Carburetor Refinishing

[shoprat]

Like many auto enthusiasts, I would like to be able to give my carburetors a "new" look. Generally carburetors come with a yellow gold finish over the aluminium. They do not appear to have a "coating". The finish appears to be more of a coloring. Can you identify the finish, and what kit do you recommend for refinishing carburetors?

The finish seems most likely to be like IRIDESCENT YELLOW CHROMATE & BLACKENER. I have used a blackener on metal parts and all they need to be is clean. Is this the case with the yellow chromate or will it only work after plating as described here http://www.caswellplating.com/kits/zinc.htm ?

[seanc]

Re: Carburetor Refinishing

shoprat:

Most carb bodies are zinc die-cast, and the yellow/gold color is indeed a chromate. If the particular carb has a high percentage of zinc, it may only need to be re-chromated. If it's a relatively low percentage, it may not chromate very well, and you might need to zinc plate it first. Only experimentation will tell.

Stripping the old finish off first is required. Strip/clean thoroughly, then activate the zinc die-cast in a weak acid dip for a few seconds, then into the yellow chromate for 15-60 seconds, depending on how strong you want the color to be.

I have some carb bodies I'll be experimenting on in the near future. I will be soda blasting rather than bead blasting, so as not to damage any of the delicate ports, or leave any bits o' glass embedded in it.

Sean

[dfarning]

Re: Carburetor Refinishing

What is the preferred treatment for the older cast iron carb parts? I have seen references to black phosphate and blacking.

Some of the cabs I am working with are from the 20s and 30s and pretty badly pitted. Should I re-zinc? As I understand it, the chromate is just a coloring while the copy cad and zinc are sacrificial protective coats.

Also, how should I protect the carbs between blasting/degreasing/identifying and coating. They sometimes sit for a few weeks.

David

[seanc]

Re: Carburetor Refinishing

David:

Cast iron parts can be black oxided, phospahted or zinc plated/chromated. Zinc w/chromate is the most durable & corrosion resistant.

Chromate is far more than just a coloring. It provides the majority of the corrosion resistance. IMO, chromating is required if you want a long-lasting finish.

What many don't realize is that zinc is a very reactive metal. It WILL oxidize ("white rust") in fairly short order unless it's "passivated" somehow. The best of the passivations is chromate conversion.

So, the zinc protects the steel (or other metal you're plating), and the chromate protects the zinc.

Industry has a standard test for corrosion resistance known as the "salt spray test". I'm not familiar with all the details, but in a nutshell, they expose parts to a continuous spray of salt water in a controlled environment, and see how long it takes to produce corrosion.

In a salt spray test, raw steel will produce "red rust" in a matter of minutes, plain zinc plate will produce "white rust" in a matter of hours, and chromated zinc will last for tens & hundreds of hours( 60-200, depending on the particular chromate).

I prefer not to clean/strip parts until I'm ready to plate them, but in a pinch, wd-40 or some oil-based coating will protect them for a while. Degrease w/SP degreaser right before plating.

Sean

[dfarning]

Re: Carburetor Refinishing

Sean

Thanks for the feedback I am going to add restoration to my carb rebuilding services. This is my first attempt at plating, so I am a bit overwhelmed

Under the grime there is often layers of whitish powder on the zinc die-cast pieces. That must be the zinc oxide you are talking about. So I will want to re-zinc those pieces.

Then the cast will get dipped in zinc blackener before being chromated while the zinc die-cast will go from the zinc to the chromate without being blackned.

I would also like te verify that the Zinc Plating kit and the Cadmium Plating kit are the same think. They have diffenent entries on http://www.caswellplating.com/kits/index.html but the online manual referes to them as the same thing. Just a little different surface prep. Both are listed as part numbers zn1, zn2, or zn3.

Will a 3 Amp power supply be enough to get started? The manual states a current of about 1A per 40 sq"

Will the three gallon kit, zn2, and a three amp power supply get me started?

