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MG MGA - Welding uncertainty

Hey folks, I have had the replacement body panels coated in a zinc/epoxy primer and baked on, in an effort to prevent rusting. Will this effect the welding properties of the panels? I realize I will need to grind "clean spots" at the weld sites. Also, are plug welds a better choice than Mig at the seam edges? Thanks, Tom
Thomas McNamara

Tom, I don't think the primer will affect your welding, but you are right, the weld areas will have to be cleaned down to bare metal. Best to clean both sides of each piece to be joined by the weld, just a small area where the weld will be is all thats needed. You can Mig plug weld near seam edges, but practice first. The closer you get to the edge the more likely the weld will blow thru at the edge. No real need to be on the edge, the original spot welds weren't.
G Goeppner

Tom, plug welds are quite sufficient about an inch in from the edge of the panel where the original spot welds would be. Much easier than seam welding the edge and probably a better bond. The idea is to replicate the original attachment as close as possible without the specialized spot welding equipment the factory had. At points where you will be welding another panel on directly above the plug welds you'll have to grind the surface smooth, but where there isn't another panel to add then you can leave them raised without problem. It's just a cosmetic thing at that point, your choice wheither to grind or not. As for removing the zinc paint coating, yes grind that away anywhere you are welding. I know that when electrically welding galvanized metal (zinc coating) some fumes can be generated that are harmful to your health, so get the zinc off the surface before welding.
Bill Young

So the guy gets a welder and goes right to the most difficult master task; "welding uncertainty" comes AFTER "fixing a broken heart" and "mending the crack of dawn"!

So Dr Tom "Heisenberg" McNamara, are you having fun now? I told you you were going to wind up taking it all apart!

Seriously, clean off the primer to weld, use really good ventilation, and plug weld. Do NOT be tempted to run long welds along the seam edges, as things will distort horribly.
I learned this many years ago when I most meticulously rebuilt a BMW 2002 floor and sills, carefully checking all alignments, especially the doors. Perfect! Then I got the bright idea to seam weld all the sill/floor joints to absolutely keep water out. The door opening shrank about a half inch lengthwise. Wound up heating it red hot with big jacks across the opening, and hammering all the flanges as it cooled. Worked but took a lot of very hard effort and a LOT of heat.

FRM
FR Millmore

Some zinc primers are "weld-thru". IMHO, it's better to leave as much coating on the part between the welded surfaces as possible - so you might want to test a piece first to see if you can weld without grinding the primer off first.

I think the holes my punch makes for plug welds are 5/16". Get a good set of vice grips (several) and really really really make sure there is no gap between the two pieces before plug welding - or you'll regret it.

Make sure you have an auto-darkening helmet or you'll have a devil of a time hitting the 5/16" bullseye with your shades on.

JIM in NH
AJ Mail

Sometimes there is an area that you want to weld a continuous seam. The way you do it is to make lots of 1/2"-3/4" welds about 6' apart. then after letting it cool make more 1/2" welds to join the welds into a "continuous" seam. Practice on junk this technique takes more skill than you have yet. Plug welds are easy to master. Harbor freight has a Punch /Flange tool, one side punches holes the other forms a flange. With it you can overlap and still have a flat result.

R J Brown

I have the same tool - LOVE it.
AJ Mail

Hey good folks, thanks for all of the input, what a great geoup. Hey FRM, you are, as usual, correct. The car, except for the shiny red paint, was, (is?) a total disaster. At this point I am attempting to make the body strong enough to remove from the chassis. At least the mechanical part will be easier to access after that. I have a neighbor who is a body shop guy and he will do the actual body welding.

Regards, Tom
Thomas McNamara

This thread was discussed between 02/02/2010 and 03/02/2010

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