I am still uncertain whether to use zinc or aluminum anti-seize. Aluminum alloys appear all down the anodic series. I have an assumed aluminum mount and tranny (unknown specific alloy) with grade 10.9 bolts (unknown plating). The previous bolts were yellow something plated (Cadmium or Zinc…?), and had good amounts of red rust… so I think anti-seize is at least called for even though I never read about it with this Porsche 944, though I have read about this part seizing up on people.
here’s a bigger question - is there any grease that lacks a dielectric component? such that a grease would prohibit dielectric contact between metals. Dielectric grease I assume has dielectric in the medium, to allow charge transfer - but I think the grease component must exclude water - that’s how I explain dielectric grease keeping battery terminals healthy.
No grease will prevent the metal-to-metal contact in a tight connection. Anti-seize contains powdered metal to inhibit corrosion. The type I use has nickel in it.
I’ve been using that red stuff as a thread lock. I’m getting older and I think the skin on the back of my hands is getting thinner. That blood will dry and lock that screw in place.
And i’m wondering about @JuniorMint’ I’ve heard that Zink Oxide is good for diaper rash.
If you’ve ever used the stuff it doesn’t wash off very easy. I heard that a couple had a new baby. The father got up one morning and didn’t want to turn on the bathroom light because it might wake the baby. In the dark he washed up and brushed his teeth. The problem was the grabbed the tube of Zink Oxide instead.
Dielectric grease is measured in volts per unit thickness. The thicker the grease, the higher the voltage it will withstand before allowing arcing. Even before arcing occurs, there can be some current migration through the grease as measured in micro amps or pico amps. There is no such thing as a pure dielectric.
When you clamp two conductors together that are coated in dielectric grease, the grease gets so thin that it will conduct current between them. I generally like to keep my contacts dry but there are some cases, like spark plug boots that I will grease up to prevent arcing outside the boot.
As far a spark plug threads are concerned, they sell tubes of anti-seize specifically for spark plugs in aluminum heads. If you are using unplated plugs or reusing plated plugs, just use what is specifically made for that purpose and not sweat the alternatives. Its proven to work. If it ain’t broke…
thanks for this helpful discussion - here’s possibly a discussion-changing comment:
I started this discussion because I broke a bolt - maybe yellow zinc or cadmium plated - off inside an aluminum component (among other things). misery ensued. On assembly, the bolt of course must be torqued to spec in the service manual, however, that is a dry torque spec.
… how much are dry torque specs increased when adding things like anti-seize? I have never seen a clear cut description of this, so I figure it is complicated.
It kind of depends on the purpose of the torque spec. If the torque spec is to apply a certain clamping force, such as a head gasket, you would use less torque, not sure how much though. If the torque spec is to insure a holding force so the bolt or nut does not back off, then it may require a little more torque, again, nit sure how much.
The short answer is, if calls for a dry torque, then use a new plated nut or bolt as specified and follow the instructions.
The “Handyman in Your Pocket” reference book by Richard Young and Thomas Glover, sold at your local ACE Hardware, has an excellent 2-page table with torque correction factors for all kinds of anti-seize compounds, lubricants, platings, etc. You just find the particular compound in the table, take the associated correction factor, and multiply it times the specified dry torque number.
Some examples:
Cadmium plating: multiply dry torque by 0.80
Zinc anti-seize: multiply by 0.75
Moly grease: multiply by 0.70
Graphite-50 anti-seize: multiply by 0.50
No guessing required. And lubed torque spec will always be lower than dry torque spec, because the lube reduces the amount of torque required to produce a given clamping force/bolt stress.
Well, Copper-Coat has been around for decades and used without issues on head gaskets affixed to aluminum heads and blocks so I would think that copper is not so bad on aluminum.
Same goes for copper head gaskets. The old Harley flatheads used copper head gaskets on aluminum heads without any issues. The heads on one of my old HDs are 70 years old and there’s no hint of a problem yet…
Old Triumph motorcycles also used copper head gaskets and there are even copper head gaskets manufactured for V-8 automobile engines.
