Interesting power separation.

[Aztec Driver]

I have noticed a new development in my Twin Comanche.

All seems normal on runup, takeoff, and cruise. Even on a full power static runup. When at low power, especially when in landing configuration, the props become uneven when at the same indicated manifold pressure. The lower the pressure, the more uneven it becomes. At landing power, on final, the props are at least 200-300 rpm different, causing a slight yaw.

This is a difference than what it used to be.

I originally thought it might be prop governor problem, but I believe it should be below the governor power level by that time. It almost seems as if the right engine is not producing the same level of power as the left on the same indicated manifold pressure. Almost as if the manifold pressure gauge is reading inaccurately.

 

[JHW]

Look for an intake leak, probably on one of the rubber hose joints on the intake joints.

 

[Henning]

What is your oil pressure at low RPM? Perhaps one engine is not carrying enough to maintain prop pitch against the spring. I would look there, and do an oil and filter change gathering a good sample set to send for analysis and cut open the filters. Do this as well, spin up the prop to 1600rpm then chop the throttle. Any extra little knock or hollow sound differential between the two engines? Maybe also service the oil pressure control valve.

This will eliminate or confirm both the simplest and the worst case possibilities, the regulator or a spun/worn out bearing.