Hi All,
Remember me asking about tricks to use to remove BAD rust THROUGHOUT the inside of a tank ?
Thought i would update you on the status of removing HORRIBLE rust from the inside of 17 litre tank of 2157........
First, i would like to say the tank spent 17 years on the bike in a shed in Alabama. There was about 3/8" thick layer of nasty dried concrete like rotted gasoline residue on the bottom of tank. Nasty as it was, the dried layer of rotted gas served a purpose in protecting the bottom and lower sides of the tank from being rotted through by the rust.
The rust it's self is the worst i have ever seen with the tank still appearing to be intact and really solid looking from the outside. The rust was very scaly, in some places like large warts, and in a number of places at least 1/8" thick.
The tank spent 2 months at the local radiator shop being "boiled out." This process removed all the dried gasoline and about 75% of the rust. The remaining rust was on the top inside of the tank, on the rear of the tunnel and the very rearward sides and back of the tank.
The tank still in unuseable condition, I then did two weeks of the electrolytic rust removal method. This procedure can be found on a number of websites. With a caveat, I will say the electrolysis process removed 100% of the rust. This method does not affect the unrusted steel, by reversing the rusting process, the rust literally drops off the affected areas, leaving the lovely silvery gray color of bare steel.
Upon draining the electrolytic solution (H2O/NaHCO) into a 5 gallon bucket, there was approximately 1/2" of the constituents of rust in the bottom of the bucket. However, there was still some very scaly rust on the back of the tank and tunnel. This remaing rust would literally drop off when touched with the tip of a long screwdriver blade. The problem was, the rust was so far back and unreachable with any suitable tool to dislodge the rust scales.
So, I poured in 2 quarts Naval Jelly (2% solution phosphoric acid) and soaked for two days. This removed a bit of the rust, but the coarse scale was still intact but even more easily removable with a screwdriver tip.
Could not get a direct blast of hi-pressure water to remove these rust scales.
So i tried the electrolytic method again, only to find out with the rust removed, i now had two pinhole leaks, one near the bottom on the side of the front corner of the tank and the other on the very top of the tank, about 3" from the filler hole.
Now, with these holes present, i could no longer use the electrolytic method nor Naval Jelly soak and i still had this damn rust adhering inside the tank.
So, i took 50 various sized nuts from 3/8" to 7/8" and put them inside the tank. I shook the tank to dislodge the rust with prodigous and waaay too slow results. What i discovered is how quickly a CB750 tank with 50 nuts in it becomes rather heavy, how quickly my pulse rate went to 140 and what a great sweat i had and how nauseatingly physically out of shape i am......... (have started taking a 30" brisk walk everyday.) (Yesterday was my 58th birthday....)
Using my brain, leaving the nuts in tank, I wrapped the tank with 3" foam layers, using duct tape to hold the foam in place. I then put this setup in the clothes dryer with no heat and ran the dryer for about 8 hours.
Removed the tank from dryer, I peered inside the tank.
ALL THE RUST HAD BEEN PULVERIZED AND THERE WAS NO RUST WHATSOEVER ADHERING TO THE INSIDE ANYWHERE OF THE TANK !!!!
A friend brazed the two holes in the tank, pressure tested and found no more holes.
I then washed the tank out with water and put a pint of Naval Jelly in for 4 hours. I then drained the tank and the entire inside of the tank was the perfectly lovely color of silvery gray raw steel.
I used POR-15 to seal coat the tank.
The tank is now ready to be painted Candy Tone Blue-Green !
Made a save on an otherwise trashed out 17 litre wrinkle tank!!!!
Thought you might find all this interesting........