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Q9 (16 Marks) Engine Construction & Components 🔥 Repeated 2x in exams
MEP • Written Exam

(a) If soon after joining as a second engineer on a motor vessel, you observed that number of holding down bolts are slack, and fretting has occurred around slack holding down bolts. Describe what actions do you take. (8)

(b) Explain the correct procedure for checking the holding down bolts' tightness. (8)

Appeared In: Feb 2025Feb 2025 - 1

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Part (a)

ACTIONS ON FINDING SLACK HOLDING-DOWN BOLTS AND FRETTING

  1. Report and record: Inform the Chief Engineer immediately, log the finding, and photograph/ record the affected bolts and the fretting.
  2. Investigate the cause: Determine why the bolts are slack - e.g. incorrect initial tightening, bolt stretch/ relaxation, foundation/ chock deterioration, engine vibration, or a previous repair. Check the chocks (epoxy/ metal) and the foundation for damage.
  3. Assess the extent: Check all holding-down bolts (not just the slack ones) for tightness, and inspect the bedplate/ foundation for fretting, cracks, and movement.
  4. Rectify:
  • Re-tighten the slack bolts to the correct torque/ stretch using the correct procedure (see part b), in the correct sequence.
  • If fretting has occurred, clean the fretted surfaces, and repair/ renew the chocks and foundation as necessary (e.g. re-chock with epoxy resin, or re-metal the chocks) to restore proper support.
  • Renew any damaged/ stretched bolts.
  1. Prevent recurrence: Ensure correct tightening procedure and torque, use the correct locking, and schedule regular checks of the holding-down bolts. Investigate and correct any excessive engine vibration or misalignment that caused the bolts to work loose.
  2. Record the action and monitor: Record the repair and re-check the bolts after a period of running to confirm they remain tight.
Part (b)

CORRECT PROCEDURE FOR CHECKING HOLDING-DOWN BOLTS' TIGHTNESS

  1. Preparation: Stop the engine, secure the turning gear, and ensure the engine is at a safe condition. Obtain the maker's manual and the correct torque/ stretch specification.
  2. Clean the bolt heads and nuts: Remove any paint, dirt or locking to allow accurate measurement.
  3. Check tightness by torque: Using a calibrated torque wrench, apply the specified torque to each nut and confirm it reaches the value without further movement (i.e. the nut does not turn at the specified torque). If the nut turns before reaching the torque, the bolt is slack.
  4. Check by bolt stretch/ elongation: Where specified, measure the bolt stretch (elongation) using a micrometer/ stretch gauge between the bolt head and the nut, or by measuring the bolt length before and after tightening, and compare with the specified stretch value.
  5. Check by hammer/ feel: A light tap on the nut/ bolt head (using a hammer) and feeling for movement/ ringing can indicate looseness, but this is a rough check only.
  6. Tighten in the correct sequence: If re-tightening, slacken and re-tighten the bolts in the correct sequence (e.g. from the centre outwards, or as per the maker) to the specified torque/ stretch, in stages.
  7. Record: Record the torque/ stretch values and the date for the maintenance record.
  8. Re-check after running: Re-check the bolts after a period of operation (e.g. after the first few hours) to confirm they remain tight.
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