Rust is the process of iron in the steel turning into soil. Your tank was originally cold formed supposedly using new steel, now it's old rusty steel so it is thinner in places then it was originally, if you just try to hammer it into a different shape I would expect a better then 50% chance you will end up with a leaker. :I think you need a new plan.
Tank tunnel widening technique
Hi. I have a CB200 tank to go on my XBR500 build and need to get clearance where my frame rails attach to my top tube. At this location, the tank tunnel is 130mm and if possible needs to become 160mm. Having googled around, I hope to be able to use a plastic mallet. Any advice on weight/shape of mallet and technique - do I strike against the inside face of the tunnel first, or the bottom edge where the wall and bottom of the tank meet? Any prep to help move the metal most effectively? I thought about filling with boiling water, but I could always purge the tank of petrol/gas fumes and use a butane torch. Many thanks.
