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Old 02-15-2021, 07:38 PM   #1
Seabees
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Default Firewall welding

Howdy boys, another question, if I may. What are your experiences with welding up the cracked firewall at the hood rod bracket? Yes, you're correct! It is very close to the gas tank! So, I'm a little queasy about wire feeding a weld that close. What are your thoughts? Would a 1/16" piece of sheet metal be enough to shield the tank safely, between the tank and the firewall? I'm not so sure, but it might. On the other hand, I saw a gas tank at the Portland Swap Meet that looked like a Model A tank, but it was "bulged" out somewhat. Must be some off brand, I thought to myself. Then it hit me! It touched off for some reason. I asked the vendor. Yup. He wasn't sure how, but it did "blow"! I don't think I would want to perform this task, even on a good day. So, what do think? Thanks guys!
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Old 02-15-2021, 08:19 PM   #2
J Franklin
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Default Re: Firewall welding

You can remove the tank before welding.
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Old 02-15-2021, 08:42 PM   #3
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Default Re: Firewall welding

X2 I would remove the tank first. A pain to do, that's for sure.
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Old 02-15-2021, 08:43 PM   #4
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Default Re: Firewall welding

Correct don’t do it
Remove tank or fill with water then drain
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Old 02-15-2021, 08:56 PM   #5
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Default Re: Firewall welding

Here is an eariler thread on what may be a similar issue.

https://www.fordbarn.com/forum/showthread.php?t=167860

Note that the fuel tanks are different, earlier cars vs the later ones, and model to model.

Mine is a 29, the tank and upper firewall are one assembly. Take the tank out, you get the upper portion of the firewall along with it.

What I did was make a backing plate larger than the hole, a "plug" plate that was a tight fit in the hole, bonded the two together using panel bonding adhesive, then fitted that assembly in from the back/tank side and bonded it in place with the panel bonding adhesive. A new repop radiator support rod bracket was installed and it works fine.
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Old 02-15-2021, 10:49 PM   #6
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1955cj5, sounds like this might work, since you've had no issues with it. I could pull the tank, but this sounds easier. How long has it been in place? I'm not familiar with panel adhesive. I'll have to talk to my body guy. Thanks for the suggestions!
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Old 02-15-2021, 11:37 PM   #7
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Default Re: Firewall welding

You can drain the gas and put dry ice in it. The CO2 from the evaporating dry ice will displace any oxygen in the tank and there will be nothing to ignite. Along with the sheet metal barrier between the tank and firewall, lay a cloth soaked in water across the top of the cowl covering over the filler neck as a back up measure.

If you are working on an early '30, this is a common problem. In mid '30, they added reinforcements to the back side of the firewall where the hood rod brackets attach.

Chris W.
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Old 02-16-2021, 08:25 AM   #8
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Default Re: Firewall welding

If you don't want to remove the tank, one solution to is to drain the tank, fill it with water to the top, pass a charcoal lighter over the fill hole and burn off the fuel vapor. When you refill the tank, any water left in the tank will be at the bottom and can be drained into a container until its all gone. Have personally welded a motorcycle gas tank outlet with water in the tank.
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Old 02-16-2021, 08:36 AM   #9
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Default Re: Firewall welding

I like the dry Ice Idea. Always something new to learn.
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Old 02-16-2021, 09:56 AM   #10
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Default Re: Firewall welding

Geez, I'd be scared to death to weld on a Model-A gas tank!


Ohh wait, I do weld on Model-A gas tanks.

My suggestion is use your instincts as your guide. Then common sense.

I will tell you from personal experience that a drained gas tank (-with fumes only present) that has the filler neck, gas gauge opening, and fuel outlet bung all open to atmosphere does little more that go 'woof' for a brief second when introduced to fire.

FWIW, I have tried to intentionally see what it takes to make one explode. Using starting fluid to spray a fire trail to the fuel fill opening, -and with a drained tank I had a bigger fire with the starting fluid than the inside of the tank. As someone mentioned above, if you are concerned, fill the tank with water and then weld all you wish.
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Old 02-16-2021, 10:19 AM   #11
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Default Re: Firewall welding

His question was about welding the firewall, not the gas tank, I thought.
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Old 02-16-2021, 10:35 AM   #12
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Default Re: Firewall welding

First,are you talking about the hood rod bracket,that is held on with 2 screws? Or,do you mean the radiator support rod brackets?Those are notorious for cracking the firewall,at least here in New England,with our rough roads.If it is those spots that are cracked,I wouldn't think much about welding them.They are a few inches from the tank.I guess my only worry would be vapors coming out from under the cap and dropping down to where you are welding.A wet rag draped over the cap would take care of that.Also,a hose hooked to an exhaust pipe with the other end in the tank would displace any oxy in the tank.Car exhaust won't support combustion.
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Old 02-16-2021, 10:40 AM   #13
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Default Re: Firewall welding

Quote:
Originally Posted by Planojc View Post
His question was about welding the firewall, not the gas tank, I thought.
You see, needing to stay on topic, -or answering the original poster's question does not apply here.
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Old 02-16-2021, 08:43 PM   #14
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Default Re: Firewall welding

Quote:
Originally Posted by Seabees View Post
1955cj5, sounds like this might work, since you've had no issues with it. I could pull the tank, but this sounds easier. How long has it been in place? I'm not familiar with panel adhesive. I'll have to talk to my body guy. Thanks for the suggestions!
Five years and still no issues.....maybe 2500 miles?

