Opel GT Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
74 Posts
Discussion Starter · #1 ·
O.K.
I'm pretty new to welding and am going to be attempting to repair a rust hole on the rear of my manta-the patch will probably end up being about 8" square. I was planing on using some 18 gauge sheetmetal for the patch and my new oxyacetylene set up but am worried about warping the panel from the heat of welding. Anyone have any tricks or tips to keep the heat affected area small-what size tips should I use? I 'm just affraid of making it worse than it is. I do plan on practicing on some extra metal but any help is greatly appreciated
 

·
boomerang opeler
Joined
·
5,634 Posts
hi first off practice on scrap till you get good use 1/16th filler wire and clean everything
its not easy to do body work with a gas torch as you have to put so much heat in to the panel that distortion will allways happen
keep a bucket of water and a cloth at hand so you can weld a bit then cool it with the wet cloth
this will help cut distortion
only do 1/2 inch or so at a time and cool or it will twist and move from one spot to another as you go to spred stresses that build
being new to gas welding you might want to look at brazing the patch in
to do this cut your patch bigger than the hole by 1/2 inch all around set it on the inside of the hole (make sure that there is nothing on the inside [paint and such] ) drill some holes through and snap rivet the patch in place then use brazing rods and flux to join as it works at a lower temp and is quicker it helps to cut distortion down
after you can drill out rivets and fill holes then wash all down inside and out with hot water to get rid of flux
then you can smooth down high spots , skim with bondo and prep for paint
PS check local laws with respect to welds
here in uk only mig or tig welds are allowed on bodys
no stick(MMA) / gas / brazing
 

·
boomerang opeler
Joined
·
5,634 Posts
just had a thought
if its reasonably flat shape then why not bond it in with epoxy
no distortion at all then skim and sand
we have cars made in europe now that have medium carbon and high carbon steel panels [saves weight for given strenth ] and you can not weld them because of the temper and work harderning when they are made
must be a fender or other none structural panel not near suspention or such
 

·
4ZUA787
Joined
·
665 Posts
well i brazed a giant section in the rear of my opel it came out looking perfect u cant tell anything wus ever done there. i used my oxy actelyn setup and i used a flanger and did the whole trick and just brazed every inch or so and filled the rest in with bondo then smoothed and sanded for a few days then painted primed sanded and finally the finish paint job came out perfectly
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #6 ·
Thanks for the tips,
I know it can be done with little to no distortion-almost all body work done prior to the 70's or 80's was supposedly done with gas. I do plan on quite a bit of practice before I do the real thing, I was thinking of just doing it one tack weld at I time and letting it cool in between. Also, does anyone know of any heat sink compounds that would stick to a verticle panel-maybe some kind of clay? -and how wide of an area do you think I should remove the paint from to prevent burning?
 

·
boomerang opeler
Joined
·
5,634 Posts
your local welding supply store will have heat sink compounds just ask there
and the paint should be taken back about 2-3 inches

if you have trouble with the weldind most places have some kind of evening class system where you can go for instruction
especialy auto body shop
 

·
4ZUA787
Joined
·
665 Posts
i believe the company is called west wood they sell heat compound ive never used it but i no they sell it, also anthor trick i did just rembered this i brazed the panel on every inch or so and at the top of the curve were it would be more noticible to see a low spot i used lead or as they call it now a days silver soilder and a lot of that flux that u use on wires when u are soldering it filled in the gap pretty well made for less use of bondo. just an idea for all to use.
 

·
Super Moderator
Joined
·
5,882 Posts
I might sound like a broken record here, but as someone who did his first GT restoration in 1979 using an oxy-acetylene kit and brazing, I wouldn't do it again. Less than five years later, here is what it looked like.

First, it is VERY difficult to braze (or gas weld) sheet metal and prevent panel buckling. There are commercial "putty's" available that you soak with water and surround the welded area to absorb heat. I had an old Austin Healey manual that showed the factory recommended-practise of using wet ASBESTOS putty as a heat-absorbing material, and the panel was repaired using a butt-welded gas weld, and lead as a filler! How times change. In lieu of commercial heat sink putty, you can also use lots of wet towels, and surround the welded/brazed area to soak up the heat. Keep the welded/brazed length to no more than a half-inch at a time, with an inch in between each "stitch", then repeat until the panel is welded/brazed. VERY messy, difficult to do properly, and you will regret it later if you braze.

Here's the point behind the picture. The brass in a braze and steel sheet metal are "dissimilar metals". Sounds familiar? It should, because I have raised this issue before. Dissimilar metals, in the presence of an electrolyte (water), make a tidy little battery. And that GREATLY speeds up nature's little battery, iron oxide. Now, the front panels on our GT's are actually brazed at the factory from a bunch of smaller panels, but that is a low temperature process and the brazing is very carefully isolated from moisture. NOT! So that is one reason that the GT rusts so easily.

Take my advice, and buy a nice little MIG welder. One with the inert gas kit, and small (.025 inch) solid wire (not flux core). You won't regret it for a moment, compared to the trials and tribulations of brazing, along with the short life that all your troubles will endure.

