9-Series Ring Mount (Suspension Frame) Rubber Mounts

Hi John

"Thanks for the catalog link. Looks like I've got some studying to do tomorrow."

To be honest I am having a little difficulty with the problem/question, so the following may have no relevance whatsoever;

Have you considered Barry 22002 range?

5 diffrent durometers -  Axial Load: 60-380 lb.  Radial Load:40-280 lb.

ID .500" -  so bolt OD 7/16 should fit.😈

You can get the complete rubber/steel sleeve/ end caps/bolts assembly from Kitfox Aircraft. It works fine.

Sean Griffin wrote:

Hi John

"Thanks for the catalog link. Looks like I've got some studying to do tomorrow."

To be honest I am having a little difficulty with the problem/question, so the following may have no relevance whatsoever;

Have you considered Barry 22002 range?

5 diffrent durometers -  Axial Load: 60-380 lb.  Radial Load:40-280 lb.

ID .500" -  so bolt OD 7/16 should fit.😈

 I actually already printed out all those 22000 Mount Series pages. You are right, the 22002 series looks promising. However, I would never be comfortable pretending to be a structural vibration engineer and choosing one of those isolators for the 912. It would be a total crap shoot. Also, you'd still have to find a sleeve for the 7/16" bolt to fit snugly in the 1/2" hole in the isolator.

I'd rather hear from people who have flown other rubber mount systems that work. The Kitfox motor mount uses a dynafocal ring and matching rubber isolators which apparently works quite well. That's good information and I would consider buying and modifying some of those parts had I not already spent $1200 on a Rotax ring mount (assuming Kitfox would sell them to me in the first place).

I've got some ideas I'm working on to make everything fit together. If they work I'll post the results here.

"..........have to find a sleeve for the 7/16" bolt to fit snugly in the 1/2" hole ......"

I admit to finding imperial dimensions challenging to work with, but does not a 7/16" OD fit  snugly enough into a 1/2" ID? 

By my calculations  a 7/16" bolt into a 1/2" hole leaves 1.57mm ( .065" clearance). 

If you are going to "sleeve" it the wall thickness would be less than half of the above (about .5mm) - may need to go for a smaller OD bolt with tickr sleeve walls or custom make a larger OD shank on a 7/16" bolt.

Just an update. I was building my motor mount (truss mount for some) to interface my Onex to the Rotax ring mount when I discovered that Sonex, starting in December of 2024, now offers a motor mount for this application. I can't begin to tell you how happy and relieved I was to hear that. It took a while but I have mine now. My problem was solved. 

In the mean time I had already built my own "cups" for the Lord J3608 and found shims for the bolt holes in the ring mount. They are shown below. I built my welding jig and was cutting tubing when I saw the EAA podcast announcing the new Rotax support at Sonex. My welding jig had a 2 degree right thrust built in. The geometry was interesting since the pivot point has to be where the prop flange goes through the cowl, otherwise there would be interference. A complicated math problem to be sure since everything swings 2˚ from that point. I ended up making a drill guide with a 2˚ shim under it to drill the holes for the threaded rod coming up out of the double thick 3/4" ply that made up the "firewall". The metal spacers in the cup ends are slid in for welding so that the cups sit at the correct height on the jig.

I happily threw the whole thing away after I got my order in.

Thanks to all for the suggestions!

John