BTW, did you have visible smoke trails?  I don't.  I wonder if there was some sort of change in the way the riveting was done. 

Dave;

There were maybe a couple very slight trails on the flange side (toward the re-drive).  On the other side (I guess the head side of the rivets) where I could only see about 4-5 of them through the holes in the flywheel (ring gear); all had distinct dark trails.

It's possible that power is the main issue (average torque), but it seems to me that peak torque and torque variation amplitude are what are going to matter most.  You and Mark are going to have lower peak torque than those of us with turbo engines, and with 20B's you are are going to have lower torque amplitude than even those with n.a. 13B's. 

One would think that is true; but you can’t be sure.  It is possible the 20B may have some harmonics (resonance vibration) somewhere in the range of operation that the 13B doesn’t have. Seems unlikely with the snubbers and the ‘play’ in the system, but . . .  We need more feedback from all the users with more than 150 hours, or so, to see what the pattern is.  I’m not aware of rivet changes – Tracy?

Mark and I both have constant speed props and I think Al does also. Don't see how it could make any difference but worth considering in the investigation.  Bobby

I have a fixed pitch Catto.  The mass of the prop would likely be a factor – if there is some torsional vibration involved.  My Catto only weighs about 16 lbs; plus 3-4 for the extension and spinner. I have 180 hours and barely detectable rivet wear; Mark apparently has more wear at about 150.

Al