So, the inside of the motorcycle’s gas tank is fairly rusty. Not so much that it’s falling apart, but there’s enough surface rust and gunk that I’d be concerned about particles floating into the fuel system and clogging something up. Clearly I must clean the inside…except this is a sealed metal bubble with no hole in it bigger than 5cm, and the inside shape is surprisingly complicated (the better to fit around the electrical parts that sit just below it on the frame). How can I reach all those corners to remove the rust?
Electrically! By filling the gas tank with an electrolyte, floating an anode in the liquid, and using the tank itself as an cathode, we can electrically convert the rust back into elemental iron, which is only loosely bound to the underlying metal and can be scraped off very easily. You can’t repair rust damage this way, but the process will only attack oxidized iron, so at the end you’ll be left with a relatively clean piece of bare steel showing pitting or roughness where the rust was.
First, sand off some of the paint on part of the tank, exposing the bare metal. This is where you’ll make the cathodic connection.