Connecting rod bolt inspection

1) Product appearance inspection

Check whether there are any visible defects on the surface of the bolt, and no defects such as bruising, fraying, deformation, cracking, thread damage, and loose fit are not allowed.

2) Crack inspection

Use methods such as magnifying glass, tinting flaw detection or magnetic particle flaw detection to check the fillets of the bolts and the transition between threads for cracks.

3) Measure the length of the bolt (Guide: Analysis of the quality of the screw and its cause analysis)

Measure the length of the bolt to find the permanent deformation of the bolt. When the extension of the connecting rod bolt of a four-stroke diesel engine exceeds 2% of the original design length, it shall be scrapped and replaced.

The extension or necking of the bolt is mostly caused by excessive force during installation, or the result of excessive tensile stress on the connecting rod bolt due to the cylinder pulling or biting of the diesel engine. When installing the bolts, it was wrongly believed that the bolts should be tightened as tightly as possible, so that the nuts were tightened too much, causing the bolts to deform or break. For example, the 6135 diesel engine requires a torque of 180-200Nm for tightening the connecting rod bolts. If the bolts are tightened to 400Nm, the bolts will elongate or shrink; if the bolts reach 450Nm, the bolts will break.

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