Zinc Pest

[SGKent]

I was reading in a forum on something and people were having problems with "Zinc Pest." I thought maybe it was something like rough owners with things but in googling it, it is a real problem with things made with high concentrations of zinc but less than 100% pure. The zinc crystalizes and basically falls apart of its own weight. Are there any things made on bays that have high concentrations of zinc other than a protective coating? I have read that German Solex carbs had a high aluminum content and that is why they hold up better than many of the off brand carbs.
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[busdaddy]

I've seen some seriously rotten VW's and none have any parts that crumble like on 50's USA cars, or even worse 30's English cars. It's pot metal gone bad in a severe way, it destroys itself from the inside out it seems.
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[SGKent]

[Wildthings]

Pot metal certainly didn't have a very good reputation way back when.

Injection molded plastics and die cast aluminium have been steps up.

[Abscate]

Every cheap metal part you buy from a China is poorly spec pot metal, essentially, to 99 44/100% accuracy.

That’s why you can get that $10 lawn mower carb , with free shipping. It’s made from old 23 window splits , zinc, lead, and Frosted Flakes

Zinc copper magnesium lead iron aluminum . It’s just a big metal party.

The white crud you get on pot metal parts is zinc oxide but it not the dreaded zinc pest , it does not mean your carb will crumble.
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[RWK]

Zinc is also injection molded, I have built several molds for various products, not sure where the term pot metal comes from, ingots of zinc are put into a large
"pot" where they melt and are shot in to mold like plastic, Zamak was the material I built molds for from what I remember, been 15 years ago.
Company I built molds for did alot of small engine carbs also.
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[Bonesberg55]

According to what I read, pot metal & white metal are apparently the same. It is aluminum based or low-temperature based zinc and may have some copper, tin, or magnesium. Carburetor bodies were typically made from white metal all the way thru the early 80s. I never saw one that disintegrated.

[Abscate]

It literally gets its name from throwing all the crap on the floor Into a pot with a lot of zinc, which melts at low temp.

Early 20th century is was a higher quality controlled product for better castings and prototyping.

Modern pot metal has its place but it’s a real mishmash
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[raygreenwood]

As mentioned....the metal that was developed to be "free", of this issue was trade named zamack. It's 99% pure zinc.

It's the addition of lead in cheaper alloys. The lead was used in complex castings because it greatly lowers the melting point and is more ductile.

The problem is that the lead does not alloy or blend perfectly well and shrinks at a different rate. This is not a huge issue depending on the percentage of lead and its purity. Lead and since are generally a good mix and had been used as structural solder for pipes for a long time.

The shrinkage is at a microscopic level. It admits oxygen....which contains moisture. This is where the problem really lies.

Zinc is VERY electrolytically active. It's whole purpose is to oxidize into white rust as is a sacrificial anode. Lead is very a very poor electrolytic and actually a poor conductor. This is why it's very hard to plate lead....well. it's surface is not able to be electrolytically activated easily by acids.

This same combination is happening inside of the lead zinc alloy so over time, the zinc corrodes away from the lead. The fissures and pores get bigger and it just crumbles.

Ray

[Kirk]

[ToolBox]

[SGKent]

[ToolBox]

[wildDogPizza]

I believe bus door handles and deck lid releases are plated pot metal. Also side mirror arms and mount pieces I believe are. Windshield wiper squirters nubs may be also, but I'm not sure about that. Mine all have some degree of pitting, but not too bad.
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[alaskadan]

Hey man why do you have an old Lionel train screwed to your boat?! Well it's kind of a long story....

[rsbadura]

Zinc Pest was an issue in Germany in 1939 - because of WWII material shortages...
(and much later around 2010 to some companies as Märklin toy company while some cost-cutting production moved to China).
In the 50s this was not anymore an issue and so not an issue to air cooled VWs.

The zinc alloy die casting parts need to have contact to humidity for zinc pest -
a lot of these parts at VWs are also protected by chrome.
Others are not made of zinc - made of aluminum etc.
So I'm not very concerned about that...

Well, but nothing lasts forever...
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[raygreenwood]