Diesel Generators - General Overhauling

Technical Management
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Let’s say that your diesel generator is approaching maker’s limits and is due for a general overhaul.

What would be your advice to the Chief Engineer in regards to main areas of concern during overhauling and in order D/G to be brought back to service safely?

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Statistics and experience have shown that the majority of severe damages of Diesel Generators occur a few hours after completion of the general overhauling.
Most of these damages are related to failure of connecting rods or connecting rod bolts leading to subsequent failures of the crankshaft, cylinder units and engine block.
The outcomes of such damages are: Diesel Generator out of operation for a significant period of time, reduced safety, commercial damage, expensive repairs (ranging 300-500k), potential injury of the crew by debris.
In other words, the ship management company invests 25-30k for a planned overhauling and may end up with a 500k damage and an unsafe vessel!

Here are some recommendations in order to avoid Diesel Generator damages due to failure of connecting rods:

  • First of all, confirmation of the good condition of the special tools such as hydraulic jacks, hydraulic pump, connectors, supports, extension screws, lifting devices, guide supports, honing tool, inside/outside micrometer, before overhauling.
  • Careful inspection and dye penetrant testing on the serrations of the connecting rod big ends (where applicable)
  • Correct connecting rod big end ovality measurements and replacement, if necessary.
  • Correct crankpin ovality measurements.
  • Proper assessment of the condition of the connecting rod bearings and replacement, if necessary.
  • Correct mounting and alignment of the connecting rod bearing shells.
  • Correct hydraulic tightening procedure (steps, angles, pre-tensioning, gaps etc,) at specified pressure of the connecting rod bolt/nuts. Check that the elongation of the bolts is within the specified limits.
  • Replacement of the connecting rod bolts / nuts. The replacement cost is small and will help in avoiding damages due to defects that can go unnoticed.
  • Complete replacement of the lubricating oil.
  • Re-confirmation of the hydraulic tightening pressure after the first few running hours (it can be after the first 50, 100 or 200 hours, in accordance with the maker requirements). It is recommended to mark the position of the nuts and check if the nut is rotating.
  • Inspection of the crankcase and temperature check of the connecting rod bearings after the first few running hours.