The Stovebolt Site Forums The Shop Area Engine Shop Acid bath

I did some acid. An acid bath that is. No bad trips the way I do it.
I’m posting this in the engine section because I’ve mostly found it useful in preparing a cast iron intake. I also used it on a water pump last night too.
I’d like to avoid discussing the merits of media blasting. We probably all agree that media blasting gets the best results when cleaning up old rusty part.
The merits of an acid bath will be discussed here. I’m posting so that I can hear what other bolters on here do in these situations.

For years I’ve read posts on other forums where people submerge rusty parts in apple cider vinegar and wait weeks to get rust off. Me? Nope! I’m not gonna build big vats and buy gallons of cider just to wait and wait.

My methods are my own. I used an acid bath because I wanted to treat rust INSIDE passages in the intake that media blasting couldn’t get to.

***EDIT*** Here’s what I did. I cleaned grease and grime off of the cast iron 283ci intake. Stripped any remaining paint with aircraft remover and a pressure washer. Wire brushed any heavily rusted areas. The water jacket passages had some “tree bark” scale rust which I partly knocked off with long screwdrivers and rags.

Here’s what I did.
I poured 3 gallons of cleaning grade vinegar into a large tub. I wanted enough to submerge the intake.
Overnight soak worked pretty well but I wanted to speed things up a bit. So I added some already diluted muriatic acid to the tub. That sped up the process quite a bit.
(I’ve used diluted muriatic acid before to wash out a rusty gas tank before sealing it with KBS tank sealer.)
Another few hours and the intake was a nice even gray.

The second intake only took overnight, so the increased acidity definitely helped speed up the process.

Removed intake from the acid bath and rinsed with water and then a baking soda spray to neutralize all the acid. I was impressed with how much rust was removed from the cast iron, including the interior passages. I then used a propane torch to quickly heat and dry the intake to avoid flash rust. A little flash rust is inevitable. A hot oven would work just as well if your wife isn't home.
I was very pleased.
I then let it cool and finished with an even coat of high temp engine primer.

Did the same for the water pump. Should I be concerned about the pump bearing being exposed to acid? I don’t know. I’m thinking it’s a sealed bearing.

I submerged a rusty 283 rocker cover today too but I was NOT impressed with the results. I’ll have the rocker covers media blasted.

Be careful when using acid. Don’t breath the fumes. Wear old clothes. Never add water to acid . . . ALWAYS do it the other way . . . . Add acid to water! Neutralize it with a base prior to disposal, unless it’s vinegar, then just make cole slaw. Store bottles of acid away from metal building walls and away from areas where people, children or pets might get ahold of it.

Oh that looks great
The cleaning grade vinegar did a wonderful job
How much more use would you get out of that vinegar do you think?
Or it is pretty much done after this job?
-s

I have another intake soaking right now. I plan to pour it back into the original jugs and keep it. I’ll add more muriatic acid if needed. It should be useful for a few more parts. Best of all, cleaning grade vinegar is readily available and cheap.

More pictures. This second intake wasn’t fully submerged and you can see how well it’s working. Notice in the second picture where the acid level mark is. Bare cast metal is a nice gray and what was above the acid remains rusty. The rusty areas that were submerged wipe clean with a toothbrush.

Looks good Jay, .....as they say "the proof is in the pudding". You should get a commission on all the new sales on cleaning vinegar.
Keep trucking brother.

Jay

What percentage is cleaning vinegar? My wife got some agricultural vinegar that is 20% strength (normal vinegar is around 10% IIRC).

I've been using Evaporust with decent results, but it tends to leave a black residue that takes a little elbow grease to get off. I may have to give cleaning vinegar a try on the cast iron stuff.

Vinegar is acetic acid- - - -the same stuff is available in stronger concentrations on Ebay. Try adding some of the strong stuff to the vinegar instead of playing Russian roulette by mixing different types of acids together.
Jerry

Those are some impressive (and fast) results. Where do you buy cleaning grade vinegar? That is not something I have heard of before.

