How to inspect bottom end bearing?

17 Sep '17, 18:25

Sept. 17, 2017, 6:25 p.m.
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Before inspection could be conducted safety precautions to be followed:

  • Engine shut down and secured.
  • Turning gear engaged, indicator cocks open. 

  • Carry out a risk assessment. 

  • Check all lifting gear and tools within certification & free from defects. 

  • Obtain Enclosed Space Permit to work (crankcase is an enclosed space). 

  • Obtain the clearance to turn engine from the bridge. 

  • Check that no other jobs carried out elsewhere on the engine or on the shaft. 

Bottom end bearing inspection procedure

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  • Turn engine to TDC.

  • Mount a chain block either side of the crankcase.
  • Screw eye bolts into threaded holes on either side of lower bearing half.
  • Attach chain blocks, wire strops, and take up the slack.
  • Remove locking plates and slacken bearing stud nuts using hydraulic jacks.
  • Remove jacks and nuts.
  • Using chain blocks lower the bearing cover, taking care not to damage the threads of the studs or the crankpin journal.
  • Remove the bearing cover from the crankcase.
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  • Turn the engine while pulling the lower part of the connecting rod with the lifting tackle so that the crankpin turns out of the top half of the bearing. Take care that the crankpin does not foul on the top edge of the bearing.
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  • Fit four guide shoe retaining blocks into the crosshead guides. This will prevent the crosshead and connecting rod from moving down the engine when it is turned.
  • Wrap a strop around the bottom of the con rod and attach to a chain block mounted on the side of the engine.  - The crankshaft can be turned to Bottom Dead Center and the top half of the bearing examined or removed.
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When inspecting

  • Check the pin for ovality. It caused by the varying downward load on the con rod in both the power and compression stroke. If the ovality is more than 25% of the bearing clearance then there is a danger of the hydrodynamic lubrication being affected.
  • Check the top bearing shell for evidence of the bearing material separating from the steel shell backing. This is caused by the high-pressure oil supply from the crosshead acting on the back of the shell and deforming it. Shows by cracking of the white metal.

Before returning the engine to service check:

  • Oil flow through bearings: start the pump and ensure oil is reaching the bottom end and flowing out of bearing sides.

  • Engine turns through at least one revolution with turning gear whilst observing ammeter for signs of excessive current.
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17 Sep '17, 18:42

Sept. 17, 2017, 6:42 p.m.
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