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I was doing some RNAV approaches the other night when on long final the engine began to run rough. I immediately gave full power, fill mixture, fuel pump and switched tank as if instinct. I was plenty high (2500'). As you can see from the time-lapse graph on the GRT EFIS, my EGT for  It could only really be two things that would cause such a drastic drop of EGT's - stuck valve or clogged injector. A partially clogged injector would cause a spike in EGT, as it would cause a lean condition to occur. A fully clogged injector would be tough to clear out so soon. I was crossing my fingers for a sticky valve, as I know it's a relatively easy fix. Sure enough upon initial investigation the  To access the exhaust port for the #4 cylinder, all of the exhaust needed to be dropped.  After removing the spring, it was clear the valve had a lot of resistance in the guide.  I dropped the valve in the cylinder and reamed out the guide. Not a whole lot of buildup was removed, but it was like night and day when I reinstalled the valve. Moves freely now!  The last thing I did was inspect the #3 exhaust valve - it is the only guide that I have not reamed out yet. Since the exhaust was dropped, it was an easy inspection and fix. Of course when I removed the spring, there was zero resistance in the movement of the valve in it's guide. I put everything back together and started the engine. Everything ran smoothly! I have no idea why I have been haunted by so many sticky valves. Seems to be well above average. 
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Last Modified: August 13, 2023 |