Belly Pan

My hands hurt from turning the screwdriver and squeezing the rivet gun. Also, turning the 1/4-20 tap. Rivets, and also screws now adorn the Spyder’s bottom. Now the old adage “keep the shiny side up” is pointless.

Spent most of 22 hours this week cutting, drilling, gluing and riveting the last of my 50-foot roll of valley flashing under the car. Work went slowly, in part, because I wanted to re-use all the rivet holes that came on the car. So I’d drilled out all the rivets, then taped paper up under the pan and found them all with an awl, then transferred the pattern onto the aluminum sheet.

It was a big PITA but I managed to get most of the holes close enough so that the wide rivet heads covered any gaps. Again, the look we’re going for (courtesy of the Spyder Factory):

Since the Thunder Ranch is put together a little differently (belly attached over the rockers, nut under; rivets up the spine; big-head pop rivets, etc.) I can’t approach this exactly. But the spirit is there.

After sanding the bottom of the car with 80-grit and wiping it down with acetone, I started in back so as to overlap the panels to the prevailing wind.

Aside from the rivet holes, I had to remember to drill-out the nut-access ports for the seats. These will be plugged later, of course.

The thin-gauge aluminum is glued to the fiberglass substrate with the strongest construction adhesive I could find. This stuff hates to flow so much that I broke my old caulk gun with it when I did the tops of the floors last month. So I bought the heaviest-dutiest caulk gun, loaded the stuff in it and rested it on my electric heater for a while while I prepped the panels.

That did the trick.

I put the 80-grit random orbital sander on the aluminum to promote adhesion, applied the adhesive to that and spread with a fine-tooth trowel. From there it was down to lining up the holes.

Simple stuff, but time-consuming.

When I got to the driver’s foot well it got complicated. I want that to remain an access panel, so I needed screws. But I didn’t want sharp sheet metal screws jutting into the passenger compartment, even though I plan to cover the front area with a floating floor.

So I went with 1/4-inch 20-tpi machine screws. The flat steel “spine” plate is thick enough to put three threads in, so I tapped it. The frame tubes I used sheet metal screws in.

Since this piece is removable I used the heavier-gauge aluminum on it as well.

Finally it was time to make the final access panel to cover the gap between the front firewall and the nose piece. It’s only 14 by 30 inches or so. I used the thicker stuff for that too since there’s no fiberglass to bond it to. Contemplated using a reinforcement piece or rolling a bead in it, but with the screws it feels plenty stiff enough as-is.

For this I had to drill eight new holes in the frame rails, which was tough going. I broke off one bit.

With the rivets removed from the front piece and replaced with tapped-in 1/4-20s, it all looks neat and clean and suitably aircraft-esque.

Not an exact copy of the original but I think it’s pretty decent.

Now, making that rear underpan piece is going to be a chore…

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