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Seam Welding

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  • Seam Welding

    have any of you had chassis seam welding done to your car?

    those building cars currently, do you plan on getting this done, or do you think it's not worth the trouble.

    I for one think it's vital.

  • #2
    One of my friends did it to his '88 Honda Civic Si. He loved it. (But then he wrecked it.) He said the increase in stiffness was great. I'll have it done to my Coupe when I get it.


    • #3
      Well its not needed to drift but its definately worth it if you can do it. Its very very very time consuming and if its done wrong you can ruin the chassis so watch out. I would like to do it to my Camaro, but I dont have enough time welding yet to be confident that I'll do it right. You see, when you weld you are changing the tempering of the metal when you heat it up. The goal is to make the weld stronger, but if done wrong it can make the metal weaker. So if its done wrong then the chassis will be weaker in certain spots than it was when you started. I'm having a hell of a time just welding together my rollcage. But yeah, seam welding correctly will greatly stiffen up the car and give you the benifit of adding no weight.


      • #4
        Seam welding itself ought not be that difficult, but I would reccomend putting the car on a lift or blocks so that the suspension pickups are not stressed during the heating and cooling of the metal. Also be sure that the voltage is turned down as far as possible while still getting good penetration to the metal. Marking off the length of each stich beforehand is also crucial to making good consistent welds, and even having a friend with a stopwatch to keep track of your rate of motion isn't a bad idea (plus it's always a good idea to have a friend around for safety, as long as they have a mask and long sleves). Be sure to let the metal air-cool as well to avoid stress cracks from expiated cooling. I would hope that it goes without saying to grind down the areas to be welded so as to prevent contamination. If you get yourself a MIG and the welder's handbook, I don't think that this project would be out of reach and you would save a lot of money as long as you're patient.

        Seam welding is one of those things that by all means should have been done at the factory but was omitted in the assembly for money saving reasons and is tricky to do after the fact....

        I've heard about injecting 2-part expanding foam into a seam-welded chassis for even more rigidy and not much increase in weight, but that is a risky operation and should be left to the pro's.

        IMO if you want to increase stiffness a rollcage is better than seam welding becuse of the increased safety factor. Sure it adds weight, but the stiffness increase more than makes up for it.



        • #5
          Actually cages are less safe for everyday driving and will not make your chassis as stiff as a good stitch welding job. If you just put a cage in a car it will help the rigidy a little but the chassis can still flex around the cage. Seam welding (running a continueos bead) is very dangerous because if you get into a accident then the crumple zones are elimanated and the car would crush in not so driver friendly ways.

          When you stitch weld you chassis you are going to want a chassis frame becuase as the metal heats and cools it will warp your car and ruin it. The frame must be squared up and securely mounted to the car. You can get by with pinch weld stands (i think that is what they are called) which are like jacks with clamps on them ( i think). If you do this than you have to be sure your garage floor or whatever you are welding on is flat or it will make your car that shape. The best way to do it would be find a friend with at a bodyshop and use their frame rack.

          Cleaning and prepping the surface is a huge step in the stitch welding proccess. All paint and glue adhesive must be removed or the weld can actually weaken the metal. When doing the car move from one side to the other, instead of running a line of welds on the right do one right one left and so on. This greatly minimizes the warping. Also you can cool the welds with compressed air which should not crack them.

          When doing a job this big you should deside early in the project what parts of the car you are going to do. The first one should be the door jambs and then the strut towers, followed by rear strut towers, then the window sourroud (taking out windows and welding seams).

          Another great body stiffener at least in the s13 is filling the rocker panels with a 2 part foam (stiffest one you can find). This alone will stiffen to a point of being able to see it if you jack up one wheel (before the chassis would rotate and make your door hard to shut). I think anybody wanting to stiffen their car should do this first it is relatively easy and doesnt require welding skill or stripping your car.

          I can not take credit for all this. I have learned it over the years from reading on the internet, talking to local subaru guys, and for informative posts from the greatest man to ever roam the forums of DX.


          • #6
            Mranlet and CH where both in origanal seam welding thread and you guys should have remembered more of it. Stitch welding is also called spot welding.

            Do a search and you will find the thread i took most of my info out of. DX is the man and knows his stuff, I didnt not copy any of his posts. I did this all by memory. Then went back and made sure it was correct. So if I got some of it wrong then im sorry. Go and find the original one it has loads more info.


