Maybe someone can help me with this?
My C90 showed low compression on the #4 cylinder at annual. Its 250 SMOH. I could hear an intake valve leak during the check. The compression was 60. All the others were 78. I flew it a few more hours and it seemed not as strong as it was after overhaul (lost about 100RPM static and on takeoff). I pulled the cylinder and found the intake valve was not seating mid face and reground the seat to correct it. After reinstalling it the static RPM is still down about 100RPM and power just isn't what it was 100 hrs ago. Ive flown 265 hours on it in 2 years. It is flown often. I'm running a 71 inch prop at 46 pitch and was getting 2350RPM static and 2425RPM or so in a 55mph climb. I'm now getting just over 2200 static and only 2250 in the climb.
In flight at cruise I have a very slight roughness. Almost like an occasional miss. But not as pronounced as a normal miss. I cant feel it in the floor. There is no vibration associated with it. It does the same on either mag or on both. It almost sounds like a "pop" type noise. At 1500-2000RPM when I add power I have a definite stumble (popping noise) for about 2 seconds. The temp outside was about 35 F (during all the test hops) and the altitude about 4000. It acts like it is too lean? Climb performance is down from 650fpm to more like 450fpm solo at 60mph. Idle is normal and smooth.This is what Ive done so far and cant find the cause of the problem;
-Cleaned, gaped and tested all the plugs. One was suspect for weak spark. Replaced it. No change.
-Check all lifters for collapse and proper valve lift
-checked routing of plug wires and looked for evidence of arcing
-removed carb and checked float level, made sure all passageways are clear and checked to insure the right metering jet is installed, right carb etc. The float level was actually a bit high. I expected it to be too low......(stromberg) The carb was overhauled by an "authorized repair station" at engine overhaul.
-Replaced Brackett air filter element. Gained about 25RPM. It was a bit dirty.
-checked all induction tubes, intake system for leaks.
-checked for loose windshield seal, loose wing root fairings etc (Ive been fooled before by a popping noise!)
-Mags were new Slicks at overhaul...... I haven't checked anything there except timing at the annual
Just prior to pulling the cylinder I changed the oil from aeroshell 80 to 15w50. No metal in the screen.
Any ideas on what I'm missing? Any help is greatly appreciated! My head has callouses from being scratched..........
My C90 showed low compression on the #4 cylinder at annual. Its 250 SMOH. I could hear an intake valve leak during the check. The compression was 60. All the others were 78. I flew it a few more hours and it seemed not as strong as it was after overhaul (lost about 100RPM static and on takeoff). I pulled the cylinder and found the intake valve was not seating mid face and reground the seat to correct it. After reinstalling it the static RPM is still down about 100RPM and power just isn't what it was 100 hrs ago. Ive flown 265 hours on it in 2 years. It is flown often. I'm running a 71 inch prop at 46 pitch and was getting 2350RPM static and 2425RPM or so in a 55mph climb. I'm now getting just over 2200 static and only 2250 in the climb.
In flight at cruise I have a very slight roughness. Almost like an occasional miss. But not as pronounced as a normal miss. I cant feel it in the floor. There is no vibration associated with it. It does the same on either mag or on both. It almost sounds like a "pop" type noise. At 1500-2000RPM when I add power I have a definite stumble (popping noise) for about 2 seconds. The temp outside was about 35 F (during all the test hops) and the altitude about 4000. It acts like it is too lean? Climb performance is down from 650fpm to more like 450fpm solo at 60mph. Idle is normal and smooth.This is what Ive done so far and cant find the cause of the problem;
-Cleaned, gaped and tested all the plugs. One was suspect for weak spark. Replaced it. No change.
-Check all lifters for collapse and proper valve lift
-checked routing of plug wires and looked for evidence of arcing
-removed carb and checked float level, made sure all passageways are clear and checked to insure the right metering jet is installed, right carb etc. The float level was actually a bit high. I expected it to be too low......(stromberg) The carb was overhauled by an "authorized repair station" at engine overhaul.
-Replaced Brackett air filter element. Gained about 25RPM. It was a bit dirty.
-checked all induction tubes, intake system for leaks.
-checked for loose windshield seal, loose wing root fairings etc (Ive been fooled before by a popping noise!)
-Mags were new Slicks at overhaul...... I haven't checked anything there except timing at the annual
Just prior to pulling the cylinder I changed the oil from aeroshell 80 to 15w50. No metal in the screen.
Any ideas on what I'm missing? Any help is greatly appreciated! My head has callouses from being scratched..........
