Thanks for the resonance data and photos Steve.

A questions. I’m thinking the larger photo of the original C4 splined female part was what I was thinking of doing.
Ie. Removing Tracy's rivets and turning it down before drilling the 6 holes to match the Eccentric shaft.
Is the original splined part from the C4 also in the photo with a spacer? Or is this another different part?

Thanks Steve



> On 12 Jan 2025, at 8:43 am, Steven W. Boese SBoese@uwyo.edu <flyrotary@lancaironline.net> wrote:
>
> When the Flexplate is bolted to the eccentric shaft without the damper plate it rings with frequencies of around 320 and 1340 Hz.  It doesn’t ring with the damper attached.
> This gives the possibility that the Flexplate without the damper may resonate being excited by the engine harmonics at rpm ranges normally used in flight.  Such resonance could accelerate Flexplate cracking.  For this reason, I would be reluctant to eliminate the damper while retaining the Flexplate.  Converting to Tracy’s recent solid coupling design may best be done by also replacing the Flexplate with a manual transmission flywheel.
>
> The photo shows a couple of possibilities to convert to a solid coupling while retaining the original splined input shaft.  The thickness of the aluminum spacer or the steel part can be adjusted to accommodate the thickness of a flywheel.
>
> Steve Boese
>
> <image0.jpeg>