AUXILIARY ENGINE BREAKDOWN DUE TO FAILURE OF CONNECTING ROD BOTTOM END BOLTS :
The incident occurred in a bulk carrier. The vessel had 3 nos auxiliary engines, of DAIHSTSU make. AE1 was decarbonised and after decarbonisation, regular checks like no load running, ½ load running were carried out. Found all parameters normal.
The AE1 was taken in parallel with the running alternator and the load on the busbar increased. Constant watch was requested on AE1, and 2/E left for lunch. 15’ after he left the engine room there was a big sound, and power started fluctuating and the non essential loads tripped off. There was no blackout. After hearing the noise and having felt a heavy vibration, 2/E and C/E both rushed down to E/R. They found the AE platform full of oil spray and smoke. Since there was no blackout, and the power was available, they analysed the situation and found unit 3 connecting rod of AE1 had come out, rupturing the crank case door. Unit 1 crank case door was also found ruptured, but connecting rod was in place but connecting rod got bent and one bolt found missing. Watch keepers were not near the AE1 though they were instructed to keep proper watch on AE1.
On investigation and enquiring the people involved in the o’hauling, it was found that though they followed the tightening instructions as per the manual, certain other things have been neglected.
1.cleaning of serrations were not taken care of properly. It is advised that the cleaning is important to ensure that the both the halves mate and bed properly to carry the load.
2.the elongation of bolt was not checked before refitting, though it had been mentioned in the manual. It is not the tightening torque, that alone matters. Though the manufacturer recommends the renewal after certain running hours, it is better that at each o’haul, the elongation is checked with the gauges provided or compare with the new one.