Mark,

I have built these mounts for engines as large as 2.2 in the past with no additional material between the rings....only fuel proofing (epoxy coating). The engine in general will pull the rubber enough even at low-mid power settings, eliminating contact at the ring interface. The rings are capped with 1/64" aircraft ply regardless so this is not a big deal. I have the original mount I built about 5 years ago still in use today for my Webra 160, some 1700 runs later. One of these years I will disassemble the thing and take a look. Merle Hyde gives a 3000 run warranty on his mounts with good reason.

At idle, the engine bounces enough to make the rings slap one another and you can hear the slapping of the surfaces. Actual experience notwithstanding, I felt that couldn't a good thing so I started lining the face of the backplate ring with thin rubber stock from a bicycle inner tube. This is adhered the same way as the rest of the rubber.....cleaned with rubbing alcohol and ca'd in place. It's a simple add-on during assembly and is only added to areas between the bolt holes.

I am sure the slapping of the rings is still happening except the potential effect is eliminated and noise gone..... always a good thing on a pattern model. I do not recommend that a harder substance like monokote or even teflon be added. They are slipperier than rubber for sure but are also much harder and don't absorb any vibration. I'll post some photos of that later this week.

MattK