PROCEDURE FOR REPLACING A MAIN ENGINE CYLINDER LINER

General preparation

• Obtain the engine maker's overhaul manual and the vessel's planned maintenance and risk assessment for the job.
• Inform the chief engineer, obtain permission, log the job, and prepare a permit-to-work / risk assessment covering hot and moving machinery.
• Stop the engine, close the engine room ventilation to that space as required, and drain and isolate the cooling water and lubricating oil to that unit.
• Bar the engine to bring the piston of the unit to about TDC or a position where the connecting rod is accessible and the piston rod can be disconnected from the crosshead.

Dismantling sequence (removal of old liner)

1. Shut and blank off the cylinder jacket water supply and return valves of the affected unit; drain the jacket cooling water.
2. Remove the cylinder cover (cylinder head) complete, together with its exhaust valve, injectors and starting valve, and land it on a suitable crib.
3. Remove the piston: secure the piston rod from turning, slacken and remove the crosshead/piston rod clamp or shrink-fit coupling, then lift the piston (with rod) out of the liner using the ceramic piston lifting rig or appropriate tackle, and land it on blocks clear of the work area. Protect the piston crown and ring grooves.
4. Remove the scavenge/ piston underside parts as required and relieve the liner lands.
5. Remove the stuffing box (piston rod gland) from the liner bottom to clear the bore seating.
6. Mark the liner and the liner land for correct replacement orientation and for the port alignments.
7. Disconnect the liner cooling water connections and any liner lifting/pulling gear arranged.
8. Using the lightweight jacking screws or the purpose-made liner lubricant/ lifting arrangement provided, break the liner from its seating; support the liner on a sling and lift it cleanly out of the jacket, watching the scavenge ports and the symmetrical handles.

After removal, examine the liner water side and jacket bore for scale, corrosion and fretting.

Parts requiring close attention during the lift

• The piston rod clamp joint and the sealing faces.
• The liner seating faces and the jacket top face - any dirt or burr will distort the new liner.
• The scavenge ports, liner lands and flame ring (if fitted) at the bore.
• The condition of the port area and the seating at the bottom of the liner.
• The O-ring or soft packing seals between liner and jacket water side - replace with new ones of the correct material.
• The crown of the liner bore (top) where the compression ring and worn ring grooves have the highest temperature.

Fitting the new liner

• Clean the jacket bore thoroughly, inspect for cracks and verify the fit-up dimensions and that the water spaces are clear.
• Fit new rubber O-ring seals (or annealed soft packing) in the grooves, thoroughly greased.
• Lower the new liner using a suitable sling arrangement, entering the jacket gently.
• Set the liner lands to align the scavenge ports with the jacket ports, checking the axial and circumferential location marks.
• Check the liner sits in full contact on its seating by feeler/gap; the liner and jacket must mate without rocking.
• Jack up and re-check.
• Reconnect the piston rod clamp, refit the stuffing box, re-land and secure the piston in the liner with new ring condition checked, and refit the piston crown.
• Refit the cylinder cover and torque the studs in the correct sequence to specified values.
• Reconnect the water and oil connections, ensure the ports and sealing are correct.

Important checks before and after fitting

Before: liner bore and surface finish, correct liner identification/oversize, ring/groove dimensions, port alignment, cleanliness of jacket, condition of new sealing rings, torque specifications.

After: scram the piston in TDC/B DC, check piston/liner clearance and ring gaps, verify scavenge port alignment, pressure test the cooling water side, bar engine round to check no tight points, and finally leak-test and run the unit up.

Pressure testing the cooling water side of a cylinder cover

• With the cover removed from the engine and cleaned, blank or cap all water passages including the injector and valve cores as required.
• Fill the cooling water space with water and apply hydraulic pressure using a manual or powered test pump.
• Use the maker-specified test pressure (typically 1.5 times working pressure but as per class standing instructions).
• Hold the pressure for a specified time (usually 15 to 30 minutes) and examine all welded seams, machined surfaces, the nozzle deck and the valve seats for weepage or leakage.
• Any leak is a condemnation; the cover must be repaired or replaced.
• On successful test, drain, dry and apply a protective coating (or re-fit with new seals), then refit to the engine.