Finally persuaded a friend to visit and turn the pedals while I watched to see if I could spot what was causing the jumping around. From what I could see the cause is most likely to be balancing… or lack thereof.
The wobbles are tolerable while the turbine turns slowly. But once things begin to speed up it takes on a regular pulsing sound and movement – that might be exacerbated by the shape of the piece of metal onto which the cogs are welded.
Talking with Eirbyte about this, the solution might simply entail replacing the existing wooden disk with a larger one. Then putting lead weights on various parts of that bigger disk to balance the rotor as it turns.
I might also replace the existing piece of metal onto which the cogs have been welded. Because it itself is probably not helping. However I could balance the turbine without doing that… so it’s really a cosmetic desire.
But then again, this yoke is sitting in my house so it’d be nice for it to look good! 8)
That said I’ll only do it if grinding off the current back plate could be done without damaging the cogs.
But now have hope that I can get rid of the thumping and vibrating. It’s about the only thing stopping me clocking up the miles!