I've done it but with some very careful planning, but first the frightening disclaimer statement:
The information contained in this series of paragraphs is intended for educational purposes only. It does not constitute fabrication or remedial repair advice. If you need remedial repair advice, you should consult a qualified aluminum fabricator licensed to practice in the country, state, province, town, city, hamlet, borough or village where you live. Unless otherwise noted, the information provided in this posting does not represent any official aluminum manufacturer/fabricator fabrication techniques from Kaiser or US Aluminum. The author has not made ANY efforts to ensure that the information contained in this posting is accurate, sound or safe. In fact, portions or the whole darn posting may be totally inaccurate. Neither the author of this posting or his dog, Buster assumes any liability for any inaccuracies, errors, or omissions contained in this posting.
As a courtesy to you, the readers, this posting presents information that was gathered from wild LSD users. The author did not evaluate, endorse or guarantee the accuracy of the remedial repair technique being presented or whether it is foolproof or safe, nor does Café Husky. The author does not assume any responsibility whatsoever for the content or the use of this content. The use or reliance upon the information presented here is entirely at the users own risk.... scary, huh?! DON'T BE STUPID AND BLOW YOURSELF UP or you'll have every neighbor calling Homeland Defense to raht you out.
O.K., here's the theoretical, hypothetical , spurious, ersatz methodology only ever done as a computer model... but first inspect the tank for ratty seams or other areas of concern:
1. Fill the tank tunnel with Plaster of Paris to keep the tunnel from collapsing;
2. Stop off the petcock hole with a threaded cover - make one if you have to by welding a blank over the top of a nut. When you install it, use Teflon tape to seal it up good;
3. If your tank has connecting undertubes, connect them together with a thick walled connecting hose and two stout band clamps;
4. Make a self sealing gas cap out of two pieces of 1/8" aluminum - one a simple rectangular length, which can fit down inside the tank and the other, a round piece with a matching piece of neoprene. Drill two hole in this one; one hole off-center so you can install a threaded air fill valve (off-center)and another centered hole so you can have a connecting bolt that will go thru to the center to the rectangular piece. Lower the rectangular piece into the tank so it can be drawn up to brace against the inside of the tank against the opening. This piece is aluminum for a reason; so you can shape it ever so slightly so you don't add any more dents to the tank from that rectangular piece - shape it to soften the corners and sharp edges. The neoprene will serve as the gasket so it will be air tight.
5. Now dab-nabbit you guys, don't go getting all reckless here! It doesn't take a lot of air, maybe five to seven pounds****************************************! And remember, as you heat the tank, the air will expand and built up even more pressure. I solved this problem by installing another bung hole in the air fill cap equipped with a length of hose and a pressure gauge so I can watch the pressure as it builds.
WARNING! WARNING! WARNING!
If you get inpatient and start putting in too much air, it is quite possible to "Plump Out" your tank or blow out a seam! And that can really suck! I know this first hand!
6. Take your mapp gas torch and started drawing concentric circles around the dent working from the exterior to the interior of the dent. Use a high temp thermometer as a guide to let you know if you are getting the aluminum anywhere close to it's melting point (1218 degrees Fahrenheit and 659 degrees Celsius for you Euro-bubbies). Keep the circles going... wax on, wax off, grasshopper, wax on, wax off! The dent will slowly become shallower and shallower... IF you work from outside to inside. Don't be tempted to blast the whole bloody dent with eat all at one time. You're asking for it. The center of the dent will serve as a temporary heat sink while you work your way to that point. Keep your hand on the cooler side of the tank so you can feel whether it is getting horridly hot or incrementally expanding. Thump on it with a rubber hose once in a while and you'll hear that the harmonic response will change pitch. Careful now! Don't want to draw back a stump due to carelessness.
Like magic, the dent will oh so slowly begin to disappear except for that nasty little point indentation where you best friend hit the tank with his beer bottle. If that little dent won't come out, it's time to make your other best friend who is a TIG welding superstar, fill in that teeny-weeny dent with his molten metal magic. Then when it cools down, you can take your die grinder with various grits of sand paper and some 3-M pads and make short work of the aluminum weld. If I learned one thing it is this: GRIND THE WELD AND NOT THE FIVE INCHES AROUND THE TANK!!! My pop would smack me up side the head if he caught me grinding the entire damned surface. Don't do that. You're smarter than that! Now polish that bad boy to match the desired look you're after.
7. Slowly chip away the Plaster of Paris and here too, don't get all impatient and reckless here. Forchrissakes, you don't need another dent.
8. Prepare tank to receive your finish of choice.
9. Mail $29.99 US CASH to Desmo for me if it works. If it doesn't, mail Desmo $29.99 US CASH for me anyway.
10. Sit back with a smug look on your face as your friends (mates if you're across the pond) ask how you did it and reply, "If I tell you, then you'd be as smart as me.
signed:
The Author who commandeered Desmo's computer