Answer MEP Question 19

Q. Describe the procedure for replacing a Main Engine cylinder liner and explain using sketches where necessary, those parts, which require close attention during lifting of the cylinder liner. Also, describe the procedure for pressure testing the cooling water side of the Main Engine Cylinder head.

Preparation

Cylinder mountings removal

- Considering that the piston is already removed the following procedure is given for liner removal post removal of the piston.

- Dismount the four cooling water pipes between the cooling jacket and cylinder cover and clean them carefully. Remove the screws of the cooling water inlet pipe.

- All mountings like the sensors, lube oil connection, quill accumulators are disconnected from the liner body and the liner is free to move from its position.

Inspection connecting the lifting:

Ensure the liner lifting tool is properly inspected and free from any damage or cracks that could cause accidents while lifting the liner.

Lifting screws on both sides of the liner are used to fasten the tool and the liner with the correct torque mentioned in the manual.

Ensure that there is no gap between the liner surface and the screw landing surface after lightening, using a 0.05mm feeler gauge. The lifting hook is connected to the tool.

Lifting the liner

Ensure there is no one present in the under piston area and personnel are standing well clear of the rope area.

The crane is slowly lifted upwards until there is no slack on the rope and the liner is ready to move, use the vertical bar provided by the manufacturer, connect it to the liner and gently try to move the liner in athwartship direction while the crane is lifting the liner.

Ensure the line moves up gently, do not force the crane if the liner is not lifting, the liner may have seized in the way of sealing surfaces. Repeat the process one more time to see if the liner is free to move.

Seized liner:

If the liner is seized and no movement is seen while lifting through the crane, the next step is to jack the liner from the bottom.

Follow manufacturer recommendations in jacking the liner. Use proper cover to place the hydraulic jack as an improper backing plate may damage the parts.

Describe the procedure for pressure testing the cooling water side of the main engine cylinder head.

Blanking off:

Cylinder head cooling water ports to be firmly blanked using proper blind flanges supplied.

The bottom-most port is usually the testing water supply port and the top port is usually used for venting purposes.

Such port allows connections for water and air which is used for pressurizing the cylinder head.

Pre-heating

The Cylinder head is preheated slowly by pumping hot water from the bottom port and recirculating back using the top port, the water is heated slowly in the container to a temperature of 85-90deg C.

Once the temperature is reached the recirculation is carried out a little longer for the cylinder head to heat up to the temperature and then the circulation is stopped. The supply port and venting port is closed to ensure the cylinder head is full of water.

Pressurizing

Now the outlet port is connected to an air hose, the valve is slowly opened observing the pressure, the is raised up to testing pressure as recommended by the manufacturer usually for medium-speed engines it is 6-10 bar and for large slow-speed engines 3-6 Bar.

Inspection for leaks

Check the cylinder head for leaks, check the area around the valve seat and the injector sleeve for leaks and cracks.

Check for leaks around the valve cage, valve insert etc.

Leave the valves firmly closed for up to 30 min to ensure that the pressure is holding without any drop. Slightly drop is acceptable considering that the temperature of the water may drop in these 30minutes.

Restoration:

If there is any leakage observed or a drop in pressure is seen, then the cylinder head must be discontinued and a proper note is made on the checks made and sent ashore for a thorough inspection of the cylinder head using imaging and ultrasonic methods.

If no leakage of pressure drop is observed, the cylinderhead is completely drained and dried thoroughly prior to storing on the shelf.