I. Tightening Method (Most Commonly Used): Apply force smoothly with a torque wrench. Record the torque value when the nut begins to move slightly. Note:
Apply force with the wrench at a uniform speed to avoid impact.
The operator must be experienced and able to accurately judge the moment of fine movement.
Suitable for most scenarios, but may require secondary tightening.
II. Marking Method (Preferred for High Precision)
Mark the bolt and connector with lines.
Retighten to the original position after loosening.
Actual torque = reading × 0.9 - 1.1
Small error, suitable for precision equipment. Recommended by Volkswagen and other standards.
III. Loosening Method (Special Scenarios)
Slowly loosen the nut and record the initial torque value.
Suitable for high temperature and high pressure systems. Requires experience to judge the moment of loosening.
IV. Key Precautions
Tool Calibration: Torque wrenches must be calibrated regularly.
Standard Basis: Determine torque values according to GB/T 38343-2019.
Operating Procedures: Digital torque wrenches are recommended for high temperature and high pressure systems.
V. Common Problems
Insufficient Torque: Flange clearance exceeds limits (e.g., aluminum gasket ≤ 0.3mm)
Excessive Torque: Bolt exposed length less than 1-3 thread pitches
Abnormal Data: Compare dynamic torque and static torque.
