Weld nuts instead of rivnuts for flares

[fusion]

Any downsides to tack welding nuts behind the sheet metal for ZG flares instead of using rivnuts?  Car is still in primer.  I was thinking of drilling holes slightly oversized and using flange nuts to give more area to weld to.

Is there room to fish a flange nut between outer and inner sheet metal on the rears after the first cut on the outer skin?

 

For the fronts I think it's pretty straightforward.

 

Any comments?

[AydinZ71]

That’s what I would do. I’d use a fender washer on the other side to spread out the load, then tack weld it to the fender. Just need to make sure you get good penetration so it doesn’t break loose  

[JMortensen]

I think you're probably more likely to warp the sheet metal welding than installing rivnuts, and rivnuts can be easily removed if they get messed up or cross threaded. Rivnuts are easier and work great. I'm sure the welded nuts will work, but I just don't see the benefit.

[Dat73z]

Only when I've needed to have the part sit flush with the surface, and I can't counterbore the part have I gone through the hassle of welding nuts. 

 

For something like flares, you'll probably be running some fender welting right? As indicated above imo I'd rather due rivnuts here as you can easily remove them with a countersink etc. and replace if they get damaged

[AydinZ71]

Agree @JMortensen and @Dat73z that welding definitely poses a risk of warping over rivnuts. I’d only recommend it if you already have some experience with welding thin sheet metal and metalwork in general (hammer/dolly). I’d want the flares to sit flush without having to use body filler at the seam, hence welding, but I’m looking at it from the perspective of someone who has now done two years of sheet metal welding so I’m bias. Also, welding to the wheel well will naturally ruin or eliminate your existing finish at those locations. I’m dealing with mostly bare metal on mine. 
 

the welded nut can give you a nearly flush surface (w/ pan-head) on the wheel-well side in case you have a super tight tire clearance at that specific location. 

[fusion]

My main reason for wanting to weld nuts instead of rivnuts is to have the flares sit flush on the metal.  I am really hoping to not have to use welting.

[JMortensen]

I think you'll have a hard time finding flares built to the precision you'd need to take advantage of that tiny gap from the rivnut being reduced. I only have experience with the zccjdm flares and the MAS flares from back in the day, but neither of those was a super tight fit.

Another option is to silicone them on. Saw a video of a guy in Japan doing a RWB 911 and he just used a bead of black silicone to fix the seam, looked good to me, but I don't mind the welting either and just have the flares screwed on with nothing at all to fix the gaps on my own car, so YMMV.

[tube80z]

You can also glue them in.  Weld the nut to the fender washer and then glue that into the car using any of the newer panel bonding adhesives that are used in modern cars.  No shrink/stretch, allows for some small gaps, seals the entire surface from water getting behind it, and won't mess up any paint or lead to increased corrosion down the line.  Just a thought.

[AydinZ71]

Here is what the PO did to my street Z. MSA flares (which I hear are not the best, but not the worst). Sheet metal screws for temporary fastening until the epoxy cured. Looks like he used JB weld or some other more flexible epoxy. i believe the idea is to remove the sheet metal screws now that the epoxy is cured. As you can see, you still have to finish the seam and the surface of the flares with some kind of filler to eliminate the dimples caused by the sheet metal screws. 
 

if I were confident about how to remove these, I’d take them off and put them on the race car. I’d rather have the Japanese marugen flares for a street car. I might still try. The race car needs flares for the 245 cantilevered slicks. 

Edited May 21, 2022 by AydinZ71

[fusion]

Thanks guys.  I do have the Marugen flares so they should fit tight