Plane: Commander 114 - 1976 SN: 14007
Engine: Factor re manufactured - IO-540-T4A5D, tested 12/19/2000, SN: L-22326-48A, shipped end of 2000
Propeller: 3 bladed McCauley - just overhauled and balanced - July 2005

The current engine was put into service in March 2001 with the existing prop. There were engine vibrations and 13 washers were required to balance the prop as best as could be. I never felt it was as good and smooth as it should be considering it was a new engine.

This July 2005 (at the time of my annual) we had the prop overhauled at Memphis Prop at Memphis, Mississippi. They said they balanced the prop. It was installed and there was engine/prop vibration. There was also a resonance vibration that has a maximum at 1500 rpm and a second lower magnitude harmonic vibration at 750 rpm. I brought it to a nearby airport for dynamic engine/prop balance. The vibration at 2000 rpm was close to 1 without weights and they thought there was a problem with a bulkhead crack. We dye tested the bulkhead and there was no crack. We flipped the prop 180 degrees to see if that reduced the vibration. It did. This was actually the orientation of the prop when the prop was removed for the prop overhaul.

I brought the plane to another airport for engine balancing. They found that the vibration was about 0.9 without weights and they were able to bring the vibration down to about 0.12. Probably could have even improved on that, but the concern was that they needed about 13 washers. We flipped the prop 180 degrees and found that the vibration without weights was 1.4. Again the vibration could be lowered with the use of about 17 washers in the same direction on the bulkhead (same direction as the balancing of the new engine in 2001 with 13 washers). There still is this noticeable resonance vibration at 1500 and less intense resonance vibration at 750 rpm.

The difference in vibration with the two prop orientations is about 0.5. That probably suggests that the major vibration is in the engine and not static prop balance.

People have suggested that the vibration could be caused by a number of things. The Insight – GEM gauge show even CHT/EGT readings for all cylinders. The engine mounts were new at the time of the engine installation in 2001. The governor was overhauled in 2001 and yellow tagged. One observed problem is that prop cycling at 2000 rpm only produces a 250 rpm drop and one would expect least 300. Before the new engine and overhauled governor the engine rpm drop during prop cycling easily went to 300 and lower if I did not stop it by bring the prop forward. Currently, At 2300 rpm the prop cycling drop will go to 500 rpm. Is this an oil pump pressure or governor problem? Could this be the source of the vibration or the resonance vibration at 1500/750?

My problem is that I am not sure what to do. It is being suggested that I could replace the motor mounts at about $360 plus labor (They were new in 2001 and look good/new.). I could have the governor overhauled for $500 plus labor. I could have the prop sent back to the prop shop to check their work and re-balance. I will throw money at the problem, but I want to make smart choices on where to spend the time and money.

The other fear is that the vibrations are in the engine and related to the crank shaft recall. I certainly do not want the engine to fail when I am IMC or at night even if VFR. The resonance vibration coupled with the recall has me concerned. Having a doctorate in physics probably has me overly sensitized to the potential problem.

Thanks go to any and all who have comments and suggestions.

Allan Fuller