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When you touch a MIG to that, it is going to really burn up the holes way bigger. I'd almost consider using it as a plug for a fiberglass mold, and making a fiberglass tank out of it. They're so rare, with the left over mold (I'd do it in halves, easier to put together) it would become very easy to reproduce many times. Just a thought. I would still carefully cut out the bottom, and fix it from the inside. You would have a solid tank after that. My personal experience with fiberglas tank repairs is that they eventually leak, and not at the most opportune moments.
 

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Bultacos used fibreglass tanks that did not leak. Well mine leaked after I collided with another motorcycle and it punched a hole right into the tank. I slapped a fibreglass patch over it and rode it for years without any further leaks.

I think a lot depends on proper prep and proper application of the glass patch. Since most of the damage is where you won't see it, you won't have to use any body-fill to blend the patch.
 

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I have no problem with fiberglass tanks. Quite the contrary. That's why I suggested he consider making a plug one out of the original to fabricate a fiberglass tank. I have seen many people do fiberglass patches on metal tanks. They all eventually leaked. I think doing a repair with Brazing would yield better results. :)
 

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Well, my patches never leak and I have patched quite a few car and motorcycle tanks with fibreglass.

I will say this though. You have to be very careful that the patch goes well beyond the rusted area into good, clean metal. And you must then treat the inside of the tank to try to prevent future rusting. Otherwise, as Kawasakian points out, eventually it will leak due to further rusting that will extend beyond the patch.
 

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Gettting to the inside of the tank is the problem. If you prepare the surface properly, it won't leak. I'm surprised no one has come out with fuel bags, like that ones used in aircraft.You could use air to inflate the bag inside the tank, running the fuel tap out of the petcock hole, and putting your On/Off switch there. You wouldn't have to have a perfect fit, the tank would fill itself, the intial filling with air would push it to it max capacity. Just dreaming. :)
 

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Products like this, if properly applied can work wonders for an old tank. I prefer to first use an environmentally friendly rust remover first, but you would temporarily have to plug the pinholes with duct tape or something.

I have had good success with a product called Enviro Rust Wash.


 

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Discussion Starter · #27 ·
I usually use the POR-15 products. This tank is so far gone though, that I've been trying to get the worst of it out before using the regular de-ruster. After all those days in vinegar, and getting pressure washed as well as I could, there are still big flakes of rust coming out as I turn the tank over to strip the paint. I'm gonna have to open it up and clean it "manually" if I want to ever have a sealing product actually stick, I think.

Jake bought me some kit that I'm not familiar with, but it's the same sort of thing. A de-ruster, detergent, and sealer. I'll try to remember to share the name of the kit later. Today, the paint is gone and it's ready to be cut open. I'm not the first person to work on this tank. I removed some brown stuff that I think might be skim-coat, as well as some body filler that was covering a dent in one of the lines on top of the tank. I also found a sticker in the back that had been painted over. It said something like "don't restrict the engine". Some words were missing.

I bought a brazing kit a few days ago. I have MAPP gas and propane, but I can't find anyone who has oxygen in stock. I hope I can get the tank hot enough with just the gas. I tried aluminum brazing a cracked clutch cover a couple weeks ago, but I just couldn't get it hot enough for the brazing to stick. I think the cover just had too much mass to heat. I bought a sheet of welding steel, in case I have to make some patches for the parts that are too far gone to fill in. I've never done that before so we'll see how it goes.

But I'm getting ahead of myself again. Still have to cut the thing open first.
 

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Discussion Starter · #28 ·
Opening up the tank was quicker than I thought. Here's a couple pictures:
Food Cuisine Amber Dish Gas

Automotive lighting Wood Bumper Vehicle door Automotive exterior


Some of this is just surface rust that's showed up since I washed it. But there's a lot of old junk still on there after tumbling, electrolysizing, and soaking in vinegar. I don't think it would have come out. Now I can go after it with a wire wheel. I wonder if some of this junk is a previous attempt at coating the inside of the tank. Oh yeah, that kit I have is from Caswell. I've never heard of them.
 

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Discussion Starter · #29 ·
Wire wheeling the rust off wasn't so bad. There were a few areas that were hard to get to, but it's done. Here's what I've collected since starting:
Ingredient Fluid Wood Insect Cuisine

That's not even including all the mud that's come out after soaking, and all the dust that's gone up my nose. Anyway, it's ready to be cleaned with some degreaser, and the repairs can start.
Helmet Wood Bumper Artifact Automotive exterior

Automotive lighting Gas Luggage and bags Automotive exterior Rectangle

It looks like the pipes are brazed in place. I'll try to remove them. They're not doing any good anyway. One is clogged, and both have cracks and pin-holes. They also had rubber plugs on the ends when I got the tank. I'll ask Jake, but I think they've been bypassed anyway. I'm guessing one is an overflow drain for the tank, and one is a breather tube? Better to just have them out of the way I think. I'm surprised at how many pin-hols are in the top of the tank.
Wood Tints and shades Twig Kitchen utensil Close-up
 

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Discussion Starter · #31 ·
Thanks!
Despite all the damage, both halves are still pretty solid except for a couple thin spots. I think I'll remove the tubes first, and then see about welding patches on the two worst spots. One is flat, so it should be relatively easy. The other is all curvy, so I'll have to do my best to shape a new patch. I'm thinking of brazing all the pin-holes from the inside because of the super rough texture of the metal. I'm hoping that will help the brass form a really strong bond. If all goes well, I'll weld the two halves back together, fill it with water, and check for leaks.

