Zinc plated fasteners

[Ed S.]

I have a question for the electroplating experts re zinc plated fasteners. I am doing some "attention to detail work" on my '64. The bolts that secure my rear bumpers are correct (size and head markings) but a PO spray painted them silver or aluminum. According to the judging manual they should be zinc plated.

I removed one bolt, nut and LW and ran them over a wire wheel. They came out looking great, no rust or pitting.

My question is, does the action of the wire wheel remove the zinc plating as well or is the plating durable enough to withstand the wire wheel cleaning? Can I use these fasteners without worry of rusting over or do in need to do a DYI zinc plating job with one of those kits available from various vendors. I've attached a few pics for your evaluation.

Update / edit. Ok, the Judging Guide says "cadmium" plating on the fasteners, I was wrong when I said they should be zinc plated. Which brings up another question. All the cadmium plating services show fasteners with a yellow or gold tint. Vendors (like Paragon) show the fastener sets to be a silver color. I assume silver colored plating is correct, is that right?

Thanks for your comments and good council.

[Gene M.]

Re: Zinc plated fasteners

The original zinc plating was only zinc. GM did not waste money on chromate secondary finishing. Will it hold up to wire wheel?..... possible if heavy zinc to start with but in all probility no, it goes to polished bare metal.

The guide is WRONG no cad on the typical hardware. Typical plating was zinc. Typical finish on graded hardware was phosphate. It was well known even in the 60's that cad is toxic.

[Ed S.]

Re: Zinc plated fasteners

Gene - thanks for the advice. I've decided to give the bolt, nut & LW that I ran across the wire wheel a 6 hour swim test. It has been completely submerged in water for about an hour now - still looking shiny. Will report results later. Thanks again.

BTW - I recalled seeing a fastener and finish explanation somewhere ---- found it, it is at the back of the judging guide. It was helpful but you put the finishing touches on the answer.

[Gene M.]

Re: Zinc plated fasteners

Gene - thanks for the advice. I've decided to give the bolt, nut & LW that I ran across the wire wheel a 6 hour swim test. It has been completely submerged in water for about an hour now - still looking shiny. Will report results later. Thanks again.

BTW - I recalled seeing a fastener and finish explanation somewhere ---- found it, it is at the back of the judging guide. It was helpful but you put the finishing touches on the answer.

Ed, to see rust on the parts they need to be in the air. Remaining under water it may take way longer than you want to wait.

[Ed S.]

Re: Zinc plated fasteners

Gene,

Thanks again - no problem - a perfect environment can be arranged. I am in central Virginia. Current temp is 83, humidity is 70%, and rising. Hardware is on the porch enjoying a great Virginia evening. If I don't have at least a slight coat of surface rust by tomorrow morning I don't think it will ever corrode.

Will report results.

[Ed S.]

Re: Zinc plated fasteners

Test Results:

After sitting in water for about an hour yesterday then, sitting outside (humidity & air temperature in the 70s & higher) for about 12 hours my 53 year old zinc plated fastener had no visible difference in appearance. My wire wheel cleaning process apparently did not remove enough of the zinc coating to the point where the parts would flash rust. I am going to remove the paint from the remaining fasteners with an environmental friendly paint stripper then lightly run them across a softer wire wheel for the final cleaning. Hopefully, they will not rust.

[Michael G.]

Re: Zinc plated fasteners

The corrosion performance of zinc is mainly dependent on two things: 1) thickness of the plating; 2) porosity of the plating.

You are reducing zinc thickness (bad) and increasing porosity (also bad) with your wire wheel. How much, depends on how aggressive you are. The zinc thickness applied to GM fasteners did not afford much corrosion protection originally, even when plated properly, As such, you can expect rust at some point, much sooner than the original parts rusted. Your experiment might have rusted bare steel, but it wasn't severe enough to give much in the way of results with even a badly plated part.

Your saving grace may be that the silver paint probably sealed some the original porosity in the zinc. Removing that paint may actually hurt your results. (That's what they put the chromate on zinc for, sealing). ( I was on GM's fastener plating committee for many years, so take this for what that's worth)

Good luck,

[Ed S.]

Re: Zinc plated fasteners

Mike,
Thanks for the insights on GM zinc plating. FYI - I have already begun to experience what you described / predicted. After a few days the fastener I ran over the wire wheel has begun to show signs of some surface rust. Ya just can't win! I have been exploring DYI zinc coating processes and will likely go that route for fasteners that the JG or AIM specify to be zinc. While a home brew coating may not be as good as a quality commercial process, it will be less expensive and faster and...... I do not expect the parts to be exposed to a lot of moisture, i.e. rain so hopefully, the shine will last a number of years. This hobby is getting more complicated by the minute!.

[Tony S.]

Re: Zinc plated fasteners

Ed. There is no visual difference between recently plated zinc or cad silver plating. Over time, zinc tends to produce a yellowish tone; whereas, cad silver tends to produce a brownish appearance. I have freshened up older plated bolts with a light lick of a brass wheel on my bench grinder. I don't push it--just a light freshening so that I don't remove the plating. I admire owners who take the time to remove, bead blast, wire wheel and then replate their original fasteners. Good luck with your project. Tony

[David R.]

