How to Clean Rust from a Motorcycle Gas Tank
Whether you're storing an irreplaceable fuel tank on an old machine or just getting an old bike back on the road, here's everything you need to know to remove rust.
You're tired of replacing fuel filters, cleaning your carburetor, or putting an abandoned bike back on the road. You are looking for the solution. I know, of course, because I learned how to do this moons ago because I was in a bind like you. I had a fuel tank that was deteriorating from the inside out, and it was a problem for my tank, my fuel filter, my carburetor, and my engine. Your service manual probably won't tell you much about how to deal with a rusted fuel tank ("Remove and replace" I'm sure, if it even mentions such a thing), but given how expensive and / or the impossible-to-get tanks Sea (! and how expensive that colorful material is on the outside!), you are doing the right thing by rejuvenating yours.
So, as a motorcycle rider who has salvaged a tank or two throughout my career, let me give you a few things to think about, a process, and a few photos that you may find helpful. You will probably want to read the whole thing before you begin.
Each tank differs in terms of its level of degradation. I've seen a few tanks with a slight rust on the surface and a concerned owner, and I've also seen (and had!) Some fuel canisters that had more barnacles and scales than the hull of the Queen Mary. The course of action one would take may differ enormously in those scenarios, or they may be exactly the same.
First, it is very important to think about removal and replacement. I mention this because this is a very viable option today, especially with so many replacement avenues online. Simply spending a hundred or two hundred dollars on a brand new replacement tank that could basically screw in and function properly once again may be the wisest course of action. Also consider used tanks that may be in better shape than yours. And if your bike isn't too old, heck, a dealer might have a new one on a shelf somewhere.
Old fatbobs tend to stay in service for a while simply because they were built to last. They are not lightweight, but for a device to rust you almost have to drop them into the ocean for a few decades. In general, the newer a bike is, the thinner the sheet metal tends to be in order to save weight and form more complicated shaped tanks. Photo of Lemmy.
Also consider the tank construction. Old Harley-Davidson fatbob tanks, for example, have excellent survival rates simply because of the incredibly thick steel used in their construction. However, generally, newer bikes have tanks that are made of lighter gauge metal. If your tank is made of thin steel and the rust and scale inside it is heavy, correcting the problem will be more difficult and take longer. If your tank has rusted in any area, that can also be an indicator that the tank cannot be saved, depending on your time and finances budgeted for the task.
Obviously, weirdness comes into play; A tank of a certain condition that can be considered junk for a high production bike can be the holy grail for a lower production bike. The exterior of the tank is also taken into account: the original paint certainly helps an original bike retain its value. It is quite possible that it is worth putting a little effort into a motorcycle tank that is still in its original livery, simply because of the value that component brings to the entire motorcycle. Similarly, even a repaint that cannot be easily reproduced to match other elements of the motorcycle can be expensive to duplicate.
Once you've determined that a particular tank project is worth your time, money, and effort, it's time to quantify the damage. A flashlight, mirror, cell phone, and telescopic sight can all come in handy at this time. Mild rust or flaking problems are generally not too difficult to deal with. Heavy pitting, pinholes, and / or missing metal will generally require both metal fabrication and body work to remedy. We will assume in this article that the structural integrity of your tank is not compromised, but if it is, additional surgery may be required, up to and including opening the tank for further inspection and repair.
Johnny Greaser's YG1 tank you see here had about 50 years of neglect and scale for me. That was wrong. Really bad. Not rotten, but definitely one of the most troublesome tanks I have ever fought.
Most fuel tanks require a two-prong treatment fork. The first tooth takes care of removing the heavier oxide deposits and the second involves rejuvenating the finish, possibly in preparation for the installation of a tank sealer. In my experience, heavy deposit removal is best handled mechanically, and finish restoration is generally approached chemically, although that's not always the case. (If you have your own methods, feel free to add them!)
For mechanical rust removal I will typically choose an abrasive element, something that can be put inside the tank to help remove scale manually. Nuts and bolts are a popular shaker, and I know a few people who use plain gravel. I have used pellets successfully before and often use them in tanks that have cracks where something bigger may not reach or lodge. Because they are round, they are not very likely to get caught in a tank that can have very pronounced "lobes" with very sharp walls. I'll tell you about my secret weapon a little later.
And when it comes to the chemical aspect of things, generally an acid will help remove rust through etching action. I like to start with a mild acid (white vinegar) and then work your way up to something stronger if necessary.
Remove the tank and empty it of fuel first, of course. At the very least, you'll want to seal the holes in the tank. Most tanks will have a fill cap and petcock, but others may have crossover tubes, such as double tank Harleys and dirt bikes with two large lobes protruding from the engine.
