NGK and the "Anti Anti-Seize Letter" October 15, 2012
I was recently browsing eBay and stumbled across a listing for
a
Mazda B2000 Cylinder Head. As I scanned the listing, the seller revealed
that the head still had a broken spark plug in it. He even
had some pictures of it. “I wonder how that happened?” I
thought to myself. “Over-torqued it? Didn’t use anti-seize
compound? Or maybe he did when he shouldn't have!” It reminded me of a technical
bulletin that NGK put out several years ago recommending
against using anti-seize compound on
most plugs.
Who’d of thought that using anti-seize could result in,
well, a seized spark plug? Seemed pretty counter intuitive
at first glance. It reminded me of comedian Tim Allen, who
told about the time his wife yelling at him for putting dirty
dishes in the dishwasher. Apparently, as she explained to him,
“you have to wash them first ,“ before you put them
in the dishwasher!
As it turns out, NGK went on to explain that all of their
spark plugs are manufactured with a shiny special “trivalent
zinc-chromate shell plating” that is designed to prevent
corrosion and seizure to the cylinder head. The shell
plating acts as a “lubricant” that helps the plug release
from the cylinder head during removal. In fact, on aluminum
heads, they recommend only using plugs with the
special plating to act as a safeguard against damage to the
head and plug.
But a little anti-seize couldn’t hurt, could it? Well,
the problem it seems, is that using anti-seize on plugs with
the shiny metal plating can cause the installer to
inadvertently over-torque the plugs, by as much as 20%.
“Over-torque stretches the
metal between the last thread and the seal between
the cylinder head and the spark plug, causing a much
higher probability that the spark plug will break
during installation or removal.”
Ever since reading this bulletin, I have avoided using
anti-seize on NGK spark plugs. Although I've never had any
trouble using anti-seize in the years prior, I figured I
might as well follow the experts advice. Here are a
few more tips I picked up over the years:
Always use your vehicles manufacturer's
recommended plug specifications
Installing a spark plug that protrudes longer the
recommend could result in interference with the cylinder
- causing significant damage. Using a hotter than
recommended plug could result in pre-ignition, reduced
performance, and damage to the plugs and engine.
Using a colder than recommended plug will likely result
in increased plug fouling. If you have modified
your engine to increase performance, you might benefit
from using a colder plug.
Always remove and replace spark plugs in a
cold engine
Since aluminum cylinder heads expand when heated, they
can increase their grip on spark plugs and increase the
chance of breaking one during removal. Installing
a spark plug in a hot engine will not yield the proper
torque values.
Always Torque to your manufacturer's
specifications
An under torqued spark plug may rattle loose and leak.
It may also fail to adequately dissipate heat to the
cylinder head; resulting in a hotter spark plug and
possibly causing pre-ignition. An over-torqued
spark may seize, cause thread damage to the cylinder
head or plug, or cause internal damage to the spark
plug.
