Fabricating Fiberglass sunroof plug

[Xploitn]

I will be fabricating a fiber glass sun roof plug for my 96 GSX that I am building for autocross (classed in ESP). This plug will replace the entire 27.5lb sunroof assembly. The purpose of this project is to reduce the weight at the top of my car which will help the handling, roll center and the center of gravity. It will be nonfunctional, but leakproof. I am choosing fiberglass because it's not heavy and I've done some FG with subwoofer boxes in the past. Carbon fiber is too expensive for this project and would only serve as icing on the cake since the plug would be made with primarily FG anyway. The plug will be finished off with some comprehensive applications of primer, paint, clearcoat, and sealer... rattle can style! The goal is weight reduction so the lighter it turns out, the better!

After going through most of the threads on this site and many outside of it I have a pretty good idea on the design.

I will be pulling the stock glass. I will try to peel off the seal around the glass cleanly so that I can reuse it on the plug if I decide to. I will then wrap the glass in a layer of cellophane and duct tape where its necessary. This will be the template or mold for the new plug. I will then stretch a piece of fleece over the glass and test for fitment /clearance. The resin will be mixed and applied right to the fleece for the first layer, each subsequent layer will get a layer of FG weave and resin. I will let this piece cure. then peel it off and test it for fitment in my roof hole again. Hopefully it fits!

Unknown #1: I want to bolt in down for safety and then seal it with black silicone. I am still not 100% sure how I am going to bolt it down. I am open to suggestions but I might use rivets, T bolts, or clips. My two concerns are that the FG plug will not be thick enough and that the vibrations from the road will crack the FG if I start drilling holes through it. I thought about laying T nuts or washers into the FG as I'm laying the layers down. Would this increase the possibility of cracking? If I did the washers, I would probably do pin latches similar to aftermarket hoods. I would probably only need two in the front and two in the back. These would only be for safety so that the plug doesn't eject itself when going around the course!

Unknown #2: I still need to inspect the edge of the roof when I take the old sunroof out, but I think I will be mounting the bolts/rivets/clips using L-brackets so that the plug sits flush.

Now to my questions,
Does anyone have any better ideas for a more flush solution for the safety bolts/rivets/pins, please let me know.
Unknown #3: Once I get the shell of FB done by using the stock glass as a mold, can anyone think of a good solution to use as a core for thickness?

I have most of the materials on hand from a past project which is why I'm willing to jump into this DIY project with so many unknowns.

The project will be documented with pictures, measurements, and documentation on the parts and supplies used.

As always thanks for any help and input!

 

[grothe3297venge]

This seems like a great concept that you have going, but if you don't want your sunroof (unless I missed it somewhere you want to change between the two), why don't you just weld it, paint it, get a non-sunroof headliner and call her good. I mean this will eliminate all riveting and drilling and no use of an L bracket, and less weight..

 

[Xploitn]

Yeah this is a dedicated racing car. I'm okay with not ever being able to switch back and I wont miss the sunroof. I've already taken the A/C and emissions systems out, so I'm not worried about ruining the "resale value"

I could do what you are suggesting but how much would that cost? Seriously, could someone give me some insight on the cost? My DIY solution will be less than $50-100 bucks especially since I'm reusing the FG materials I have just lying around.

There is a DSMtalk tech guide with pics of a guy doing almost exactly what I am proposing. It solves some of my mounting questions. He uses only urethane to mount it, think that'll be "safe" enough? I might get lazy and not go with bolts/rivets/clips...

If I just do FG and urethane stuck to aluminum L brackets would be lighter than welded steel right?
(This isn't a deciding factor, I'm just curious)

 

[awdrst]

When I've made sunroof panels in the past with carbon and fiberglass we made L brackets and bolted it into that. We used nomex honeycomb for reinforcement but you could just as well use the foam to make it stiff.

 

[gixrman]

What you can use for a core material is elmers foam board (1/4")from any CVS, walmart, etc. And saving yourself the agrivation of building a mold just cut out exact copy of the hole or sunroof, lay one layer of FG on the foam board, cut it oversize slightly and then shape it size. lay on more layers of glass, paint. I've used this before, but just with epoxy resin as the poly resin will eat the foam. Also its cold and resins dont like temps below 60. So plan on doing this in the spring. YOU DO NOT WANT TO DO THIS IN AN ENCLOSED ENVIROMENT!

To make a mold, a good mold your going to want to use a good gel coat and and have a plan on selling a few to make up the cost of building it.

