I began by making a template to locate the filler hole. I drilled a 2 3/8" hole in a scrap piece of aluminum being sure to leave enough room around two sides to line up with the screw holes in the wing. Then I used a hole finder to locate and drill four alignment holes in the scrap piece. I screwed the template to the wing to check fit.
I had purchased a couple of rubber tank seals that go around the filler neck and sit on the cover. I couldn't resist trying them out to see if they would fit. They do, and have a snug fit over the neck but are a bit too tall. The cap pushes down on the rubber distorting it a little bit (lifts the bottom off the cover). This can be remedied by a belt sander, removing a little at a time until the piece fits perfect. These seals are from WagAero and are for Piper Aircraft. They'll be a nice addition to the SuperSTOL and will seal up any gap between the cover and filler neck. This should prevent a lot of crap from entering the upper wing around the fuel tank. These seals are rubber and are not compatible with E85 gas. I have not been able to find anything similar made out of Viton but will keep looking. Nevertheless, I'll be careful as I can when filling the tanks trying not to spill.
With the template made, I had to transfer the hole to the tank cover. First I had to match drill the template to the cover and cleco it in place as I went. I drilled four alignment holes and cleco'd in place, I took a fine line marker and traced the hole on to the fuel tank cover.
Then I had to find the center of the hole for the pilot bit on the
hole saw. I did this by using a square. I set the square to touch the
sides of the circle and drew lines. I set the square on the opposite
side of the circle and drew two more lines completing a square around
the circle. Then I just had to connect the corners of the square making
an X in the circle, thereby locating the center. Next, I
set the cover up in the drill press the best I could and drilled the
hole. Not bad. Maybe 1/32 off which some of that could be the curvature
of the cover when installed on the wing.
