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How to Deal with Rust in your Motorcycle Gas Tank...

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Rust in your Gas Tank?

Rust can occur on the inside of any metal gas tank that is not kept full of fuel all the time, especially while parked or stored for extended periods of time. The rust is primarily caused by the oxidation of the metal from water occurring in the form of condensation from the air within the tank, and is more likely to occur in high humidity locations (such as the coastal states) than in very dry locations (such as deserts).

   This is a sure sign that there is rust in your fuel tank that needs to be addressed (image of carb float bowl with rust residue from a KR member's carb jet-kit installation instructions -- I annotated the image with the text):


1. How to prevent in-tank rust before it occurs:

  • Corrective Action:
    Fill gas tank to maximum to displace any air any time the bike will sit for more a day or two. Make it a habit to take on enough gas to top off your tank as your last stop before returning home from rides. If the bike will be stored or parked without running for more than 6 weeks, place a fuel stabilizer into the tank before filling it to the rim. If bike will be parked or stored for more than 3 months, drain a half-cup of fuel from the bottom of the tank (or enough to remove any standing water), and top off the top of the tank with the required amount of fresh gasoline every 3 months to keep it full. If bike will be parked or stored for more than 11 months, drain tank completely and air dry, then place silicate packets inside and seal tank at all openings against moisture/air intrusion.

2. How to remove surface rust:

  • Symptom:
    Interior of tank has surface rust, or heavy rust.
  • Probable Cause:
    Tank or entire motorcycle was stored or parked for a period of time with less than the maximum amount of fuel in the tank (possibly stored with tank empty).
  • Corrective Action "A" (Wet Sanding, aka The Old School Method):
    The old school way of doing a rust removal was to remove and drain the tank, remove the plumbing (fuel sender, fuel selector valve, etc), then add a quart of distilled water and a quart of pure sand or fine gravel. Shake for a while, rotating. This will actually sand out the surface rust. Rinse out, and repeat sand-shake-rinse procedure if necessary. Then use a higher-abrasive material (such as quartz dust or BB's) to repeat the procedure yet again if required. Rinse repeatedly with a garden hose, then again with distilled water, and finally with gasoline. You should use this method if you actually have any flaking rust before proceeding with any other method, to remove the flaking and expose the metal underneath.
       Reinspect tank's interior. If any rust remains, utilize the solution mentioned below in step 2(C) OR 2(B). If no rust remains, change your fuel filter (replacing it with one with a paper element), and then change the filter again after about a week of riding with the factory-specified fuel filter (sooner if you didn't rinse properly and get all the sand out, as the paper filter will become clogged).
    Note that not all fuel filters are the same, and some are more appropriate for use after this procedure than others. Specifically, many OEM stock fuel filters contain a metal screen mesh and magnet combination, and while this is good for picking up extra rust that may come from the tank, it is not good for picking up fine bits of sand. Thus we recommend using a paper-based fuel filter at first, to ensure you capture any excess sand from the process.
    For those who appreciate such things (as I do), it is quite feasible to install dual fuel filters inline in your fuel hoses on many bikes -- one paper element filter and one magnetic/screen OEM filter.

  • Corrective Action "B" (Chemical Sanding/Rust Removal):
    The new school way of doing a light rust removal is chemically, via Yamaha's Fuel Tank Rust Remover ($14.95, Part Number ACC-FUELT-CD-KT). It's a two part kit, with part A being a pint of phosphoric acid and part B being a sodium metasilicate solution (absorbs any remaining acid and dries out the interior). To use, you remove & drain the tank, seal the bottom openings, then fill it half way with water. Add the phosphoric acid and top off the tank with more water. Cap and seal, agitate. Remove cap (to vent), and let sit for four hours (their recommendation -- I'd visually check before draining as you may need as much as 24 hours). Drain, rinse (a pressure washer is recommended), repeat drain & rinse operations several times (hey, we're talking about an acid here!). Then pour in part B, and agitate to coat every nook and cranny. This will absorb any remaining moisture and any remaining acid. Drain and allow the tank to air-dry completely.
    Note that this general process conversion is a part of POR-15's conversion/sealing process (listed below) and does not require purchase of Yamaha's kit if you are going with Corrective Action "C" (below).
  • Corrective Action "C" (Chemical Sanding/Rust Removal, plus a hard surface sealant):
    Utilize a rust-remover or kit including a rust-remover & stripper such as POR- 15 to remove the rust, and then coat with the same firm's coating material (since the products are designed to work together). No sanding necessary! POR-15's coating is an epoxy-like two-part thin-coat material that is hard as a rock (and is humidity-cured, so it cures better/faster the higher the humidity level). Allow to dry for the specified period of time (or longer) before reinstalling tank. Change your fuel filter when reinstalling tank. Use tank as usual.
    Note that POR-15 kit listed above also contains a stripper specifically designed to remove Kreem and/or RedKoat tank liners, if you've gone that route before and run into problems. They also offer a cheaper kit that doesn't include a stripper for previous coatings. Also note that the POR-15 route will typically take about 4 to 7 days to do it's magic (all the steps, plus curing) for a heavily rusted tank -- it's not a fast process.

