The radiator is an AFCO 80125n 19" x 26" double pass radiator, core size is 22 ½" x 18". The cut down fan would only cover part of the core so I made a shroud out of aluminum sheet, to mate the fan to the radiator, covering the entire core.
I started by making a paper template. I wanted to have 45 degree beveled sides instead of just making a box shape and have a depth of ½". I played around with the paper until I got the corner pieces shaped correctly, and then tried it with some scrap metal. The large piece of paper ended up being 21 3/8" W x 20 ½" H then I formed a ¾" lip and ¾" bevel. The side piece, only made one because it works on both sides, is 19 ½" H x 1 ½" W bent at a 45 degree angle down the center (two ¾” sides).
Finished checking shape of template.
Next step transfer pattern to aluminum sheet, cut to size, make bends, double check fit, and rivet the three pieces together. Make sure to mark a straight line to keep the rivets in line and also evenly spaced.
Now on to the shroud. The stock shroud is somewhat oddly shaped and has tabs that are not going to be used; also the bottom edge is not flat.
I used a radial arm saw with the blade horizontal and removed the bottom 5/8" of the shroud. You could also use tape to mark the shroud and use a cut-off wheel or other saw to make this cut. This removed the flange and made the bottom edge uniformly flat (sits flush on the table) except for one area on the bottom side of fan shroud. The fan is now 20 3/8" W x 16 ¾".
Next step is to locate fan assembly on the new shroud. I wanted to get as much offset to the side that I could, so set the fan assembly all the way to the driver side edge (water pump clearance). I used tape to outline the shape of the fan then put another line of tape just inside the first tape to give me a ¾" flange and something easy to mark on.
Next I drilled the four corners and cut out the center section with a jig saw. The hole in the center was so the fan hub was not resting on the shroud (so fan assembly would fit flush).
Here is how it looks after the cutout.
So, how do you go about mounting a plastic fan to an aluminum shroud? I suppose there is some sort of glue that might work, but I wanted something a little more substantial. Rivets! I marked up the flange to cut tabs leaving about ¼" for the thickness of the edge of the plastic shroud to sit on.
I used the jig saw to make the cuts because I thought the snips would deform the metal too much.
I used tape to mark an edge on the plastic shroud to keep a straight line for the rivets, about 3/8" from edge.
Bend the tabs down and mark on the tape where to drill for the rivets.
I drilled right at the edge of the tape, make sure and pull the tape down so you don’t have it stuck under the rivets.
The last step is to bend down the unused tabs, I used a small hammer. I also had to make five L shaped tabs for the narrow side (see pic below); there wasn’t enough material on that side to make the tabs as on the other three sides.
Here is the one opening left in the plastic shroud after cutting it down; I used a piece of aluminum to block it off.