Welding Unibody Seams For Strength

[v6spider]

Hi everyone!

I have been reading a lot about welding the unibody seams to add to the rigidity of it and strengthen the unibody. I am pretty sure I am going to do it. I have read about on Grassroots Motorsports' website and on various other racing websites on the net. I am also tying the front frame to the rear frame by welding in some framework while I am doing this. I am curious if anyone else has done this and how they liked the results. I know there are some performance/racing shops that do this. However, some people don't understand how it is a benefit and are against it. The theory is that instead of relying on the factory spot welds which are at the most in places a 1/4" in diameter spread an an inch or 2 or more apart, The seam is tack welded along the entire seam which distributes the stresses more evenly. I want to do this to the entire underside of my spider and leave the body panels alone in case the need to be removed for repairs...

Comments? Thoughts? Experiences?

Thanks!
Rob

[vandor]

Yes, it definitely makes the body stronger. I have done this on a few places on the front box section on my car, and also on the engine crossmember. A few years ago I did the entire engine compartment and front part of an Alfa GTV6 racecar.

As far as I know you do not have to weld the seam continuously, for example1/4" every 1" is enough. But I am not an expert.

[v6spider]

Thanks for the reply Vandor!
Yeah I got some mixed info on that.. Some said weld the seam entirely others suggested as you have to only weld a 1/4" or so every inch.. sure would like some more input on this... anyone?

Thanks!
Rob

[djape1977]

if you seem weld all along the length of the seem, you'll get very stiff body and stresses of driving will be transfered into material itself, increasing potential to develop cracks in the metal.
around my parts, we do it to race cars to stiffen the shell, but those aren't meant to last and coupled to very stiff suspension, they usually develop chasis cracks within a racing season and need to be repaired at least by the end of the reacing season.

if i were you, i'd just make one additional spotweld every inch or so. that's what i did to my 131 and am now doing to 124

[v6spider]

Well guys I met a pro welder today at the hardware store when I was getting wire for my mig. He said the same thing that you guys mentioned don't weld the seam entirely do tack welds one inches apart. ...so that is what I'm doing. Appreciate the smart advise guys just wanted to make sure I was helping more than hurting..

Thanks again!
Rob

[Daniel]

this is a good tip i'm glad my car isn't painted yet now i have another mod to try

[v6spider]

Daniel,
My spider is THE poster child for MODIFICATION!

Btw I am only doing the underside and places that are not related to a body panel...I'm leaving them so if there is an accident the panel will be easy to remove...

Next thing I'm doing is the tying of the front framework to the rear framework...that will be the next round of posting for me.

Rob

[Daniel]

would there be a noticeable difference if the upper body had welded seems as well in your opinion?

[v6spider]

We are talking about a 1/4" tack weld every inch here...I don't see why it wouldn't. But it would make it tougher to remove that panel if there was a wreck..I should point out that I welded my sill panels in completely and inset them as well so it blends in with the rest of the body..so I guess I did part of a no no..but there is specific look I'm going for here...

Rob

[geno58]

I would think, you would need to set up the body so it is square and level, prior to welding.

[v6spider]

If the body was flexing then it would need to be in a jig. But I did measurements prior to turning it on its side. And after turning it on its side and there was no change or flexing noticed. I've done quite a bit of tack welding on the underside and still no changes in the measurements ...

Rob

[Daniel]

if the body is bare no engine trans seats suspension then the chance of flex while on jig/Rotisserie would seem to be
very low.

[geno58]

My concern would be the sides of the body being paralle from side to side.
There are four points under the car, such as the suspension mounting points, that I would want to be exactly paralle with each other. Just my thoughts.

[v6spider]

I am curious as to why you would think that the body has to be in a certain position in order to ad tack welds to what is already there when the body framework isn't flexing like at all? As long as there is no twisting or flexing when the body is on its side or upside down or whatever what difference would it make. The welds I am making are 1/4 or less long just a tack weld and then I move to a different section and make a tack hopping around so that the welds cool quickly and the welding process is short so it doesn't get too hot in the first place. At least that is my take on it..

Rob