I have a spot on the roof of a car I'M restoring. Not sure why its there but it easily pops in and out with no other damage or welds around. It has an 6" ring when it pops inward. Is the excess, stretched metal in an "Oil-Canned" area in the center?. To heat shrink, would you heat at the edges or start in the center. I'M new at this so need a good step-by-step
Thanks
Eric

Eric,

It is hard to say exactly where you have to shrink to fix the oil can, because the stretched condition may not be in the center of the oilcan.

You should make absolutely sure that there are no small low spots or high spots away from the oilcan area that are effecting the panel before any shrinking is done.

It may be helpful to push the oilcan up from below a little, prop it into this position if possible, and check the surface flow to see if you have low spots on the periphery when the dent is up. If you do, these need to be raised first. This does not always apply, but may help with smaller low spots. If there is a large low spot popping in and out when you pop the original oilcan area up, Try lightly stretching that whole low spot with hammer and dolly to add a little surface tension. This may help hold the oilcan part of the panel closer to where you want it for shrinking. You can always shrink the area back down if you over stretch.

I usually work an oilcan condition from the outer edges of the panel checking every tiny area for damage before addressing the middle of the oilcan. It takes a lot of patience to fix some oilcans, but if you can stretch and shrink easily, it takes the worry of over working the panel away.

The work is a combination of moving the metal by bumping, pushing, or propping. Smoothing, stretching, and shrinking...and checking the flow of the panel in all directions over and over until you have it right.

What shrinking method are you using?

John www.ghiaspecialties.com

I am with John and feel that you don't have a shrinking issue at all here.

To "stretch" the metal as you are assuming has been done takes a pretty solid hit from something, how does that happen on a roof? It doesn't, a roof usually gets a soft hit by something like a fist, a butt (a jerk sitting up there), a ball, something like that. Following Johns post, read the following "Basics" a few times and then go on out there and see what you can find on your roof. I will bet you a crisp dollar bill there is a crown near that "oil can" that is effecting it.

Brian


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“Basics of Basics” Flat panel repair
By Brian Martin

When you have a large flat panel that is flexing the first thing you need to do is find out why. Sometimes you can stop it, other times you can’t. But if you can stop it, you’ll have a much easier time with the body filler work. Hoods, decklids, and the roof are particularly difficult because the heat and weight of the plastic filler can have an effect on the metal. The good news is many times it is very easy to repair.

First off, there is no such thing as a “flat” panel. All panels that appear flat actually have a slight crown or gentle bow up in the middle. Go to a flat panel and lay a straight edge across it. You will see that the straight edge in not touching the panel at the on the outer ends. If the panel were perfectly flat it would appear to the eye to be concave. It would also have no “body” and flex very easily. This is the problem with your large flexing panel; it has “lost” its crown and is now weak and flexible.

The first place to start your search for a culprit is under the panel. Many panels have inner structure that supports the outer skin. When the outer panel has been damaged the inner structure was bent down along with the outer. This inner structure can be in the form of just a simple inch or so wide support running across the panel to the complete support by a stamped panel that goes covers the underside of the panel. These full inner structures can commonly be found on hoods and decklids. The inner structure can sometimes be bent down, causing your flexing. It usually is very close to the outer skin, with just a thin layer of a foam or urethane adhesive. It may have small “dollops” of this foam or adhesive that has been squished between the inner structure and outer skin or even a thin piece of tarpaper.

You can push up on these low spots to return it to supporting the outer skin, as it should. But it is difficult because you can’t push it past where it needs to be. On this particular type of damage, the inner structure would need to go past the correct shape and then “relax” back down to where it belongs. It can’t do this of course because the outer panel is there and limits the inner structure from going up where it needs to go. Just as with looking at the “big picture” when you look at any dent, you need to search for a kink or bend that is holding the inner structure down in that area. If you apply pressure up on the low area and tap out these kinks, you may get it to stay back in shape. If these methods don’t get it back up to support the outer panel properly, you will need to “shim” between the two panels to get the outer panel up where it belongs. This can be done with sheet of tarpaper or more adhesive. As a last resort a thin piece of wood like a paint stirring stick can be used. Of course, this is a little on the funky side but if you are haven’t been able to correct the problem, something has to be done. What you have to watch out for is applying too much pressure in one area. If you were to force a piece of wood in there, you will likely be making a high spot on the outside. That would just give you in a whole new problem.

Sight down the body lines that are nearest the low, “oil canning” , or just plain flexing area. A body line is effectively the “edge” of the panel. Those crowns in the flat panel that I mention end at the body line. So each area in between the lines is sort of like an individual panel. Look to see if the body line is low, it may be holding down your panel. If it is, you need to push it up. To help you determine how straight the line is sometimes you can use a metal ruler as a “straight edge”. How can this be done on a crowned panel you ask? A metal carpenters yard stick will bend very easily, right? So what you do is lay the yard stick on it’s back against the panel and apply a little pressure on the outward edges low area where the metal is OK. You will then have a “curved straight edge”. I have a drawer with a number of these metal or aluminum rulers in it and find them very useful. I treat them like rice paper and they will last a lifetime.

