Hi all. I am having serious trouble installing an engine mount on my Yellow Aircraft 1.20 Sukhoi. I bought the plane used, and at the time it contained a G23 gas motor which I found to be inadequate power. I have taken the motor off, bought an OS 1.20, and drilled holes in the correct location to install the new engine mount rails. This is where the problems start. The firewall is 1/4 inch hard ply. When I try to seat the blind nuts by tightening a bolt into them, one of two things happen: either the spikes fold and the nut starts spinning around, or the nut spins around even without the spikes folding up. So far, I have ground two "circle tracks" into the area where the blind nuts should be going in, which is not going to help the structural integrity of the engine mount. Additionally, I cannot access the rear of the firewall with anything but my fingers, so hammering the nuts in is out.

I am using good-quality hardware (Great Planes) and have never had this problem before. Does anyone have any tricks they use to install blind nuts when this kind of thing happens? The only other solution I can think of is finding an engine mount for an OS 1.20-sized engine, but with a backplate on it with holes where the G23 would mount (that way, I could use the holes that already have the blind nuts installed).

Any help in this little misadventure is greatly appreciated!

Thanks,
Jake