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What are signs of main or crank bearing failure? Which corrective actions to be carried out?

17 Aug '17, 06:25

Aug. 17, 2017, 6:25 a.m.
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If main or crank bearing failed its temperature will rise accompanied by a deaf, growing or sharp metallic knock. Modern engines have advanced condition monitoring systems where bearings temperatures are indicated and logged. Attention must be paid and normal operational temperatures kept in mind for early discovery of any abnormalities. In the case of older engines or absence/failure of engine monitoring system bearing failure could be judged by increased temperature of crankcase hatches or doors opposite the crank bearing. The other sign of bearing failure is an activation of the oil mist detector. Every alarm/activation of oil mist detector must be thoroughly investigated as high oil mist content in the crankcase is extremely dangerous.

1. Reduce the load (speed) of the engine and record the time. Report to the bridge and Chief Engineer.
2. If after a decrease in speed, the knock does not stop, stop the engine to inspect the bearings. If it is not possible to stop, cut off the injection pump of the subject cylinder.
3. After stopping the engine, close the starting air, open the indicator valves, insert a shaft turn and rotate the engine while simultaneously pumping the lubricators.
4. After 15 to 20 minutes after stopping the engine, open the doors in the crankcase of the desired compartment and check the temperature of the bearings, pay attention to the oil drain from them and check the oil gaps.
5. If it is possible, replace the defective bearing with a spare one. Investigate the cause of the bearing failure.
6. If there is no possibility or time for repair, prepare the engine for operation with the cylinder cut-off:
a) disconnect the fuel pump (lift the pusher over the fuel cam) of the subject cylinder; b) stop the oil pumps, and the piston together with the crosshead, hang it on the special tool;
c) disassemble the bearings and dismantle the connecting rod;
d) disconnect and shut off the control air line to the subject cylinder start valve;
e) remove and plug the supply line of the starting air to the cover of the failed cylinder;
f) set the cylinder oil supply to the minimum for the subject cylinder;
g) disconnect the lubricant supply to the connecting rod bearings (put the plug).
7. Close the crankcase and start the oil pumps (check the tightness of the plugs first).
8. Prepare the engine for start-up and put it into operation.
NOTE: If the engine can not be started in the desired direction, rotate it in the air in the opposite direction, and then start it on the fuel in the desired direction of rotation. Warn the bridge about the possibility of poor maneuvering.
9. Increase the monitoring of the engine, engine operation with a normal number of revolutions is not allowed. In the event of an increase in exhaust gas temperatures and surging of the GTN, the load must be reduced. Observe the color of the exhaust gases.
10. Due to the violation of the equilibrium of the engine in certain ranges of revolutions, significant fluctuations (vibrations) may occur. The critical speed range will be new etc. If these fluctuations become excessive, the engine speed should be reduced. In such cases, as far as possible, avoid prolonged engine operation.

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17 Aug '17, 09:18

Aug. 17, 2017, 9:18 a.m.
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