 

[mike96]

I would think the best way would be to see if you could pic up a sunroof top of a car from the junk yard. That way you could put your glass in it temporarily, fiberglass over the top of it (using something to keep the fiberglass from sticking to the glass and or seal) so that you have a good general shape of the entire roof. Flip it over and pull the glass out. Fill in/shave down any imperfections you don't want in your sunroof plug. Then, tape or use whatever to keep the fiberglass you are going to put down next from sticking to the old fiberglass and the inside of the roof and fiberglass away... This way, you will get the general shape of the roof correct and you can make the plug big enough so that it could be bolted into place using the existing bolt holes/studs for the factory sunroof frame (with some some sealant for good measure of course).

And if done correctly you have the perfect mold for making "bolt in" sunroof plugs.

 

[Xploitn]

I started the process yesterday, here is the progress, I did all the work outside then moved it into the laundry room of my apartment building to cure.

I did plastic wrap, then stretched fleece, then coated it with A LOT of resin, then put a layer of fiberglass matting down and put resin over that. at this point the piece is about 90% cured as its still tacky in some places.

Here is the photo dump

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

The rust from 17 years of age, It was all hiding under the seal. It's been about a week since the last time we got rain and there was about an once of cruddy water that came out when removing the seal. The seal remained in good shape after removal, I might reuse it for cosmetic looks on the new FG plug.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

Back to work:

You must be logged in to view this image or video.

Wrapped in Fleece:

You must be logged in to view this image or video.

You must be logged in to view this image or video.

One layer of matting:

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

The underside is a bit rough because gravity was not being very friendly. I'm probably going to cut off the bottom edge and redo it after I take the stock glass out. When I go to redo it, I'll get some foam that Gixrman recommended and tape the foam along the edge and reglass.

Unfortunately, all that's going to have to wait because I used up all the hardener and resin that I had

I eyeballed the mounting area before going to the store and I got 8' of aluminum L brackets that measure 1/8" thick and extend 3/4" in each direction. These might be too big and meaty so I might go return them for thinner smaller ones after I take proper measurements.

 

[eligst21]

I'd be interested to see how this turns out. I've always wanted to close my sunroof hole as well.

 

[Xploitn]

Yup, I just removed the rest of the sunroof assembly today, I'm very curious to see how much this ends up weighing. I am debating whether it's worth it to use bondo to smooth it out before the paint. I probably will do it but I'd hate to add weight since I'm going through all this work to get rid of weight! Keep in mind that the car isn't ever going to see the street so not having a finished look wouldn't be the end of the world either...

I'll be continuing to document and take pics. Unfortunately I just blew most of my paycheck on supplies and I need more resin, hardener and cloth to finish this right.

I'll be glad I have a good cover if it rains in the next two weeks

 

[gixrman]

Please tell me you checked that the poly resin does not eat through the plastic wrap before you put this on. Polyester resin will not react well with some plastics and melt it.

 

[Xploitn]

I actually laughed out loud when reading your post! Nope. I didn't check. Wish me luck! It's smooth glass, I'm assuming the resin won't be able to stick to it even if the plastic melts. I should be cutting it off tomorrow night.

I'll be taking precautions to keep fiber glass particles out of my skin, eyes, and lungs!

 

[DSM Jeff]

Just a thought based off something I've done in the past. Take a piece of glass. Clean it and the wax it, I used a carnuba paste. Once buffed out, I laid fiberglass down and applied resin to it. I worked the air bubbles out. Then added another layer and resin. Once cured I separated it from the glass. Now you'll see when you pull it the glass side is perfectly smooth and no sanding needed. So if you did this to the inside of the sunroof, when you pull it, the top will look great.

 

[Xploitn]

This great suggestion is about 48 hours too late! I hope someone else can use this suggestion though!

Have you done this to your DSM? Do you have any other tips? mounting or otherwise?

 

[DSM Jeff]

This great suggestion is about 48 hours too late! I hope someone else can use this suggestion though!

Have you done this to your DSM? Do you have any other tips? mounting or otherwise?

I had just seen this. I used my method to make block off plates or trim rings. Couple layers, then trim as needed. Then a light sanding so the paint could stick and you'd always have a smooth finish.

As far as mounting, maybe run some thin aluminum straping across using the frame mounting bolts to hold it, then fiberglass that to your piece?

 

[gixrman]

Just as an FYI there is a great site full of useful info on composites and mold building called fiberglassforum.com
Also you want to keep the resin to fabric ratio as close to 50/50 as possible. To little resin and poor wet out, weak part. To much resin and weak part, and the resin will crack. After all it is plastic.