Quote:
Originally Posted by DannoXYZ
Clean tanks seem to be toughest to find and they're often in bad shape. On both my pre-gens, tanks were rusty with one being extremely thick and foamy rust. Following some guides from vintage bicycle forums, I soaked them in oxalic acid (easy to find and use). Little did I know that oxalic acid eats both rust and good metal at same voracious rate. I ended up with holes in both tanks.
I bought two more tanks, both equally rusty. This time I researched topic a little more and used phosphoric acid on one of them (available as concrete-cleaner/rust-remover at hardware stores). Phosphoric acid preferentially eats only rust and stops at clean steel, leaving mild protective coating. I put tank on spit and rotated 90-degrees every couple hours. I went through 4 pint-bottles of it on this tank in 2-weeks and was left with nice clean metal! Coated it with POR-15 then followed up with diluted epoxy resin.
On 2nd tank, I tried electrolysis with washing soda. That worked pretty well and was faster than phosphoric acid. Also POR-15 coated and sealed with epoxy resin.
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I'll remember that phosphoric acid process. I've found something that works pretty well on rust it's called "Evapo-Rust". It's not cheap and you would probably want to pour in a whole gallon of it. The cool thing is that you can drain the Evapo-Rust (pour it through a piece of cheesecloth) and reuse it. I imagine you would have to rotate the gas tank 90 degrees every 12 hours or so, The metal needs to be submerged in the solution. While you're at the tank clean-up be sure to run a 0.060" - 0.080" piece of piano wire down the overflow tube that runs inside your gas tank. The tubing is raw steel and rusts. I cleaned out the tube on my bike and it was plugged with rust. I then sprayed G-96 gun treatment down the tube. I did that in 2017 and 2018. If that rusts out you'll only be able to fill your tank to the point where the rust hole is on the tube.
Cheers,
Bill