Q7 (16 Marks) Engine Construction & Components
MEP • Written Exam

(a) As second engineer, describe the procedure involved in the complete inspection of a cylinder liner and piston assembly, indicating areas of significant interest. (5)

(b) Explain with reasons, possible faults which might be found. (4)

(c) Suggest how such faults might be avoided. (4)

(d) How liner wear and wear rate is calculated? (3)

Appeared In: Jan 2024

Verified Model Answer (Text Solution)

Structured for DG Shipping MEO Class II examination scoring criteria.

Exam Ready
Part (a)

Procedure for Complete Inspection of Cylinder Liner and Piston Assembly:

As a second engineer, inspecting a cylinder liner and piston assembly is an important maintenance task. The procedure begins with examining the cylinder liner. First, inspect for any carbon accumulation around the scavenge ports, clean them thoroughly, and check for damage, such as cracks. Then, ensure the liner's internal surface is smooth; any signs of burns or protruding metal should be addressed using an oil stone or portable grinder as per recommendations. Pay special attention to the quill areas for corrosion or cracks, and manually pump oil to ensure all quills are functioning correctly. Additionally, inspect the liner for honing marks; the absence of these and the presence of a mirror finish indicate lubrication failure. Black patches on the liner surface suggest leaking piston rings, which need replacement. It's also essential to measure the cylinder liner wear and compare it to previous records, ensuring the wear rate is within the manufacturer's limits. If the liner is withdrawn, examine the water side for scale or deposits and clean as necessary. Also, check the condition of the O-rings and renew them if needed.

The piston assembly inspection involves checking for burns at the top of the piston, wear on the side walls of the crown, and ring grooves. Look for any cracks due to thermal or mechanical stresses, high-temperature corrosion, or sulfuric acid corrosion. Ensure the piston rings move freely, and check the ring grooves for wear, steps, and scuffing. If the piston is water-cooled, inspect the underside for scaling, or if oil-cooled, check for carbon deposits. Finally, inspect bolts, locking wires, studs, and O-rings for integrity.


(b) Faults in cylinder liner:
  1. Cracks on the liner due to excessive tightening/ incorrect tightness of cylinder liner bolts
  2. Cracks due to hoop stress because of poor liner support
  3. Circumferential cracks along the wear ridge due to stress concentration or, more likely, because of new rings hitting the ridge
  4. Cracks in the shape of a star due to flame impingement in combustion space
  5. Cracks in the shape of stars around the lubricating quills due to water leaking
  6. Corrosive wear leading to clover leafing near the lubricating quills injection
  7. Cracks across the scavenge port due to overloading, poor cooling, scavenge fire, etc
  8. Excessive wear of liner surface due to friction, corrosion, adhesion or abrasion and improper lubrication
  9. Mirror finish of liner surface due to lubrication failure

Possible piston faults:

  • Cracks on piston due to thermal and mechanical stresses
  • Excessive wear down of piston rings and grooves due to insufficient lubrication and poor combustion leading to carbon deposits
  • Burning of piston crown due to fuel impingement
  • Breaking of piston rings due to excessive clearance
  • Fouling of piston cooling water/ oil space due to scale deposits

Part (c)

Preventive measure:

  • Ensure proper lubricating oil supply and proper lubrication
  • Proper maintenance of fuel injector and fuel system to ensure no flame impingement after burning etc
  • Correct grade of fuel oil to be used with minimum impurities and proper purification
  • Ensure proper cooling of liner and correct jacket water temperature to be maintained to avoid thermal stress
  • Inspection and maintenance of piston and liner at regular intervals to prevent faults
  • Correct tightness of bolts and nuts
  • Proper treatment of jacket cooling water
  • Lube oil analysis at regular intervals

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