Piper Navajo PA-31 Service Manual page 37

2-7. TORQUE REQUIREMENTS. The torque values given in Table II-II are derived from oil-free cadmium
- plated threads and are recommended for all airframe installation procedures where torqueing is required,
unless otherwise noted in sections where other values are stipulated. Engine torque values are found in the
latest revision of Avco Lycommg Service Bulletin No. 268, and propeller torque values are found in Section
VIII of this manual.
2-7a. TORQUE WRENCHES. Torque wrenches should be checked daily and calibrated by means of
weights and a measured lever arm to make sure that inaccuracies are not present. Checking one torque
wrench against another is not sufficient and is not recommended. Some wrenches are quite sensitive as to the
way they are supported during a tightening operation. Any instructions furnished by the manufacturer must
be followed explicitly.
When it is necessary to use a special extension or adapter wrench together with a torque wrench, a simple
mathematical equation must be worked out to arrive at the correct torque reading. Following is the formula
to be used: (Refer to Figure 2-5a.)
T =Torque desired at the part.
A = Basic lever length from center of wrench shank to center of handle (stamped on wrench or listed for
that model wrench).
B = Length of adapter extension, center of bolt to center of shank.
C = Scale reading needed to obtain desired torque (T).
AxT
The formula:
EXAMPLE
A bolt requires 30 foot-pounds and a 3 inch adapter(one-quarter of
a foot or .25) is needed to get at it. You want to know what scale
reading it will take on a one-foot lever arm wrench to obtain the 30
foot-pounds at the bolt.
Remember, the 3 inch adapter must be projecting 3 inches straight
along the wrench axis. In general, avoid all complex assemblages or
adapters and extensions of flex joints.
T
Figure 2-5a. Torque Wrench Formula
Revised: 9/23/80
HANDLING AND SERVICING
1B13
PIPER NAVAJO SERVICE MANUAL