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

Since you have "chewed up" the wood a bit in the area where the spikes should bite, try filing the points a bit sharper using a Dremel cut off wheel or flat file (Dremel is much easier). If you shorten the spikes a little it won't matter, they just need to hold enough to get the engine on and the bolts in and tight. If you can get your finger in where they are, you can dob a bit of epoxy on the edge to hold it after they are seated. That must be some kind of hard wood, or the blind nuts are very dull. If that doesn't work, ........?

.....drill the holes out just a bit larger to allow the nuts to be pulled into the hole easier.
The holes are too tight, that's why they won't pull in properly.

FBD.

I actually drilled the holes out one size bigger than the engine mount instructions specified; I thought that this might be the root of the problem. To make a long story short, it worked to the point that the blind nuts went part way into the holes...and then, after digging into the wood just a tiny bit more than before, they started spinning around and folding up again. I may try to find blind nuts with short spikes--I've seen them on the shelves before, so I know they're out there.

Thanks for your help!
Jake

Hi!
What you do is to hammer in the blind nut in small piece of 6mm plywood (diametar around 30mm) and then glue this in on the back side of the firewall.
You glue it in and at the same time screw in the engine mount screws.

What if you made an aluminum backing plate large enough to cover the engine mounting holes and use PEM nuts in it. You could set the PEM nuts using a vice and then slide the backing plate in place. Of course, that's accuming you have access to the back of the plywood engine mount. You can find info on PEM nuts at [link=http://www.pemnet.com/fastening_products/prod_desc.php3?cat=Fasteners+for+Sheetmetal&df=nex t&sp=16]http://www.pemnet.com/fastening_products/prod_desc.php3?cat=Fasteners+for+Sheetmetal&df=nex t&sp=16[/link]

What you would want is on page 2. They are type CL. It might also work to use PEM STUDS (on page 1) with elastic stop nuts (available at ACE Hardware).

Good luck with your efforts.

I dont use the hobby brand for the bigger T-nuts. The hardware store T-nuts have never let me down. It sounds like the wood it really hard. In that case, I would use a smaller allen head bolt thru the T-nut then a washer and nut on the inside. Hold the nut with pliers and screw in the allen head bolt. The T-nut wont spin and should seat straight in. Remove the small bolt setup and install the proper bolt and seat it really good.
Edwin