Home Depot sells 30% cleaning vinegar, https://www.homedepot.com/p/Harris-...Cleaner-Concentrate-VINE30-128/309463051

Im going to add/edit info on the original post.
Here’s what I did.
I poured 3 gallons of cleaning grade vinegar into a large tub. I wanted enough to submerge the intake.
Overnight soak worked pretty well but I wanted to speed things up a bit. So I added some already diluted muriatic acid to the tub. That sped up the process quite a bit.
(I’ve used diluted muriatic acid before to wash out a rusty gas tank before sealing it with KBS tank sealer.)
Another few hours and the intake was a nice even gray. The second intake only took overnight, so the increased acidity definitely helped speed up the process.

The 30% cleaning vinegar linked above is NOT what I used. I saw it on the shelf but I was not interested in buying 3 gallons at that price. The stuff I bought is less concentrated I’m sure.

Here’s what I would recommend. Safety first!
If you feel comfortable handling acid, the get muriatic acid and dilute it 1 part acid to 4 parts water. That should be very effective. Fast results will depend on acid concentration and time. It’s a chemical reaction after all. Some good prep work to get the “tree bark” rust off first will also help.

Never use the acid on an aluminum intake or aluminum parts (which don’t rust anyway)!

Here’s the second intake results. This is a 1958 283ci cast iron intake obtained from Jerry!

More pics of the 1958 intake.



While the 30% vinegar is safer, it’s much more expensive than muriatic acid.
Muriatic acid

A gallon of muriatic acid would make about 5 gallons of very strong acid bath for much less.

I
Evaporust works but also drains the bank account. I checked the bottle of cleaning vinegar but there’s no info about the concentration. The vinegar works slowly. Muriatic acid diluted 1part acid to 4 parts water should be cheaper and faster. However, it is more caustic and must be used with caution.

50 years ago pro stock cars (especially Chrysler) were acid dipped
The ones that were only rinsed with water completely disintegrated in 1-2 years
The ones rinsed with baking soda at least once lasted a few years more
Despite the after care, almost all of them are piles of dust now

Be careful.

Agree. Acid bath methods here are for cast iron.

My point was that all of those builders thought they were safe, and none were.
Acid left in a cooling passage or exhaust cross-over will be a vacuum leak next year.

Well said. Unless you are a chemist I would tread lightly.

Do I understand correctly? Are you saying that this cast iron intake will develop a vacuum leak or a coolant leak if acid has not been completely washed away? I feel that the circulating antifreeze will certainly dilute any hint of acid remaining in the coolant passages. The intake air passages will have atomized fuel and are certainly too thick for any chance of acid eating through.
Perhaps I misunderstand you.

You're right if the cooling passages are still "wet", but any dead end or non-circulating area may not flush out.
Yes, I'm exaggerating

Make sure you neutralize the used up acid solution with lots of baking soda before you pour it down the drain or dump it in the driveway AND don't use it in your shop as the fumes will corrode everything.

Be safe!

Mike B

This sounds like a problem that I'm having with a 235 intake/exhaust that I was having trouble with. JonG gave me some excellent advice. I have to change out a 235 intake/exhaust on my 54. Is it ok to spray the inside with exhaust paint or should I take it to a friend and have it sand blasted inside. I do have a black sand blaster system in the barn. However this is Central Florida and the humidity is almost always above 70+%. If I heat the intake /exhaust to about 160 degrees then spray the high heat into the chambers will it help? From the forever mold state of Florida. Doc

Putting anything inside an intake passage that might slough off later and end up in the engine probably isn't a good idea. Once a part is de-rusted, use a garden sprayer to fog it down with Diesel fuel, and then seal it inside a plastic bag if you're not going to assemble the engine right away. One of my students used to preserve entire engines for years by disassembling them, putting the pieces into a ring-top 55 gallon drum, and filling it with Diesel fuel or agricultural hydraulic fluid. If the humidity can't get to the part it can't rust.
Jerry