BOTTOM END BOLT FAILURE


Occurrence :

Daihatsu cylinder generator engine big end bearing bolts fractured & sheared off causing irreparable damage to hearings, connecting, rods, and pistons to crankshaft.

In 1982 the vessel was sailing enroute Kharg Island to Japan when at around 1140 AM prior taking over watch the 3rd Engineer heard some unusual sound from the generator platform. Rushing over to the site the observed that one crankcase door of the generator engine was blown out and there was the big end bottom half thrown on the floor plate. The 4th Engineer was busy writing the log book in the control room, and quite unaware of what happened since there was no alarm or indication of any kind. The generator was still running.

Taking the chances, the fuel lever of the damaged generator was shut off to stop the generator, immediately without taking off load etc. The standby generator started after a partial black out & slowdown of main engine etc till all normal running conditions of other machinery was obtained. Bridge was informed of the situation other engineers and crew were all in the E/Room

.Investigation was started on the shut down damaged generator which revealed the following.

1)The piston, connecting rod of the damaged cylinder was stuck up in the liner & part of the liner was smashed.

2)Big end bearing cap and hearing shells, bolts completely damaged.

3)Crankpins were scoured and damaged.

4)One big end bearing bolt nuts found loose & hanging also damaged completely. In all, the generator was a total write off & had to be replaced completely with a new one, which was done in Japan within a couple of months of the tragedy.

Conclusion:

It was informed by Daihatsu that the same occurred on a few more of their generators during that period, it was attributed to a wrong design and the material of big end bearing bolts, which was the cause. Daihatsu informed the companies having their generators, to change over to the new designed carbon steel bolts which were supplied free of cost, and to strictly follow the new tightening torque values in 3 stages and markings to be made on the bolt with a set maximum tightening angle, for the max torque value. Tightened by only one person using the torque wrench and fabricated template with marked angle.

It was very fortunate that there was no other accident or damage to any of the engine room personal and other nearby machinery with respect to this explosion since this was a very serious damage to machinery.