            • #7
              "Put about 4 5/8" holes evenly spaced in the rocker pannels and yes when it expandes and dries sand the overflow off. Most good foams have a 50% expansion rate so you dont need to fill the rocker, a liter or so of mix should do one side. The spot weld drill bit can be purchesed where ever body shop supplies are sold if they dont know what a spotal tool is head for the door. When you spot the car do all the way around the door openings on the body side of the car. Pay attention to where the floor boards meet the rockers this is a good place to stiffen up the car. Also another good place is the trunk area. Sand or gring all the paint away with 80# grit to bare metal and lay down 3-4 coats of heavy fiberglass mat. Over the tire wells and down into the spair tire hole. This will stiffen up what you cannot spot weld in there.

              HINT when you spot weld always remove the seam sealer and paint from around the areas you will be working on . The chemicals in these products will mix with the welds and render them useless. I use a stripping wheel usaly made from SCOTCHBRITE, but there are other types you can use. Do all the surroundings with this first then drill the holes and weld them back in. For grinding I use a 1/2" air belt sander to grind them down there is less heat build up and the finnish is perfect. A 60# grit belt is best. also cool this down with air after each one.

              HINT DO NOT do these in sucsesion do them random like left door one right door one and so forth. OR bottom door then top door. If they are donne in sucsesion this will also warp the body and pull at the meatal."


              "OK we have gone over the how pretty much. But lets recap. It is very important to stabalize the chasis when doing this I cannot stress this enough. A frame rack with pinch weld clamps is the only way. I have seen dumdasses do this and total there car before they even finnished. Also while doing this you can check for any bent components. Acid dipping is not needed If you want to fully restore, a good glass beed striping works fast and is cheepest. The glass beeds will not make any heat unlike sandblasting, this will keep the intact parts from warping. When we do this in my shop we charge 7k for a full front to back this is labor intensive. We totaly strip the car to just the bare chasis, all wiring components everything but the roof panel and the quarters are left. All seams are ground and prepped. Then every accesible point that we can drill the top metal is drilled and filled with a mig and mild steel wire. A spotwelder like they use when asempling is awsome but about 15k so we do this by hand. If you intend to drive and do this you can break down the areas. here are the areas and the procedures

              Area 1 Door jambs.

              Remove the doors and all the moldings and whether striping If you look closly there are spotwelds round markes they resemble a cigarett burn in the metal. You will want to drill and fill inbetween each one the entire diamiter of the door jamb on both sides. BE SURE TO COOL EACH WELD with a blow gun. DO NOT USE WATER YOU WILL FRACTURE THE WELD AND RENDER IT USELESS!!!!!

              Area 2 under hood and inner fenders front

              From the doors to the radiater support you need to do the same as the doors. If you pull the engine you will want to do the frame rails as well. Also do the strut towers and accross the firewall.

              Area 3 trunk and surrounding as well as window openings.

              Inside the trunk you will find the same spotwelds like the doors in the floor and around the rear wheel houses. Do all the ones that are accesseble.

              Area 4 Window openings

              You need to pull the glass if you cannot do this on your own have a mobile glass man remove it for you then when you have finnished and painted have him replace it for you. If he breaks it he will pay for it. Do the same as the doors hear as well.


              Use the strongest foam you can find, Stay away from the can crap it sucks. I use SOLAR 2 part its a 1to1 mix and has a 50% expansion rate, It dries like fast be prepared. Drill 4 5/8" holes in the rocker pannels under the sill plates and the length of the opening, evenly space your holes. Mix the foam and use a funnle to poor it into the rockers. it will take about 1 1/2 liters to do one, this is mixed and ready to poor. Let it expand and harden. After it is hard you can sand it flat and use plastic hole plugs to make it look nice.


              In the trunk you will want to lay at least 4 coats of fiberglass over the wheel wells and accross the floor down into the spair tire well, and into the areas between the floor and the quarter pannels. Remember to strip all the paint and sealer before you do this as well.

              POINT#### always remove any sealer and paint from any place you will be welding, so as not to contaminate your welds. After you have drilled and filled use a belt sander or a grinder with a 60# grit sanding disc. To prep for paint a 2 part surfacer can be sprayed or a 2 part epoxy sealer. You need to use somthing to treet the metal so it will not rust under the paint. I use an etch primer then a wet on wet system.

