A Word of Caution

Olie

XS650 Junkie
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I know everyone's sideways glanced at their dishwasher thinking "If it cleans dishes..." Well I've tried it. Wasn't too thrilled with the results.

But first a little background. I dipped the parts into a solvent tank to get rid of most of the oil and then soda blasted everything. Then I threw them into the dishwasher on the pots and pans cycle using Cascade powder soap and here's what they came out like.

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The aluminum flash oxidized and so did the iron that's integrated into the head. The flash rust on the combustion chamber I already wiped down with a clean, dry rag before I took these pics. Actually, the aluminum oxides kinda cool. Definitely different but not at all what I was shooting for. Is it clean? Most definitely. Did I just trash the cases? Doubtful, just made it all darker. It might be kinda hard to see in the pics but they're a dark grey color. Not the nice shiny aluminum color i was going for. I'm painting the cases anyway and going with bronze valve guides but if I wasn't I'd have to clean them up some more. Going to throw some oil on the iron so it doesn't rust again and then prep for paint. I'm not sure why they didn't come out all sparkly but just wanted to share this with anybody who's thinking that's what they might get. Because they might not.
 
Caustic - which is in dish washing soap will etch the alloy to a matte finish. Strong caustic solutions actually dissolve alloy.
 
When my dishwasher is done, I still smell detergent, so I rinse again. What I'd worry about with your parts is residual detergent. Highly alkaline (dishwasher detergent) or highly acidic solutions will corrode aluminum, as hotdog said. You can clean kitchen pots with cream of tartar and water, which is mildly acidic. It might help neutralize anything that's left. I'm not sure how much you'd have to use - likely a lot. I usually put a few tablespoons of it inside my aluminum pressure cooker if it starts to turn color.
 
So how is it that aluminum dishes don't corrode the same as my cases? Perhaps they're simply just a different aluminum alloy? I was planning using just plain water and flushing everything out. I know for copper you can mix a little lemon juice to make them shiny again. Think this will work in neutralizing any remaining residue in my cases?
 
So how is it that aluminum dishes don't corrode the same as my cases? Perhaps they're simply just a different aluminum alloy? I was planning using just plain water and flushing everything out. I know for copper you can mix a little lemon juice to make them shiny again. Think this will work in neutralizing any remaining residue in my cases?

I would think just a good wipe down with acetone, which is just on the acidic side of neutral. Since you'll be painting, you'll kill two birds with one stone. In spite of what I said about residual dishwasher chemicals, I think I just have a shitty dishwasher that doesn't rinse well, so I wouldn't worry too much about that, on second thought.

EDIT: I think it looks cool, too! I don't know what would happen if you left it that way. Aluminum forms aluminum oxide corrosion on the surface, which actually inhibits further corrosion. It doesn't look pretty, which is why we polish it off, but nevertheless it protects from pitting. If your parts were left raw like that, I wonder how they would look once the aluminum begins to oxidize. Just curious.
 
I did some more digging and this is what I found
"Just wanted to warn everyone that I found out the hard way that all dishwasher detergents sold after July 1st this year [2010] have no phosphates. That is good and bad. Since it has no phosphates all of them WILL turn anything you have that is aluminum or even aluminum clad black and discolored."

and...

"In the chemical reaction between soap and aluminum ATOMIC hydrogen is formed. Atomic hydrogen has a very weird property of actually being able to move completely through solid aluminum......because it is such a small particle. Atomic hydrogen cannot be contained in an aluminum vessel.....it moves right through it as though it weren't there. It remains in the atomic state only until it meets another atomic hydrogen atom which then produces the hydrogen molecule H2. Molecular H2, which is a gas, cannot pass through solid aluminum. This process of hydrogen going from the atomic form to the molecular form causes the metal to actually flake (sometimes even crack) :yikes: helping produce the powdery residue that you saw. The hot water in the dishwasher greatly accelerated this reaction."

So in short it probably wasn't my brightest moment to throw my cases into the dish washer but I'm REALLY glad I don't have any signs of flaking or cracking going on. I have one more side of the case to do and I think 'll just throw it in there without any soap.

Like Mister Mellow said I did read that 2-3 tablespoons of cream of tarter with 1 quart of water boiled over the stove could help bring back the shine. I didn't bring it to a boil but just let my sump cover (aka the dick plate) soak for about 20 minutes in the solution. It helped a little but not much. So I jumped up to 1/2 vinegar and 1/2 water :D and scrubbed it down with a new toothbrush. Sadly, it didn't do much either. Now to make this thread useful, pics!

First two show the slight color reversion back to the clean aluminum color.
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And these two show the contrast between a new bright, shiny aluminum piece and how dark the pieces actually got.
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We use a 15% phosphoric acid solution on aircraft parts to etch the surface. It will be bright white when done. It also dissolves iron oxide. It is flushed with water to neutralize. The hydrogen embrittlement you talked about is not really very common. Even though the hydrogen CAN move directly through, it seldom does, unless elevated temperatures start moving those molecules around. Heat treartment of wrought aluminum alloy sheet can produce pits in the surfrace from hydrogen particles exploding in the heat treatment process. I liked the color. There is a product called aluma-prep that is used as the etchant prior to paint in most aircaft structures. It gets applied, foams up a bit (and stinks) and gets flushed with plenty of fresh water and blown dry. I don't think any dishwashing liquid comes close to 15% phosporus, so I imagine you're just fine. Now I'm thinking clear coat over the dishwasher finish!
 
I finished cleaning up the rest of my cases and I still threw them in the dishwasher with some more soap. I like the color too, but it's not consistent enough. And I wasn't able to make the upper case half to fit-studs were too long. So I washed that one by hand. The rest of them came out pretty neat. Suppose I should change the name of the thread.

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Here's another caution about using soap....

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This is straight out of the Lycoming aircraft engines overhaul manual. They've been building aluminum case, air cooled engines for about a gazillion years. I (and the FAA) tend to take their cautions seriously. Oil is an excellent lubricant. Oil/soap foam..... not so much.
 
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