Thanks for those images. Looks like a larger AL disc could replace part of the spacer's thickness and bolt to the holes where the damper plate mounted. Does that look reasonable 'in person'?

If feasible, I'm thinking that it could serve two purposes; raise resonant freq of the flexplate to a safe area, and add mass close to what would be in an AL flywheel (they're getting hard to find used, and new ones are really expensive).

I suspect the extra rotating mass on the Eshaft is needed (or at least a good idea). 

Charlie

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On Sat, Jan 11, 2025 at 6:45 PM 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