Cylinder Liner in any kind of marine engine is an integral part of the combustion chamber, through which, power is generated on board. Like all other machinery and engine parts on ships, it also has to be overhauled after specific interval as described by the engine makers
Previously we have discussed Reasons for Cylinder Liner wear and ways to measure it, in this article we will discuss the liner removing procedure of Main two-stroke marine engine.
How to check wear in the liner and when to overhaul it?
The liner is an enclosed area and a part of the combustion chamber where the fuel is burnt and heat energy is transmitted to kinetic energy by use of piston, crosshead, bearings and crankshaft. For an engineer, it is important to know various ways to check the condition of the liner to ensure the combustion chamber is efficiently producing the required pressure.
Ways to check the condition of the cylinder:
1. Scavenge inspection
2. Routine Liner Ovality check
3. Piston Overhaul
4. Problem involving Liner
1. Scavenge inspection: Scavenge inspection is performed every time post the scavenge space of the engine is cleaned off from sludge and deposits.
After the cleaning is done, 2nd engineer or a responsible engineer must go inside the scavenge space to check the general liner condition using the following method:
- In order to inspect a larger area of the cylinder liner and piston, it is expedient to enter the scavenge air receiver and make observations from the “exhaust side”
- Dismount the small covers on the scavenge air boxes, and clean the openings
- When the piston has been turned below the level of the scavenge air-ports, inspect the cylinder liner walls and the piston crown
- A “tilt-able” mirror fixed to a telescopic rod can be used as illustrated. Use a powerful light source for inspection
2. Routine Liner Ovality check: As explained in the article, readings are taken at port and starboard position in different levels to calculate the change in the ovality of the liner.
3. Piston Overhaul: When the piston is overhauled as per the planned maintenance or due to breakdown reasons, the liner ovality must be checked and liner surface must be inspected for various defects.
4. Problems like leaking liner water ‘O’ ring, cracked liner, blow-past from piston and liner etc. will require an immediate action of checking and changing the piston and liner. After proper measurement and inspection of the liner, the problem source can be determined and a decision can be taken whether to change the liner or continue with the same.
Overhauling schedule of liner: The normal overhauling schedule of the liner will depend on the efficient operation of the engine, it’s operator, type of fuel used in the engine and how all the important engine parameters (temperature, pressure etc.) are maintained by the operator.
If the liner is working fine, the planned maintenance schedule is followed and the liner will be checked and gauged after completion of certain running hours as prescribed by the engine makers.
12000 to 16000 hrs are the normal running hours schedule to open and inspect/ gauge the liner of 2 strokes marine main engine, depending upon the maker of the engine.
The general lifetime of a cylinder liner will again depend on the way engine is operated and type of fuel oil used for combustion. The normal lifetime running hours of the liner will vary from 40000 RHs to 90,000 RHs. The size of the liner bore is directly related to the lifetime of the liner hence liner with small bore will have less lifetime with a liner with large bore and size.
Following Procedure has to be followed when opening Liner (common for all)
1) Inform company and take permission.
2) Take immobilisation certificate from port state control.
3) Read the manual and have a tool box meeting with everyone involved in the job. Discuss the complete procedure.
4) Prepare important tools and spares required for overhauling liner as given in the manual
5) Prepare risk assessment and make sure all personal safety equipment are used
6) Shut starting air for Main Engine and display placards
7) Engage turning gear
8) Open indicator cocks for all the cylinders
9) Stop main lube oil pump and switch off the breaker
10) Once the engine jacket temperature comes down, shut the inlet water valve for the unit to be overhauled
11) Keep other units in Jacket preheating system to maintain the jacket temperature
12) Drain the jacket water of the concerned unit from exhaust v/v and liner.
13) Shut the fuel oil to the particular unit whose liner is to be removed
14) Dismount the cylinder head using dedicated lifting tools
13) Discard the sealing ring from the top of the cylinder liner.
14) Turn the piston down far enough to make it possible to grind away the wear ridges at the top of the liner with a hand grinder
15) Dismount the piston by following the procedure given in Manual
Liner Removal procedure for MAN engine (MC and ME engines)
16) Ensure the Liner lifting tool is well maintained. Two lifting screws are used with a lifting hook connected via chain. Ensure chain, screw and lifting hook are fastened together with no deformation.
17) Ensure the safety strap in the lifting hook is working properly.
18) Tighten the two lifting tool screws in the liner as per the rated torque is given in the manual on both sides.
19) Measure that there is no gap between liner surface and screw landing surface after tightening, using a 0.05mm feeler gauge.
20) Disconnect the cylinder oil pipe connections. And screw of the non-return valves.
21) Dismount the four cooling water pipes between the cooling jacket and cylinder cover and clean them carefully.
22) Remove the screws of cooling water inlet pipe.
23) Attach the crossbar to engine room crane. This completes the lifting arrangement for cylinder liner.
24) Hook the chain from the lifting cross bar on the lifting screws and lift the cylinder liner with the cooling jacket out of the cylinder frame.
Liner Removal procedure for RTA and RTFlex Engines
25) Ensure the Liner lifting tool is well maintained, Suspension bridge beam does not have any loose connection or distortion. Right screw is used with the suspension bridge tool to lift the liner.
26) Remove the screw which fastens the supporting ring on the liner.
27) Disconnect the cylinder oil pipe connections. And screw of the non-return valves.
28) Dismount the cooling water pipes between the cooling jacket and cylinder cover and clean them carefully.
29) Remove the screws of cooling water inlet pipe.
30) Remove all the passages for lubricating quills as well as their protecting bushes.
31) Mount the suspension bridge beam over the top landing surface of the liner.
32) Fastens the screw of attached to the suspension bridge beam to a side of the liner and tighten it to the rated torque stated in the manual.
33) Attach the engine room crane to the lifting tools.
34) Lift the cylinder liner with the cooling jacket out of the cylinder frame.
What to do if Cylinder Liner is Stuck
A common way to remove a stuck cylinder liner is to use hydraulic jacks on the bottom of the cylinder liner and apply hydraulic pressure. Once the liner is slightly moved out of the stuck engine structure, it may be then lifted with the help of engine room crane and lifting tool
After Removing the liner from the engine:
- Place the cylinder liner vertically on a wooden plank
- Clean cylinder frame internally paying special attention to the contact surfaces for the cylinder liner at the top of the cylinder frame
- Discard the O-ring on the cooling water pipe
- Clean the pipe carefully
Make sure to inspect the liner for cracks and other defects
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