DIY Parkerizing...How corrosion resistant?

[Mike R.]

After reading in the archives, I bought a Shooters Solutions parkerizing kit. My initial batches have been wildly successful. My bolts came out a beautiful black...I almost cried...most people wouldn't understand like you guys...

My question is how does this process (manganese parkerizing) compare to the original black oxide finish in terms of corrosion resistance and overall durability?

I ask because, prior to this, I was soaking bolts in evaporust. Often a bolt that looked totally rusted would come out looking pretty good with a black finish. The parkerized bolts look better but it is unclear how durable the finish is.

BTW, I also bought handfuls of zinc plated nuts and washers out of the bins at the hardware store, stripped the zinc with muratic acid, nutralized the acid with baking soda and water, rinsed and dumped those in the parkerizing solution too, they look great.

[Chuck S.]

Re: DIY Parkerizing...How corrosion resistant?

...My question is how does this process (manganese parkerizing) compare to the original black oxide finish in terms of corrosion resistance and overall durability?

I ask because, prior to this, I was soaking bolts in evaporust. Often a bolt that looked totally rusted would come out looking pretty good with a black finish. The parkerized bolts look better but it is unclear how durable the finish is.

BTW, I also bought handfuls of zinc plated nuts and washers out of the bins at the hardware store, stripped the zinc with muratic acid, nutralized the acid with baking soda and water, rinsed and dumped those in the parkerizing solution too, they look great.

Manganese phosphate and black oxide finishes were both used on original chassis fasteners.

Manganese phospate is, by far, the most prevalent finish on chassis fasteners, and is always "oiled" after application. Either finish should be more "durable" than evaporust, which I suspect is nothing more than a mild acid cleaning of the fasteners...acid cleaning will enhance the speed and inevitability of corrosion. If your original fasteners are in that good condition, not refinishing may be an option.

Just in case an observer or judge actually knows the difference...I always try to refinish parts with the same finish they had originally unless there is a clear durability advantage in newer technology. However, when you chose a newer, different finish,you are accepting that it likely will be discovered by knowledgeable observers, and if the car is in judging, deductions will be made.

Edit: Be careful purchasing "hardware" store fasteners to replace original parts. Most zinc plated hardware store fasterners are likely to be made in China, and strength will not approach that of the original fasteners. Also realize there are several different strength "grades" of fasteners, and most of the stuff in hardware or home stores is low strength. In many applications, using weaker fasteners than the original Grade 5 or higher will be a recipe for disaster.

[Mike R.]

Re: DIY Parkerizing...How corrosion resistant?

Thanks Chuck. The evaporust obviously isn't any kind of coating but I like that I can often see what the original finish was after using it on a part that is totally corroded. It has allowed me to same some chrome parts that initially looked pretty bad.

Hardware store nuts and washers are fine. The female portion of a threaded joint is inherently stronger than the male portion (by a lot). The hardware store stuff is grade 5 (or 8). Automotive fasteners are not very highly loaded anyway (outside of the engine). The notion that chinese stuff is inherently bad is flawed or at least mostly outdated. A lot of raw forgings for cranks and connecting rods come from China and they aren't littering the roadways.....

Manganese phosphate and black oxide finishes were both used on original chassis fasteners.

Manganese phospate is, by far, the most prevalent finish on chassis fasteners, and is always "oiled" after application. Either finish should be more "durable" than evaporust, which I suspect is nothing more than a mild acid cleaning of the fasteners...acid cleaning will enhance the speed and inevitability of corrosion. If your original fasteners are in that good condition, not refinishing may be an option.

Just in case an observer or judge actually knows the difference...I always try to refinish parts with the same finish they had originally unless there is a clear durability advantage in newer technology. However, when you chose a newer, different finish,you are accepting that it likely will be discovered by knowledgeable observers, and if the car is in judging, deductions will be made.

