MAIN ENGINE EXHAUST VALVE FAILURE
1st Jun. 06
Departure port main engine no. 4 unit was found not firing.
Fuel injectors had been changed in that port during cargo discharge.
Exhaust temperature indicated 400C. Suspecting an air lock, injectors were primed immediately. Observed no change in exhaust temperature.
Vessel was in a narrow channel and Pilot aboard.
Fuel pump was cut out during running. During pilotage compression pressure was checked; found zero.
After completion of pilotage, vessel was anchored, exhaust valve changed. Old valve dismantled; found closing cylinder was filled completely with carbon deposit. This had prevented valve from closing.
Two faults were observed. Exhaust valve spindle bush has a seat for seal ring; this seat was corroded and damaged over 10 years of running period, and exhaust gas closing air was leaking through this seal even though seal was new.
Important point to learn from this incident is
1. During overhauling of exhaust valve bush seal ring seats need to be inspected.
2. Closing air cylinder should be checked for carbon deposit.
3. Exhaust valve air (supply) drain to be regularly checked.