Honda CB 550: Clean Tank with Toilet Bowl Cleaner: Part 2

Crazy? I know!

Well, I could have continued to sand and buff the Honda CB550 tank, but I wanted to get on to the really important part, removing the rust from the inside.  Months ago, when I knew that I would be attempting this fix, I had acquired all the pieces of the puzzle, including: The Works toilet bowl cleaner, baking soda, some spare containers to drain the rusty gas, and a plug for sealing the tank when I removed the petcock.  They had been sitting neatly in a box, awaiting the day I would finally get off my ass and fix this tank.

Toilet Bowls and Motorcycle Tanks…

I put the tank up on the bench, protected by a sheet of bubble wrap, so as not to damage the freshly sanded exterior (more on that later).  I removed the petcock, immediately took it apart and cleaned it thoroughly, then placed it in a clean humus container.  I put the rubber cap over the hole to seal against leaks.  I then grabbed a box of wood screws, threw them into the tank, and began shaking the tank vigorously.  The goal here is to knock off any flakes of rust, before you start the chemical process.  You want the chemical concentrated on the surface rust on the walls of the tank.  After a few minutes of jostling the screws around , I poured them back out.  This can take a while to get them all lined up to fall out the hole.  A bit of rust debris fell out with the screws, but not much.  If you have a large amount coming out, probably best to repeat the process with the screws until they pour out clean.

Next, I got my chemical resistant gloves, and  poured the entire bottle of The Works into the Honda CB550 tank.  I closed the cap (I ordered a replacement rubber seal for the cap, which will go on when the process is complete, if the chemicals damage the current seal).  Shook the tank around, turned it upside down, and then let it sit for a few minutes on each side, making sure that the chemicals work on all the interior surfaces.  I probably spent a good 20 minutes with the chemical inside.  I made the mistake of looking inside a couple of times, with a flashlight, too curious to not get a close look.  Getting up near the mouth of the tank, the fumes are potent, and it’s best to keep a safe distance.

Here is where the mistake came in….

I had relied on gas cap, and it’s seal, to prevent the chemicals from escaping the tank.  This was a bad move.  The cap is not completely sealed  due to the vent/breather hole (because on the bike, you hopefully never turn in over, so you don’t think about this!).  It leaked The Works down the sides of the freshly sanded tank, causing a chemical reaction with the metal, and leaving horrible lines on it.  I didn’t panic, I would just have to do the sanding all over again.  But word to the wise: Take care of any aesthetic exterior fixes AFTER you deal with harsh chemicals.

It’s amazing how quickly this works to remove the rust.  After only 5 minutes, there was a noticeable amount removed from the interior, but I continued to swish it around to make sure all the areas were treated.  After I felt the rust was completely removed, I moved on to rinsing the tank.  Pouring water into acid is not advised, so I moved directly to the baking soda/water mix to neutralize the acid.  I put about 2 cups of baking soda in a bottle, the rest filled with water.  Mixed it up and poured it in there.  Instant chemical reaction!  The liquid inside the tank began to bubble violently, and took me off guard.  I swished it around, and then dumped it into a large Tupperware container, for disposal later.  I did it one more time, trying to make sure that the chemicals were entirely neutralized, and that the interior was left with only a small amount of baking soda water mix.

I then blew out the tank with the air compressor.  It’s tough to get the air gun into all the nooks and crannies of the tank, but I did the best I could.  Then I poured about a quart of denatured alcohol into the tank (acetone could be used here).  More swishing, turning it upside down, and all around, to make sure it hit all the surface areas.  This helps evaporate any excess water out of the tank, and leaves the tank as dry as possible.  For good measure, I blew the tank out again, to get it as dry as I could.

The last step was to pour some Mystery Oil into the tank, and move it around to coat the sides of the tank.  Although the baking soda may help to prevent flash rusting which can come on very quickly after the cleaning, this oil is a safety precaution.  Mystery Oil is an additive to gas, so it is safe for when you finally get gas back in the tank.  Ideally, you would fill the tank immediately with fresh gas.  Topping off the tank will eliminate the open space for air and condensation to create flash rusting.  I was fortunate and the oil did it’s job, leaving the tank free of rust, even until the next day when I can get some gas in there.

That’s it.  Pretty simple really.  The next step is to mate the new tank with the rebuilt carbs, to see if my handiwork will have finally fixed my fuel delivery system.  The photo below shows how the tank looks now, back on the Honda CB550.  I think that I will probably do some more sanding, to get it where I want it, but this is a great start.

EDIT: Works Toilet Bowl Cleaner has a new formulation that contains less acid.  Recently we were unsuccessful using the new formula.  We are now replacing Works with straight Muriatic Acid which can also be purchased cheaply at Big Box stores.  Stay tuned for a new post about tank cleaning with Muriatic Acid…

The new look for the Honda CB550…

You can see more about the Honda CB550 rebuild HERE:

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