So lets say that you have found that you have no low spots in the body lines or there were one or two and you repaired them. Now you have to look for something else that is holding the panel down. This can usually be found in the form of a “crown” or “brow”. When you put a dent in any panel the metal has to “go” somewhere. All panels have this crown, right? So as an example picture a metal rod that is 3 feet long. This rod has a slight bend to it. The center of the rod is up from the ends about three inches. If you were to push down on the center, the rod would get “longer”, right? So, if the ends of the rod were clamped in vices, the “extra” rod would force the areas on the sides of where you were pushing to go up. You panel does the same thing only on a much smaller scale. Most brows will be found on the outer edges of a panel, this includes of course at the edge of the body line. They are VERY common around the outer edges of a roof. Search around the outer edges of ANY bent roof and you will find them.

The brow or crown is a U, C, L or even I shaped high spot. In the center of that curved high spot is a low spot, sort of like a “pocket” in the brow. Just one or two of these will make a panel, especially a large panel look like a cotton sheet! What you have to do is to push up on that low spot while tapping down on the brow. When I say “tap” I mean TAP. Just the weight of the hammer bouncing off the brow will do it sometimes. Use a large VERY flat body hammer or a flat body spoon for this repair. If you are careful you can repair these brows with little to no plastic filler. Just take you time and keep checking the area with a block with sand paper or a vexon file if you have one for low and high spots.

Now, if you simply can eliminate the brow and low spot, you have won the battle. If it takes some plastic filler, so be it, you have given the panel it’s strength back and that is what matters.

Well, after reading the posts, I went back and sanded the remainder of the paint and plastic from the roof and door posts (1968 Porsche 912) and it seems there was a weld at the curve of the roof pillar (looks like a gas weld) that was just left flat and filled. I guess that could be the culprit.
As far as shrinking methods, I have a torch, shrinking disc, and a shrink tip for my H&S stud welder. As well as the hammers and dollies. I really am hesitant to use a torch because of lack of experience. The oil can area is not far from what I thought was a clean body line (they did a nice job of putting 3/4" bondo in there). So Would I try to hammer out the old weld?. It looks like it can be worked with some time and patients. The oil can area looks like a baseball would fit in it if pushed down.
Thanks
Eric

BTW how does a shrinking disc work for welded areas, and seams that have been welded but left depressions on either side of the weld line. I have hammered and dollied them to stretch in the past, but would it help to shrink the high spots surrounding the welds, and stretch with the hammer and dolly on the weld?

Hi Eric,

You need to stretch the ares that turn blue from welding (probably where your valleys are), and then smooth with a hammer and dolly, file the weld flush etc. before thinking of using a shrinking disc in the weld area.

John www.ghiaspecialties.com

Please excuse my ignorance, but what is a shrinking disc?
Also what is a metal carpenters yardstick? I will go to hardware and ask but it probably has a different name in australia.
Thanks for the education.
I agree with the other posts if a turret oil pans you work from the outside in with the shrinks or else it just runs away from you.
I did a big shrink job on a car that had been t boned the other day. I used the oxy with a wooden mallet and dolly, i find its the quickest,easiest to control method.

Hi Franco.

After you use a shrinking disc, you will find it to be the easiest and best method of shrinking there is. You can make your own, or I have sent quite a few to Australia in the last few years. Here is an album with more information:

http://allshops.org/cgi-bin/community/c ... 0121727059

Friction is built up in the sheet metal by running the disc over the surface like a sanding disc. The heat is built up evenly and accurately on the high spots only. You quench the metal before it turns blue for a shrink that does not work harden the panel. You can shrink dozens of times in the same spot if you want to without hurting anything.

It can be used as a metalshaping tool as well. I have shrunk down large areas to make reverse shapes, and removed lumps in metal with this method.

John www.ghiaspecialties.com

John, I bought one from you a while back. It amazes me how well it works on lumpy metal, and finishing. I'M a rookie, and I can do things with it that I never thought I could repair without turning to fillers.

I watched the shrinking disc video and have been browsing through the whole metalshapers website and so far I'm facinated.

Let me give you a for instance that maybe you can help me with.

Say I'm at work and I'm straightening a fairly big quarter panel repair. The kind of repair where the quarter should probably have been replaced. I get the panel back to the form that it's supposed to be in with some serious hammer and dolly work and maybe a light tug with the frame machine. Now what I'm left with is a quarter panel that is basically straight but has all the bumps and such that I'd generally fill with a couple coats of filler.

Would something like the shrinking disc be useful on a repair like this. Would it sort of smooth out the metal. If not, what other metal shaping tricks could I learn to get a repair like I described nicer. Surely there are people that are able to straighten stuff like this without using filler. How would they go about this. I'd love to learn more about metal shaping, I think it's great, and I'd love to incorporate it doing collision repairs in some fashion.

Nate