Torque Wrenches - GMC Chevrolet Camaro 1998 Service Manual

0-18 General Information
Torque Wrenches
Torque Defined
Torque is defined as the measurement of resistance
to turning or rotating. Torque, often called torsional
or twisting movement, tends to twist a body about an
axis of rotation. A typical application is the tightening
of a screw.
Torque applied in tightening a common bolt, nut, or
screw is expended in three areas:
• The head
• Bearing surface
• Clamp load
Clamp Load
About 50 percent of applied torque is used in
overcoming bearing friction. This is the friction between
the bearing surface of the bolt head, screw head or
nut face, and the base material or washer (the surface
the fastener is rotating on). Approximately 40 percent
of the applied torque is used in overcoming thread
friction. This leaves only about 10 percent of the
applied torque to develop useful clamp load. Clamp
load is the force that holds a joint together. Friction can
account for as much as 90 percent of the applied
torque on a fastener.
Torque Techniques
The frictional characteristics of each fastener or
threaded hole can vary under a variety of
circumstances. For example, consider a joint that has
10 bolts. If all 1 O fasteners were torqued to 20 N-m
and the clamp load is measured, all 1 O bolts
would most likely have different clamp load readings.
Even though all 1 O bolts are torqued at 20 N-m, it
is not guaranteed that they have all reached the same
clamp load. A rule of thumb is that the clamp load
can vary
±
25 percent using torque control for
joint assembly.
At times, critical applications such as cylinder head
bolts require very tight tolerances for clamp load
distribution. If torque is not considered to be accurate
enough for these critical joints, an alternative
method of tightening called TORQUE ANGLE may
be used.
General Information
Torque Angle Method
65532
Torque angle is required for critical joints because it
can help eliminate frictional variations in the joint. The
following are the general steps used for the torque
angle method:
1. Tighten to a predetermined seating torque to
remove any compliance out of the joint.
2. Turn the fastener to a specified angle of rotation.
Use the Torque Angle Meter J 36660.
This is the only acceptable general method for
measuring this angle of rotation. Follow the specific
procedure where it is provided.
Torque Wrenches and Techniques
The term TORQUE WRENCH is commonly used to
describe a type of measuring tool. The tool is set
or calibrated in such a way as to make possible the
measurements of the resistance to turning (torque).
The torque wrench measures this resistance to turning
and, therefore, is the method used to obtain objective
tightening data used in the assembly of fasteners.
A torque wrench is a gage tool that can be compared
with micrometers, dial indicators, vernier calipers,
levels, and other measuring devices.
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