JM2CW
 

Attachments

·
4ZUA787
Joined
·
665 Posts
i use brazing alot on many things and have had no problems befor as long as u protect by keeping a nice coat of paint on it. i use brazing to do almost every thing on previce cars and motorcylcle work it may jus be luck though.
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #11 ·
Thanks again for the info everyone,
I have done a bit of brazing on bike frames and never had any issues with rust but feel that welding is the "right" way to do it. I know there are difficulties with gas welding, but I also know it can be done, last night I was playing around with some 22 gauge sheet steel and was able to pull off some nice tacks without distortion to the panel using a very small tip, very low gas pressure and very quick welding- I also screwed up a bunch. I think that with the body panels which are a little thicker than what I am practicing on it should be possible. I'm planing on basically tacking the whole patch until it is a solid seam, using a bunch of the heat sink goo and letting the metal cool between welds-and maybe buying an even smaller tip than the one I have. I would very much like a mig but that is out of my reach and this repair will either be done by me or not at all so I'm pretty much set on learning the black art of sheetmetal welding with gas. If anyone has any other experiences or welding advise I would greatly apreciate it,
 

·
4ZUA787
Joined
·
665 Posts
i asked a chem major today and they said the only way that that could happen like described were teh two diffrent metal act like a battery is if the piec of metal u brazed on was sumbmerged in water like say if u braze welded something on the outside of a submarin it would corrode like crazy but if u braze weld a panel on say an opel and paint it, it will never see water which in hence it cant cause any corrosion, i would have put down the whole convo about the science of why it does happen but that would be to long.
 

·
Registered
Joined
·
6,344 Posts
I'm going to go along with Keith on this. Your Chem Major is correct, if the part never sees a liquid, but how many old cars have you seen that do not have rust under the paint? It doesn't take a lot of moisture to start the electrolytical reaction, all you need is a very small flow of electrons and corrosion starts. I've removed the paint on my GT parts that I'm repainting and if I don't have them chemically treated, they will have surface rust on them within two days and they are in the garage. HTH.

Ron
 

·
Super Moderator
Joined
·
5,882 Posts
Your chem major is correct. If you can keep the electrolyte away, you won't form a cell. For that matter, if your car never sees water, it will never rust. And yet it does, with a vengeance. Even the moisture in the air, when (not if) it condenses on the panel, is enough to form an electrolyte that allows corrosion. A good paint job goes a long way to preventing rust. But it is VERY difficult, if not impossible, to perfectly seal the metal panels, let alone the welds, after a repair.

JM2CW
 

·
Opeler
Joined
·
58 Posts
Flux and Etch

For what it's worth, I'm no expert, but I've seen and made plenty of mistakes, and got plenty of advice from folks I trust.

First if you braze or silversolder the process will require a flux or a flux coated rod and the process will liquify the flux whereby it will flow into the lap joint and if not totaly displaced by the filler metal some of the crystallized flux will still be there after it cools. If the flux is not totaly removed before covering with filler it can cause problems. So the first advice I always try to follow is wash all of the flux off completely, don't just chip or sand it off.

Second is etching bare metal. After doing body work I noticed that where I had sanded down to bare metal it would rust right through the primer and even top coat after a couple years. When I mentioned it to my paint supplier he told me I should always etch all bare metal before putting body filler or primer on it. I have tried to be religious about that ever since and haven't had a problem since. I noticed it happened even more often when I bead blasted metal or heated it with a torch. I think that may be because both of these processes remove all oils from the surface and leave the surface ripe for oxidation.

Recently I have been restoring a 52 Cushman Eagle motor scooter and got tired of the tedious etching process and ran across some self etching primer and gave it a try. I have had pieces in the garage that have had primer on them for three years with no signs of rust so far. I remember the Navy using zinc cromate primer all the time on aircraft, and I surmize it was for this reason.

I have also used the product POR15 with very impressive results. They note that regular paints cure by releasing solvents and in order for the solvents to escape the paint is actually porus and that is why left unwaxed, an old paint job will eventually rust right through the paint.
 

·
Moderator
Joined
·
1,973 Posts
well I noticed bubbling under my paint at the rear lower fenders so I took the paint off and it is worse than I thought there are 3 holes the size of a pencil that broke though when I poked it with an awl Now I have to decide what to do, I have this devcon titanium putty that is very strong I have heard of it being used to skim coat piston tops and then machining them flat and fixing key ways, there is no doubt that it will be strong enough but will it work if I don't get all the rust off the area and should I por 15 the area before I put the putty on? also this is an alternative to leading or brazing for me, I will not weld this area.
 

·
Moderator
Joined
·
1,973 Posts
nevermind it was really rotted so I ended up cutting another big piece of sheet metal off my opel. I hope the repair works well
 

·
Moderator
Joined
·
1,973 Posts
pretty ugly, Im sure the other side looks the same but im going to see how this patch works before I do the other side. I just need to wait to get some por 15.
 

Attachments

1 - 18 of 18 Posts
Top