Thanks
David

[seanc]

Re: Carburetor Refinishing

David:

Under the grime there is often layers of whitish powder on the zinc die-cast pieces. That must be the zinc oxide you are talking about. So I will want to re-zinc those pieces.

Yep, that's probably the "white rust" that zinc oxide is called.

the cast will get dipped in zinc blackener before being chromated

zinc blackener and zinc chromate are both conversion processes which passivate the zinc. They are mutually exclusive. You do one or the other.

I would also like te verify that the Zinc Plating kit and the Cadmium Plating kit are the same think.

Yes they are. The "Cad" part simply describes the finish, which mimics the look of cadmium plate. It's still zinc. The difference is in the use of brightener. Without the brightener, the finish is a matte gray (ala "cad"). With the brightener, the finish is semi-glossy silver.

Will a 3 Amp power supply be enough to get started? The manual states a current of about 1A per 40 sq"

I take exception to the manual. 25 ma/sq-in (1A/40") is not enough. You need at least 50 ma/sq-in, and more is better (80-100 ma/sq-in.) So the 3A supply will be good for 50-60 sq-in at best.

How big are your carb parts?

As I mentioned earlier, with carbs being zinc die-cast, they may not need to be replated. If they are thoroughly cleaned, and activated with a brief dip in acid pickle, they may take a chromate w/out replating. It just depends on the particular composition of the die-cast in the carbs you're working with.

I would test the process on some expendable carb bodies before trying it on the real thing.

If you do decide to replate, beware that the zinc plate may reduce the size of any calibrated orifices in the carb body. Only plate it long enough to get enough zinc to hold the chromate.

Sean

[dfarning]

Re: Carburetor Refinishing

I take exception to the manual. 25 ma/sq-in (1A/40") is not enough. You need at least 50 ma/sq-in, and more is better (80-100 ma/sq-in.) So the 3A supply will be good for 50-60 sq-in at best.

How big are your carb parts?
Sean

Thanks I'll use the 50 mA number in my initial calculations. Can't say that I have ever looked at a carb and thought about it's surface area before I'll try to estimate them as solid objects they multiply by some factor such as .2 for all the irregularites.

I would test the process on some expendable carb bodies before trying it on the real thing.
Sean

I've got a couple of cracked bodies of various shapes and sizes ready as test pieces.

If you do decide to replate, beware that the zinc plate may reduce the size of any calibrated orifices in the carb body. Only plate it long enough to get enough zinc to hold the chromate.
Sean

I am working under the assumption that the zinc plate will not be thrown down the orifices very well. Still I'll start at .00025" and work up as needed.

Thanks again

[seanc]

Re: Carburetor Refinishing

David:

Can't say that I have ever looked at a carb and thought about it's surface area before I'll try to estimate them as solid objects they multiply by some factor such as .2 for all the irregularites.

I've found this is the hardest part of plating irregular shapes. I'm always underestimating surface areas by quite a bit, so I've taken to close measurements and a spreadsheet to get it as close as possible. You do have to factor in the inner surfaces, unless you mask them off.

I am working under the assumption that the zinc plate will not be thrown down the orifices very well. Still I'll start at .00025" and work up as needed.

Zinc has pretty darn good throwing power, particularly Caswells process, which uses zinc chloride in the electrolyte. Much of the zinc is drawn directly from the chloride in the electrolyte, while the anodes replenish the electrolyte. As long as the liquid is in contact with the electrified metal, it will plate, although somewhat diminished if the fluid can't flow freely through the orifice.

We're both working to achieve the same end. I've got a couple of dead carb horns & float bodies to experiment with, but it's on the back burner for now. I've got other priorities at the moment. I'm first going to try rechromating without replating. Lets' stay in touch with our findings.

Sean

[gto65racer]

Re: Carburetor Refinishing

What kind of Acid do you use to dip the carb bodies?

Do you rinse the parts after the acid dip before chromating?