240Z: Parts cleanup / degreasing / rust-removal how-to:

Sorry for the lack of updates, but I have been experimenting thoroughly with varous methods to remove dirt, grease, paint, primer, bondo and especially rust from all my parts, in preparation to get them repainted or plated with fresh zinc. Especially for that, you waant to have a nice and smooth surface, to get the OEM look.
I tried electrolytic rust removal, various acids and bases, petrol based fuels, paint stripper, etc, and used a variety of tools, like the ultrasonic cleaner, parts cleaner, rotary tumbler, etc…
Here is what I figured out works best for me:

1. Degreasing.
For big parts, I use the parts cleaner. Currnently there is a petrol based degreasing solvent inside, but I want to try more modern, more ecological and solvend free solution in the future. The workshop is full of petrol fumes after using it, and those new fluids should not evaporate, and also are biodegradable.

Make sure to remove big chunks of grease manually beforehand to not mess up the degreaser fluid too much. This was the result after a quick wash. I have figured out that if there are no critical parts (rubber, etc) on the parts you want to clan, you can easy soak it in the parts cleaner overnight for a deeper penetration.

For smaller pats, I use a household ultrasonic cleaner with a simple industrial cleaning soap solution (5 parts water + 1 part solution).

I let it run for about 20 minutes at a temperature of about 35°C. Some metals lose their specification when getting too hot, and that is not what you want (for e.g. spring-steel loses it’s tension, etc.). You can obviously run this for as much as needed.

The results are usually quite good. But this will only remove dirt and grease and no corrosion or anything like that.

2. Paint stripping.
Before paint stripping, ensure that you have degreased the parts and roughly cleaned them.
Parts which were originally sand-cast and have a rough surface anyway, or those that will get primered and painted anyway can be sandblasted:

I use standard sandblasting media “Normalkorund” in German.  and the results are quite OK if you ask me:

For parts that need to have a smooth surface in the end, I use paint stripper. Unfortunately, that strong stuff is prohibited here now, so I have to use whatever home-depot is offering. It’s usually some kind of gel, which you put on the paint in a thick layer. Optionally you can wrap it in tin-foil, I figured out that keeping it in a closed plastic box also works well:

Usually, I leave it overnight, but it should look like this after 1-2  hours already. some modern paints come off harder that some old stuff, which gets wringky as soon as you apply the stripper. Use a spatula or natural hair (no plastic) brush to remove the paint, preferably under flowing water:

I realized that those paint strippers often do not work very well with rust-protection primer (red stuff in the photo), but i have a solution for that too, see below. 

3. Rust removal (and old zinc layers)
Ensure the parts are degreased and the paint is stripped before removing rust.
I figured out the best stuff for me is Ecvapo-rust. An american product that has no solvents and fumes, is biodegradable, harmless, reusable and works really well.
You throw in the stuf fin a bucket with some of that evapo-rust:

And after a few hours, or overnight, the stuff is free from all rust, without removing any of the metal, or without atticking ruber, plastic or other stuff:

I threw in this heavily corroded bracket for two days:

And afterwards all the rust was magically gone. the rough surfase comes from the rust, and not the product itself. but as you can see, all the rust is gone:

Pro-Tip: If you use Evaporust in a heated ultrasonic cleaner, the effects are even bigger. Allthough you should not use temperatures higher than 50°C, to not damage the physical effects of spring-steel, alloys, or aluminum.

Note: This product will also remove old yellow or blue zinc passivation (which is great for re-plating). Also not that the metal is completely unprotected after this, so flash-rust will appear within minutes if not treated further.
But, if you plan to zinc-plate. the stuff will have surface-rust removal anyway again, so don’t worry about that.

4: Primer removal:
I have figured out that evapo-rust will also remove rust-protection primer. My guess is that this has to do with some chemical or physical reaction of that rust-protection paint itself. because evapo-rust would theoretically not attack any paint or primer, but it even removed some old paint in some cases. Most probably because it attacked the corroded metal layer underneath. anyway. This worked better for primer-removal than paint-stripper!!
How the same hood hinges, which I showed a few photos earlier with the red primer on, after soaking it in Evaporust for 2-3 days:

5: Old rubber & glue removal
I tried various products again, to remove old (sticky, partially hardened, degraded) rubber parts from my rear quarter window frame, and then some old glue, too. An orange-oil based label-off cleaner worked partially, but I figured out the best way is to leave the parts in the parts-cleaner with petrol-based grease-remover overnight and then remove the stuff with a plastic spatula (blue part in the photo). Sometimes 2 or 3 attempts were required to get those really hardened parts out, but it worked very nicely:

6. Surface treatment (rotary tumbler)
Some might remember that I used my rotary tumbler to clean parts in the past, but there are two flaws: It won’t remove any old paint, nor will it remove rust deeply, and then it can really smoothen out sharp edges, which is not what you always want. 

Due to the size and shape of the delfir-chips I use, it is too large to attack any threads on bolts, and screws, etc. but it will give a nice surface and smooth edges to parts. After rust removal may leave “cancer surfaces” afterwards, this can be used to smoothen it out. Note that this stuff is abrasive, so you do not want to use this for any structural important part.

This is how the water look after 24 hours of tumblering. I figured out that about 250ml of water with 1 cap (ca. 15ml) of compound works best for me together with 2kgs of delfir chips. and those chips last very long!
I talked to a specialst who manufactures those abrasives and he told me that this process should always be done with water and compound, because the water-solution will remove the dirt and dust that would otherwise remain on the chips and reduce their effectiveness.

Note, this might also remove old zinc plating, etc… You can also use walnut shells to polish things. Ore use ceramic chips for more abrasive processes, but be careful as this will remove way more material from the metal.
My setup also worked very well to smoothen (almost polish) aluminum parts. like the horn membranes of my 240Z, which are a thin alumium plate.

6. Metarex metal polishing wool.
This is one of my secreat weapons. Metarex is a wool soeaked in some polishing fluid for metal. you simply rub it on any metal and it will polish it nicely. I tried to remove some corrosion on some metal parts, but it worked so well, that it also removed the thin, old yellow-passivation on zinc plated parts within a short rub.

You can  see it here. So, While i can recommend the product for many, many applications, cleaning passivated, zinc plated parts is not one of them.

Often, a combination of of multiple of the mentioned processes is required. for e.g. Degreasing, then paint stripping and then, finally, rust removal. Sometimes manual intervention with a scalpel or so is required, to remove small bits of paint and stuff, that won’t come off with the mentioned methods, for whatever reason.

I will try to improve my processes on the go, and if I find any significant things, I will let you know.