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Metal finishing Q&As since 1989

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Zinc plating & chromating of Carburetors


Q. I have a Quadrajet carburetor that I am rebuilding. It will be very visible on the car so I would like a nice, shiny finish. I'm looking to plate the body of the carb. From what I understand the carb bodies are made from a cast zinc alloy. I have a simple home setup available for zinc plating. I don't want to deal with chromating and the harsh chemicals involved, so I'd rather just do the plating. I have a few questions:

1) Is there any special prep needed before plating? I've cleaned the carb bodies with carb cleaner dips and ultrasonic cleaner. Is there an activation step needed for zinc plating on top of zinc alloy?

2) Will the zinc plating interfere with the internal carb passages? The internal passages of the carb are small and precise. Should I be masking off those parts when plating and only plate the outside of the carb? Or is this not a concern?

3) Since appearance is a primary concern, would nickel plating be better? If so, are there any considerations for nickel plating over a zinc alloy body?

4) Are there any health concerns with doing above in a well-ventilated space with proper protective equipment? From what I understand zinc plating seems relatively safe...


Thanks for your help!

Kevin Peterson
- Byron, Minnesota
March 26, 2024


A. Hi Kevin.

1. Solvents are not proper final cleaners before plating, although an alkaline ultrasonic cleaner might be. I would suggest a final scrub with a tampico scrub brush [this product on eBay or Amazon affil links] and a paste of pumice [this product on eBay or Amazon affil links] .
2. Unless you really work at it, you're not going to get any plating in internal passages anyway. The plating only occurs where the current flows, and electricity takes the shortest, easiest paths, so there will be no current and no plating on internal passages. But you should already know this from your experiments and practice on scrap. The idea that an actual valuable part would be used for your first, surely unsuccessful, effort is not a good idea.
3. Nickel plating is brighter and shinier than zinc, but plating nickel directly on pot metal isn't easy. Usually you would start with cyanide copper plating but hobbyists should not consider cyanide-based plating.
4. Everything is a matter of degree, as I'm sure you appreciate, but acid zinc or alkaline non-cyanide zinc plating is not a genuine biggie like cadmium or hexavalent chrome or cyanide-based plating or use of hydrofluoric acid.
You should probably consider a trivalent chromium post treatment after the zinc plating. Zinc plating without chromate is susceptible to corrosion and white rust. Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey





⇩ Related postings, oldest first ⇩



Q. I am looking for info on Zinc plating carburetors and was wondering if this could be done by immersion plating?

Also black chromate on older carburetors with an aluminum alloy in them?

Robert Grabell
- Canada
1996


A. You can immersion deposit zinc on aluminum, Robert; the process is called zincating. However, this finish is neither durable nor attractive -- rather it is used as a base for subsequent electroplating. If the carburetor is zinc, you could for example copper-nickel-chrome plate it, or you could zinc electroplate it and chromate conversion coat it. A possible reason for zinc electroplating and then chromating rather than simple chromating is so that you can chromate it more consistently.

Both aluminum and zinc can be chromate conversion coated (which is an immersion process), and the chromate can be black, or gold, red, or blue. But chromating an old raw die casting, whether zinc or aluminum, will probably give you a mottled, inconsistent finish that you won't be very happy with. Chromating the electroplated zinc may be more aesthetically pleasing.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




Q. I need to find a fool-proof way to correctly 're-color' old carburetor bodies to their original "iridescent yellow / gold rainbow" coloring. These bodies are made of a zinc die-cast alloy ('ZAMAK 3 & 5'). Does anyone know the correct procedure for doing this re-coloring ? I appreciate your help! Thank you!

LARRY FULTON
- Great Falls, Montana
2000


A. Hi Larry. I am told that the best way is by zinc plating the carburetor bodies first. To me "fool-proof" probably demands "best way" not "possible ways". Good luck.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


A. Regarding recolouring carburetor bodies, particularly zinc die-cast types such as Holleys, Zinctone from Turco is a professional product used in Australia. Available from Avanti in 20L drums. In USA check with Turco division of Henkel Technologies.

Gavin Campbell
- ORMEAU, QUEENSLAND, AUSTRALIA
2003

Ed. note: We'll let this commercial response stand since it's been here for years, but technical replies only please -- no commercial replies ( huh? why?)



Carb electroplating problems

"How to Super Tune and Modify Holley Carburetors"
by David Vizard

on AbeBooks

or eBay or

Amazon

(affil links)

Q. Dear Finishing,

I work for a carb restoration shop and am trying to replate carburetors. We have purchased a small copy cad electroplating system. It does not work well for plating the complex shapes and irregular surfaces of the carburetors. After much research it seems that electroplating is not really the correct application for carbs, rather electroless. Here are my questions .

1) Can electroplating work and provide a professional uniformly plated carburetor ?

2) How would you do this ?

3) How do the big carb manufacturers plate their carbs, electro or non electroless tank plating ? How do most large restoration shops replate ?

4) Are there electroless kits for carb replating on the market ? We would like to set up a facility to plate @ two carbs a week.

