MIG seam welding - prepping?

[260DET]

Looking for some effective simple low tech ways to prepare a body for seam welding. Particularly where the seam is sealed with that putty stuff.

 

Also, is there any particular solvent that should be used finally before welding? At present using a rotory wire brush in a drill seems as good a way as any to clean away the paint and stuff. What about using paint remover first?

 

So far I'm having mixed results with the MIG doing rust repairs, for no apparent reason. Sometimes it crackes along and does a nice weld, sometimes it splutters ending up with a very ugly blobby weld.

[JMortensen]

The seam sealer is a bitch to get rid of. A heat gun and a screwdriver will get most of it, then if you really want it all out break out the picks.

 

I tried a wire wheel and it was OK, but it wouldn't get into any cracks, and as soon as you start welding that stuff catches fire and the smoke gets in the weld and makes it crappy.

 

You can use acetone to clean before welding, or I've been using NON-CHLORINATED brake cleaner, which is basically acetone, xylene, and tolulene.

 

I tried paint remover and found that it didn't work so hot. Eventually I prepped most of it with a wire wheel on an angle grinder. That works really well, but is kind of aggressive.

 

Sandblasting or soda blasting would be the best if you can pull it off, but my worry was that if I stripped the whole body bare it would be a big rust bucket by the time I had all of the things I wanted to get done finished. I think I was right about that. Some of the stuff I worked on a while back is starting to rust. Not real bad, but if it was all stripped bare I think it would be worse.

[AK-Z]

wire brush its the way to clean it. there are "weldable primers" like "galvicoat. it uses zinc as a base, when heated it turns to ash. For small parts, I use a sand blasting chamber that my dad has at his work, they usually load it up with baking soda.

 

With your problems with welding, are you using a extension cord? there could be some amperage drop because of the cord. I would go to a electrical/hardware store and buy some heavy gauge electrical wireing and put some ends on it.

[JMortensen]

One more thing Richard. A lot of racers will skip over an area that has a WHOLE bunch of sealer by making a plate that attaches to the metal on one side of the seam and the other, and stitch welding that instead. I guess this is pretty common for the dogleg area in the S30 which has a long seam with 3 pieces of metal coming together and about 1/2 tube of seam sealer in it.

[johnc]

As said above, use various sized wire wheels to get most of the seam sealer off then wipe it down with Acetone. I avoid chemical strippers because some remains behind and I would be afraid to breath the fumes when welding. For seams that you know you're going to have a problem with, I make the weld bead in 3 parts:

 

1. Put a bead below the seam (on the panel that the seam is on - the single layer of sheet metal). Do this for all the welds in the suspect area.

2. Put a bead on top of the seam. Do this for all the welds in the suspect area.

3. Wire brush with a wheel between the all the beads in the suspect area.

4. WIpe the area with Acetone.

5. Put a third bead between and connecting the two you just laid. Do this for all the welds in the suspect area.

[260DET]

Thanks all for the tips, sounds like its just an unavoidable bastard of a job so I'd better get used to it

 

One thing that I have found is by turning up the current, a lot more than usually would be used on thin metal, the weld tends to blast its way along. Got to be quick though.

[Boy from Oz]

I've decided to go the whole way - rotisserie, full-body sand blast, etc. I came to this decision mainly after I stopped and thought about the power to weight ratio of an LS1/2 240Z and what I subsequently see as a real need for seam welding. I understand the concept of seam welding and should be okay (distortion, etc.) but are there any particular issues or areas that I need to pay particular attention to on a '73 240Z? Thanks.

[260DET]

I've decided to go the whole way - rotisserie, full-body sand blast, etc. I came to this decision mainly after I stopped and thought about the power to weight ratio of an LS1/2 240Z and what I subsequently see as a real need for seam welding. I understand the concept of seam welding and should be okay (distortion, etc.) but are there any particular issues or areas that I need to pay particular attention to on a '73 240Z? Thanks.

 

Yes, and its been discussed forever. A search will reveal all, see particularly the body chassis etc sub forum.