Re: Zinc plated fasteners

I'll share my recent experience with zinc plating:

I recently had a batch of fasteners, a set of knock off wheel adapters (and many other small parts) back from a local plating company. I learned a lot about the processes and materials. I thought the cost was reasonable ($200) considering it was a batch of smaller irregularly shaped parts. I prepped all the parts myself using glass beading and wire wheeling. The plater does not clean off the crud and rust......that was my job.

• Zinc plating by itself is NOT what you want. It will be dull and it will not provide the corrosion protection you need.
• Zinc Chromate plating is a much more durable finish and has the silver color specified in the JM
• Zinc Di-Chromate is the yellow/gold finish used on some parts. Carburetors and other small parts come to mind.
• Zinc-Nickel produces a silver color and is a fairly new plating process which is more expensive, but offers a much better corrosion protection. Many of the OEMs today are switching parts over to this finish because of its superior qualities

I am located near the "Motor City" and I could not find anybody doing Cadmium plating. I assume that the toxicity of the heavy metal has made it a less desirable plating process.

There are two processes for Zinc: Barrel plating and Rack plating. The barrel process is for smaller parts that will fit into a barrel and tumble. Parts that run through this process are bright, beautiful and shiny. If the same parts were rack plated with the same materials, they will be silver in color but will not have the luster of the barrel process. I believe this is because the tumbling process also polishes the parts.

Example: I had the clutch cross shaft zinc chromate plated. It was too big to be barrel plated, so they used the rack process. It is a nice uniform silver color, but not shiny like the barrel plated parts. I am going to experiment with this part. I have a friend with a LARGE industrial vibratory tumbler filled with ceramic beads. I plan to toss this part into the tumbler and see what effect it has on the finish. I expect it will bring out a shine and improve an already nice looking part.

P.S. I used the same tumbler (7 minutes) on my Muncie case parts and they turned out OMG beautiful!!!

[John D.]

Re: Zinc plated fasteners

For what it's worth. On the '57 to 65 fuel injections the majority of the parts are clear cadmium plated. On my 30K mile 63 the majority of the hardware was cadmium plated. I can spot cad and zinc (without the blue) quite easily. Remember we are talking the 60's. Cad was used more than zinc. Cad will hold up longer than zinc also.
Like Mike Garver said wire brushing previously plated parts is not the way to go.
I use Beringer Plating, Inc for all my clear cadmium plating and also di-chromate. For my FI screw and hardware kit Beringer's blackens certain fillister screws with black zinc rather than the way GM did it with phosphate, etc.
They have a website but I can not provide a link.
Talk to Bruce Hogie at 330-633-8409
Berringer Plating
1211 DeValera Ave., Akron, Ohio 44310

They do all types of plating except for chrome. Barrel plating or rack plating. Bright zinc, Cadmium, Copper, Bright Nickel (that stays shiny),
Phophating, Dichromating, Dyes, Black Oxide, Black zinc(puts phophating to shame and lasts for years).
They bake certain parts like lock washers, springs, etc because of embrittlement.
The more you send in a batch the more bang you get for the back. Please don't send me parts for plating as I use a subcontractor to prepare my parts and can't get involved.
Anyhow I highly recomment Beringer. Been using them for 20-25 years (forget) They never lost an FI part for me. I get hardware plating typically 10,000 pieces at a time. No problem at all. John D

[David B.]

Re: Zinc plated fasteners

FOR ANYONE INTERESTED:

GM Engineering Standards stipulate ground rules for specifications of automotive fasteners. The GM preferred finish for fasteners by application are broken into 4 specific areas on a vehicle: (1) Interior (2) Exterior Trim (3) Underhood (4) chassis Application
For chassis application there are 2 parameters: Appearance and Non-appearance. Exterior appearance fasteners fall into 2 categories:
Highly visible and Somewhat visible. The chassis appearance of zinc coated fasteners in this application are described as "bright". Since it is exposed to road spray it's specification number is GM 4342-M, code 50U48.
"ENGRG STDS PAGE V - 2.105 JUNE, 1980

[Michael G.]

Re: Zinc plated fasteners

David, while that is one specification used by GM, there were many, many variations on that. 50U48 was pretty minimal specification, elected for use based on its minimal cost; it's nothing I would recommend you bother with for re-plating.

While cadmium is difficult find, if you can get it, do so, as it is far superior to zinc in its resistance to corrosion and very, very few people can tell its appearance from that of zinc. When working with it, though, keep in mind that it is a bio-accumulative carcinogen, so don't sand it, wire-brush it, or do anything that creates cadmium dust.

[David B.]

Re: Zinc plated fasteners

Agree 100% re: GM zinc code variations. For Chassis application purposes code 50U48 was recommended. GM Standards specified "Zinc plating on fasteners through which a direct electrical ground must be established, except underhood applications covered in ----etc.. zinc plating per GM 4342-M Code 20U32 etc. etc..