Thanks Al, will have to do that feel check.  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. 

 

Early drives like Tracy, Ed, Bill Eslick(? havent heard), Todd Bartrim (havent heard), Chuck Dunlap (havent heard), Tommy James (havent heard) and I (so far) don't seem to have a problem while you and Mark who have slightly later versions are having loosening.  (Have we heard from John Slade or Steve Brooks and I missed it?)  Any other high-time re-drives that I left out?)  - What about Tom Parks? (turbo 20B with Ross Drive).

 

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.  Only your average torque is higher.  Seems strange... that is why I am wondering about some sort of change to the later models of the gear drive.  Tracy?
--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net

On Wed, Mar 24, 2010 at 11:25 PM, Al Gietzen <ALVentures@cox.net> wrote:

 

I tried to check my plate for smoking rivets today, but the shop head is against the flywheel and I can't see a thing.  The round heads all seem fine.  Couldn't detect any that seem loose or smoking or anything.  Will just have to keep an eye on it.   David Leonard

 

Dave; there is a way to check.

 

I went for further checks on mine today – had to make the decision whether or not to fly it to Jean, NV, on Saturday for the CONTACT! Alternative Engine Fly-in.  (First I went flying for about an hour just to make sure I wasn’t going to be deprived of my enjoyment before I had to fix itJ)  I went to look for loose rivets, or to see is I could detect any relative movement between the spline adapter flange and the aluminum plate.

 

No way to get at the heads of the rivets without disassembly, and everything ‘looked’ fine on the front side of the flange. So I pressed my fingertips onto the plate, overlapping them onto the beveled edge of the flange; then pulled a prop blade back and forth with the other hand. I could detect that there was relative movement; however miniscule, as in maybe a few thousandths max, but it was there. I could not detect it visually, but I could feel it.  So after some considerable deliberation, I decided that this should be fixed before more flying. 

 

I suspect if I done the same thing many flight hours ago it would have been similar, so a few more hours wouldn’t really matter, but I had to consider that aluminum rivets will work-harden, and become brittle, and then at some point possibly subject to breaking, especially if there is any operating regime where there could be torsional vibration with force reversal.  No way of knowing when that point would be reached.

 

So I think you should give it the ‘sensitive fingers’ check, and feel for relative movement. Not that you necessarily have to replace the rivets right away, but if you are quite certain there is any relative movement it is definitely a cause for concern, and should be checked again after a few hours and see if you can detect a difference.

 

I’m planning on replacing the rivets with AN173-6A bolts, with MS21042-3 metal lock nuts over AN960-10L washers. Maybe Mark can tell us if the thin washers are enough to sure the threads don’t bottom out. About 4 or 5 of these bolts would be as strong as 20 aluminum rivets, but I guess all 20 would be good to distribute the stress in the aluminum plate.

 

Al G