My shop is in an over-sized two-car garage attached to my home. My work is a calling, in the theological sense of the word. Ethical and moral questions arise every day – they are hard, sharp, unambiguous and unavoidable.

Cleaning/lining a gas tank

Posted: April 1st, 2012 | Author: Administrator | Filed under: Fuel & Air, Motorcycle Repair | 4 Comments »

If it’s not leaking, just clean and de-rust it and put a filter in the fuel line to the carbs. The risks of a less-than-perfect lining job are greater than the benefits – on a non-leaking tank. If the liner starts to come off, it’s pretty much curtains for the tank.

The right way to clean a tank is to first mechanically remove as much rust/crud from the inside as possible. Get a length of light chain – the stuff sold in hardware stores in bulk for hanging lights and so forth is ideal. The length is not important – 3-6ft. is fine. Some folks use a large handful of nuts/bolts – which works – but it can be hard to get them all out again. The chain is easy.

Put the chain in the tank with a quart/liter or so of kerosene. Lay a plastic shopping bag over the filler hole and then close the cap. This keeps the kero from finding its way out the vent in the cap. Now shake the tank turning it this way and that. So it until your arms get tired and then set it aside. Repeat this a number of times until the rust and crud has been scoured away and the metal is clean and bright. Extract the chain and drain off the kero/crud solution. Rinse with fresh kero until it comes out clear. Pour in a quart or so of Evap-o-rust or similar de-rusting solution. They are all based on phosphoric acid which chemically converts iron oxide – rust – to a moderately inert ferric phosphate. I use Milkstone Remover – a dilute solution of phosphoric acid sold through Tractor Supply for cleaning dairy lines. I mix it 1:5 with water – making six gallons – in one of those large blue plastic storage totes from Kmart/Target/etc. Now I can fill a tank with de-rusting solution and let it sit for a day or so. This stuff is highly reusable – and you can just toss smaller rusty bits in the tote. At this weak concentration, the acid is completely safe – you can put your bare hand in it. If you have a cut or nick, it will sting just a little bit.

Here’s a bit from Wikipedia on the chemistry:

“Phosphoric acid may be used as a “rust converter”, by direct application to rusted iron, steel tools, or surfaces. The phosphoric acid converts reddish-brown iron(III) oxide, Fe2O3 (rust) to black ferric phosphate, FePO4.

“Rust converter” is sometimes a greenish liquid suitable for dipping (in the same sort of acid bath as is used for pickling metal), but it is more often formulated as a gel, commonly called naval jelly. It is sometimes sold under other names, such as “rust remover” or “rust killer”. As a thick gel, it may be applied to slopi ng, vertical, or even overhead surfaces.

After treatment, the black ferric-phosphate coating can be scrubbed off, leaving a fresh metal surface. Multiple applications of phosphoric acid may be required to remove all rust. The black phosphate coating can also be left in place, where it will provide moderate further corrosion resistance (such protection is also provided by the superficially similar Parkerizing and blued electrochemical conversion coating processes).”

If the tank is still solid and leak-free, just use it as is but fill it with Stabil-treated gas if it’s going to sit unused for more than a couple of weeks.

If, however, you want or need to line the tank, your work has just begun.

Rinse the tank well with water – several times – to remove all traces of acid. Now dry the inside with compressed air or a hair dryer on low heat. You can speed up things by shaking/blowing most of the rinse water out and putting the tank in a slow oven – about 120-150 degrees F – for a couple of hours. Shake the tank – if you can hear any liquid inside, it’s not done yet.

Now let the tank cool, if you have used the oven method of drying, and then pour a quart of acetone in. Replace the cap and shake well turning the tank over and round about. This does two things; it picks up and eliminates any remaining traces of water and leaves the surface squeaky clean for max adhesion of the line.

The coating should be applied immediately. The acetone washed metal will flash-rust very quickly. Use a liner that is explicitly resistant to the ethanol that is present in most gasoline these days. Good liner is expensive – Caswell’s and POR-15 are said to be very good. I use Red-Kote, and industrial tank liner available through some auto parts stores for around $60/gal. I thin it with MEK – nasty nasty stuff put the only thing that will thin this stuff – and give the tank a thinned wash coat first to ensure that it penetrates every tiny nook/cranny/pore. It needs to air-dry for a couple of days before applying the second un-thinned coating – which needs to dry several days before contact with gasoline. The nice thing about having way more liner than you need is that you can pour lots into the tank to ensure that the coating reaches/covers everything – but you must take pains to ensure that all of the excess drains out so that what remains dries completely before contact with fuel.

If you are using a coating, you must either first remove the petcock and plug those holes or use a crummy old petcock as the sacrificial plug. Also make sure you put a layer or two of plastic between the filler cap and the hole before closing the cap. Otherwise, the liner can plug the vent hole in the cap and your tank will not flow gas to the carbs.


4 Comments on “Cleaning/lining a gas tank”

  1. 1 Tony Markus said at 4:14 am on June 14th, 2012:

    Well said…we’ve been lining motorcycle gas tanks for awhile and this is one of the best descriptions on how to do it yet. I would suggest the use of a catalyzed product that cures for lining instead of a single component product that simply dries. Ethonal can dissolve many single component liners…Good Luck!

  2. 2 Eric said at 8:04 am on November 15th, 2012:

    Thanks so much for sharing this article! I’ve been attempting some DIY motorcycle repair on my Honda XR650R and this really helps.

  3. 3 John O said at 4:18 pm on November 8th, 2013:

    I have read articles and watched many videos about cleaning motorcycle gas tanks. With regards to my Kawasaki Concours with light rust, I will follow your instructions for cleaning the tank with a kerosene and a length of chain followed by a wash in a phosphoric acid solution. I have used phosphoric acid in the past with success. I will not apply a liner which was really a dilemma for me. I worry about the tank rusting again but I also know that liners are irreparable.
    Instead of manually shaking the tank with metal abrasive objects. I will wrap my tank in an old blanket and see if it will fit in my over sized clothes dryer for tumbling. I don’t feel like shaking a seven gallon tank.
    Thanks, I now have a clear plan that seems very reasonable.

  4. 4 Administrator said at 6:17 pm on November 8th, 2013:

    John,

    The dryer method is brilliant! I’d want to do a proof-of-concept run with a tank I did not care too much about.

    Cheers,
    Chris


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