One day morning we were working  in auxiliary engine compartment.  The  ship was UMS class, product carrier.  The  engine was Daihatsu. That generator was O/Hauled (Major decarb) and already around 500 running hours completed.  All of a sudden we heard  a major sound is coming from one unit. Immediately started stby generator and stopped running generator. We suspected the problem in the cylinder head. We removed head, found that hole in that piston. 

Piston was replaced from spares.

Reason :  Intake V/V seat had come out of place and V/V spindle got stuck in open position and hit the piston and made a hole.                                                                                                                                                                                                                                                                                                                                                                                              G.PRATHAP KISHOR KUMAR                                                                                                                                                                                                       Batch - 45