Just a thought, would changing the prop position in by one or two bolt holes make a difference?

Georges B.

Hi Georges,

Thanks for the comments, but I don't believe it would make any difference.  Rotating the prop is a trick to try to get the prop imbalance, to cancel out the engine imbalance.  In this case, I don't think either is actually out of balance, but rather there's a resonant vibration being caused by the single rotor torque reversals. 

Cheers,

Rusty (never seen a "good" used rotor housing I'd call mint)