I think I'm getting the hang of it. The top and sides of the snake's
gas tank look ugly as hell and will require some going over, but I
learned a lot from the practice. The number one most important top
priority primary requirement when tinning bare steel is that the surface
be ABSOLUTELY POSITIVELY PERFECTLY SPOTLESSLY CLEAN! I figured that out
right off. The problem was how to get it that way. My first idea was
to use a wire brush attachment on my Makita 4" grinder to remove all
traces of rust and dirt. The problem with that was the brush tended to
pick up whatever crud was on the surface and to spread it evenly
everywhere. Not only that, the heat produced by the friction put a glaze
on this coating which wasn't easily removed. A secondary problem was
that the brush also tended to seal up rust in the deeper pits that the
brush wires were too fat or stiff to get into. Even acid base solder
flux had a tough time eating through this glaze. Next I tried a sanding
disk on the Makita. This work nicely in flat areas with minor pitting,
but not so hot in dinged areas and in tight corners. Also I didn't like
the idea of grinding out rusted pits because it thinned the metal too
much. So I figured, what better way to get at remote rust than with
acid. I tried both a bio-degradable organic type and phosphoric acid.
Both worked well getting at hard to reach rust but they removed solder
at an even faster rate than the rust. Even worse, solder wouldn't stick
to the coating these acids left on the surface. And this coating didn't
seem to be much easier to remove than the rust itself.
Once I got the top and sides more or less tinned, I made a pleasant
discovery. The tank had been sand blasted by some goon at the radiator
shop I had taken it to be cleaned. The top and sides of the tank had
been stripped to bare metal and were well pitted and starting to rust.
I had taken the dull frosted look of the surface areas of the remaining
sides as sand blast pitting on the bare metal there too; but this turned
out to be a pitted thin layer of tin/lead plating. There were still
plenty of rust spots, to be sure, but about 2/3 of the area had retained
its original coating. That made my day. For these surfaces I decided
to try something different. I started by squirting small amounts of
tinning fluid (diluted HCl and other gunk) on isolated rust spots and
working away at them with a small wire brush. This accomplished two
things. I could keep the acid confined to the rust spots and away from
adjacent tinned areas, and the brushing lifted loosened rust to give the
acid better penetration. It was as if the acid was a rust detergent.
Every so often I wiped away the dirty rust colored acid so I could check
progress. It wasn't long before I could see bright shiny metal at the
bottoms of the previously rust blackened pits and gouges. I continued
this routine until the metal was shiny and clean looking. Finally I
cleaned the surface one last time, brushed on a coat of tinning compound
and heated it with a propane torch. The result was a relatively even
coat of solder on the entire prepared surface. A variation on this was
to use a diluted solution of muriatic acid (also HCl) in place of the
tinning fluid. This worked even faster as was less goopy.
Another improvement in the process was to replace the small propane
bottle for my torch with a hose attachment connected to a 5 gal propane
tank. The problem with the little bottles was that tilting them tended
to change the flow of gas so that the flame varied wildly and often went
out. I even tried a 175-watt soldering iron briefly, but gave up on
that.
I checked several local auto parts stores for fuel tank slushing
compound but didn't have any luck. Finally I followed up on the
suggestion of a coupler of SOLers to try a motor cycle shop. I bought
one kit which contained a bottle of cleaner, a bottle of etch and a pint
bottle of sealer. I also bought an additional pint of sealer because
most of the kits I've seen advertised for cars come with a quart of
sealer. I'm not sure if the rest of the kit will be enough for an 18
gallon tank but the etch is just phosphoric acid and the cleaner is
mostly MEK. I have plenty of both on hand. Of course this presents a
dilemma: the phosphoric acid etch is to used to remove rust; but it
also removes solder; which is what seals all the seam in my gas tank.
Sigh. Nobody said it would be easy.
Roland
|