Alright, I am going on record here and saying that we are NOT doing the full Monty on this bike, this is not getting restored, we're just putting it back into the world to be enjoyed, and just this once we are NOT getting (entirely) carried away.
OK so I made one of those knucklehead errors I am supposed to know better about - the tank looked great after a multi-day vinegar soak, so we emptied it (and a cup of flaky rust) out, gave it a good drying rinse with acetone, and then quick like a bunny with the reversed shop vac to dry it. And that is the moment I would normally dump a cup of WD40 into it to stabilize the steel somewhat, but my painter's wibbling about the evils of WD40 on soon-to-be-painted items echoed in my ears and I left it be. And it flash rusted, as I guess I knew it would. Compounding my folly, we had already blasted the metal spotless and so the re-soak resulted in some vinegar on the outside of the tank, which put a quick patina of rust on it too.
D'OH!
SO... we gave it another day with the vinegar, and that cleared up the flash, gave it another good shaking rinse with the acetone, and it looked great inside again, and then we dried it again, and then we gave it a nice coating of the Caswell epoxy, and that is curing over the weekend. And then we will dust off this exterior rust and that will be that. And I don't mind sharing my folly, even though I knew better, and didn't do it, but this is my takeaways and best practices for anyone that hasn't treated a tank:
1. You should really do your best to get any heavy rust and crud out of it before you do anything else with chemicals or coatings. My personal favorite is to jam a pressure washer into the neck and try to blast out any loose dirt and sediment first, then use a length of sash chain obtained from Home Depot to shake around there to dislodge anything that remains. Sash chain is easily retrieved with a magnet.
2. All vinegar is not created equal, and the cheap #$%* I buy from Costco is diluted with water to achieve a specific 5% acid concentration. It still worked, but I think undiluted vinegar would be better, or one of the commercial solutions like Metal Rescue, and I am going to see about that next time. I favor vinegar because I feel no pangs about sending it down the drain when I am finished.
3. You really have to go end to end with your process if you can. If you're going to coat, it should be done as soon as the tank is clean and dry. Anything else is inviting Extra Fun.
3a. If you're going to strip the exterior for paint, do it AFTER you clean and or line the inside.
Monday we will dust this off again...
But the inside looks like this, and you are looking through the Caswell epoxy here:
...so I am declaring victory over the tank for the moment and moving on.
