Grassroots Motorsports

Register Log in to GRM
- Community

Birthdays
Recently on the Classic Motorsports forums

Subscribe get a full year for only $23.95 Sample Free Test Drive—no strings attached

Login to post Forums » Grassroots Motorsports » Learn me seam welding?

June 26, 2009 4:54 p.m. M030 Reader

Can anyone shed some light on what seam welding is, who can do it and whether or not it's worth it?

I'm building (among other projects) an older Porsche 911 and would really like to stiffen up the chassis. I intend to install a full roll cage as well, but I've read that seam welding can substantially increase the structural integrity of the unibody.

Is this a $10K process that is really just overkill on a car with a good roll cage or is it one of those fairly inexpensive things that is really worth doing?

The car will be a street car / occasional track toy with waaaaayyyy too much power...
June 26, 2009 4:59 p.m. Nashco SuperDork

If you have a welder and some time, seam welding costs nearly nothing ($20 worth of gas and wire?). If you're paying a race prep shop to do it, including pulling things out of the way for good access to the body seams, prepping the surface, welding, and putting it back the way it was when they started, you're going to pay a lot. Hundreds, at the very least, more likely in the thousands.

What are your own resources? Do you have a welder? Access to one? Are you going to have it stripped to a bare shell already? The devil is in the details...

Bryce
June 26, 2009 5:04 p.m. Dr. Hess PowerDork

Seam welding: If you have a unibody car, the panels that make the chassis up are just spot welded together. If you take everything out and go over every single seam and weld the two panels together along the seam, that's seam welding. "They say" it stiffens the chassis.
June 26, 2009 5:07 p.m. Per Schroeder Technical Editor/Advertising Director

Best to do it in 'stitches' every couple of inches.
June 26, 2009 5:18 p.m. M030 Reader

It's already stripped to a rolling shell.

I can weld, but not well enough to actually weld anything I intend to keep... I'd be paying a shop to do the actual seam welding, if it's worth doing...
June 26, 2009 5:54 p.m. racerboy000 New Reader

From the reading on specialstage and rally anarchy seam welding should be done after the cage install
June 26, 2009 6:20 p.m. Appleseed HalfDork

I was under the impression that seam welding is worth it if you do it yourself. I'd think you'd be paying out you butt to have a shop do it.
June 26, 2009 6:47 p.m. Keith UberDork

Definitely worthwhile. For example, on the 200,000 mile shell for my Targa car, you could flex the windshield frame by hand. After some seam welding (not stitch welding), you couldn't do this anymore.
June 26, 2009 7:28 p.m. modernbeat HalfDork

Here's a post from Rally Anarchy about seam/stitch welding.

http://www.rallyanarchy.com/phorum/read.php?5,14375
June 26, 2009 7:31 p.m. ncjay Reader

If it's something you really want to do, it's also worth the extra time and expense to put the chassis on a frame machine. No sense in stiffening up a bent chassis. Welding the seams up makes a big difference. I started doing it on my cars a few years ago and immediately noticed a difference. As mentioned above, the factories usually just spot weld all the individual panels together. They can flex quite a bit when you start running the car hard.
June 26, 2009 7:57 p.m. MrJoshua SuperDork

I've heard the argument that you should not seam weld beyond the shock towers. Popping those spot welds dissipates lots of energy in a crash.
June 26, 2009 9:09 p.m. zoomx2 New Reader

Another thing a lot of people do when seam welding is to have the car dipped in a caustic acid to remove all remains of the seam sealer and paint. If your going this route (seam sealing) getting the metal as clean as possible is a necessity. I don't know how well a media blast will work.
June 26, 2009 9:38 p.m. M030 Reader

In reply to zoomx2:

That's a great idea! Does anyone know of a place in the northeast that does that?
June 26, 2009 9:56 p.m. zoomx2 New Reader

In reply to M030:

Stolen from from anither thread from another forum...

So here are some shops that dip car bodies: Redi-Strip in Indianapolis IN, Roselle IL, Joliet IL, and Oak Creek WI; International Paint Stripping in Belleville MI; Kwik-Strip in Allentown PA; Metal Strip of New England in Worcester MA; Restoration Depot in Wauchula, FL; Pennsylvania Metal Cleaning in Monaca, PA.

Also, a place where that type of shop often advertises is Hemmings Motor News

Never had it done (thinking about it) but I've read it runs about $900. There are pros and cons to it and reading up would be good.
June 26, 2009 10:29 p.m. modernbeat HalfDork

zoomx2 wrote:

Never had it done (thinking about it) but I've read it runs about $900. There are pros and cons to it and reading up would be good.

Prices have recently gone up. Dipping my Miata tub and doors I was quoted $1800 minimum by the cheaper place in Texas. As late as December it was only $800 or so.

And the good places don't use caustic acid. They use lye or other caustic BASE that don't dissolve the metal. And it's a multi step process using dips, pressure washing, some media blasting and more.
June 26, 2009 11:09 p.m. Shaun New Reader

I have never welded seams on a car, and I have welded a fair bit here and there. Please do correct me if I am wrong, but learning to mig weld 16 ga (or 14ga or 18ga ) mild steel with a simple wire feed machine is a couple hour thing with the help of some one who is experienced or some good info a dead car or a few pieces of the appropriate scrap steel. Read a bit on how much material and where, wire brush the areas you want to weld and have at it. When one is adding material to huge structures like a car, ugly ass welds that are at a decent temperature with approximately the right amount of material are just dandy. I would not say that for a bicycle or suspension bits, but the chassis? sure. Is it necessary to hot tank a car to nothing but metal to do this? I would not bother myself unless I was stupidly rich.
I like the strait chassis before you start tip, never thought of that.
June 27, 2009 9:43 a.m. kb58 New Reader

zoomx2 wrote:

Another thing a lot of people do when seam welding is to have the car dipped in a caustic acid to remove all remains of the seam sealer and paint. If your going this route (seam sealing) getting the metal as clean as possible is a necessity. I don't know how well a media blast will work.

Trouble with that is that it's very difficult to make sure the chassis is truely clean after the dip. Even after a neutralizer bath I've "heard" stories of corrosion (from the acid bath) continuing way down deep in the seams where nothing can get to it...
June 27, 2009 11:28 a.m. modernbeat HalfDork

kb58 wrote:

zoomx2 wrote:

Another thing a lot of people do when seam welding is to have the car dipped in a caustic acid to remove all remains of the seam sealer and paint. If your going this route (seam sealing) getting the metal as clean as possible is a necessity. I don't know how well a media blast will work.

Trouble with that is that it's very difficult to make sure the chassis is truely clean after the dip. Even after a neutralizer bath I've "heard" stories of corrosion (from the acid bath) continuing way down deep in the seams where nothing can get to it...

That's why the good places don't use acid. I've got two friends in the car building business. One builds high end hot rods ('32 Fords) and the other restores quarter million dollar Maseratis and Cadillacs and recently built some pro-touring cars. Both of them dip every project body and sandblast every frame. Neither one has had issues for the last fifteen years. Places that specialize in dipping automotive bodies should be using the right chemicals. The issue is with the industrial places that DO acid dip that will dip whatever you bring them. Find somebody that knows what they are doing if you're going to dip.

Alternatively, clean off all the soft crud with liquid nitrogen or dry ice. Then clean the paint off the seams with a wire wheel. I've found knotted or twisted wheels work best without coming apart. I'll dig up a photo of a Subaru my girlfriend did with liquid nitrogen. Had all the undercoating, exposed seamsealer and tar boards off in 30 minutes.
June 27, 2009 2:51 p.m. MrJoshua SuperDork

Can you do liquid nitrogen yourself?
June 27, 2009 6:13 p.m. MadScientistMatt Dork

Buy it yes, make it no. Liquid nitrogen isn't too tough to handle, but you'd need to rent a suitable container. If you have any left over, use it to make ice cream.
July 8, 2009 2:44 p.m. Izzy's Cages New Reader

If you have stupid amounts of $$$ to throw at the car, then by all means, have it dipped. I wouldn't necessarily dip it if there's already a cage in it as the fluid wont have a way of draining until you're on the track with the help of some G-forces (ask me how I know).

You're looking at anywhere between 15-20 hours welding from shock tower to shock tower, and that's if it's clean. Toss in prep work mentioned above and you're looking at 40+ easily. If you're having someone else do the work, bank on 1-2K on the low side ($50.00 per hour shop rate), 2-4K on the higher side.

If you're caging it anyway, I wouldn't worry too much about anything higher than the rockers in the cabin. Tieing the cage into the A/B pillars and windshield frame will do way more than the seam welding up there. Be careful though. If you have ANY aspirations to take the car wheel to wheel, seam welding is usually a no-no in most classes.
July 8, 2009 3:09 p.m. DrBoost Reader

Keith wrote:

Definitely worthwhile. For example, on the 200,000 mile shell for my Targa car, you could flex the windshield frame by hand. After some seam welding (not stitch welding), you couldn't do this anymore.

For clarification:??? I think when Per mentioned stitch welding he meant, for example, weld 1 inch, skip 2 inches, weld 1 inch, skip two and so on. When you are at the other end of that seam go back in fill in the 2" gaps. This keeps the metal from distorting? Now, I've only read about seam welding so I'm really asking for clarification, not giving it.
July 8, 2009 3:29 p.m. Carrera30 New Reader

Stolen from another poster on this thread:

zoomx2 wrote:

In reply to M030:

Stolen from from anither thread from another forum...

Metal Strip of New England in Worcester MA

Looks like you may have a winner - right in our back yard ;)
July 8, 2009 6:09 p.m. NOHOME New Reader

If you are not a good welder at the start, you will be at the end.

Stitch welding where you weld one inch beads separated by one inch gaps is much discussed in terms of how to do this. There are people who argue that the oneinch skip is better than a continuos weld bead.

I had my latest project dipped and while it is a great aid in a restoration, I do not see it as that big of a deal for a seam weld project. A wire wheel in an angle grinder is going to get that metal nice and clean.

When you see what heat does to twist metal, I am not sosure that I would not want to weld the car in a jig or check it AFTER welding.

You'll need to log in to post.