Torsional vibrations
So you have a little more insight to the issues.
leemind
I am aware of these engines. Yet the engine does have a reduction gearbox and a torsional vibration damper fitted as well which more than likely only matched to the MT propeller. This part of the adaptation probably accounts for 30% of the weight. Add in the torsional vibes from a rotor system and you have some major issues.
Ideally of course the drive system will need better integration to achieve the desired result - read clean sheet.