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Old 03-26-2014, 10:22 PM
4 Jaw Chuck's Avatar Moderator
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How to clean aluminum with acid and baking soda

Having seen a lot of posts on the subject. I thought I would post my technique since it works, isn't hard to do and doesn't involve any special processes or media blasting which can embed glass on surfaces which are sensitive like piston tops or interior intake passages.

You need the following to proceed:

-Rubber gloves, safety glasses and typical PPE for dealing with acids as well as proper ventilation.
-Orange extract based degreaser.
-Regular CLR cleaner, contains phosphoric acid.
-Baking soda, one box.
-Spray bottle.
-Scrub brushes to reach every surface you want cleaned.
-Bathroom shower or hot water spray, whichever the wife lets you get away with.
-Oven to bake the part in to eliminate hydrogen from embritteling the aluminum.

To start you need to clean the component so it is grease free, a car wash is a good start but a good scrubbing with orange based cleaner works best without discoloration. Simple green seems to stain aluminum so I avoid using it only since it takes longer to get that fresh cast aluminum sheen. It is important to note this process will not remove baked on carbon or brake dust for example, you need to scrub these deposits manually to get to bare aluminum. What this process does is restore the fresh cast silver finish typical of fresh cast aluminum. Polished surfaces will be slightly dulled after this process but can be easily polished with Mothers Mag cream polish in the little tin or any other polish like Flitz etc.

Mix up a 50/50 mixture of hot water and CLR in your spray bottle, you can use deionized water if there are many white corrosion deposits as this will assist in removing them. DO NOT USE UNDILUTED ACID, the water component is necessary for the reaction to occur.

Wet your piece(s) under hot water to get them hot, I use my shower and lay down towels to avoid scratching the tub but you can do this outside if you have hot water and a spray nozzle.

The trick when doing this procedure is to always keep the part wet and hot while applying the acid and always be scrubbing while its wet with acid, CLR has mild detergents which will help in keeping the part from drying out and also help in floating off dirt and debris and aluminum oxide which will form as a natural part of the process.

While your scrubbing with the phosphoric acid mixture the part will turn black, your goal is to keep scrubbing to float that oxide away and expose clean aluminum. Each acid application and scrubbing should take a maximum of five minutes between rinsing with hot water, after each rinsing lightly sprinkle baking soda on the part to neutralize acid and add abrasive for the next acid application.

You will see foaming each time you spray acid on the part covered in baking soda, this is important as what you are doing is turning the water layer from acidic to basic with each application cycle with a hot water rinse at the end to keep the part hot and wet. Normally it takes at least 5-10 applications to restore the finish but that depends on staining and corrosion deposits and their severity.

Once your done and the part is clean but still wet, apply the baking soda coat and scrub and give a final rinse in very hot water. Blow dry or wipe down to prevent water spots but as long as the part is well drained the heat usually will evaporate the remaining moisture quickly

Last step is baking, typically done at 250F-350F but the higher temps tend to add a blueish hue to the part. I do aluminum intakes at 250F for 6-8 hours and pistons at 350F for 4 hours which is plenty to remove entrained hydrogen.

I know a picture is worth a thousand words and here is an intake manifold I did last night. I don't have a before picture but anyone who has bought a decade or older aluminum intake before can attest to how bad they can get, this manifold had very serious discoloration where a fuel leak where had turned the manifold brown and yellow under the rear float bowl.

I washed the intake in my dishwasher to remove heavy deposits of grease with common dishwashing detergent which left the discolorations and turned the manifold a dark grey, this photo shows the worst area under the rear float could never tell it was ever discolored.

Good luck boys, this works well and keep scrubbing!

BTW this is a simplified technique I learned working in a chroming shop, we had heavier duty chemicals and hot dip tanks but the theory is the same but with less caustic household chemicals.

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Old 03-26-2014, 10:44 PM
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quote"I washed the intake in my dishwasher"
are you still married? I have to take my shop clothes off outside,,,,
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Old 03-26-2014, 10:49 PM
4 Jaw Chuck's Avatar Moderator
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I do it when she isn't home.

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Old 03-28-2014, 07:10 AM
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I'd be killed. Her retribution would be swift and brutal.

Heres what would happen.

Car parts in the house. Bad.
Car parts in our bathroom. Worse.
I'd invariably use the wrong towels and "ruin them". This was obviously done as a personal attack to her.
I'd try to do this when she wasn't home because I knew it was "wrong". Biblical sin.
And the dishwasher and or oven? LOL you're a lucky man 4Jaw.
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Old 03-28-2014, 11:57 AM
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Yes I am!

The trick with getting her to allow me to do this kind of stuff in the house has been making sure I didnt make a mess or stink the house up baking oily stuff in the oven or leaving the dishwasher dirty with metal oxides inside...being careful is a big part of it.

I forgot to mention not to use battery acid or muriatic acid as the reaction is severe and fast and will turn the AL grey faster than you can scrub it off and the oxide formed is very tough to remove...this adherent oxide coating is what is used to dye anodize aluminum...good luck getting it off after.

Of course you could use this coating to your advantage, I did a set of heavily pitted cast off road rims for a Bronco I used to own. Looked nicer in grey AL oxide than clean and pitted.
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