Flat Hood Weld Repair

Thank you, all. I'm going to order the spoon and try plannishing with that first. If that doesn't work I'll try cutting away the structure to access to the under side of the patch. Failing that, I'll follow up on the two leads from crashtech for salvaged hoods.

MP&C. That's a great video on tin snip use.

I'll have more photos as I progress.

Again, thanks to all for your help, especially Roger1.
 
I just want to say one more thing in this thread, even though it's not really what anyone wants to hear.

Despite all the really good repair advice being given, not only are we here after the fact, but this kind of repair is difficult even for accomplished metalmen. At this point, it really looks like the hood in question needs the attention of an expert, or the chances of it coming out acceptably well will be very low.

There is something called the sunk-cost fallacy that we ALL fall prey to that makes us keep going sometimes when we shouldn't. It's also called "throwing good money after bad."

Now I am not saying that the OP can't get the skills to make this work, but at what cost? How much valuable time will it eat up? In the end, will the result be worth it?

Anyway... good luck, grogetter. You are in the right place to stay on track with your project, the guys here really know their stuff.
 
Crash, good point. Once complete the hood will need to be checked for oil cans and I would suggest after passing that test to then move it into sunlight for a good "baking" and check it again. If you don't have it stable, it's not ready for paint..

Grogetter, in the meantime, where are you located? In case this comes down to referring you to someone who could help you out of a jam, it would help to know your location...
 
Crashtech, thank you for your honesty. I'm very much aware of what you refer to as the sunk-cost fallacy. I would call it "false economy". That is, putting more labor cost into a project than it would cost to buy a direct replacement and move on. Fortunately for me, this project falls more into the "hobby" category and allows me to use it as a learning tool. I am being paid for working on this car but I would never charge more time to my friend than it's worth.
I see it as a way to learn as I go and pick up new skills or improve old ones. For instance, one of the front fenders was severely damaged by some roofers that were working on my house. My friend found a replacement fender (which I reimbursed him for) but it's, in some ways) in worse condition than the original so I'm going to try to repair it, at no cost to him. If the result is good enough, he'll have his original fender and I'll have the skill and satisfaction. If not, the replacement fender will be used.

BTW. The first work I did to the Chevelle was repairing the windshield, front and back, trough. After that, replacing the floor pans then the trunk pans then both rear quarters. I'll have to say, though, that the hood is by far the most challenging.
 
Here are a few photos. Before and after dashboard/windshield channel and after shooting SPI gray epoxy on replaced quarter panel.
 

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Here are photos of the visible part of the patch welds from the bottom side.
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That top picture with the seam still showing underneath is a good candidate for cracking in a couple years. No weld penetration to hold the two together.
 
Would you recommend cutting it out a little larger then start over?
 
Is the hole in the structure from a weld blow through or was there a rust hole there previous to the heat?
 
Rust. There are several places where the adhesive between the structure and the skin apparently held moisture causing rust. None of them are as severs as the two that rusted thru but if I wind up taking the structure/skin apart this will allow me to address these rusty spots so that it never happens again.
 
When you weld and fail to get full penetration with your MIG, seldom does adding more fix the issue, It merely makes a bigger blob on the outside... (not my work)



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This shows why you need to do some practice coupons the same thickness as your hood to get comfortable and properly dial in the welder settings. If you don't see good weld penetration on the back side, you aren't done practicing and you aren't dialed in just right.

So yes, my recommendation would be to cut that out and start another patch. You may want the outer hole a bit bigger so you can fix the rust in the structure while it's open. But you would need to also keep the weld seam close enough where you could reach it with your spoon for planishing. On the other hand, if there is enough give, perhaps a piece of leaf spring that would fit in there would also serve well for planishing. Everything's a tool, you just have to see it..
 
Thanks, Robert!! For all of your advice.
I've decided to go ahead and separate the sheet metal from the structure. With that in mind, would it be ok to weld from the back side where I had little or no penetration instead of cutting the patches out and redoing it?

Robert, since I'll have full access to the underside of the panel, what dolly and hammer would you use and from which side? Roger1 suggested a slapper rather than a hammer. What do you think?
 
I think that separating the hood from the inner structure is the right thing to do. It will also allow a total cleaning and you will able to spray it with epoxy primer before reassembly too.
I will be interested to see what Robert says about your what your approach to those patches should be now that it will be clear underneath.
 
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Will do. I've got all of the spot welds drilled out and now need to go around and make sure they are all truly separated.

BTW. Does anyone know why some OEM spot welds are just that, spots, while others look more like a smear?
 
I got the hood apart. No real surprises, just a lot of cleanup to do. However, I will have to make a temporary brace to hold the back edge of the hood for work and handling. With all those spot welds drilled out, It is VERY flimsy. I'm thinking cutting a 2x4 lengthwise to match the curve of the hood then keeping it clamped together while I work on the skin.

A friend of mine has a wet crushed glass blast rig. I'm thinking it might be worth looking into. Does anyone have any experience with this process?

Thanks and have a good weekend, everybody.Hood taken apart 005.JPGHood taken apart 006.JPG
 
I would not want to blast that skin. Blasting can so easily warp something like that even in skilled hands. Now the frame, that is a candidate for blasting, for sure.
 
Heat is not the reason why panels warp while being blasted, contrary to popular belief.

The reason is because every abrasive particle is acting as a tiny hammer, which on sheet metal stretches the side that it is hitting. Billions of tiny hammers.
 
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