I recently welded a plate of steal to the bottom of a forty eight tank to cover the fuel pump hole and covert the tank to work with a carbed 05 XLC.
Do I need to reseal the inside of the tank? It was sealed from the factory, but I'm afraid the welding could have damaged it, or the new plate could rust from the inside. I put 3 coats of rustoleum on the weld which is located on the bottom of the tank.
I called a radiator shop and they quoted me $180 to clean and seal the inside. Seems a little pricey.
I would seal it just to be on the safe side. Here is what I just used over the weekend. It's pretty easy but there is a lot of drying time in between steps. It took me all Saturday to complete. They had it shipped to me the next day too.
It's the same as Red Kote. I bought the complete motorcycle sealer kit.
I've did some more reading, and some guys say if the tank isn't already rusty you should be fine. My tank isn't rusted. They say if you always keep fuel in it, you should have a internal rust problem. Some say they never coat their tanks...
It's risky, but I might just leave it as is. I don't want to pay for the radiator place to do it, and I've heard horror stories about sealer kits you can buy. Knowing my luck, I'd make things worse by trying to seal it myself.
Metal tanks have a "patina" (I think I spelled that right) on the metal that helps slow down rust. Welding will do some damage to the patina but not as much as sandblasting it. They do make a rust removers that also restores the patina.
The one I used ( there must be others) is not cheap. "Rustol" ( http://www.sudco.com/rustol.html ) , around $47 a quart last time I bought some. Good part is that it mixes with water (5:1 or 10:1 depending on how much rust you want to disolve ) and it can be re-used up to 5 times.
1986 XLH 1100 (fixer-upper) // Engineers design things, Technicians make them work. --- 30% of being mechanical is confidence/30% is knowing to go slow when needed/30% is looking repeatedly at what you have/10% is dumb luck .