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Bonding or welding sunroof panel

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  • Bonding or welding sunroof panel

    A long time ago I considered reskinning the roof to get rid of the sunroof. That was back when non sunroof skins were still available. Theyíve been NLA for years now. The next best option now seems like either welding or bonding the factory sunroof panel in place. Iíve done a bit of searching and it seems like welding the original panel in place is a common choice. Iíve seen people mention bonding it in place but I want something that looks like the sunroof was never there once the roof is repainted. People seem to have mixed success in making the seam disappear when the panel is bonded in place. Does anyone have any experience with either method? I considered using a carbon fiber plug instead of the original panel (I know they used to be available), but it seems like having dissimilar materials would make it even harder to blend when everything is finished.

  • #2
    Unless you really REALLY know what you are doing, I would bond the plug with structural epoxy adhesive rather than weld it. Welding thin sheet metal creates all sorts of distortions no matter what you do....

    If you weld it in I can pretty much guarantee you most of the roof (well past the plug joint) will need at least a skim coat of filler to get the ripples out....

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    • #3
      Sage advise from the voice of experience. Unquestionable reduction in resale value. Remember: ultimately all cars are sold, either by you or your heirs.

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      • #4
        I have no doubt that bonding would be easier than welding. I just wonder what the final product will look like and if there will be any long term issues with the bond. Obviously, this depends a lot on the adhesive used and I donít have any experience in that area.

        Ií have been making modifications to the car for the last 15 years that have surely negatively affected the value. Yes, one day it will get sold but Iíve never viewed this car as an investment. I bought it to have fun. It makes me smile every time I drive it.

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        • #5
          Originally posted by rewilfert View Post
          I have no doubt that bonding would be easier than welding. I just wonder what the final product will look like and if there will be any long term issues with the bond. Obviously, this depends a lot on the adhesive used and I donít have any experience in that area.

          Ií have been making modifications to the car for the last 15 years that have surely negatively affected the value. Yes, one day it will get sold but Iíve never viewed this car as an investment. I bought it to have fun. It makes me smile every time I drive it.
          My point wasn't about which would be easier....welding might actually be "easier". I think bonding the plug with adhesive would just work better...because it wouldn't distort the crap out of the roof, which welding inevitably would.

          Some of the modern structural adhesives are amazing if they are used in a properly prepped and designed application. On carbon fiber driveshafts the U-joint yokes are only held onto the carbon fiber tube with these sorts of adhesives. Think of the loads involved in that application.

          The thing I hate most about the sunroof....other than the fact that I never use it....the additional weight high up.....and my opinion that a sunroof doesn't belong on a car of the E30M3's character....is the amount that it decreases head/helmet room so damn much. But removing the sunroof framework would be quite a chore. I have never heard of anyone actually doing that.

          I wasn't really commenting on resale value one way or the other.
          Last edited by Ironhead; 05-16-2019, 04:38 AM.

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          • #6
            I removed the sunroof cassette from my 88 M3 and welded the sunroof back in place. It's not a terrible job but it takes some time to do it properly. When the car got painted there wasn't much work needed on the roof for my painter to do.

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            • #7
              Originally posted by bmwdayz View Post
              I removed the sunroof cassette from my 88 M3 and welded the sunroof back in place. It's not a terrible job but it takes some time to do it properly. When the car got painted there wasn't much work needed on the roof for my painter to do.

              I found a good write up with pictures on a BMW forum that detailed the removal of a E30 sunroof cassette and it wasnít that difficult.

              What did did you use to bridge the gap between the sunroof panel and the roof skin? I was thinking that sheet metal strips the same thickness as the roof skin would do the trick.

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              • #8
                Originally posted by Ironhead View Post

                My point wasn't about which would be easier....welding might actually be "easier". I think bonding the plug with adhesive would just work better...because it wouldn't distort the crap out of the roof, which welding inevitably would.

                Some of the modern structural adhesives are amazing if they are used in a properly prepped and designed application. On carbon fiber driveshafts the U-joint yokes are only held onto the carbon fiber tube with these sorts of adhesives. Think of the loads involved in that application.

                The thing I hate most about the sunroof....other than the fact that I never use it....the additional weight high up.....and my opinion that a sunroof doesn't belong on a car of the E30M3's character....is the amount that it decreases head/helmet room so damn much. But removing the sunroof framework would be quite a chore. I have never heard of anyone actually doing that.

                I wasn't really commenting on resale value one way or the other.
                The reason I think that bonding would be easier is that you could align/fix the panel in the hole and then fill the gap with the adhesive. Thatís assuming the adhesive is designed to bridge that large of a gap. Then skim coat the area and youíd be ready for paint.

                I never use my sunroof either. In fact I hate having sunroofs in general. I understand why they were offered as options but I agree they have no place (along with a lot of other options) on these cars.

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                • #9
                  I gutted mine out of my race car, every last stich of it, wasnt super hard, just a shitty job, working over your head inside the car, scraping the cassette and drilling the spot welds was a little bit of work, but I had it all out reasonably quickly. We took a FG plug off of my stock sunroof and I have that bonded in there with Fusor structural epoxy. Its been in there like that for probably 18 years.

                  I'd never do it on a street car though even with a windows out repaint. I think its way too invasive to the car. Only way I'd ever consider it would be with a roof skin change.
                  I also never understood the sunroof hate (unless one is a really tall person).
                  I love my sunroof on my street car, I use it almost every time I drive the car, mostly rear tipped up but I open it alot..
                  I have always said there is about 1/10 of a percent of drivers that could (a) notice the "weight up high" and (b) exploit the "weight up high" on street or track.
                  jimmy p.
                  87 E30 M3 Prodrive British Touring Car
                  88 E30 M3 Zinnoberot - Street
                  88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
                  92 E30 M Technic Cabrio - S14 POWERED!
                  98 318Ti M44, Base - Morea Green
                  04 Ford F350 - V10

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                  • #10
                    Originally posted by jimmy p. View Post
                    I have always said there is about 1/10 of a percent of drivers that could (a) notice the "weight up high" and (b) exploit the "weight up high" on street or track.

                    So true....LOL.

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