Petrol tank rust removal

piranha-bro2 said:
How do you set up the electrode/s? What was the ratio for the caustic soda? I'm guessing you wouldn't want it anywhere near your paint?
Click to expand...
The anode (+ve) was an allen key poked through a piece of ply which sat in the filler hole, whilst the cathode (-ve) I clipped onto the tank at the point where the rubber strap hooks over by the seat - see photo. The ratio was a bit of a guess - I poured about 2 tablespoons of caustic soda into 10 litres warm water x 2, and filled the tank. It took three attempts to get a consistent power source - the first battery charger seemed to stop transmitting current quite quickly (presumably thinking it had finished 'charging'); the second was a LiPo battery that was a bit buggered so failed to provide any good duration; and the last, and successful one, was a charger for NiMH batteries which did not stop charging even though it indicated that the tank full of solution was fully charged...I left it hooked up for 24 hours.
 

Attachments

  • setup2.jpg
    setup2.jpg
    75.4 KB · Views: 23
  • setup.jpg
    setup.jpg
    278.5 KB · Views: 22
As to paint - the solution did drip onto the paint but without any impact that I can detect - although I did give it a wipe wherever I saw it, and I think I read that it is relatively benign...but I would avoid spillage as far as possible
 
Famous very early local here, Caustic Chris once soaked a Laverda head in that solution, he managed to miniaturise said head by a considerable size.
 
Vince said:
Famous very early local here, Caustic Chris once soaked a Laverda head in that solution, he managed to miniaturise said head by a considerable size.
Click to expand...
Yes, caustic soda will dissolve aluminium. I found that out the hard way - trying to clean up an aluminium saucepan with pea soup burned onto the bottom. I left a concentrated solution soaking in it overnight. It got rid of the carbonised food OK, but also got rid of a lot of the pot.

The dilution that Nick used (2 tablespoons of caustic crystals in 10 litres of water) isn't concentrated enough to do much damage to anything if spilled. Just clean it up if you get it on the paintwork. I don't think it would even be strong enough burn your skin. Don't get it in your eyes though, unless you're a masochist.
 
Yep, caustic soda is used for the extraction and refining of aluminium from the bauxite ore. This, as I explained to my wife, is why our Ali SEB pressure cooker had such an interestingly eroded geographic pattern in it after her soap making enterprise.
 
ngiles said:
The anode (+ve) was an allen key poked through a piece of ply which sat in the filler hole, whilst the cathode (-ve) I clipped onto the tank at the point where the rubber strap hooks over by the seat - see photo. The ratio was a bit of a guess - I poured about 2 tablespoons of caustic soda into 10 litres warm water x 2, and filled the tank. It took three attempts to get a consistent power source - the first battery charger seemed to stop transmitting current quite quickly (presumably thinking it had finished 'charging'); the second was a LiPo battery that was a bit buggered so failed to provide any good duration; and the last, and successful one, was a charger for NiMH batteries which did not stop charging even though it indicated that the tank full of solution was fully charged...I left it hooked up for 24 hours.
Click to expand...
And was it a success?
I think that it's best to use a piece of flat steel or iron as an anode, the more surface, the better.
As I mentioned, it's best to do it over a few days, taking the anode out every 24 hours to wipe the oxide off it.

Paul
 
Last edited:
The soda is just an electrolyte for the electrons to pass through isn't it? Not used for it's etching properties, I used potassium hydroxide (or calcium hydroxide) also very weak solution and a bit of flat bar.
 
I completely cut the bottom out of my tank and then had it grit blasted inside and out, the holes that I knew about were obvious, but many more tiny holes "appeared" you cant see them unless you hold the tank bottom up against the sun, or a 500 watt halogen lamp, then you can see tiny little stars twinkling through, and randomly all over the place, truthfully its the only way if the tank has had an internal coating, much metal removal and patching will take place, when I get some more oxy acet Goddammit! is it worth it? no not realy, but it is an enlarged recessed, round badge Jota tank, so its a one off which I want to save a reuse on TOG.
CLEM
 
Paul Marx said:
And was it a success?
I think that it's best to use a piece of flat steel or iron as an anode, the more surface, the better.
As I mentioned, it's best to do it over a few days, taking the anode out every 24 hours to wipe the oxide off it.

Paul
Click to expand...
Short answer - yes it worked. It ended up a lot cleaner with some residual 'staining' still visible but overall a big improvement. Agree with the point about flat steel or whatever; I used what was lying around.
 
