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Fuel Tank Rust


(Hasn't Kreem been supplanted with POR-15?)

Deal with this with a liquid tank liner. The standard product for bikes is called Kreem. It is available from MO houses. You may also be able to find similar products at auto supply stores. If you use Kreem, you basically follow the directions, with the following exceptions and cautions. Before you start, find some way to get excess liquid out of the tank. Most tanks cannot be drained completely. You'll need this for all 3 solutions. A 60cc syringe with a piece of ¼" plastic tubing works. Don't buy the kit containing one bottle of each of the three solutions. You will need more than the one bottle of etching solution even if you don't have a lot of rust. The stuff is just phosphoric aid, and you may be able to find it locally either as the acid or disguised as liquid rust remover. The Kreem bottle of MEK is plenty for one job. An alternative is to substitute acetone from a paint supplier or hardware store. One bottle of the liner is plenty, enough for 2 or 3 tanks.

All of the solutions will damage the paint, and the process is unavoidably messy. A heavy coat of wax might help, but be prepared for the chance that you'll have to repaint. IOW, if the tank needs paint, do that after the Kreem.

If the tank is badly rusted, Kreem recommends you shake around some nuts & bolts in the tank to knock it loose. Some list members report that this works OK, others that getting them back out was a bitch. One suggestion: use a piece of chain instead, and hang onto the end of it. You might as well use water instead of using up the etching solution for this, and you may have to repeat this step. Expect to leave the etching solution in the tank longer, maybe a lot longer, than the instructions indicate. If the metal is pretty clean, overnight to a day or two will probably do it, but if there is a lot of rust it could take several days. If that is the case you probably should rinse out the loosened rust after a while and add fresh etching solution to finish up. If the tank is badly rusted, don't be surprised if it develops leaks while being etched. Put something under it to catch the acid if this happens. A good way to dry the tank is to set up a shop vac with the hose on the exhaust side to blow into the tank to dry it after the the MEK step. Be sure to do this in a very well ventilated area so there is no chance of the motor setting off any fumes. Before putting the tank aside to dry after the last step, make damn sure the fuel hose connections are open. If that stuff sets up in the vent hose connection you will have a fine time getting it out.

Jason’s de-rusting method

Hi all, I've gotten a few requests for the magical gas tank derusting process. Wonder if it deserves space in the faq?

Empty out all the gas, take out the petcock and remove the fuel cap. Remove any old fuel residue and varnish with a good rinse of naptha, make it petroleum free and then drain / dry. using a sock with a handful of small nuts/washers etc, add a little water and shake this all around inside the gas tank to loosen the big chunks, rinse with clear water scrub well. In a decent pail (not oil drain bucket), dissolve some of the sodium carbonate in water, 1/3 cup for say a Magna, ½ cup for a Sabre in a gallon of clear water, when its dissolved all the way stir it a bit more!

Seal up all but the filler cap opening on the top, pour in the well stirred mix using a funnel if you've had too much coffee. Fill the tank right to the top with water, set the tank so that the cap opening is the highest part, burp out as much air as possible and keep the tank full for the process.

Wrap a half dozen or so turns of the wire around the bolt to hold it secure, twist it tight so the bolt won't fall off. Attach the (-) lead of the battery charger to the outer shell of the tank, attach the (+) to the other end of the copper wire, suspend the bolt in the solution and turn on the battery charger to a fairly high rate, an amp or two flowing is good, then wait. Time to process is ~48 hours and it won't overdo itself.

The bolt gets nasty after a day, I cleaned mine now and again to remove the crud but not sure it helps. After a couple days, remove the leads, discard the bolt, save the wire, drain and rinse the tank well, drag out that sock and slosh it all around to remove any loose material. Rinse a few more times until the rinse water seems clean, shake well and then use a bit of the alcohol to fetch out the rest of the water.

Once the tank is dry, you're all set to put it back into service. More coating not required

Science: The process by which rust forms is electrochemical in nature so this method employs a reverse current flow in an alkaline bath at a higher voltage to reverse the process at a quicker rate. There are actually two forms of rust: iron III oxide or red oxide (Fe2O3) and iron II, III oxide or black oxide (Fe3O4)(FeO). Black oxide is a smaller molecule. The electrolytic process converts red rust to black rust and in the process the black rust becomes weakly bonded to the base metal. The black rust that takes the place of the red rust can be easily wiped, washed, or brushed off leaving rust free base metal. Any pitting that has occurred will remain, this method will not repair damage, but the pits will be rust free.

This is an alkali process and not acid, so you don't have a lot of pits in the steel filled with stray hydrogen ions which would just love to start rusting immediately instead of a much less active coating of black oxide.