Plugs, plugs, vacuum plugs, threaded fittings - I have all of this, but that's because I've done it a time or two. Order the right equipment to get the job done right and your results will be indicative of your diligence. Photo of Lemmy.
You have a few options here. I've had good luck with silicone plugs and rubber or vinyl vacuum plugs for small holes and plugs. If you are working on a modern motorcycle, you may need to remove the fuel pump plate. They can be difficult to seal because they are so big! A gasket combined with a lock plate you buy or make is usually the order of the day here. If you are using vinegar, you can seal the filling with the cap, with the understanding that you may need to purchase a new cap or a replacement seal after cleaning.
You need to do this in a well-ventilated area, and since acid can splatter, you don't want to be near anything that could harm. Even if you're using a relatively mild acid like vinegar, you don't want acidic fumes to build up inside. They may not be as harmful, the smell can be unpleasant, and having acid vapor near items that you don't need to strip is probably a bad idea.
Personally, I like to set up my tanks with a collection container underneath that contains all possible leak points. That means a plug or cap that fails and leaks is just a wasted day of soaking time. Vinegar can be recovered, and if the tank is raised above the container (rather than inside), the paint is never compromised.
Before you start loading your stirring substance into your fuel tank, you may want to place a few test pieces in a glass or ceramic container and make sure your acid doesn't have an adverse reaction. The odds are low if you are using vinegar, but you don't want to ruin anything, dirty the bowels of your tank, or poison yourself. And if you are using something stronger, there is a possibility that the items will react violently and turn to dust.
I would recommend not using an acid stronger than vinegar for a few reasons. It is possible to go straight through metal and it is also very easy to damage paint with such a strong acid. Disposal requires extreme dilution and the risk of personal injury is quite high. It is an effort that I would consider the last resort. Highly dilute acetic acid dissolved in household vinegar isn't particularly fast-acting, but that's the point. Removes rust and metal fairly gently.
Faucets are usually made of pot metal. I would remove them even if you used vinegar, but this is a must if you are using something stronger. If you don't, they could disintegrate by the time your tank innards glow. Photo of Lemmy.
If you use something stronger, you may want to think about protecting the paint, and you definitely want to protect yourself. Have a garden hose close by and a base to neutralize any acid in case you see it on your paint or other delicate items ... or on you! With all those warnings in place, in some tanks, something like vinegar is not going to work.
Note that with something fairly weak like vinegar, you may need to let the tank sit for some time; a few days is not uncommon. Fill it up and let it cool. If you're using something like phosphoric or muriatic acid, it's a different story - you'll want to start churning the infusion in the tank as soon as you put the stirrer on. They work much faster than vinegar and will start to etch the tank. almost immediately.
Once you're satisfied that your chosen mechanical abrasive is somewhat inert in your chosen acid, add your screws, hardware, or sheet metal BB. Use some common sense here. Huge bolts are likely to dent a tank. Smaller is better, up to a point.
You are not trying to fill the tank. Instead, you'll want a handful or two to remove rust and dump your acid down the tank into nooks, crannies, and crevices. If you're particularly paranoid, you can count the items you're using so you can count them when you empty them again. Oh, and do you remember that secret I told you about earlier? It's a piece of chain. Use it and you won't have to worry about keeping track of your rust removal agents!
Like a Polaroid photo, for those readers old enough to remember both the song I'm referring to and the actual act of shaking a Polaroid photo. I use my arms. I have two so I pick up the tank and shake it until I'm out of breath, open the filler and see how things look. I repeat this process whenever the need strikes me (a few times a day, maybe?) Until I see shiny bare metal under the fill plug.
You can try other stirring methods. I knew of a guy who would wrap the whole thing in heavy moving blankets, tape them in place, and put them in an old clothes dryer without heat for a while. I also heard of a guy who would lift the back of his lawnmower and use elastic straps to secure the tank to the rear wheel, then put it in gear to slowly roll the tank 'round and round'. I'm not telling you to do that (I never have), but I can understand why someone might try. It will probably work well if you use your noodles.
Repeat until you are satisfied with the cleanliness of the tank. Depending on the level of scale and rust in your tank, this process can take up to a few weeks. The Greaser tank you'll see in the photos stayed for eight days, and it probably could have lasted longer without any ill effects.
Since you will most likely do this on a different day, before you go to wash, place a five-gallon pot of water on a stove or hot plate at the store and heat it up. It doesn't need to be boiling, but it should be uncomfortably hot to the touch. We will come back to that in a moment.
Once you're done and everything looks shiny and clean, remove your plugs / plugs / fill plug and pour the acid into that bucket you've been waiting for (which won't be damaged by acid!). Empty the power washer you used (the nuts and bolts) and get the garden hose flowing. He wants to get all the acid out, of course. Pick it up, shake it, carry water everywhere, even with the hose hanging down. Prepare to get wet.
