How To Build a Hardtop
This is, briefly, how I built a hardtop for my Cobra Replica.
This was to be a low-buck approach. I wanted a winter project, and I also wanted something to make the Cobra a little more weatherproof. I didn't think that I could make a soft-top, but I figured a hardtop wouldn't be too hard to make. Naturally it was harder than I thought, but it did turn out pretty good.
I first mocked it up using cardboard (I can't find those pictures, so they aren't here!).
I traced the cardboard patterns onto 1" thick styrofoam sheets, and taped it together. It was
just a rough, kind of boxy, design at this stage but I would fix that up later.
I wanted it to be high enough to give a decent amount of head-room inside. If it went over the roll bar I didn't think it would look right (too high). So I made a cut-out to clear the roll bar to keep the roof a reasonable height. I would later cover the roll bar "hole" with a thin layer of glass cloth and epoxy.
Obviously very boxy at this stage. Since this was winter, I was working in a single car garage. Since I built the whole car in this garage, I was used to working with a limited amount of space.
I cut the rear window opening, obviously keeping it small and then gradually opening it up until it looked the right size. The original plan was just to have a rear window. When I sat in the car at this stage, I realized that the visibility out the rear quarters was poor. So I decided to cut some small openings in those panels as well. As this was a low-buck approach, I didn't want to get into bending the windows, so I made sure the panels that they were mounted in were flat.
It still looked a little too flat at this stage so I thought I'd better add a bit of a curve to the top.
Into the workshop with it. I added a few more layers of styrofoam to it and cut and sanded a bit more shape to it. Since I also build radio-controlled airplanes, I had a hot-wire which made shaping the foam a little easier. As you can see from the floor, it still is quite a messy job; the thin pieces of foam love to static cling to everything.
That's better! At this stage I actually felt that it may turn out OK. One of the reasons that I started with a "low buck" approach is because I didn't really know if it would work out or not. If it didn't, I figured that I could throw the whole thing in the trash and not lose much money. How's that for a positive approach to a project?!
Back into the workshop to start the glassing. I used West System epoxy and fiberglass cloth. By using this in the inside and the outside it makes a very strong, light top. You can see that I covered the roll bar opening with a layer of cloth and epoxy.
I "scooped" out the extra layer of foam from the inside to give more head room. There are 4 mounting brackets epoxied into the rear portion; 2 at the back and 2 on the side panels. You can't really see in this picture, but there is an aluminum angle piece epoxied in along the front edge. I shaped this to match the curve of the windshield. I drilled 4 holes in it to attach to the windshield. What I did was grind the heads of 4 bolts so they would slip upside down into the channel opening at the centre of the windshield. Then I slide them over, 2 on each side. The top fits on and the bolts pass through the holes in the aluminum angle piece. There are small cut-outs in the foam so I can put the nuts on from the inside of the car. Nothing shows from the outside. Is that description as clear as mud? You can just see that I cut channels around the window openings so I could glue in the windows (Lexan sheet) from the inside. The inside was all glassed just as the outside was. The only mistake I made was buying a quart of epoxy and thinking that would be enough. I ended up buying 3 more before I was done.
I used the same epoxy mixed with various thickeners to build up a sandable layer on the top.
OK, a trial fit on the car. This was the first spring running of the car. You can see the condensation dripping from the side pipes and the centre caps not on the wheels since I was checking the torque. Oh yeah, I also had to find the hood!
I was pretty happy with the way it came out. Now for a final painting and it was just about done.
I decided on a reverse colour scheme for the top for a number of reasons. The main one was the low buck approach. Since I wanted to paint it myself, I figured it was easier to match the white to the white stripes, and get some trim striping to match the blue. If the blue stripes were a little off in colour, I didn't think it would be noticeable. If I followed the colour scheme of the car, I would have to match it exactly or it would look funny. Since I didn't want to get it done at a body shop (low buck, remember?) I went with the reverse scheme. I first tried both out with a paint program on the computer and actually liked the reverse scheme better.
So there it is. The winter was filled with a useful project, it kept me off the streets, and now it was time for a spring drive.
I "sealed" it to the rear of the car using silicone seal. No, I didn't glue the thing down. I covered the rear portion of the car with waxed paper and basically applied a thick bead of silicone to the top and lowered it in place. Once it cured I took the top off and trimmed it to shape on the inside and outside.
So how did it all work out? Well to be perfectly honest, not quite like I expected. I thought it would cut down the wind and also reduce the noise level in the car. It really didn't do much of either. The wind seemed to come around the wind wing and into the side of my head, no matter how I positioned the wing. Other than that, it did cut down the wind somewhat. As for the noise level, well, I sort of equate it this way. Without the hard top it was sort of like sitting beside a speaker cabinet. With the hard top on, it is like sitting in a speaker cabinet. Maybe side windows would have helped. That was the next project, but I ended up selling the car before I got serious about it. Anyways, it was a fun project and it did draw a lot of attention at the local cruise night (not that Cobras don't on their own). Not only did I have the first FFR in Canada, but I may have had the first hard top on one.
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