The gas tank is very much the center of attention on any givern bike. With that said dents take away from this quickly. This is a method of dent removal that has proved very successful, as well as tank cleaning.
This was a 1971 Honda Cl 175 Tank that caome to me with one large dent on the top and two on the left side. This tank also had heavy rust inside.
We started by cleaning the tank with muratic acid. This is nasty stuff to deal with as it will knock you down faster than a straight on punch from Mike Tyson.
We introduced about 1/2 gallon of acid to this nasty tank. It was fairly heavy in the rust department inside. Within a short period of time the tank was improving inside. This stuff fumed like mad as it powered through the old rust in the tank. It took three treatments of acid, each one smaller than the last to get the trick done. The tank was clean for about 10 minutes and then developed a thin layer of rust all over the interior of the tank.
We flushed with about 1/4 gallon of fuel three times until we had no MUD!
The last treatment of acid was about 8 ounces of acid swished around in the tank and then once drained followed up with a 1/2 can treatment of Loctite Rust neutralizer. This stuff sprays on like penatrating lube and neutralizes all rust present plus stops the formation of rust that we all know will happen after an acid treatment. This leaves the interior of the tank a nice slightly dull finish, free of rust!
Ok now we still have dents. This one was the size of my palm around and had no sharp edges. I ratchet strapped the tank to keep it from over expanding and loosing shape (tanks will try to butterfly and open up as you over pressurize them). I gave the tank about 10 psi through the Bung with a rag wrapped around the blow gun and the petcock installed. It wistled a few times and then doink! Out came the dent. I have guided people 4 times on the same tank to the old location of the dent and they can not see it in anyway. Plus it did not remove any of the original paint.
Stubborn dents can be handled by filling the tank with water and allowing to freeze without the cap on the tank. If you install the cap on the bung there will be nowhere for the excessive expansion to go and WILL result in a ruptured tank that may become useless. Leave about 1/2 inch in the tank open so that the water when frozen can expand properly. As this water expands it will push out the smaller, sharper dents. For stubborn dents you can heat the location of the dent (which softens the metal) while the tank is frozen with a heat gun. And then allow to refreeze again and the dent should come out slowly as the water behind the dent starts to freeze again. Do not do this more than twice as the metal becomes tempered with the heat and thus becomes more brittle.
When you are done your strapped tank should easily hold 15 PSI of pressure without leaks. Leaks at this point can be detected by monitoring the pressure or dunking the tank in water after pressure has been applied. NOTE: The tank must be completely clear of the previous frozen water.
Hope these thicks help you. As always, error on the side of caution. Be careful not to over pressurize the tank as it will blow your fool head off!
