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MG MGB Technical - Gas tank welding (revisited)

Looks like I'll be brazing a small gas tank, 3 quart size. It's the 'swirl pot' for my fuel injection, and once it was filled I found a leaky seam. Starting over isn't an option and I have no inert gas on hand or dry ice. I do have some r134 freon. Anybody know if that stuff is either a fuel, an oxidant, or breaks down with heat to something nasty? The tank has 4 small fittings only, about 1/4" so taking the cap off isn't an option either. Definitely need to purge the oxygen out of it before starting.
Jim Blackwood

Jim, Can you get water into the tank? No idea about the r134 though. Perhaps an a/c place might be able to advise? Cheers, Pete, Sydney, Australia.
Peter Thomas

Jim,

I believe the 'Eastwood Company', and maybe 'MOSS' sell a fuel resistant sealant that you could use to coat the inside of your tank/s if the damage is not too extensive, and avoid the hazards of appying heat. I have had some success sealing motorcycle fuel tanks (pin holes) years ago with this product, and they all held up quite well. Try them at: <www.eastwood.com>, or <www.mossmotors.com>

Regards,

L.C. '74 B/GT

Larry C.

I just was reminded that carbon dioxide can be produced from baking soda and vinegar. It's also twice as heavy as nitrogen and oxygen so the simple solution is to fill the tank most of the way with water, prepare a container with a lid and hose barb, connect the hose to the tank drain, fill the container with soda and maybe rig a drip for vinegar, then give it a few minutes to evacuate the oxygen and make sure I can hear bubbles all the time I'm working on the tank. I think this will work for the small tank I'm using. I've got some left over "Redcoat" sealant, but I'd rather have it brazed up. It's a good idea though.
Jim Blackwood

R134 is a fluorocarbon, the "greener" version of R12 which is destroying the ozone layer. I don't know what happens if you burn it, but I suspect the chlorine, fluorine or whatever halogen gas is tied in on the carbons in the R134 molecules will zip off into the upper atmosphere and make driving open top cars less fun.

If you don't know what to do with it, I would suggest taking it to be recycled.

Mike
Mike

Jim:
I would be very careful about using any of the freon compounds as you suggest. R12 when subjected to an open flame produces a deadly nerve gas. Not being familiar with the properties of R134 the same may or may not apply. Don't think you want to find out the hard way! Good luck, Tom
Tom Sotomayor

Jim,

Don't use the refrigerant as a purge, Tom is correct in that CFCs (not sure about HCFCs, but it isn't worth the risk.)

CO2 is available at sporting goods stores, used for paint gun propellent.

If you can't come up with anything safe let me know, I have a source for N2 and Argon gas. N2 is just as good for brazing and not as near expensive.

PS - if you use the R134 can I have your specialized tools????

Bud
Bud G

I agree with tom on this, when r12 is burned it gives off Fosgene gas........its what the Nazi's used in their "Death" camps.Enough said! My fuel tank was completely empty of fuel for a week(checked with a flashlight and mirror)then i let an air hose run in it for about an hour to remove any fumes left.Squirted a bit of a Co2 from a fire extinguisher in the filler hole before i did any cutting/welding......good luck!
Dave ross

Jim, jeeezus, I want to see that amazing supercharged car completed, so please just buy a new tank before you braze a swirl pot in. Or have someone make one up ... I think they're around $250 all in, new. Every non-pro I've ever heard of try to weld a used gas tank will NEVER repeat the experience!!! ("Sorry about my hands being blown off, honey, but hey, I saved us a coupla c-notes!")
David

Well that's pretty hilarious. I'd have to agree though. it's not an experience you'd want to repeat.
I found out the freon does in fact burn at elevated temps so there's another reason it would've been a bad idea (reminds me of Cartoon Network's "Good Idea, Bad Idea")
Well you guys will love this one. I built a co2 generator from a couple of old pickle jars and some brass tubing so that vinegar was metered from the top jar into the soda in the bottom one. Didn't produce anywhere near enough co2 for my taste, but by the time it quit I had started brazing so I continued and made sure I kept the tank hot so it wouldn't suck in air. It had a little water in the bottom which kept evaporating so that helped. Also, (now bear in mind this is only a 3 quart tank, I was wearing full leather garb, gloves, and full face shield) there was still a little gasoline in the tank so every now and then one of the top fittings would ignite which was a considerable distraction. It was worst after I had decided to overbraze the main seam around the sides and the tag on the end caught fire. The flames from that kept lighting up the fitting on that side. Well, I deduced that as long as gasses were blowing out of the tank and *then* igniting it only proved there wasn't a combustible mix inside the tank. Still and all, when at one point on the second go around to fix spots I'd missed all three fittings caught fire, and at the same time spewed some water out on the bench, along with a little gasoline which also promptly lit up, I actually considered giving it up. At that point though I had the tank full of water up to the spot I was welding and figured the chance of explosion was slimmer than the chance of fire, so I put out the bench and finished up. Looks like I might still have one extremely small pinhole and a fitting that needs re-sealed, but I'm not real anxious to repeat the experience. I banged on the brass around the pinhole and pretty much closed it up, and teflon tape is all that's needed on the fitting. That'll get me by for startup and maybe later I'll have another go at it.
Jim Blackwood

This thread was discussed between 20/01/2002 and 23/01/2002

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