Thank you very much.

Fred Haring
carb restoration shop - Fargo, North Dakota, USA
2004


A. I believe the answer to your third question is that big carb manufacturers don't plate their carbs. The carburetors are diecast zinc, so they prep them, then chromate conversion coat them. Chromate is a product that works on aluminum, zinc, zinc plating, and cadmium plating; it is not really either a plating process nor an electroless plating process. However, once the casting is old and pitted, it's a different matter since the chromate will not properly treat pits, bloomed areas, and differentially corroded areas.

At that point the carburetors can be zinc plated before re-chromating, but that's no assurance of good appearance or corrosion resistance since it will not restore pitted areas.

Probably the ideal way to go would be to cyanide copper strike the units, acid copper plate them, mush buff them to fill pits, then nickel plate or electroless nickel plate them. This is not easy, and for this low volume it might be better to make an arrangement with a plating shop than to try to get into the business yourself.

Another writer suggested that you powder coat the carbs instead of plating them, put paint really isn't the same thing as metal plating and may not satisfy your needs.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




Q. I need information on the process for recoloring classic car carburetors to the original yellow dichromate color. I believe it is a hot dipping process.

Lynn Palmer
Car restorer/hobbyist - Houston,Texas, USA

----
Ed. note: We appended your inquiry to a thread which may answer it for you, Lynn. It's an aqueous process and may be warm (say 100 °F), but not hot. But feel free to follow up if this is insufficient.



"Holley Carburetors: How to Rebuild"
by Mike Mavrigian

on AbeBooks

or eBay or

Amazon

(affil links)

Q. I am curious if anyone here has vast experience with zinc plating carburetors, or doing the original zinc dichromate finish on them when they were brand new.

I've heard it may be necessary to zinc electroplate a stripped carb body before immersion dipping them in dichromate, to prevent blotchy results. I have also heard that if you zinc plate a carb, and then dichromate it, you will end up with that cheap China tool look, instead of the nice original zinc dichromate finish.

If anybody worked for Holley or other manufacturers and did this process when they were new, I would love to know if the carbs were electroplated first.

On a related note, does anybody have experience with any other colors than yellow? It seems like some carburetors were more of an olive-drab color than yellow. And I would be interested to hear about results using black, or a more tan than yellow.

Could it be possible to mix say the yellow with a little black, to get a more tan color?

Steve Hulett
- Ocala, Florida USA
June 21, 2013


A. Hi Steve.
New carburetors are not / were not zinc plated, they were just chromated directly. The problem is that the surface of old carburetors is not clean and uniform, and it may prove very difficult to uniformly chromate them ... so zinc plating them first is usually done.
Chromating is first and foremost an anti-corrosion finish, not a decorative one. In the old days of hexavalent chromating olive drab chromate offered extra corrosion resistance; but today chromates are almost uniformly trivalent, and any coloration is just dye, so olive drab may be very hard or impossible to find. Black chromates should be available.

As for mixing, chromates employ carefully controlled conversion coating processes; they are just a dip in a coloring agent, so mixing different ones together will probably just ruin them. Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


Carburetor cleaning and refinishing has been a perennial subject. Please see also --

Topic 11847 "Restoring gold Iridite color to diecast parts"

Topic 16200 "Zinc plate carburetors & diecastings vs. chromating"

Topic 33779 "Clean and brighten carburetor bodies"

Topic 35697 "Carburetor re-plating / re-coloring"

Topic 37255 "Restoring the yellow dichromate finish on automobile carburetors"


"How to Rebuild & Modify Rochester Quadrajet"
by Cliff Ruggles

on AbeBooks

or eBay or

Amazon

(affil links)

Q. I too am trying to electroplate my Rochester quadrajet carb for a restoration project. I have the plating rectifier and am try to determine if I can make the kit myself? I believe I need to zinc-nickel plate, with brightener and then dip in a chromate of some color. Has anyone had success in this as I would be very appreciative for some expert advice. I know hobby plating suppliers have a kit but I was hoping to build the kit on my own or find another supplier. Thanks in advance.

Todd Anderson
hobbyist - Winston [Georgia]
October 30, 2021

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)





"Holley Carburetor
Haynes TECHBOOK"

by John Haynes

on AbeBooks

or eBay or

Amazon

(affil links)

A. I have re-chromated Holleys and other die cast carburetor bodies for 30+ years. The original process was more than likely right out of the mold and into the chromate and rinse. Problem is with used metal that has been exposed to the elements it is difficult to properly prepare the metal to take the chromate evenly and not burn the metal which gives an ugly grey color if the chromate is too strong or the part is dipped too long.

I glass bead the bodies then go into a very mild nitric bath to "open the pores" so to speak, rinse, then into the chromate. The chromate I use has been off the market for 20 years so no help there. Darker tan or lighter green/red/gold is not in my control. The alloy controls that and these parts were not strictly controlled.

Donald C Dorfman
Retired Machinist / Engineer/ Business Owner - Edgewood, Washington
December 11, 2021




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