I am expecting my Direct Sheetmetal firewall for my 40 Willys any day now. I am doing some advanced brain storming. I have to cut the cowl back about 6 inches. I plan on mig welding (tack) the firewall in place, and I know I've seen articles on this before. Are there any critical preperations that should be done? Will the tack welds be enough to seal and hold the firewall, or should I run a bead of sealant on the inside, at the joint? As I said, I'm just planning, but I like to get my ducks in a row. I want to do it right the first time!

Thanks,
Bob
aka MrWillys

Youll need seam sealer if you ever plan on driving it. If you only are going to push it from the garage to the trailer to the show, you wont need it.

Fas as welding it in, Im just now in the process of getting mine ready to weld in, so not much help there. Im making mine myself outta approx 12 ga sheet metal so I dont have to have beads rolled to keep the flex and vibrations out. Little too thick, but I dont have a bead roller or access to one.
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Damn, I wish I had more time.
35 Ford Pick-Up

i will seal it for sure. Any reccomendations?

I'm not sure what you mean by cut the cowl back 6". Most after market firewalls are made to replace the original at the factory seam. If you have cut away the cowl, you are going to have to do some "custom fitting" If you haven't cut into the cowl, wait till you get the new firewall! To replace it drill out the spot welds holding the firewall to the cowl. Seperate the pieces with a thin chisel. Fit the new firewall and plug weld it in using the holes that you drilled out. Use weld-thru primer on the mateing surfaces of the two panels. Seam seal both inside and outside of the seam, after you prime with epoxy primer! Use a quality seam sealer, get it from a automotive paint store. You are not just preventing water leaks, your sealing off the seam to prevent rust. If you want a smoother look, clamp the new firewall into place, and weld it in solid from the back. Then you can cut off the flange on the front side, and grind it smooth. Most times you will have to do more welding on the front side, and grind it smooth. Like any welding go slow and move around to keep the warpage under controll. Allow lots of cooling time. If you want to cool it faster, use an air blower, not water. Make good solid welds, 7/16" at a time. Not tiny 1/8" welds, you won't get good penitration, and will end up with pinholes.

Bob, I think your question was how to seal the firewall, not how to insulate it, but that will be next. I weld a few 90 degree pieces of sheet metal to the outside edges of the firewall on the inside. Then cut 1" x 2" Oak strips and attach them to the pieces with sheet metal screws forming a wood outline of the entire firewall. From there you have at least 1 inch of space to install insulation of choice. I used a number of pieces of the white hard foam found in most shipping containers. It comes in various thicknesses from 1/2 inch to 3 or 4 inches. I cut them to fit a particular section (about 12" x 15") and wrap them with several layers of aluminum foil. They can be glued to the back of the firewall and provide execellent insulation from the engine heat. Your upholstery will attach to the wood pieces with snaps, screws, etc.. It is very easy to cut holes for throttle cables, A/C/Heat lines, etc with just a sharp knife. It then seal with some type of "dum-dum" or rope caulk as some call it. Try it and see how nice it works, and its cheap. My 46 Ford Coupe has 12K miles on it here in Texas and I don't feel any heat from the firewall area. Cheers - Johnnie

Thanks guys. No, I did mean I have to hack the cowl. I'm putting a hemi in my Willys, gotta cut it back like the gassers. There is literally no choice. I've studied it to no end, becuase I hate to cut this area out. I will have to reinforce and support the area. So, this is not a simple swap.

In that case, weld it in solid. I'd bend up a brace out of tubeing that matches the opening, and weld it in, then weld the firewall to that.

Not a lot of experience here, but I installed a Direct Sheet Metal firewall in my 32. It was a weld in model and I basically followed Tinbenders advice (without knowing it). I welded it solid, but from the outside. The inside is not accessible/practical to weld in the '32. It came out great. I did not seam seal it yet, but after reading this, I guess I will.