PIREP - Low Static RPM, Higher CHT/EGT on cylinder

[elimansour]

Aircraft:  '98 M20J Allegro with original engine and prop, both approximately 20 years old with ~ 1700 hrs. 

Symptoms: Inability to reach static RPM (usually ~ 2550 was best I could achieve - 100 RPM less than min. per service manual); CHT/EGT on #4 Cyl running 50-75 degrees hotter than other cylinders; Airspeed seemed 10 kts slower than POH speeds (using same MP & RPM); and needed approx. 1gph more fuel flow than POH (using MP & RPM).

Diagnosis:  After discussing with mechanic, they suggested that RPM/ speed issue could be a propeller issue but that the other factors (hotter CHT/EGT on 1 cylinder and higher fuel flows) pointed to a worn cam lobe.  They tested for the worn cam lobe by removing the cylinder covers and measuring the movement on the valves.  #1-3 cylinders had normal movement within limits; #4 cylinder valves exhibited measurably smaller movements - less than 1/2 of normal travel.  After verifying the cam lobe was worn, prop was ruled out as issue (although they recommended OH due to time in service).

Resolution:  Engine and prop sent out for OH  to new limits.  This was sooner than I had planned but having one cylinder have such bad intake/ exhaust is not a good idea. 

[carusoam]

Well written report, Eli!

Did you get any metal bits in screens, filters or oil analysis...

Sorry to hear the bad news, and thanks for sharing the details.

Best regards,

-a-

[elimansour]

Oil analysis did find some wear metals which were indicated as being consistent with the age of the engine.  Funny enough, wear metals actually trended down the last oil change as the plane was being used more frequently in the past 2 months.  Visual inspection of screens did not indicate metals but when using magnet a little metal was found last couple of oil changes.