              If you are going to do the full blown race fram remember to have boxes and cups with lids to put all your hardware and parts in. Mark each one with whats inside. You can take before pics so you can remember how it came apart or draw little sketches, and mark what went were.

              lastly DONT BE A MORON

              Use safty glasses when sanding, grinding. A welding hood and gloves. And some type of dust mask. You dont want to breath any of this. If you are going to paint this yourself us the proper components and safty eqipment as well

              The more complete and profesinal you do the job the better your car will perform. It takes me about 30 to 45 days to totaly strip, fill drill and reasemble a S13- S15 this is long hours and intensive work but I garentee my work and ALL my customers a totaly satified. I can make a body strong enough to takle a H2 Hummer and still be light weight and rigid. "


              After you have read all that 10 times you will be good. Get a welding book I have heard many of them mention spot welding and roll cages/racecar welding.


              • #8
                I have an unhealthy obsession with structural rigidity. Proper seam welding and some hardcore foam seem like great ideas. How streetable is it, actually?


                • #9
                  I dunno, I think a properly built rollcage will properly stiffen the car with no seam welding done. It needs to be tied into the chassis properly. It is possible that the body panels can flex around the rollcage, but that does not really matter. What matters is greatly strengthening the chassis and keeping the suspension points from flexing, thats what makes the difference. A properly built rollcage will accomplish this, but it also adds weight. The reason people seam weld is because it adds little to no weight while strengthening the car and you dont have to build the rollcage as heavy to achieve the same ammount of support. So you combine the two and you save weight. Its not like seam welding itself will make the car stronger than a rollcage, sorry. And I dont know what you mean by saying rollcages are not safe for daily driving. I know if I get into an accident on the track or on the street I'd much rather have a rollcage. They are not practical for daily driving, but they make you much safer.


                  • #10
                    +1 to CH's post, which reiterated a lot of my points.

                    Car manufacturers go to great lengths to make the structure immedeately surrounding the passengers as impervious as possible to deformation, and they design the front and rear of the car to crumple and absorb impact.

                    Seam welding will help a LOT, but a well built cage will help more - the right cage will be almost as good as a tubeframe chassis.



                    • #11
                      I'm a proponent of cages because 1. I'm a lazy person and wouldn't want to spend days just prepping a car to be seam/stich welded. 2. I don't know how to weld, thus I'd have to pay someone else... and I don't pay people to work on my car unless they're aligning it, mostly because I'm a penny-pinching cheapskate. 3. High-density foam renders the car unrepairable in the event of an accident that screws up the frame rails. 4. I like the idea of a cage when half the other vehicles on the road around me are SUVs and large trucks. (With a good eighth of those SUVs and trucks lifted)

                      That said, care must be taken when driving with a cage on the street. Any part of the cage that one's head may come in contact with should be padded with high-density foam padding. Remember that your head (and arms) moves around A LOT during an accident, so pad pretty much everything within 36" of your head and arms. It's always a good idea to have a harness bar (replete with harnesses, who'd a thunk it?) built into the cage so your body doesn't move around so much and impact the cage in any untoward ways. Plus, it'd provide a mounting point for a two-piece seat for even more safety.
                      Last edited by GRiDRaceTech; 07-03-2004, 10:01 AM.


                      • #12
                        My vote is for a cage also. I have built many race cars and a well built cage will do more than any seam or spot weld job.

                        There are a couple things you guys missed as well.

                        Todays cars come galvanized which really doesnt like to weld. In order to weld you must take off this coating. If your planning on seam/stich welding your car, you should send the tub out to get ether bead blasted or acid diped. You can use a sander on the areas before you weld to get to bare metal but this usually takes off too much material.

                        Second, the reason why they just spot weld the chassy together is to allow movement. If the car is ridgit, it tends to crack or bend. By stich/seam welding the car, it hardens the material you weld and causes cracking which will be worse in the long run. In WRC, a chassy is only used for 1 main event and a couple practice runs because of the amount of ridgitity change. They also spend almost 400 hours of prep time on one tub.

                        I personally would not spend that much time on a tub. I'd rather just build a good cage.
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                        • #13
                          use a combination of rivets/spot welds/cage.


                          • #14
                            I wouldnt use rivets Ive heard they loosen and rattle and dont work well.


                            • #15
                              Originally posted by Ichi-Go
                              I wouldnt use rivets Ive heard they loosen and rattle and dont work well.
                              sometimes they do loosen, you are correct. But in some places, like the strut towers, I prefer to use the rivets because they dont tend to warp the sheetmetal like spot welding, (but you can always reinforce the sheetmetal with some heavier gauge sheetmetal spot welded over the factory one).