The catch is, it's sort of expensive, comes in a two part cartridge and requires a special dispenser.

The auto paint store that I got the adhesive from had loaner dispensers, and the adhesive itself was left over from a previous project.

If you know someone in the body repair business that would be a big help.

Good Luck!
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Old 02-17-2021, 02:25 PM   #15
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Default Re: Firewall welding

Any electrical welding process associated with a fuel tank can lead to sparks in places you don't want them. If a person welds with O/A gas then the fire will still be a bit too close for comfort to the filler opening. Better safe than sorry.
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Old 02-17-2021, 03:32 PM   #16
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Default Re: Firewall welding

Thanks guys, talked to my body man yesterday, he recommended the panel adhesive. Says it's pretty tough stuff. I'm going to leave it up to the owner. Just needed some suggestions for him. Thanks again!
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Old 02-17-2021, 08:11 PM   #17
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Default Re: Firewall welding

Gas cap on and spark arrestor in the tank, What are you worried about?

The firewall is not close to the actual tank. Unless there is a fuel leak you have nothing to worry about. Just drain the tank and weld it up.

Did you ever think how they fix cracks in the huge fuel tanks at the fuel farms??

The guy gets in the tank with a special hosed mask that does not allow air out of the mask. He welds up the hole from the inside. My brother was friends with an old time (he was old in the 1970's) welder and that was what he did for a living.
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Old 02-18-2021, 11:43 AM   #18
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Default Re: Firewall welding

So to get off on a tangent of safe welding on fuel tanks (I know the OP asked about firewalls, not gas tanks, but we've gone adrift a bit) - something I do know a bit about (I spent most of my career as a safety engineer) - there are two different methods of doing this safely. In an effort to help us all learn something, here goes a brief discussion:

Gasoline liquid itself does not pose much flammability hazard - it's the vapor that's the issue, not the liquid (that's why there are jets in carburetors, to create vapor from liquid). Gasoline is a mixture of a bunch of primary solvents like toluene, benzene, ethylbenzene, and more, but in general it takes a mixture of ~1.5% to 10% gasoline vapor in air to be flammable if an ignition source is present. (This can only take place if the vapor/air mixture is above the flash point, which for gasoline is ~-45F. Diesel, on the other hand, has a flash point of around 125F, which is why you use glow plugs to heat it up to start ... but I digress).

So in theory, if you keep the amount of gasoline vapor in the gasoline/air mixture below 1.5% (too lean) or above 10% (too rich), you are golden to introduce a source of ignition - spark, flame, whatever.

In practice, you shoot for 25% of LEL for safety to account for possible vapor density stratification. So this would mean that an atmosphere of ~0.40% gasoline in air would be safe. That's the concept behind inerting the inside of the tank with dry ice. Gas CO2 displaces air. A pound of dry ice (solid) creates around 6 gallons of gas CO2, and you should use at least 3x the volume of inerting gas as you are trying to inert. So a 10 gallon Model A fuel tank would need about 5 pounds of dry ice, completely converted to gas (warmed up). If you go with this approach be sure to seal all openings (fuel gage, fuel valve, fill neck) - I would leave the fuel neck slightly ajar then tape it closed after the dry ice has evaporated. That's the concept CWPasadena notes in #7.

Inerting is not practical on a multi-thousand barrel stationary tank in a refinery. So the welders take advantage of the upper flammable limit and work with the atmosphere too rich - above the 10% UFL. At room temperature the saturation level of gasoline vapor (level of vapor above the liquid, having displaced an equivalent amount of air) is ~40-60%. That's not compatible with breathing, so the welders use a supplied air welding hood that doesn't leak air into the local environment. That's what Kevin in NJ is talking about in #17.

Having said the above, welding on a gas tank is not a good idea unless you are really, really sure you know what you're doing. You don't get many do-overs if you make a mistake.

Now, back to the news...

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Old 02-19-2021, 10:55 PM   #19
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Default Re: Firewall welding

The OP hasn't said what year his car is. The fuel tank/cowl setup is different in the two versions of the Model A. If it is the early one, simply take out the cracked panel, weld it and reinstall. It is not part of the tank. All this talk about welding fuel tanks is irrelevant if it is one of the earlier cars.
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Old 02-20-2021, 01:23 PM   #20
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Default Re: Firewall welding

I patched up several bullet holes in 28 -29 tanks and fire walls . fill with water and weld away . Keeping the tank full of water was the hard part .
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