Finishing The Firewall Assembly
Van's instructions basically say rivet firewall components together. Not a lot of detail.... After looking at other builders web sites, the method pretty much used is to lay the firewall down on a bunch of blocks and put your back rivet plate on top of other blocks and back rivet everything together. For the edge stiffeners, you can get a squeezer in and do those. They were no brainers. Anyway, I had a couple of problems with riveting the firewall:
- Most of the rivet callouts appears to be 1/2 to 1 length short of what they should be. This was somewhat frustrating in that when I used the size that Van's called out, the shop heads turned out really short. When I bumped the rivets up one size, I got the right sized shop heads, but I ended up having to drill several rivets out as they would tend to bend over. I ended up drilling out more rivets on the firewall than I have probably drilled out on the whole rest of the plane. I ended up getting nice looking rivets, but it was a long painful process.
- It is very difficult to get the firewall to lay down flat on the back rivet plate. Because of that, I had several rivets set high and had to be drilled out. Good thing about these, they drill out pretty easy...
I bucked a couple of rivets on the engine mount brackets and the challenge I had here is that there is really no good way to hold the firewall while you do this. The best thing I found was to put blocks on both sides of the firewall and then clamp the blocks down to the table. It didn't totally immobilize the firewall, but it held it well enough I could buck a couple of the hard to get at rivets.
The reason that I bucked a couple of the engine mount rivets was that it was next to impossible to get at them with a rivet gun and it was also impossible to get the firewall to lay flat against the back rivet plate. What are the other options???
Anyway, I bucked the two rivets on the lower left of this mount. I am really happy with the shop heads on all of my engine mounts. I used rivets that were 1 size larger than Van's calls out and all of my shop heads look great.
When I got to the F601J angles, the rivets along the inside angle are impossible to back rivet because you can't get your rivet gun in along the angle and you can't buck the rivets because you just end up disfiguring the shop heads and gouging the inside radius of the F601J angle. What I ended up doing here is setting the firewall on the back rivet plate and taking the shaft out of my C-frame dimpler, installing a flat rivet set and striking the C-frame shaft with a hammer to set the shop head. It actually only took 3 or 4 blows with a hammer to form the shop heads. Considering the rivets set on the inside radius of the F601J angle, they turned out pretty well. They are not great, but they are good....
Anyway, the firewall is done. For a structure that looks like it would be easy to rivet, it was sure time consuming and I ended up drilling out a ton of rivets in order to get them right.