Purging the tank

[billygoat]

Hey ya'll,
 It's been a while since I checked in.

 I need to paint my tank now but first I decided to fill in a small dent with my mig welder. You think I can use water to purge the tank? I'm weary of wealding on a tank but it's worth a try. The dents are smaller than I thought so I will have a near perfect looking tank when I'm done. Thanks for you input.
-Billygoat

[steve hawkins]

My tank was braised up years ago, as it had rust holes along the bottom seam.

I emptied the fuel and flushed it through with water and let it dry.

The chap that braised the tank still had to flash the tank over to remove the fumes.  He basically took the tap and cap of and then held the torch over the fuel hole etc.

[drewboid]

A long time ago I used steam to purge a tank before I brazed a crack. No explosion so I assume I got all the gas vapor out.

Be sure to do a sniff test before you start.

If you have access to it a shot of CO2 into the tank might also be a good idea. YMMV but I don't think water alone would do the job.

[weasel01]

My Dad had a VERY bad experience with the fuel tank from his Ercoupe.
I would recommend going very slow and flush it and let it dry multiple times.
Years after his accident he was working on another fuel tank... he was so cautious that it was almost comical but it was well warranted.
After several water flush and dry cycle he placed the tank with the cap off pointing away on the other side of a block retaining wall mounted a torch on the end of a pole and carefully tested the opening for flash.
Fortunately the second tank was a success.

[Justin B.]

I don't understand why you want to weld in a small dent!  You may very well cause yourself mucho grief by warping the surrounding metal.  If it is that small just slap in some good quality filler (I use 3M) and be done with it - the factory does!  On larger dents I've used a "Ding King" to pull it most of the way out and then putty to smooth over.

[billygoat]

 The dents have been welded and jb welded before. I am really looking to learn the skill. Someone sugested I use dry ice to purge the tank during the welding. Yeah I know the tank is rusty. [smiley=embarassed.gif]

[billygoat]

pic

[Lucky_Lou]

I don't understand why you want to weld in a small dent!  You may very well cause yourself mucho grief by warping the surrounding metal.  If it is that small just slap in some good quality filler (I use 3M) and be done with it - the factory does!  On larger dents I've used a "Ding King" to pull it most of the way out and then putty to smooth over.

Plus 1 fill it !!!!!
Lou
ps are the grab handles standard ??

[billygoat]

 It's a LS tail on a 1980 r65.

 I could fill it with metal! It was puttied before butt the po did a lousy job so now I must reconsider.

[Justin B.]

If you must fill with metal use the proper body-solder/lead like the old pros did back in the 50s (being the origin to the name "lead sled") or blast around your welds real good and go back with plastic.  There is absolutely nothing wrong with plastic filler if it's good quality and applied correctly.

[drewboid]

Dry ice is solid CO2 so that would work for purging the tank. As for filling the dent lead or solder or even brazing would be easier to work with than welding.  I'm told that the bodymen used greased oak sticks to smooth the melted lead - never tried it myself. Use a good flux to ensure a bond between the steel and the lead filler. Lead can easily be worked after it solidifies but it is toxic - wash very carefully after you finish filing it.  
Good luck.

[Justin B.]

There are special paddles used to spread the lead and they are often coated with beeswax.  I've seen it done but my only attempt was a puddle of solder on the ground under the spot I was trying to get it to stick to!

[montmil]

In the early 60's, my brother and I shared a Porsche 1600N Coupe for our high school transportation. Don't get excited, lads... the little car had a 1600cc twin-carb engine and about as much acceleration as my Vespa. Handled nicely, though. But I digress...

Little brother got center-punched by Detroit iron when a little ol' lady ran thru a Yield sign. We visited the body shop as they began disassembling the car for repairs and watched as the torch was laid on the car and lead rolled off like rain!

After all the bent bits were replaced, out came the paddles and lead. It was a pleasure to watch the craftsmen put the car back together. Very old school.

Then the old man Sold it! Quoting, "I won't have a car that's been wrecked."

Monte

[billygoat]

 That leading stuff is cool but too much involved, torch,flux, and where do you get the solder? I thought about 50/50 solder and the the dent is too shallow for the bondo to stick I think was the problem last time. I can easily build up the surface with a few mig passes and then file smooth. I'm supposed to know how to do this as a welder so it looks easy enough to me.

 The tank still smells like gas after two days drying and the inside looks like it was just re-lined, the red coating looks nice. So I may try water then purging it.

 I put some gas in a small aluminum fuel bottle years ago and I noticed it still stinks like gas after a few soap and water washings.
I'm going to consult my welder friend next week.

[montmil]

... the inside looks like it was just re-lined, the red coating looks nice...

Will the MIG work require re-lining the tank?   Monte