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Old 02-18-2018, 06:29 PM   #1
Deucefanny
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Default Safe fuel tank repair

I have no idea what I did in a past life but this bike fucking hates me. Went to the shed this morning to find a small amount of fuel running down my fuel hose. On closer inspection I could see it was coming from the tank. I took the tank off and removed the paint from the area and found a small split on the underside in a seam. I really don't want to buy another tank or strip all the paint off the as it cost me a shit load to get painted.
So what's the best way to fix it. I spoke with a mate and he said to just give it a really good hot soapy water wash out and tig it. The split is about 1/2" or so long.
Will this work or will it blow my eyebrows off?
Cheers DF

I have looked for a thread but can't find one on here. If someone has a link post it on here.
Thanks.
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Old 02-18-2018, 08:08 PM   #2
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Default Re: Safe fuel tank repair

Give it a GOOD washing, then wash it out again, let it dry, stick your nose in and if you smell any gas wash it again.

Once you get it cleaned out tig it or mig it.Since its in a seam you'll have a little more meat to work with then give the inside a good coating with red-kote and I'll bet you'll be golden.

When I was a welder in my younger days in the refineries we would fill the offending container with water after a good cleaning to weld it saving our eyebrows and more. That's an option for you but I think you'll be fine going the above route.
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Old 02-18-2018, 08:40 PM   #3
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Default Re: Safe fuel tank repair

Alcohol to get the fuel out, soapy water to get the alcohol out.

I have a little rig to whisper nitrogen into a tank for filling; that's another way you can keep from a-sploding. Maybe you have a bud who can help you out?

Surround the area being welded with wet rags; it will give your paint the best chance at surviving, IMO.
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Old 02-18-2018, 09:07 PM   #4
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Default Re: Safe fuel tank repair

When I weld a used tank I wash it out with acetone and drain it well, put an air hose blowing into it for a few hours to blow as much of the vapors out as possible, and then purge the tank with argon and keeping the argon flowing while welding. Never any issues since I started doing it this way.

Once upon a time, when the only welder I had access to was a mig, I was told that purging the tank with exhaust from a running engine was the way to go, so I tried it. ran a hose from my truck exhaust to the tank, left the truck running, and welded the tank. No explosion and that tank is still the left side on my Shovelhead today. The problem is that the exhaust had a reaction with the bare metal inside and it is constantly rusting still, after about 20 years. I've acid etched it, coated it, cleaned it out completely, and nothing sticks to it and the rust comes back. I have to run a filter and clean it regularly, and I'm just waiting for it to rust through but it hasn't yet. At this point it's just an experiment I'm running. Long story short, use argon to purge, not exhaust from an engine, LOL.
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Old 02-18-2018, 09:29 PM   #5
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Default Re: Safe fuel tank repair

Thanks for the advice fellas. I might go and see a few joints in town to see if they can do it for me. I'm just a little scared to do it myself.
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Old 02-19-2018, 04:13 AM   #6
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Default Re: Safe fuel tank repair

Quote:
Originally Posted by WhizzbangK.C. View Post
Long story short, use argon to purge, not exhaust from an engine, LOL.
that made me laugh, what an end to your story lol
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Old 02-19-2018, 04:24 AM   #7
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Default Re: Safe fuel tank repair

I just leave a running hose in the tank and flush it for a good while.... all fittings, hoses, filters ect removed!
If the tank is not mounted with rubber gommets it will happen again.

L
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Old 02-19-2018, 06:16 AM   #8
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Default Re: Safe fuel tank repair

Hate to be the bearer of bad news...forget mig, And possible tig ..you may have a chance at oxy welding this with a small (and I mean small) torch.
If this is the bottom seam... this is where all the condensed water (extracted from the air-ethenhol gas) has settled over the years and rotted through the seam.
The metal isn't just paper thin where that pinhole is, it is thin all around that seam (lowest part of the tank)... and you use s mig welder, you will continuously "blow through" and chase that hole" ending up with a "gorilla weld"....and a 90% chance it will leak again where the welds ended.
You may get lucky since this is a older tank and the metal is thicker... a friend of mine asked me to "weld a pinhole" in a "newer" tank.. I ended up chasing that weld and I was using a small oxy torch... I have found that lead brazing is better suited.. you can knock the pinhole "low" and not only just fill the leak with lead..,you will have a bit of the surrounded surface covered as well.. not sure how long it will hold up to "new" fuels.. but radiators for years were soldered and antifreeze is mostly acolhol and they are under constant heat and pressure...
The tank I "tried to fix" was far gone .. the pinhole worked to 5 inches .. leaking at the weld ends .. a "liner /sealer was used.. still leaked .. the tank was cut in half and I was amazed just how bad the rust and seam was...
Just my .02
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Old 02-19-2018, 07:45 AM   #9
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Default Re: Safe fuel tank repair

I do however remember using a 2part "putty" appoxy deigned specifically for fuel tanks years ago (auto)... this maybe your best bet.. drain, flush the tank.. grind that spot to bare metal and use the "putty". I say bear metal because if you just scuff the painted surface the fuel could eat through the paint and "wick" between the "putty" and metal surface.
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Old 02-19-2018, 11:31 AM   #10
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Default Re: Safe fuel tank repair

