Background
The plan was to remove the top of the cowl, trim the metal and weld in the replacement 'hats'. But as these things go, a closer inspection showed that someone had done work here in the past. They had cut the top off and just sealed off the grille from underneath with a metal plate. Leaves and dirt had already gotten stuck inside.
I considered trying to work with what was still left but there was just to much damage to fix. The was even a nasty crease on the passenger side in a very conspicuous place. There were also some rusted out edges along the firewall that would take pounds of seam sealer to waterproof. Shopping around, I found that it was cheaper to purchase the entire assembly so it made sense to place the whole thing.
Removal
Don't forget to support the car with jack stands under the frame rails just behind the firewall or the empty cowl opening will collapse together a little (or a lot if your floors are rotted). To remove entire the cowl assembly, I began by drilling out all of the spot welds around the perimeter, starting with the apron extensions. Make sure you have a sharp 5/16 or 3/8 drill bit and be careful not to drill all the way through. For most spot welds on the cowl, you have to cut through the metal of both the top and lower parts to free it from the firewall and cowl sides. There are also a bunch of spot welds along the windshield flange that attach the cowl to the dashboard metal. In my case some of my spot welds were in rotted areas so I didnt have all 150 to drill out. After some chiseling and prying, and cutting a couple factory braises, the cowl was free. Note that the rear of the lower half does not attach to the dashboard flange and is welded only to the upper half of the cowl. Did I mention this would be much easier to do when the engine is not there?
Looking at the old cowl, it turns out the the plate just under the grille was meant to catch water and route it off to the passenger side. When they welded the plate on, it caused the crease in the upper surface of the cowl.Cleanup and Repair
Next its time to break out the flap disc, clean up the mess and assess the damage. I ended up cutting out the cancer in the flanges along the outer edges of the firewall. I had some left over edp coated metal that was the same thickness and used some thin cardboard to make templates and trace out on the metal.
Once the patches were welded in, I added some seam sealer in the hard to reach spots. A coat of primer on the entire flange surface was next. I used weld-through primer but I have seen some people use regular primer over dots of tape where the spot welds are going.
This was also a good time to patch up some unneeded holes in the firewall. Reassembly
I have seen a few different ways to assemble the two cowl pieces. Some attach the lower part first then the top. Some attach the two parts together completely then attach to the car. I decided to do a combination of both.First, I added a little seam sealer around the bottom edges of the hats to reduce the chance of water getting in.
Next, I set the lower part in place and chose and marked all the points that were to be spot welded to the flanges taking care not to line up with the old drilled out spots. You'll notice that rear part of the lower cowl doesn't reach the dashboard metal. It is supposed to attach to the bottom of upper cowl piece (it helps to look at the old cowl). I used my hand punch to punch 5/16" holes around all the edges of the lower cowl. The plan was to spot weld the bottom half to the top just along the back edge. The idea is that you will see little or no evidence of welds on the top making less work later. This area is under the windshield clips so not too much to worry about.
Before attaching the bottom to the top, I lined up the upper and lower parts using the alignment holes and clamped them together so I could mark top through the punched holes. The idea here is to spot weld the top and bottom and firewall/dashboard together through the same holes.
With the two pieces partly welded, I placed them on the opening and used the large holes to line up with the alignment holes in the firewall and clamped everything together and started spot welding. The corners near the pillar posts may need a little extra hammering and clamping to get things to sit right. Make sure all of the spot welds penetrate well. There is a lot stress on this part of the body. Its a good idea to tack the cowl assembly in a few spots then place the fenders to make sure the cowl lines up right and the gaps are good.
Finally, I spot welded the original apron extensions in place and lined up using the drilled out spot welds.
Later, a nice bead of seam sealer will go in underneath along the firewall and cowl sides.
