I spent most of my time reading up on fuel tank sealing tonight (and re-watching the Van's video). For whatever reason I just didn't have a lot of motivation to get out in the garage, which I've learned is a definite reason for me not to. Many of my best idiotic mistakes have come when my head just wasn't in the game for one reason or another. I did go out for a few minutes to do a couple of steps, just to feel like I'd made some progress today.
The inboard Z bracket for the fuel tank attaches using 3 bolts, but unlike the other Z brackets, the inboard one has the nutplates attached to the spar vs attached to the bracket itself. Usually attaching nutplates is pretty easy, but the location of these created a little bit more of a struggle. To start with, the outer rivets (the ones that are angled) are too close to the edges of the spar web, so the countersink cage won't fit. Even grinding down one side of the cage wouldn't have made a difference. For those countersinks, I took the cage apart (still needed the innards to hold the countersink bit) and very, very careful countersunk by eye. I went super slow, and in the end it worked out just fine. Maybe a little uneven, but the reality is that the rivets holding on nutplates aren't structural. Their purpose is solely to hold the nutplate in place to accept the bolt. They can be pretty ugly and still accomplish that. The access underneath was also really bad, so bucking the rivets made the shop heads pretty ugly too, but solid enough for nutplates. I wasn't happy that a couple of the manufactured heads did sit proud of the surface of the spar, which would interfere with the Z bracket a little bit (very little, but still, this thing holds a fuel tank on). Because of the access underneath, I don't think I would have done any better on attempt two, so instead of drilling them out I just hit them with the 1" Scotch Brite wheel, essentially sanding them level with the surface. The photo doesn't show that part, but you can see one or two of the rivets sitting above the spar.