Finally, recap the tank and put some dish soap in there to neutralize the acid. Then add the hot water that you took from the hot plate. The idea here is to neutralize any remaining vinegar with the dish soap. You are using hot water because it will quickly transfer heat to the metal in the tank. Once everything is drained, the resulting heat will help to remove moisture quickly.
Make the air flow through the tank. The best I have found for this is a heat gun or a hair dryer. Be careful! Heat guns can get hot enough to damage paint locally. Use low heat, keep the gun moving, and use your fingers to feel for parts of the tank to make sure nothing is getting too hot. If you're going to do this in your winter project, put some on and put it on your wood stove.
You may see rust reappear quickly if you don't work quickly and / or the moisture content in the air is high enough. This is known as "flash rust" and we are trying to avoid it, so it is important to work reasonably fast at this stage. A little is good; do not go crazy. Instant rust is usually fine enough and builds up in such a thin layer that a fuel filter will catch it, and what you lose will likely go through your carburetor with no problem.
Some people like commercial tank sealants. Kreem, Redkote, and Caswell come to mind as products that have enjoyed a good reputation over the years. I? I hate them and will only use them in super specific scenarios, like when a replacement item cannot be reasonably obtained or crafted. I've had too many bad and mushy and then ended up clogging my carbs. In my opinion, a tank that needs sealant needs to be replaced. There are many people who will disagree with me, and that's okay: there is more than one way to skin a cat. If you want to use one, now is the time.
Otherwise, I would recommend sealing the metal in a different way - with a fuel soluble sealant. If you're going to reinstall the tank right away, add a little kerosene in there, seal it again, and shake it, completely covering the innards of the tank. That will prevent the formation of that flash oxidation we are talking about. If you're building a bike and the tank is likely to stay on the shelf a bit, I would recommend something a little thicker, like some motor oil or a nice sticky two-stroke oil.
I have an admission. The YG1 tank from Greaser here is actually the first tank I've cleaned with vinegar. (I have cleaned many other steel items this way, but this is the first fuel tank I have on board this way.)
Over the years, I have actually used much stronger acids to clean the tanks. Phosphorous is said to work well, and my choice has always been muriatic acid cut 50/50 with water. (You can get it from your local hardware store.) This is unpleasant, but it works very, very fast. It is recorded in almost no flat time. Fifteen minutes normally works wonders even on deeply damaged tanks.
As such, there are a number of caveats that you should be aware of if you decide to go this route. First, those things will chew up the solder quickly, so if you have a valuable old tank that's been soldered in manufacturing or repair, avoid muriatic acid. You'll also want to find a different method of sealing the filling; Muriatic acid can damage caps, which may have elements that do not resist corrosion. (Or get a scrap plug and a new seal.) Remember that fuel caps are vented, so even if it seems to seal well, it may not be liquid-proof, which brings me to the next point.
Acid does not care what corrodes: paint, human flesh, clothing, environment ... it does not matter. As such, you must take great care in protecting yourself, protecting paint, protecting people and property around your agitation zone, and neutralizing and removing acid responsibly.
It works well, but keep in mind that the pro-level option as well as the last resort option. I often used it to deliver customers' bikes quickly, but starting with weaker acid and repeating only if that doesn't work makes perfect sense - think about how much material you're removing. The acid will eat away the rust, but it will also eat away some of the raw steel it reveals, and that steel has already been thinned by the portions that have been oxidized to rust and scale. If preservation is the goal, leave as much meat in the carcass as you can in case another rider has to repeat the process decades later.
We have shown you how to do this at the grocery store. There are other products designed to do this that are amazing. EvapoRust comes to mind, as does Metal Rescue. Generally, they convert iron oxide (oxide) to ferrite, which is a bit more stable and resistant to moisture. They work very well, albeit at a higher cost. Especially if you are trying to save something valuable, the cost of specialty products can be a good expense.
If you're using it right away, here's a tip. I have very, very old fuel tanks, and they don't rust because I keep them full of fuel, and I ride the bikes! Filled tanks displace air, which is necessary for rust to form. Frequent use prevents moisture from the air that modern ethanol fuel carries into the tank from adhering. It causes the fuel inside to spill out, which helps to naturally hit the condensation formation on top of the tank, and use burns that stuff too, allowing you to refill it with fresh fuel. If you need to store your bike with a repaired tank for an extended period (years), drain the tank and repeat the lubrication process. I have met some people who fill a tank with oil specifically for this purpose. If you don't mind draining it along the way, it can be a great way to remove rust.