What could be the cause of diesel generator stopped suddenly?

The diesel generator engine may suddenly stop because of following:

1) Protective device activated

a) Overspeed
b) Lub oil pressure low. Check LO pump functioning and LO filters condition. Check for leakages.
c) An excessive temperature rise of cooling water. Check that sufficient coolant in the system. Check thermostatic valves functioning.

Check sensors for correct functioning, no medium by-passes the sensor, repair or replace defective parts

2) Governor or governor gear failure

Inspect the governor and its drive

3) Fuel control linkage seized or damaged

In this case, engine can not react properly to load changes and may suddenly stop or overspeed (and be stopped by protection)

3)Fuel oil pressure insufficient.

FO filters clogged, the fuel tank is empty or fuel pump defective.

4)Air in the fuel system.

Bleed the air/prime engine fuel system before restarting

5)Seizure of

a)piston
b)main bearing
c)crank-pin bearing
d)timing gear
Try to turn engine by turning gear to confirm seizure and investigate exact defective part