JorgeKitfox
Member
Hello everyone,
My name is Jorge and since a year I've been fighting with my rotax 912 ul (80hp). It is installed on a Kitfox III. I desperately need help! I hope any of you guys could bring some light to this issue...
The vibration started like 30 hrs ago. When I bought the plane the engine was running super smoothly and the vibration appeared after about 5 hrs of flight. It started easy at first and became greater with the hours. It's sounds like one of the cylinders would be missing ... it is worst on lower RPM's and smooths out, just a bit, on mid range-full power but generally shakes as a tractor! The vibration is such that one of the air filters will come off and fuel will spill over the air intake of the carburetor. Surprisingly, ignition test is OK with a drop of about 100 rpm's with no variation on the shake on one particular ignition side ...
A "funny" detail about this shake ... it will be hard to start the engine in a cold morning but once it fires up for the first time, it will start up easily after. Then the engine will run smooth for the first 15-20 seconds until it will start to shake .... any clue ????????
Believe me when I say that I've tried EVERYTHING to fix it and so far the problem continues.
Mechanically the engine is been thoroughly checked: crankshaft eccentricity, camshaft, tappets, valves, valve springs, segments, pistons, compression, reduction gear tested on press, etc. New style fuel pump. So for me doesn't sound like a inner-mechanical issue.
Carburization. My carburetors has all its components new (diaphragms, needle, spring, needle jet, main jet, new floats, new float valve etc). I even tried with two different pairs with new components as well. Every time I swoop them, performing mechanical and vacuum synchronization. Primer circuit closes properly on both carbs.
The mixture manifold is inverted on my engine (left is on right) so carburetor levers are inboard. This is due to the throttle mixer design in the Kitfox III. It leads to a lot of play and therefore, possible unbalance on the carburetors, but I minimize that as far as practically possible ...
Propeller. My prop is a warp drive, I balance it, checking all the blades has the same angle and nothing. I also checked with a different prop and the vibration was still the same...
I also checked the engine mount for cracks, checked the bolts torque and replaced the engine mount shock absorber ... nothing!!
I then tried by isolating the engine from the airplane sytems by feeding new fuel from a canister directly to the carburetors and attaching a direct cable from the frame to the CDI boxes ... any of this worked.
So now my suspicion ....Ignition. I virtually checked all the components of the system either by checking the resistance with multi-meter or replacing parts. New spark plugs and connectors, new ignition cables (properly screwed on both ends), replaced the dual coils, tried with different CDI boxes, all connectors cleaned and tested, trigger coils gaped as per manual, etc. No change on the vibration.
I found however that the cables from the stator to the CDI boxes were in real bad state, thinking that they were shorted at some point. I replace those with proper quality cable and covers, re-checked again the resistance values and isolation of both coils. But after reinstalling the whole thing was still shaking ...
I am not a mechanic myself, and I just can't understand electricity, so my question here: I believe that a stator is a quite simple design but is it possible that, even with new cables and with all electrical values as per rotax manual, this stator could be the cause of the vibration?
I keep suspecting of a electrical issue so I checked the quality of the spark by removing the plug and grounding it to the exhaust pipe. Then I did crank the engine observed that the spark wasn't rhythmical as expected and looks like it was missing ... ???? however the ignition test didn't showed any failure or excessive drop... how is that possible??
I am running out of ideas ...
Any help welcome!!
Jorge
My name is Jorge and since a year I've been fighting with my rotax 912 ul (80hp). It is installed on a Kitfox III. I desperately need help! I hope any of you guys could bring some light to this issue...
The vibration started like 30 hrs ago. When I bought the plane the engine was running super smoothly and the vibration appeared after about 5 hrs of flight. It started easy at first and became greater with the hours. It's sounds like one of the cylinders would be missing ... it is worst on lower RPM's and smooths out, just a bit, on mid range-full power but generally shakes as a tractor! The vibration is such that one of the air filters will come off and fuel will spill over the air intake of the carburetor. Surprisingly, ignition test is OK with a drop of about 100 rpm's with no variation on the shake on one particular ignition side ...
A "funny" detail about this shake ... it will be hard to start the engine in a cold morning but once it fires up for the first time, it will start up easily after. Then the engine will run smooth for the first 15-20 seconds until it will start to shake .... any clue ????????
Believe me when I say that I've tried EVERYTHING to fix it and so far the problem continues.
Mechanically the engine is been thoroughly checked: crankshaft eccentricity, camshaft, tappets, valves, valve springs, segments, pistons, compression, reduction gear tested on press, etc. New style fuel pump. So for me doesn't sound like a inner-mechanical issue.
Carburization. My carburetors has all its components new (diaphragms, needle, spring, needle jet, main jet, new floats, new float valve etc). I even tried with two different pairs with new components as well. Every time I swoop them, performing mechanical and vacuum synchronization. Primer circuit closes properly on both carbs.
The mixture manifold is inverted on my engine (left is on right) so carburetor levers are inboard. This is due to the throttle mixer design in the Kitfox III. It leads to a lot of play and therefore, possible unbalance on the carburetors, but I minimize that as far as practically possible ...
Propeller. My prop is a warp drive, I balance it, checking all the blades has the same angle and nothing. I also checked with a different prop and the vibration was still the same...
I also checked the engine mount for cracks, checked the bolts torque and replaced the engine mount shock absorber ... nothing!!
I then tried by isolating the engine from the airplane sytems by feeding new fuel from a canister directly to the carburetors and attaching a direct cable from the frame to the CDI boxes ... any of this worked.
So now my suspicion ....Ignition. I virtually checked all the components of the system either by checking the resistance with multi-meter or replacing parts. New spark plugs and connectors, new ignition cables (properly screwed on both ends), replaced the dual coils, tried with different CDI boxes, all connectors cleaned and tested, trigger coils gaped as per manual, etc. No change on the vibration.
I found however that the cables from the stator to the CDI boxes were in real bad state, thinking that they were shorted at some point. I replace those with proper quality cable and covers, re-checked again the resistance values and isolation of both coils. But after reinstalling the whole thing was still shaking ...
I am not a mechanic myself, and I just can't understand electricity, so my question here: I believe that a stator is a quite simple design but is it possible that, even with new cables and with all electrical values as per rotax manual, this stator could be the cause of the vibration?
I keep suspecting of a electrical issue so I checked the quality of the spark by removing the plug and grounding it to the exhaust pipe. Then I did crank the engine observed that the spark wasn't rhythmical as expected and looks like it was missing ... ???? however the ignition test didn't showed any failure or excessive drop... how is that possible??
I am running out of ideas ...
Any help welcome!!
Jorge