Adventures in 750 rusty tank world

When putting the 750 back on the road, i had 4 tanks to choose from. 2 where decidedly rooted, one had really nice black paint, but was a bit rusty, and my old SF0 tank previously crashed by me, also a bit rusty.

I went with the black tank, and Will used evapo-rust to treat the inside. The job came up great, clean as a whistle. Unfortunately, what I didn't notice, until the tank fell off the front locating pins onto the motor, was that it had been pranged and badly repaired at the front, the locating hooks where about 15mm wider than they should have been.

Out with the oxy and a rachet strap, and the front of the tank was brought back in, unfortunately the paint was now fooked, the nylon strap mark is very evident across the top where it sank into the heated paint, and there is a crease in the metal at the top. Oh well. I dragged out my old 750 tank, still full of dents on the lh side, and thought, no probs, going to be covered by a tank bag anyway. Some grey primer, and some caustic solution to clean out the rust. I wasn't worried about the paint now. Tank came up clean, and pressed into service.

Got back from the run to Canowindra, and it was a bit down on power on some of the hills. Pulled the carb bowls, full of rust! WTF!

Brett advises me that all fuel can legally have up to 5% ethanol, and still be marketed as non ethanol. I think the way the caustic solution has etched the metal has opened it up to allowing agreesive rust. If i look down in the tank, its not too bad, but the roof is bad.

Evapo-rust says it leaves a protective coating. Maybe. I grabbed the repaired black tank, now been sitting on the shelf in my shed for 6 months at least, in a very wet and humid sydney summer, it looks ok.

Now the next twist. 12 months ago, evapo-rust guys (from NZ), sold the name to CRC. Not the same formula, but the product is advertised as the same. Price is the same. I don't know what the difference in the product is, waiting on a call back from the ozzy guy in mackay, QLD, who can supply me direct the original formula.

I will keep you posted.

So the question is, once you have etched the steel with caustic, short of lining it, (I hate tank liners), how do you stop modern fuels rusting up your tank.
 
Just spoke to Nick in Mackay, he is sending me a 1 litre concentrate which makes 6 litres, original formula. It leaves a residue on the metal to help against future rust. See how we go.
 
Last edited:
I dunno what's in Evapo-rust (it's probably a secret recipe), but I think it's sold as a rust remover. What you need is a rust converter like tannic acid or phosphoric acid. They convert the surface rust into ferric tannate or ferric phosphate (respectively), which forms a stable protective coating. I presume the original formula for Evapo-rust had one of those compounds in it.
 
I just used Rust Buster on my Mini rims, which I think has phosphoric acid in it. So I probably have ferric phosphate which is also a hard black substance. It seems to form a pretty durable coating.
 
MSDS will reveal the constituent chemicals, in Australia it is a legal requirement to list the chemical composition. Quite revealing just what poor grade/cheapo chemicals are used in well known brands. Tip for free, in my researches i discovered the "rust" particles, in suspension or sitting on the bottom of a Laverda tank remained magneticly attracted. Had a problematic tank with rust ( pre molasses use ) couple of neodymium 10m/m magnets adjacent to the taps on the under side of the tank trapped the rust from entering the reserve inlet ( and i suppose the normal spigot for suspended/disturbed rust particles ), once a year i removed the magnets and cleaned/washed the tank... stopped the clogged carbs problem in one step. Make do solution though very effective when other methods will be lengthy in solution application, HTH j
 
Today I started the "Metal Rescue" process on my tank. It's an RGS with the long fuel neck. Before I started, the top of the tank looked great, the bottom looked real bad (large flaked rust). I bought an endoscope to probe down into the tank but I did not record it (I simply forgot...or didn't care). I will post the "after" shots. This is an RGS with 5500 original miles and all evidence points to being stored indoors in the Chicago area since 1993.

UPDATE: So I used "Metal Rescue" which I think is like evapo-rust. It's not an acid. I didn't feel dealing with flash rust. Here's what I did...

  1. Filled tank with metal rescue and let it sit for 24 hours, periodically agitating
  2. Drained and rinsed with garden house about 6 times
  3. Used a hair dryer to dry it out.
  4. Added isopropyl alcohol and splashed it around to absorb any water
  5. Used the hair dryer again
  6. Added some 2stroke gas & oil mix and splashed it around and drained
  7. It did not turn out perfect but it is way better
The pics were taken with an endoscope
20220512132957.jpg20220512133051.jpg
 
Last edited:
You must log in or register to reply here.
Back
Top