On one of my ships I was doing my night turn from 23.00 hrs to 07.00 hrs.
I was supposed to check the sump oil level of the Running / Standby generators. So I started the stand by generator and took it on load and stopped the running generator.
After checking the oil level I turned the flywheel of the generator by hand cranking and found it hard to turn. I informed the Chief Engineer about this but he but he started the generator on air. After 5 minutes there was white smoke coming from the crankcase, followed by an explosion.
On opening the crankcase we found the connecting end of no 3 unit fully twisted and water was leaking on the piston head of the unit from the exhaust manifold cooling pipe.
Due to water accumulation the connecting rod got bent and led to the crankcase explosion.