This post is primarily about how I was able to remove the rust in my tank with almost no work. I was planning on coating the inside of the tank with an epoxy fro Caswell Plating, and I still might, but since I was able to get ALL the rust out of the tank, I figure I might as well see if it comes back with normal use before I get around to sealing it like that. If it doesn’t, great! If it does, well it was a cheap attempt. In either case, it gets my bike on the road that much sooner because I don’t have to wait until I get a 65+°F day to do it. The epoxy should be applied at 70°F or more.

The key to this endeavor was oxalic acid. It’s basically a low-level acid that is pretty safe for paint and your skin (I accidentally got a few drops on some exposed skin, despite wearing gloves and it didn’t hurt or have any detrimental effect) but it attacks rust aggressively. This is how I did it.

As with anything chemical, do this at your own risk. Use proper protection (at the very least, heavy rubber gloves and safety glasses; this stuff didn’t hurt my skin but it will sure as hell hurt your eyes)! Always add acid to water, not water to acid. Beware of fumes. All the usual things that you shouldn’t do unless you’re stupid. I am in no way responsible for anything bad that might happen, even if you follow these directions precisely.

This is what you’ll need:

Oxalic acid (this is the one I used, Ace is the best place to find it locally, or you can order it online; any oxalic acid will do)

Two 5 gallon buckets

A funnel

Baking soda

Acetylene (or methylated spirits)

Something to block your tank openings (I followed these directions; Home Depot did not have the stopper I needed, but Lowe’s did. I got some aluminum flat stock for the petcock hole there as well)

Rubber mallet (any soft, heavy thing you can hit with will be fine)

Flat head screwdriver (any flat, sturdy thing you can pry with will be fine)

Heat gun or hair dryer

A few hours of your time

I did the whole thing in a Sunday, starting around 3 PM and finishing up around 7 or 8. It could easily have been done quicker if I’d planned it better.

Preparation

I put about a gallon of hot water in one of the buckets and added half the 12 oz tub of oxalic acid to it. I later realized I needed about 3 gallons. You could easily get away with 3 gallons and the whole tub of acid. It did the job even after being diluted to 3 gallons with no extra acid, just slowed it down some. I mixed up the acid with a dowel I had hanging around, being careful to spill as little as possible. It will mix clear, then turn yellow and get darker with use.

I used a short piece of aluminum flat stock with two layers of Gorilla Tape on it as my seal for the petcock area. It worked almost flawlessly (see the end for where it failed slightly). I measured and drilled two 1/4″ holes 1 3/8″ center to center for the bolts. It’s easiest just to use the bolts that were used with your petcock. Chances are that, like mine, they have rust on them too, which will get cleaned off in this process.

I used the largest stopper Lowe’s carries (1 3/16″ x 1 1/2″ x 1″) to stop up the fuel filler hole. Obviously, you’ll want to take off the fuel door too.

I did stop up the small hole near the fuel filler and the fuel overflow exit, but I found out later that was entirely unnecessary. They’re connected by a tube that doesn’t connect to the rest of the gas tank and are for any kind of overflow or spill you might have in that area.

Make sure the tank itself is dry and free of fuel.

Once your acid is mixed and your petcock hole is plugged, you’re ready to move on.

Treatment

This is what my tank looked like to start with:

Place the tank somewhere it will be level-ish. Insert the funnel into the filler hole and dump all the acid in. Put the stopper in and seat it by whacking it a few times with a rubber mallet.

Every 15 minutes for an hour, rotate the tank 1/4 turn and agitate it. At the end of an hour, if you mixed it at 1 tub/3 gallons, you’ll likely be done. This is where I realized I had a problem. One gallon of acid doesn’t cover the center hump in my tank. So I got all the sides, but there was still plenty of rust on the center hump. This is where I poured in an extra 1.5-2 gallons of hot water. That got it above the center hump. I let it sit for a couple hours that way.

That picture was taken about halfway through the 2 hours. It’s nearly rust-free, though there was some rust where I couldn’t really get a good picture. I used a small steel brush that I dipped in the acid to clean the rust around the rim. Took the rust out in about 3 minutes. This is really effective stuff, even very diluted.

You can use the screwdriver to pry out the stopper for checks and then whack it back in so nothing spills.

Cleanup

Once the rust is gone, it’s time to clean up. You have a couple options for the acid. You can keep it and continue to re-use it until it becomes quite black, or you can dump it and dilute the area. It won’t harm the environment (several people reported dumping it into the grass with no ill effects, but I wouldn’t want to do that). I am planning to dump it, but it’s still cold and my hose is frozen, so I’m saving it for now and will dump it when it gets warmer.

Fill the other bucket with 3 gallons of warm water and add a bunch of baking soda to it (I put 5 or 6 good shakes out of a medium sized box). Mix it up. Baking soda is basic (the opposite of acidic) and will neutralize the acid left in your tank when you dump it out. Dump the acid wherever you are dumping it (in my case, back into the bucket I mixed it in) through the filler hole first. When the flow begins to die down, remove the plate from the petcock and dump the rest from there. You’ll have to turn the tank so that all the acid flows over the center hump to the petcock side in order to get it out. Replace the plate over the petcock area and fill it up with your baking soda mix. Put in the stopper and shake the tank around until you’re sure you’ve hit every area with the baking soda mix. Dump this stuff anywhere you like, no danger to the environment. Use the same procedure as last time and replace the plate over the petcock area one more time.

Pour about 1/4 – 1/2 gallon of acetylene or methylated spirits into the tank, replace the stopper, and vigorously shake it for a good 5 minutes or more. What you’re trying to do is get all the water to mix with this stuff and evaporate MUCH faster, giving less opportunity for re-rusting. This is where my petcock plate failed. It let a small amount of acetylene through. I’m not really surprised, to be honest. Dump the acetylene out into a container for disposing (it’s almost certainly not good for anything else now).

Use the heat gun to dry out as much of the tank as possible. If you have an air compressor, that will really help as well as you can direct air to the corners of the tank the gun can’t reach. Once the tank is dry, you’re good to go! You may want to mist it with WD-40 if you’re going to be storing it for a long time. This is how my tank looks now:

This gets my bike that much closer to being ready to get on the road! The next big thing is to do the tires, and then after that the chain (slack check, clean, lube). Once that’s done, it’s just a bunch of minor things until I can get it outside and do the carb work.

I got a mount for my phone from RAM mounts (this ball, this link, and this holder). The ball screws into an unused side mirror socket on the left handlebar. Presumably there is one on the right as well, but it’s under the brake fluid reservoir.

I got a weather resistant USB charger that I plan to attach to the front accessory wires. At 2.1 amps, it’s more than powerful enough to charge any phone I might put in there. I plan to convert my accessory wires to switched as well so that I don’t passively drain my battery when I might not use it for a while. You can see the USB charger in the gallery below, along with any other pictures I didn’t post in the main body of this post.

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Tags: EX250F, Motorcycle, Ninja 250R, Oxalic Acid, Project, Rust