Although I've never brazed anything before, and I have very limited welding experience, I feel pretty confident at this point that it will turn out good.
 

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I would glass bead blast that tank before I brazed it. It is the best way to clean the tank. Don't sand blast it, the heat from the sand could destroy it. A Bag of sand to hit the metal against, and flat peace of metal, some plastic forming hammers from Harbor Freight, you should be able to bang out a working bottom. I'd get new tubes, and fix that. ;)
 

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Discussion Starter · #33 ·
A media blaster is definitely on my wish list. For now I'll have to make due with the wire wheel. It's doing a pretty good job.

Welding started pretty slow, and really bad. The gas tank metal doesn't behave like the sheet metal I practiced on. Didn't help that I've been using an old welding mask with a #9 filter and I still can't see anything through it. Most of the time I didn't even hit the spot I wanted to weld.

On Monday I picked up an auto-darkening helmet. Makes a world of difference! My welding still sucks, but now I can instantly see how bad it sucks. I decided to replace a whole corner of the bottom piece, as it's full of holes and super thin.
Helmet Jaw Window Bumper Automotive tire

I set the bottom back in place to see if I'm anywhere close to copying the original shape. I think a few adjustments will get me where I need to be. The weld still has a bunch of holes in it. I'm sure a proper welder would have got it in one or two passes. But this is only the fifth thing I've ever welded, and my first using sheet metal. So it will be a while yet before I'm done. Here's a view of the inside:
Wood Natural material Close-up Artifact Metal

I'm thinking of setting up some kind of light behind the weld so I can see the holes better. Here you can kind of see that I've got five or six holes still to fill. I've heard people say to build off the previous weld because its thicker and will absorb the majority of the heat. That will help prevent blowing through the old sheet metal. I've been doing that and it seems to be working.

I'm also thinking of welding a strip of new sheet metal all the way around the edge. I think that will help make welding the tank back together much easier.
 

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"My welding still sucks, but now I can instantly see how bad it sucks." :LOL:

Welding is not as easy as it looks. I have my own MIG, Stick and have access to TIG in my shop and I suck at them all.
But yeah, welding on thin rusty metal is jus not fun regardless of what kind of welder you are using.

I admire your perseverance.
 

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If the welder is blowing through the adjacent metal, then your patch needs to be bigger, as that metal is also corroded on the inside. I would try and fabricate the largest parts possible, with the minimalist amount of welding, then you will have a solid tank. I don't think I would use any part of that tank bottom, it's shot, looking at the pictures you posted. Also, on one pic, it looks like the top part of the tank has pin holes. Why wouldn't you fix everything from the back side? You got the whole bottom off, fix the top part first, then sand smooth the outside. You will have a much better seal. It's hard to tell from the pics as to what you are doing, but you can bang out a bottom that works from a few flat pieces and that nice thick steel will weld up easier. :)
 

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Discussion Starter · #36 ·
Well, it's really just around the edges that are super thin. I'm hesitant to build a bottom piece from scratch, because I don't have the bike here to make sure it would fit, and I'm not sure I can recreate all the weird shapes effectively. I do plan to fix as much of the top half of the tank from the inside as I can. I've been concentrating on the bottom piece for now, since it's not something that will be seen and I'm hoping to get better with continued practice. I took yesterday off, but at the end of Monday, I was blowing through a lot less. When I get to the top part though, I may replace that hole central piece since it's full of pinholes and is relatively flat.

I also still want to try brazing some of the smaller pinholes. I bought a brazing kit, but I can't find any oxygen locally. I hope just the MAPP gas torch will be enough heat to melt the brass rod. I tried aluminum brazing once, and couldn't get the aluminum hot enough for the rod material to stick. That was a big chunky aluminum part though. Anyway, we'll see what happens.
 

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There's a company called "Alumaloy". This stuff can be done with just Propane and they make a rod for steel also. Here is the link. I have fixed airplane cowlings with this stuff. It's incredible. I don't know why I forgot about it, but it may solve all your problems. It can be milled once it cools. :)


Link = Alumaloy Official Home
 

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Discussion Starter · #38 ·
Hey, that looks promising! The steel version melts at 390 deg f - 570 deg f. My gas torch can definitely do that. Unfortunately, the torch decided to partially clog today, so I didn't get to try out the brass rods. Maybe tomorrow after I clean it.
 
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