       Metal converters use a chemical-based conversion process that converts iron rust (iron oxide) to a new metal (usually magnetite, a very hard form of iron oxide that is chemically inert and therefore not prone to rust).
       Rust strippers use a chemical-based acid process that removes rust (turns it into loose particles to be washed out), and is normally followed by an application of a specific acid-neutralizer or a combination acid neutralizer + surface-prep agent (as a single step).

  • Corrective Action "D" (seal/coat - latex barrier sealant):
    Use Kreem or RedKoat to seal the tank, which coats the interior of the tank with a thick latex or latex-like substance. If you use this method, you need to use Corrective Action "A" or "B" first to remove the surface rust! Many users have used Kreem or RedKoat to their satisfaction, but a lot of users have also complained about the product breaking down after a number of months or years, flaking off and clogging the fuel system & carbs (esp. in hot-weather climates). As a result, I don't tend to recommend either these two products, but with proper surface preparation, they should work.
    Note that the POR-15 kit (Corrective Action "C") comes with an acid stripper that will specifically strip away Kreem and RedKoat linings if you are having flaking issues using one of these two products.
  • Corrective Action "E" (Electrolytic Rust Removal - aka reverse plating process):
    There is a simple way of forcing the rust to plate a sacrificial electrode (steel or iron), but the process can take quite some time. Needed are a battery charger (a weak one will do) or other power-source (an old step-down power brick for an discarded electrical device will work if you slap a couple alligator clips on the leads), a piece of bare mild steel or iron as large as you can find that will still fit through the gas-cap opening without touching anything, water and washing soda (Arm & Hammer brand will do nicely).
    Remove the fuel-tank sender assembly, the petcock, the gas cap assembly, and any other removable items from the gas tank. Seal up all the holes in the tank except the gas cap filler hole (using plastic or rubber -- do not use aluminum), so that it's water-tight.
    Mix 1 Tablespoon of washing soda per gallon of water and fill the tank with the mixture (note: stronger will not accelerate the process, so don't go overboard).
    Without plugging it into the wall, connect the battery charger or other power source as follows: positive to the mild steel or iron part, and the ground to the gas tank itself (such as to a screw that normally holds in the petcock). You need to make sure that the lead to the mild steel or iron part will not touch the tank's metal, so insulated wiring is smart.
    Figure out how to support the steel or iron part in the tank without touching the sides or bottom, and without forming a grounding circuit to the body of the tank (a bit of nylon mesh attached to a plastic ring too large to pass through the opening of the tank will work wonderfully -- or some nylon twine tied off to something above the tank). Lower the metal into the tank and double check that it's not touching anything except the solution.
    Now you're ready to energize the system -- plug in the charger. How long the process will take will vary with three factors: the amount of surface area of the metal piece being suspended into the solution, the amount of power running through the solution, and how much rust we're dealing with here. In particularly bad cases, you may have to drain/rinse out the tank every 12 hours, wipe down the metal, then start over. If the mixture looks like a dark red stew, definitely time to change it. You will also need to top off the mixture with additional water if the level falls, as the process cooks off water (electrically rips it apart).
    Electrolytic Derusting, at
    Electrolytic Rust Removal FAQ, by Ted Kinsey
    Rust Removal using Electrolysis, at
    Note 2: Reversing the polarity will give you undesirable results!



   If your gas tank has rust that has moved all the way through the base metal, as evidenced by paint bubbling on the exterior of the tank or as leaks through the tank, do not use any of these methods, but instead replace the tank with a known-good one (new or used). None of the methods above will add any significant structural integrity to your tank, and you don't want to be riding with a tank that is ready to split like an over-ripe watermelon the first time it hits the ground (or might even breach on a simple hard jostle to the suspension, such as a pot hole), because it could easily translate into meaning that you are turned into a fireball (and subsequent death or spending an awfully long and painful visit in a burn trauma ward).
   If you have a rusted-through gas tank (or on the verge of rusted-through) to a bike that is so old and/or rare that no other tanks can be found, send it to a specialized shop that will either replicate it from scratch, or will cut it open, cut/grind away the compromised portions and reweld fresh metal into the voids, and then grind it smooth again, so you have structural integrity. Do not compromise your own safety in this sense! In the USA, we suggest contacting Bob Brown at EmpireGP for this kind of work.


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