the service
Lubricating O-rings
Pure silicone oil used as an O-ring lubricant allows
for better installation and protects the gaskets from
damage.
Having wrongly thought that O-rings were simple
things, no longer will I squirt just any old spray
oil onto any rubber-like gaskets, seals, O-rings, or
the adjoining metal or plastic parts. What follows
are some basic terms and concepts worthy of
inclusion in the technician’s knowledge base.
The term “rubber” was first used in the mid-
1700s, when Europeans observed that dried sap
from a South American tree could be rubbed
across pencil marks to erase them. Working
with petroleum, chemists developed synthetic
versions of the sap. Today, “natural rubber”
comes from trees or oil wells and is called latex
or isoprene. It is used for pencil erasers, car tires
and many other things. More oil-based synthetic
rubbers were developed, and others were
created from rock-like minerals. These are called
fluorocarbons (Teflon) and silicone.
damage or distortion. Ditto for putting a dry
O-ring into the groove cut in a machine part.
(That groove is called a “gland” in many service
manuals.) The lube lets rings slide into place.
Because it doesn’t dry over the long haul, it
helps gaskets flex when heat changes and when
vibration causes movement in places where
a rubber gasket acts as a seal between metal
or plastic parts. The pure silicone oil reduces
galling and improves accuracy when fasteners
are tightened to a specific torque into plastic or
metal components.
Chemically, pure silicone oil is almost completely
inert and neutral — it won’t cause deterioration,
swelling or shrinkage of virtually any synthetic
or natural materials. It retains lubricity over
a wide range of temperatures and stays put
under pressure. There is a small chance silicone
oil might partially dissolve a gasket made of
pure silicone, but such gaskets are used mostly
in food processing equipment and rarely in
systems found on engine-powered machines.
From golf carts to UTVs and ATVs, a few dozen
synthetics are currently used, but there’s no
color code or other system to tell them apart.
You’re gambling when replacing an old black
O-ring with a new black one. When working with
a critical pressurized system, such as hydraulics
and fuel and coolant systems, it’s safest to
use parts from the OEM (original equipment
manufacturer) or a name-brand gasket kit. It’s the chemical issue that should limit use of
spray or liquid lubricants on anything other
than purely metallic components, such as
chains. Petroleum-based chemicals pose a
challenge because they can deteriorate oil-
based synthetics. Many lubricants labeled
as silicone contain 5 percent or less of the
polydimethylsiloxane or polymerized siloxane
chemical. The rest of the product is a liquid
carrier. If the package says the stuff leaves a dry
lubricant film, it’s not the pure oil.
Pure silicone oil helps resolve many of the
unknowns in the rubbery domains. It helps
prevent mishandling of O-rings or other gaskets,
and helps avoid their failure. Rolling an O-ring
down a shaft or across screw threads can cause You probably won’t find pure silicone oil in
a hardware store. Look for it online. It may
be carried by gun shops, as it’s the required
lubricant in certain firearms and air-powered
pistols.
FEBRUARY 2020
& repair hub
47