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Discussion Starter #1
Hello,

I am interested in buying a bike that has been sitting for a long time. I can handle the mechanical work but have never dealt with a gas tank with this much rust. Has anyone saved a tank that looked like this? I know it's hard to tell from a couple of photos but it's all I have at the moment. Let's assume for now there are no detectable leaks, just the rust.

The bike is an '81 GS750L. IIt looks nice with low miles since it's been sitting so long. I love those bikes but they are only worth so much. Not sure what to do with this one.

Thanks,
Joe G.
 

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ZAMM Fanatic
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A respectful memorial service is what that tank needs. I don't think even repeated overnight soaks with CLR could save it.

There are currently a half dozen GS750 gas tanks on ebay for sale.
 

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That looks like rust and some sort of decaying tank liner.

If you don't have leaks now you very well may find pin hole leaks after you de-rust the tank. If the holes aren't too bad you can sometimes solder over them, but those tanks use a relatively thin metal. Still, I'd give it a try before I decided to buy a different tank.
 

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Discussion Starter #5
Yeah it's hard to tell exactly what's going on. I don't know if the lighter color is metal - I think if I could actually see some metal I would have an idea of how deep the rust was.

Unfortunately there are no good tanks for a GS750L on Craigslist at the moment - there's one for $300 and one really beat up one, others are for 750E and others which is different.

I will check for leaks, try to tell if there are any weak spots in the tank wall, etc. Maybe this is going to be more of a restoration than I was thinking. I got excited when I saw the pictures and low miles. It would be an awesome project but I'm not sure that's what I need at the moment.

Thanks for the replies gentlemen.
 

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YOu know about the plastic treatments you can pour in the tank and slosh around? Some guys swear by it...goes right over the top of the rust...

Google motorcycle gas tank sealer
 

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The ones I've used will work okay if you do the right kind of prep work. Often that prep work will damage the original paint, but if you're repainting that's not a big deal. If there's a product that can just be poured over the insides of a rusty tank without spending hours prepping it, and that will actually adhere and STAY, I'd be very interested in that!
 

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electrolysis (google gas tank electrolysis to see how to video's and such) clean out the tank, check it for leaks and if no leaks then use one of the inner coatings they have out (POR 15 is one) if there are any small leaks, maybe get a welder to fill them in if it's possible....

cleaning out the tank should be fairly cheap, I don't know what the coatings cost or what it may cost to have any leaks welded....but I bet all of that would be cheaper than buying a new tank....
 

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Discussion Starter #9
Thanks guys. Yeah I was just trying to figure out if this tank was in good enough shape to try cleaning and coating. I have done the research and seen the available treatments and have no problem going through with any of it. Of course it would suck if I spent the time and money to find the tank unusable afterward, then have to buy another crappy old tank and go through with it again.

I will bring a flashlight and maybe something to tap on the tank with and see if I can find weak spots, and if I decide to make an offer on this bike I will put fluid in the tank to make sure there are no obvious leaks.

It is nice that these classic bikes can be had for a relatively small amount of money, but it makes it hard to justify any large repairs or restorations (unless you have time like I used to).
 

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If you just have small pin holes they're easy to solder over. If you have larger weak spots from pitting you'd have to weld a patch over that, which would take a TIG welder and some skill.

The best way to check it for leaks is to pressure test it. Go to about 5psi and spray soapy water over the tank and look for bubbles. If you put gas in the tank to look for leaks and you find one, then you have gas leaking all over. Plus, then you'd have to pay to have the tank purged before you did any open flame soldering or welding.
 

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Just make sure that tank is really well purged before putting heat to it.. Personally I like to solder pinholes and coat with Red-kote sealer.
 

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rust and de rusting...

first there are two places you don't want any rust...

tanks and bering surfaces.


so if that is really a picture of a tank....(looks like a pic of rust....)
I would truely find a suitable tank dump, and make sure it never comes back...

if that was a tank once, it looks like someone filled it with water to see if it the engine would run on that... could be alcohol gasahol that busted the lining.... high octane booster.... maybe a combo that someone thought would make it go faster like hobby fuel..

anyway. tank is shot. get a new one. hint- any rust. is rusted.
 

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I just finished 'cleaning' out my tank. It looked worse than yours. I used three gallons of White Vinegar. Pour it in and let it sit for 5/6 days. Stir it around once in awhile if you feel like doing something.

Cheap, fast, and it works. Once done, empty the Vinegar, blow in compressed air to dry it out, and add a couple of quarts of oil. I use Marvel Mystery oil. It's light weight and actually eats whatever rust is left. Slosh that around for a bit and drain. Add gas and go.
 

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A lot of the brown stuff that is on there is not rust at all,but is the crystalline form of evaporated gasoline. The problem with removing both the crystalline stuff and also the rust is that it can take two different chemicals to accomplish the task.
Oxy clean is a good start to get there. It will put the gas residue into suspension and also loosen the rust to a great extent. Use it first and dump and repeat it about once an hour [by the looks of that tank, maybe repeat 5 times] using nearly boiling water to speed the process. fill it all the way to the top,realizing that bubbles will generate and release liquid over the tank. Protect the tank paint with synthetic grease and keep an eye on it so the oxy does not wash it off and harm the paint.

The vinegar described above will work on the rust as will other chemicals. You can buy strong vinegar with a higher acedic content made for cleaning at Wal-Mart. If there is any brown tar-like substance remaining,it is also gasoline residue, and then you can pour lacquer thinner in the tank to dissolve it away.

You asked us if we had ever cleaned any tanks that looked this bad and the answer is 'Yes" The real trick is not to damage the paint on the outside while cleaning the gunk off the inside

C:\Documents and Settings\USER\My Documents\My Pictures\2014-01-31, duck
 

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No kidding, Oxy Clean. I'll have to try that sometime.

"The Works" toilet bowl cleaner is my go-to.
 

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If that was my tank, the very first thing I would do (and the cheapest) would be to throw a couple handfuls of gravel from your driveway in the tank and SHAKE THE LIVIN' DAYLIGHTS out of it for 15 minutes or so. Then dump out all the loose crap
and take a fresh look at the inside of the tank. You'll get a better idea if it can be saved or not.
 

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Well,as it happens, I just finished cleaning the worst tank I ever tried. It took three weeks,but with proper technique It probably could have been half of that. the tank is from a CL175 and the filler cap is to one side making the anode [+ charged iron rod] hard to get where it would do some good. I got 100% rust removal and that reached all the way,even revealing more pinholes. Because some pinholes were present before starting,I considered this a practice tank.

With electrolysis, the big concern is the grey smudge left behind. You sure do not want to put tank liner over that stuff as it is not really bonded to anything. Once I solved removing that in a 2 step separate chemical process,the tank came clean as a whistle, ready for a quality tank liner. I also used a fiber optic camera to confirm that everything happened as it should on the hidden areas of the tank.

I have taken pictures of the process so far,and once I patch the pinholes,pressure test,and line the tank,I could post it up.
 

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That would be great pictures and a write up of the procedure.
 

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Im looking into something like this as well. My father has a 1980 Sportster thats been sitting for 20 years. Should be a bit of work.
 
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