent inspection of the plugs were very clean. That wouldn't completely discount a valve. |
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Very glad you found the issue and it was an easy fix. Yay! |
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Easier is better . . .
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Example Publication $$: HERE Taking time to remove the VC and check each valve annually would not seem like much work. It seems a lot easier to notice abnormal engine operation and then do the check. |
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Flight Home PIREP...
3 legs, no problems!
Pushed it too, running it very LOP and looking for any issues... Ran like a top! :D Now I need to research the suggestion about running Marvel Mystery Oil as a preventative. Also chasing down a lead that we might be able to get Swift Fuels 94UL at my home base, too, the use of which I understand would help as well. Thanks again to all for the help!! Rob |
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