How to Remove Rust from Inside a Motorcycle Gas Tank

How to Remove Rust from Inside a Motorcycle Gas Tank

Rust is never a good thing.  If it’s on the outside of your gas tank, you can pass it off as patina for a little while before taking care of it.  But rust on the inside poses the immediate risk of engine damage if the bike is ran in that condition.  Debris can flake off and clog fuel filters, which can cause a lean condition if the fuel is restricted enough.  That’s bad news!

Fortunately, you have a few options if you have a rusty gas tank.  First, you can just replace the tank with an O.E.M. or aftermarket motorcycle gas tank.  Second, you can send your tank off to a shop to be professionally restored.  Then there is the third option, which is for the roll-up-your-sleeves type.  With the right supplies and some elbow grease, you can remove the rust and reseal your own gas tank.

By going with the third option, not only will you have the satisfaction of a job well done, but you are likely to save quite a few bucks as well.  Follow the process below and the inside of your tank will be shiny and smooth once more.


Assess the Damage

It’s important to take note of how bad the rust and damage really is before you just jump right into the project.  If the rust is so bad that you can poke a hole through it, you should probably just look for a new tank.  Aftermarket tanks or tanks off scrap bikes will save you time and headaches if you are not prepared for major metal work.

If, however, the rust is just on the surface, you can tackle the job on your own with a few supplies.  Small pinholes can be blocked if you are using a gas tank liner product.  If you are handy with metal work, you can patch holes, but that requires another post on that subject.

Gather Supplies & Chemicals

Now that you’ve deemed that your tank is worthy of your wrenching skills, it’s time to get everything you need to complete the job.

  • Plugs, bungs, wine corks, tape and whatever else you can find to safely plug all holes in tank
  • Cleaner/degreaser
  • Paint/seal stripper
  • Rust Remover, acid, or vinegar
  • Agitators (random nuts and bolts, bb’s, or other hard objects that won’t dissolve in rust remover)
  • Tank Sealer
  • Protective gloves and safety glasses

To save time and money procuring the right chemicals you need, look for kits that are made specifically for restoring gas tanks.  Brands like KBS Coatings and Kreem have been around for a while and make chemical products for each step of the process.

Prep Tank

The first step, if you haven’t done so already, is to remove the tank from the motorcycle.  With the tank off, remove all floats, sending units and filters that may be in the tank.

Next, you will want to plug all the holes minus the filler hole with your stoppers and bungs.  It’s not a bad idea to test how well the tank is sealed by adding a non-toxic liquid and shaking it.  If there are no leaks, you can then move outside with your tank to add in the chemicals.

Clean the Tank

Before you get to actually removing the rust, you first need to clean the tank.  Dirt, varnish, oil and other debris can collect in your tank over time.  To get the most out of your rust remover, these need to be removed first.  A good degreaser works well for this step.  If using a cleaning agent made for tanks, follow the directions.  Let the degreaser/cleaner soak. Every once in a while, give the tank a shake to help agitate.  If the tank is extremely gunked up, you may want to let the tank soak for a full day.  When you drain and rinse the tank, ensure that all the gunk is removed.  If some remains, repeat the process with the degreaser.

If the tank previously had a liner, that will need to be removed as well.  A good paint stripper that contains methylene chloride works the best.  Add a bit of stripper to the tank and seal it up.  Slowly turn the tank, ensuring that the chemical finds its way to every part of the tank.  After doing so, safely drain the stripper from the tank.  Be very careful to not let the stripper touch the outside of the tank or it may damage the paint job.

There is a good chance that not all of the old liner will be removed this first go round.  Look in the tank to see if there are any loosened pieces.  You can try using something to scrape the pieces loose or use a long pliers or tweezers to pull the pieces out.  Repeat the stripping process until all of the old liner is removed.

Add Chemical Rust Removers

With all the grease, varnish and old liner removed, it’s now time to really attack the rust.  You will want be outside or at least in a well ventilated area for this step.

The safest remover that you can use here is vinegar.  It will work slower than the other chemical options, but is safe to use, easy to discard and is the gentlest on the tank.  Simply add the vinegar to the tank and let it soak.  Turn and shake the tank every half hour to an hour if you want to help it along.  Depending on the level of rust, this step could last anywhere from over night to a couple of days.  Persistent rust may require you to add your agitators.

If using an acid, have your protective gear on as well.  Follow the directions of the rust removing product for the best results.  This will generally be to pour the entire contents into the gas tank and then seal it.  Be sure to not get any on the outside of the tank.  With it sealed, continue rotating the tank every 5-10 minutes to ensure all areas are in contact with the remover.  Do this for at least a half an hour to an hour.  After that time, drain the remover into a safe container.

After this first round of using the remover, check to see how well it has worked.  If the rust is gone, you are either done or you could add the sealing liner if you choose.  Because of the strength of the remover, you may notice that it has eaten through thin spots of the tank.  Small pinholes can be sealed with a liner.  Larger holes will need to filled with a metal putty or be professionally fixed.  If the rust persists, you can repeat the process or move on to the next step with agitators.

Shake Tank with Agitators

Agitators are sometimes needed to help get persistent rust loosened.  Add in whatever you have chosen as your agitators to the tank with the rust remover or vinegar.  Vigorously shake and rotate the tank to get the agitators into all parts of the tank.  Follow the same timeline as the step above.  If using vinegar, this process could take days to get the desired result.  Do not go too long with a stronger acid, though, as it can eat the metal of the tank and the agitators if exposed for too long.  When done, safely drain the remover and agitators, being sure to get everything removed from the tank.

Flush Tank

Immediately after removing the rust remover and agitators, flush the tank with water.  Remove all your stoppers and fill the tank with water.  Shake the tank to get water on all interior surfaces.  Drain and repeat this process several times to ensure that all of the acid is removed. 

After rinsing the tank, use forced air to dry the tank.  A hair dryer, leaf blower, air compressor or shop vac will work well to dry out the tank.  If not dried fast enough, flash rust can form.  A little flash rust is ok, but it is still a good idea to dry the tank as fast as possible.  Your fuel filter will be able to pick up most of the rust that flakes off.  Sealing the tank can also cover up a little bit of flash rust.

If you are using Kreem’s tank liner, they suggest moving on to the liner immediately after flushing the tank to avoid flash rust.

Not using a tank liner?  Use a little motor oil or kerosene to coat the inside of the tank.  This will prevent flash rust from forming.  And with that, your tank is done and ready to be reinstalled.

Seal the Tank

Not every gas tank needs to be sealed, but it can add an extra level of protection against future rust and can plug pin holes.  It’s important to follow the specific instructions for the sealer that you have chosen.  The basic steps, though, are filling the tank with the sealer and swirling to create a single, even layer around the whole inside.  Drain the excess.  Avoid pooling by continuing to drain excess and rotating the tank every 5 minutes or so.

Wipe the sealer away from any threads and fuel lines before it has a chance to cure.  It is extremely difficult to remove the sealer once it has cured.  Allow the tank to cure for a few days or according to the directions it comes with.

You should now be left with a clean tank that is ready to be filled with gas and drained with the twist of the throttle.  It’s not a bad idea to replace your gas cap gasket as it may have been damaged by the rust remover. Leave your questions or tell us about your experience in the comments below.


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