Phosphoric acid wash for mildly rusty tank?

[bwringer]

I'm working on a buddy's bike, helping him get the thing running again after a few years of inactivity.

The tank is dented pretty badly where a piece of wood fell on it in the garage, but it does hold fuel and functions just fine. However, we're reluctant to spend money and time on Por15 or professional coating for a tank with a huge square dent in it.

The tank has some surface rust on the inside. Nothing serious or flaking, but enough that I don't want to hook it up to the freshly cleaned and rebuilt carbs.

Has anyone here tried a simple wash with phosphoric acid to clean and convert the rust? How did it work out? Where did you get the acid? How much did you use?

[lord1234]

please see Jethro's recent post about his rusty tank...i described a good procedure for performing a phosphoric acid cleaning of your tank

[jpaul]

It's not phosphoric acid, but I used this stuff on some rusty bolts, and it works great.

http://http://www.evapo-rust.com/

You don't have to worry about contact with your skin, and it's readily available at Autozone. I would rinse it out of the tank with acetone or alcohol, then rinse with a bit of gas before filling it up to use.

[nichols750]

i used a phosphoris wash on my tank before i did the Kreeme. it worked wonders. i got it at home depot in the paint stripping area, they had three different sizes and i got 1/2 gallon? and then puored it all in filled the tank the rest of the way with water and let sit overnight. looked brand new when I was done. since then i have used it on all kinds of bolts and nuts to clean them up. works great.

[bwringer]

I'll have to check out that Evapo-Rust stuff -- my friend has three small children, and is pretty skittish about bringing horrible chemicals into the house. The corrosion isn't all that bad, so I bet this will do the trick easily. It should go quickly, too -- I'd hate to go through a week of drying Por15 for this junky banged up old tank. Once the bike is running, he'll likely just try and score a nicer tank on eBay.

And thanks for the lead on the phosphoric acid -- I never really thought to look in the paint dept. I know they have muriatic (hydrochloric) acid, but I didn't know they had phosphoric too.

Thanks, y'all!

[Arkaloid]

Coca-Cola.

[Billy Ricks]

Phosphoric acid works just fine. I've used it and am perfectly happy with the results. It won't hurt any solid metal.

[J_C]

Yeah it depends on the store it seems. I couldn't find it at home depot at all, but I was able to find it at Lowe's in the masonry section I believe. I guess phosphoric is also used to clean rock or concrete??

I watered it down a lot and it made it somewhat difficult. Next time I'll either let it sit longer or go with a less concentrated mix.

[b1ackd3ath]

Electrolytic Rust Removal (Could be an easy alternative to scrubbing)

I was just talking to someone about this because I am considering buying a rusty sissy bar. This method can be applied to a gas tank too. The way I will derust the sissy bar (if I can't find a new one) will be to use a large 5 gallon bucket, a batter charger, a couple of steel wire hangers (without coating) and some washing soda (or trisodium phosphate from home depot)/water.

Fill up the bucket with water and put 5 teaspoons of washing soda (not baking soda but arm and hammer makes it and you can find it at the grocery store). Bend the hangers so that they will fit nicely against one side of the tub and so that they will be long enough to stick out of the water. Hook the positive terminal of the charger up to the hanger and put it in the water so that the positive terminal does NOT get in the water. Now put the sissy bar in the solution so that it does not touch the positive hanger. Part of the sissy bar will be protruding from the water. Hook up the negative terminal to this end and fire the battery charger up.

The oxidized ions on the sissy bar will be attracted to the positive node (hanger). The rust will just start to disappear from the sissy bar and the hanger will become black. Water will be lost and hydrogen will be in the air so be sure the area is ventilated and the water supply is maintained. You will probably have to rotate the part over time if you can fit the whole thing in the water. If you can fit it in, fashion a hanger around the good part so that part of the hanger sticks out for attachment to the negative terminal.

One you have the piece cleaned, dry completely and coat if you are going to go that route.

Even better than a hanger on the positive end would be a piece of iron or crumbled piece of steel with greater surface area. The more powerful the battery charger the better. A charger with overload protection is key too because rust can form on the surface of the water when you aren't around and blowout the charger.



I went and found some links. Here are two with a gas tank, perfect!

http://650rider.com/Content/pid=6.html

http://www.aircooled-rd.com/forum/topic.asp?TOPIC_ID=8577&SearchTerms=rust

Also:

http://antique-engines.com/electrol.asp

http://www.bhi.co.uk/hints/rust.htm

[Jethro]

Dude, the phosporic acid worked like a charm for me. Easy, cheap, and it looks like it's a lasting solution to the problem.

[justin caise]

Wow! That's it! Talk about "the right stuff".
Got Behr concrete etcher and rust remover at Ho Depo for $12.99 yesterday. Just did the tank tonight- Pictures tomorrow.
It feels better than brushing and gargling.

And hey please dispose of properly. It IS an acid you know.

S'cuz me - I'm gonna go now and buy stock in Behr.

[J_C]

cool! what concentration did you use?

[justin caise]

It's concentration turned out to be about 2 parts Phos acid to 1 part water. I think I could have gone weaker than that - my rust wasn't really really bad. But I saved the used stuff because it doesn't look too discolored and will probably work for other stuff. I'm gonna make pancakes with it right now - want some?

Camara not available for pics yet.

[Billy Ricks]

You can get the acid at Home Depot in the paint department.

[themess]

I worked in a factory that made oil seals. The metal portion is stamped, and comes out of the stamping press covered with oil. The oil was removed in a bath with hot - almost boiling - lye. Parts were then dipped in a solution with phosphoric acid and some other chemicals. This removed rust and left a calcium phosphate coating, which would protect the parts from rust for a vew days, in dry weather. Then parts were dipped into an adhesive to seal the phosphate and to improve adhesion to the rubber that formed the seal. I learned that most stamped parts that will be painted are phosphate coated to help paint stick.

Phosphoric acid will indeed remove rust. It will also make the metal rust very quickly. If you remove rust this way, be prepared to paint the part or otherwise coat it almost immediately.