It is very important in a large two stroke slow speed engine to transfer the power generated in the combustion chamber to the crankshaft without transmitting transverse forces to the piston and large thrust directly to the crankshaft. Hence an arrangement is provided to compensate this which is known as Crosshead.
The reciprocating action of piston is converted into rotary motion for crankshaft by means of the cross head where the piston rod and connecting rod are attached on both sides.
A routine maintenance has to be performed on crosshead bearing as per maker’s instruction. Following procedure is to be followed when carrying out crosshead bearing removal of a MAN MC-C engine:
1) Inform company and take permission.
2) Take immobilization certificate from port.
3) Read the manual and have a toll box meeting with everyone involved in the job. Discuss the procedure.
4) Prepare important tools and spares to be used in this operation
5) A risk assessment of all personnel doing the operation to be prepared and documented
6) Shut main engine starting air
7) Engage turning gear to the main engine crankshaft
8) Open indicator cocks of all cylinders
9) Stop main engine lube oil pump after cooling down of engine
10) Open crank case doors of fore and aft unit
11) Open crank case doors of that unit in which maintenance is to be carried out.
12) Put blower and ventilate the crankcase thoroughly as it is an enclosed space.
13) Prepare enclosed space entry checklist.
14) After sufficient ventilation wearing proper PPE you can enter the C/C.
15) Turn the crank throw to 90° before BDC.
16) Check the bearing clearance by inserting feeler gauge b/w bearing cap and crosshead journal exactly next to the landing surface of the piston rod foot.
18) Turn the crankshaft down enough to give access to nuts and screws on piston rod.
19) Mount two chain blocks on the top of the crankcase for suspending the piston rod.
20) Loosen and remove the locking wire and screws on the piston rod foot.