Edit: Be careful purchasing "hardware" store fasteners to replace original parts. Most zinc plated hardware store fasterners are likely to be made in China, and strength will not approach that of the original fasteners. Also realize there are several different strength "grades" of fasteners, and most of the stuff in hardware or home stores is low strength. In many applications, using weaker fasteners than the original Grade 5 or higher will be a recipe for disaster.

[Michael G.]

Re: DIY Parkerizing...How corrosion resistant?

To add to Chuck's analysis:

Manganese and/or zinc phosphate coatings themselves offer almost no corrosion protection. On a car driven in rain or snow, a fastener with these coatings will have spots of rust after one or two short trips. They will even rust quickly in high humidity.

That is because these phosphate coatings act only as a substrate, used to absorb subsequent applications of oil and/or paint. Add the proper oil to the phosphate coating and their performance improves dramatically: with oil, such a coating will last about 72 hours in salt spray before rusting.

Its also important to note that some "oils" do not add to performance at all. The term "oil" covers a multitude of different hydrocarbons and the different "oils" and paints used on fasteners vary widely in their ability to act as a barrier to corrosion. By way of comparison, there are special oils that last significantly longer than 72, perhaps 240 hours. The oil is critical.

If your car is a show car, or driven minimally, not in rain or snow, a manganese phosphate coating should last a long, long time, but only if you oil it with the proper oil.

Regarding strength: Imported hardware sold in United States commerce is required by the U.S. Fastener Quality Act to be properly marked and meet the strength characteristics associated with its head marking. If you see any recently made bolt or machine screw (imported or not) with no strength markings, and/or no manufacturer's mark, don't use it, otherwise you're probably safe.

[John M.]

Re: DIY Parkerizing...How corrosion resistant?

Mike,
Can you expand on the "proper" oil? What should be used?
Thanks,
John McRae 30025

[Michael G.]

Re: DIY Parkerizing...How corrosion resistant?

Sorry, John, I don't know a brand name or source. If you are doing the phosphate yourself, I'd suggest that any competent plater would sell you a small amount of the normal oil they use.

[John M.]

Re: DIY Parkerizing...How corrosion resistant?

Ok Mike Thanks. I will try with the plater that we use at work. He's done some "special" plating for me that turned out pretty good.
John

[Alan S.]

Re: DIY Parkerizing...How corrosion resistant?

Hi Mike,
I've had good results using 'Prelube 6' on my phosphate coated pieces. It's described as a polymer spray that coats the part, but can hardly be seen at all. I buy it from Quanta, the fuel tank people.
Regards,
Alan

I retrieved this picture from an earlier post.

[Chuck S.]

Re: DIY Parkerizing...How corrosion resistant?

...The notion that chinese stuff is inherently bad is flawed or at least mostly outdated. A lot of raw forgings for cranks and connecting rods come from China and they aren't littering the roadways.....

I'll remember that the next time I strip a Chinese nut thread with unexceptional torque. It took a few minutes and trying a different screw before I finally convinced myself that it was the nut thread that was stripped. Incredible...I had never seen that happen before.

Caveat emptor. They can't, or won't, get lead out of kids' toys in spite of the high stakes...and that issue gets a lot more attention than industrial fasteners.

[Michael G.]

Re: DIY Parkerizing...How corrosion resistant?

Chuck,

Low-strength imported fasteners used to be a problem, but that was twenty years ago and the bad parts were coming mostly from Japan.

I'm not a necessarily defending the Chinese, but their nuts (and those made everywhere else) strip for a multitude of reasons. The most unlikely of those reasons is poor internal thread strength due to substandard material or heat treat.

Poor tapping, under-filled threads, and scrap in threads are all much more common causes of thread stripping failures. Those failures are just as common in U.S. made parts as in those imported from China.

I agree though, though, let the buyer beware: Its probably a poor idea to ever use a "hardware store" part in your car; virtually all Corvette fasteners are commercially available from reputable sources, so buy the specified part from someone you trust.