GENERAL INTRODUCTION
1–19
TIGHTENING OF BOLTS AND NUTS
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BOLTS AND NUTS
More than hundreds of bolts/nuts are used in a vehicle and improper handling of them will cause damage and looseness.
Because tightening torque varies depending on tightening condition, strength class, and surface treatment, etc., make sure
to check the types and tightening torques of bolts/nuts and use them properly.
PURPOSES OF TIGHTENING TORQUE
Predefined tightening torque must be applied to ensure sufficient tightening by threads.
It also has purposes to prevent the adverse events below due to excessive or insufficient tightening.
NOTICE
Unique tightening torque may be specified for some parts.
Tighten with the tightening torque specified in the service manual.
HINT
Check the tightening torque list for general torques.
CAUTIONS TO PREVENT LOOSENESS.
When tightening, pay attention to the followings to prevent looseness after tightening.
•
Insufficient tightening torque
•
Inclusion of foreign matters (burrs and coatings) in the tightening surface.
•
Sagging of coat
•
Sinking into the seat surface hole by omitting attaching a plain washer.
•
Defective seat surface flatness (wear-out during use)
Conditions
Adverse events
Excessive tightening
•
Stretch or fracture of bolt
•
Depression of seat surface and looseness
•
Gasket damage
•
Rounding and damage of hexagon part
•
Opening of spring washer
Insufficient tightening
•
Looseness
•
Gas and liquid Leakages
•
Continuity failure
•
Damage by fretting wear
