Customizing a Vintage Motorcycle: cleaning and sealing rusted gas tanks

POR15 Motorcycle Tank Sealer CleanerAfter checking compression and all the basics, my first major task on the GR650 was to clean and seal its badly rusted gas tank. The tank was solid and had no perforations or weak areas, but the insides were thick with rust.

I decided on the POR15 product. My background is in the industrial paint field, and the chemistry of this product made good sense to me, so after much research POR15 won out over the others. There are no shortcuts to proper procedure. It is vital that you follow correct preparation and application. My method went something like this:

How to Clean and Seal Rusted Motorcycle Tanks Using POR15

  1. Unbolt tank, disconnect wires and hoses, and remove tank
  2. Drain gas and rinse tank in hot water
  3. Remove the petcock, sending unit, and float
  4. Tape up openings. They suggest duck tape (It leaks)
  5. Mix the Cleaner/Degreaser (alkali based) 1:1 with hot water and shake/roll for 40 minutes
  6. Rinse tank a few times in hot water and drain
  7. Tape openings again. This time I used ‘Tuck Tape.’ It worked
  8. Pour in the Metal Prep, which is a Phosphoric Acid solution to change the alkali condition to acidic, remove some rust, etch bare metal and impregnate it with a phosphate surface, then roll/shake for 1 hour
  9. Rinse in hot water several times and drain
  10. Force dry (completely dry). I used my shop vac in blow mode with crevice nozzle in all openings alternated with a hair dryer sealed over the fill spout. That worked extremely well. It’s difficult to drain the water. Only the petcock opening on this tank doesn’t have a lip that restricts draining
  11. Once dry, seal the openings with masking tape this time, as the sealer contains a lacquer solvent that would eat plastic tape. Pour sealer in and slowly roll around to coat all surfaces
  12. Remove the tape and drain the excess sealer. This takes over an hour. You have to hold it in every position to allow it to slowly roll down and congregate in the only spots where it can drain. You do not want excess sealer pooling in trapped areas
  13. Set aside for 6 days to cure. I put a window screen over the openings to discourage curious insects from the exploring the tank and setting up residence

POR15 is a moisture cured product, so you want to do this in ideal humidity. It was about 40% when I did this, and that’s about right in my estimation. Overnight, the humidity will increase, and that will help the areas of greater mil thickness cure better. You don’t want to apply this when the humidity is too high, as it can skin over, preventing the sealer from curing clear through.

Does POR15 Perform Well on Badly Rusted Tanks?

Since treating the tank with POR15 and riding for most of the summer, I am completely satisfied with the results so far. There has not been the slightest sign of coating failure, and I know how to check for that. Time will tell more, but I trust that it will continue to perform well. Also, it is rated to resist ethanol and gas additives; an important consideration at today’s pumps.

Treating your rusted tank properly is a long involved job requiring attention to detail, and lots of patience. Your time and effort is well-spent though, because you’ll end up with a clean and solid, well-protected tank. Stay clear of the methods you see on YouTube using muriatic acid (dilution of hydrochloric acid) to remove the rust, then oiling the tank to prevent the resultant flash rusting.

Why? Because rusted tanks are already compromised. Using a strong acid like that can easily perforate the weakened tank walls. And the oiling to prevent flash rust? Well, that’ll disappear the first time you fill the tank, and then it will begin to rust all over again; this time with more vigor since the metal has now been corroded, pitted, and acid etched. Don’t cheap out and take short cuts that will only weaken your tank. Do it right.

Here are some photos taken during the process. Sorry I didn’t take more photos. I was busy, LOL: