Converting rust...let phosphoric acid dry on surface, or rinse with water or ???

[Burgerkong]

So I did the acid etch today to the inside of my rusty crankcase, has been thoroughly wirewheeled, but couldn't get to some pits so I got some concrete etch which was 15-40% phosphoric acid. Diluted it abit and dumped it in a spray bottle and sprayed it liberally. Stuffed the crankcase in a plastic bag and let it marinate for half an hour, then repeat.

Got tire of waiting and noticed that near the end of the half hour, the metal got to be a dark greyish blue colour free of rust, which is what I want. However, some people advocate neutralizing with lots of water and detergent, so I sprayed simple green and went to town the the hose. Got the white residue, and flash rust on the inside. Now, if I left the acid to dry, would this be better? I'm trying to lay down an alkyd-based insulating varnish, I was going to follow up on the acid etch with some foaming glass cleaner, spirits rinse and a tack cloth - would the two treatments affect the etched finish?

Also, some people advocate using acetone to neutralize, is this necessary? There's so much conflicting information out there.....

 

[jreb10]

Hmmm. I like to use a weak phosphoric acid rinse after electrolysis. I remove the part from the e-tank, give it a rinse with a watering bucket (I use lye to help with paint removal), hand wire brush the black oxide off while rinsing with water, and then hit it with the acid solution and let dry.

After it is dry I give it some more hand wire brushing and just wipe away the dust with a towel. At this point I believe there is still a phosphoric coating on the item as I have left items for months this way and have not had flash rust. When I am ready to paint I hit it with a scotchbright pad, wipe down with lacquer thinner, and prime/paint.

I would think you could do the same, modified as needed depending on your final surface coating.

 

[uart]

Hmmm. I like to use a weak phosphoric acid rinse after electrolysis.

I often do that too. Sometimes I like to leave the black oxide in place after electrolysis then give it the weak phosphoric rinse then wipe it down and just oil it. Seems to leave a nice black protective layer.

For the inside of a crankcase I think I'd just wash it down with turps (mineral spirits) after the phosphoric had done it's thing. Give it a spray with WD40 if it's going to sit around for a while before reassembly.

 

[uart]

I'm trying to lay down an alkyd-based insulating varnish,.

Sorry I didn't read that far before. Forget my previous suggestions.

BTW. Why do you varnish the inside of a crankcase? I've never heard of this before.

 

[Burgerkong]

Sorry I didn't read that far before. Forget my previous suggestions.

BTW. Why do you varnish the inside of a crankcase? I've never heard of this before.

Officially, it's to aid the oil flowback. I just don't want to have to scrub so hard next time I have it apart for a full rebuild - this is a compressor crankcase by the way.

I did one more quick wash, sprayed it on and left it for a few minutes, then wiped it off with a damp cloth (similar to what Ospho recommends, same stuff). Dried it with a mix of compressed air and a heat gun set on high. The interior is now a mix of orange, red and brown mixed in with grey all encapsulated under the white residue (couldn't get any of the 'rust' to transfer over to my finger after giving it a good rub). I presume this to be acid? In any case, if the spirits wash down, and the glass cleaner won't neutralize it all, the last step was a freshwater rinse with Dawn and then dry and quick alcohol wipe.

I think this is all slightly overkill though.

 

[ZRX61]

Varnish? The only stuff I've seen used inside motors is Glyptal 1201.

 

[ddawg16]

I prefer to rinse it with water. Assuming it's all clean, if it's going to get painted, then I prime. If not painted or I don't have time.....I spray it with WD40 or other light oil...like ****** fluid.

Later I can use a simple degreaser to clean off the oil.