Maintenance of Diesel Engine Connecting Rod Bolts

The connecting rod bolt of a diesel engine is an important bolt that connects the large end bearing seat of the connecting rod to the bearing cover, making it an integral part. The connecting rod bolts are subjected to the pre tightening force during assembly, and the connecting rod bolts are also subjected to the reciprocating inertia force during the operation of a four stroke diesel engine. The diameter of the connecting rod bolt is smaller because it is limited by the diameter of the crank pin and the outer dimensions of the connecting rod big end.

Connecting rod bolts, although small, are particularly important because if they break, they can lead to destructive accidents in diesel generators. In severe cases, they can cause damage to the cylinder head, cylinder liner, piston, connecting rod, and even damage the engine body. Therefore, connecting rod bolts must not be taken lightly. The detachment of connecting rod bolts due to the failure of locking parts will also cause serious accidents. The common forms of damage to connecting rod bolts include thread deformation and damage, bolt elongation or necking, bolt bending deformation and cracks, and loose fit between bolts and nuts. After the connecting rod bolts or butterfly nuts are damaged, they should be replaced in pairs. The inspection requirements for connecting rod bolts are as follows:

1. Appearance inspection: Check for visible defects on the surface of bolts, and no defects such as scratches, burrs, deformation, cracks, thread damage, or loose fit are allowed.

2. Crack inspection: Use methods such as magnifying glass, dye penetrant inspection, or magnetic particle inspection to check for cracks at the transitions between the corners and threads of bolts.

3. Bolt tensile inspection: Measure the length of the bolt to discover permanent deformation of the bolt. When the elongation of the connecting rod bolt of a four stroke diesel engine exceeds 2% of the original design length, it should be scrapped and replaced with a new one.

The elongation or necking of bolts is mostly caused by excessive force during installation, or by excessive tensile stress on the connecting rod bolts when the diesel generator pulls or bites the cylinder. When installing bolts, if you mistakenly believe that the tighter the bolt, the better, resulting in excessive tightening of the nut, it can cause deformation or fracture of the bolt. For example, the 6135 diesel engine requires a torque of 180-200N · m to tighten the connecting rod bolts. If it is tightened to 400N · m, the bolts will elongate or necking will occur; If it reaches 450N · m, the bolt will break.

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