Some good suggestions and a couple I don't agree with. You are concerned with paint damage so I'll give my suggestion. As everyone agrees wash it, wash it wash it, wash it.......washing it out can't be over done.
My way is to leave the tank almost completely full of water, only leaving a small air space (a bubble) in the tank. Next I leave a open hose to vent pressure from the tank, this could be attached to the petcock, or cross over nipples on a bob tank. Point is to leave it open to atmosphere, it doesn't matter if the hose for venting is above or below the level of water in the tank, as long as it is open the pressure in the tank from the welding heat has a path to escape.
A cracked seam is the easiest type of leak to repair. While tig will work I use gas welding. Get some rags and blocking, and use it to position your cracked area as the highest point so as the very small air pocket is under it. then weld it up even if it ignites there is not a large enough volume to do anything but push a little water out your vent hose.
This technique will minimize paint damage to a very small area.
What if water is coming out of the crack? Adjust the blocking your air pocket is not under the crack.
Do not move the tank if your welding, as the water hitting the HAZ will harden the metal and cause shrinkage in the area which causes stress and make your tank more prone to cracking again.
Warning again only a small bubble of air is left in the tank. Leaving a large volume of air, could well make this one of the most exciting moments in your life.
As has been posted there are other ways to purge your tank. But none will save the paint and minimize the stress in the metal.
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Old 02-19-2018, 05:06 PM   #11
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Default Re: Safe fuel tank repair

Top tip Joe
I like that.
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Old 02-19-2018, 06:21 PM   #12
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Default Re: Safe fuel tank repair

Thanks for the tips Rod and Joe. I'm going to see a bloke today that builds and races old bikes so I'm sure he's had this problem before. I like trying to solve problems myself but I have also become attached to my thumbs in the last 35 years.
Thanks again for all the advice and help fellas.
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Old 02-20-2018, 01:40 PM   #13
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Default Re: Safe fuel tank repair

Thanks richbob.
Deucefanny, I agree going to someone else is a good call, when you're not comfortable doing something. Would be nice if that guy will let you watch and learn.
I will add that brazing as a crack repair should be avoided. That said I do use brazing for some tank rust repairs by sweating in small sheet metal patch pieces. Those repairs are on car tanks. Motorcycle tanks I section in repairs either from similar tanks or fabing the piece.
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Old 02-20-2018, 09:40 PM   #14
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Default Re: Safe fuel tank repair

Keep us posted......
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Old 02-21-2018, 03:02 AM   #15
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Default Re: Safe fuel tank repair

Why not give it some thought about why it happend in the first place to avoid looking like Ghost Rider next ride out.... you got rubber gommets or mounted straight on the frame?

L
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Old 02-21-2018, 06:10 AM   #16
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Default Re: Safe fuel tank repair

Have you ever considered solder? A good hot copper or iron...I have had great luck with it over the years.
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Old 02-21-2018, 09:28 AM   #17
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Default Re: Safe fuel tank repair

I 100% agree with Joe.
That is exactly how I repaired gas tanks many years ago in a welding shop - if it's gonna blow, a small pop is waaay better than a metal tearing boom.
Used solder on car tanks usually and electric weld on bike tanks.
I fixed some and I wrecked/blew up some. The older tanks with the "rolled" seams were the worst.
Good luck,
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Old 02-21-2018, 08:53 PM   #18
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Default Re: Safe fuel tank repair

Quote:
Originally Posted by Lester View Post
Why not give it some thought about why it happend in the first place to avoid looking like Ghost Rider next ride out.... you got rubber gommets or mounted straight on the frame?

L
Yeah I know why it split. I made some new to motor mounts and I thought they cleared but I guess they didn't. I do have rubber mounts it was just a clearance issue.
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Old 02-21-2018, 10:13 PM   #19
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Default Re: Safe fuel tank repair

After thoroughly flushing the tank with water & dish soap several times I usually do the woof! test, torch to the filler cap at arms length & let it go woof! If you leave it sit, always do the torch thing before working on it again, just in case. I've never had one go off on me.

Then braze with Mapp gas & thinnest brazing rod available so you don't have to put too much heat in. Never tried silver solder but I'd imagine it would work prettywell too.
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Old 02-22-2018, 07:08 PM   #20
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Default Re: Safe fuel tank repair

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Originally Posted by zedboy View Post
After thoroughly flushing the tank with water & dish soap several times I usually do the woof! test, torch to the filler cap at arms length & let it go woof! If you leave it sit, always do the torch thing before working on it again, just in case. I've never had one go off on me...
I've repaired a TON of bike gas tanks and ^^THIS^^ is the best way to clear the tank of combustible fumes before welding. I've never had one to "WOOF" after cleaning, but the piece of mind that it's not going to go "BOOM" is priceless. I know a lot of members here are against liners, BUT if a welding repair is impractical, and you KNOW the tank does not have an underlying structural issue, Caswell 2-part epoxy liner works a treat if you want to perfectly preserve your paint.
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