Wednesday, August 22, 2007

De-rusting your fuel tank

I got this procedure from the PNWRiders group on Yahoo. It was written by BCMiller. I haven't tested it, but this might be a terrific way to solve one of the most difficult (and common) problems with motorcycle restorations.

Since the entire process only seems to take 10 minutes, a creative soul might be able to do this with a car battery (or the whole car) instead of a charger. But even with a "car" rig I'd add an ammeter and a resettable / thermal breaker for protection.

Here's the procedure: (Edited for format and readability only.)

"Here's a repost of a method I used quite successfully. I adapted it from a technique used by antique outboard restorers. There's no dangerous chemicals to spill; a consideration for me since I: a) live on a lake, and b) drink from a well.

There's also no ball bearings or nuts to recover afterwards.

You need:
1) 10 amp battery charger
2) Duct tape
3) A box of salt
4) Water
5) Funnel
6) A piece of steel rod
7) Electrical tape
8) Methyl hydrate
9) Light oil.

A) Prep the tank by removing the petcock and gauge sender.
B) Clean the paint work around the holes well and cover the holes with duct tape.
C) Stuff rags inside the hump to re-inforce the duct tape over the sender holes.
D) Pre-mix the saline electrolyte using most of a box of table salt to 5 gallons of water.
E) Fill the tank.
F) Tape up the end of a steel rod so it cannot short out against the tank bottom. (I was told re-bar, but used all-thread ready rod which worked just fine)
G) Connect the negative lead of a 10 amp battery charger to bare metal on the tank (I used the gas cap mounting screw so as not to damage any paint).
H) Place a wide-mouth plastic (non-conducting) funnel in the fill hole and put the rod in the tank through the funnel.
I) Connect the positive lead to the electrode. It's best to use a charger with an ammeter. Mine just has a silly voltmeter gauge, so I connected the positive lead through a separate ammeter.
J) Add salt as required to bring the current up to 10 amps. (The best I got was 9.4 amps, more salt didn't help after that).
K) Check every 2 minutes, and stop when the rust is gone. (It got so murky, I couldn't see the hump after a while unless I sloshed out some of the water and tipped the tank. I don't know how they do this with a marine tank and still check it.)

Total time for me on this tank was about 10 minutes.I was amazed at the results. Where there was heavy rusting, clean shiny metal magically appeared. I used a piece of cad-plated ready-rod for the electrode, and it turned black. The saline turned a weird shade of green,with chunks of rust floating around. I was concerned that the left half of the tank wouldn't get equal treatment, and I made a point of draining off some water and sloshing it around to evenly distribute the salt, and an examination through the fuel gauge hole confirms it worked on that side too. None the less, I think next time I would start off with a saline solution instead of plain water, now that I know how much salt to use (just about 1 box to get 9.4 amps).

I also blew a fuse in my ammeter when I inadvertently touched the rod against the hump in the middle of the tank trying to stir the salt with the electrode. I guess with a motorcycle tank, not only the bottom of the rod should be insulated with electrical tape, but part way up where it might contact the hump as well.

I flushed everything out thoroughly with water after, followed with methyl hydrate. Even so, I could see a faint patina of rust starting to form again within 15 minutes. I quickly coated the inside with oil, and that took care of that."


Broom said...

i'm thinking about picking up an old triumph to restore, so i might be testing this out soon!

motopacsman said...

Let us know how it turns out.

Anonymous said...

What the heck is "methyl hydrate", and where do you get it? Maybe alcohol would do as well?

Anonymous said...

Sounds like a great idea for removing rust. I'd be very sure that I flushed out everything from inside the tank with oil, though. If anything other than gas is to get into the engine, then you're going to be having bigger problems than mere rust.

motopacsman said...

BR - Methyl Hydrate is METHANOL or methyl alcohol. It's available in the average hardware store.

Anonymous - Coating the tank with oil is the final step to prevent immediate surface rust if you're not going to remount and fill the tank with fuel. Unfortunately, it will do nothing but oil the inside of the tank. Salt is not soluble in oil, nor is rust, and water will not suspend in oil without an emulsifier. A good water flushing and a rinse with methyl alcohol (methyl hydrate) is the correct thing to do.

used fuel tanks said...

I highly recommend a coating, otherwise youre just chasing your tail in my opinion. I just recently used KBS coatings sealer which comes in kit form. A bottle of tank wash, a bottle of phosphate acid and a bottle of sealer. I purchased mine locally from JEGS automotive as they had it in stock. If you can't mail order it you need to find out what products are available locally.

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