Answer
For a large slow-speed crosshead diesel engine, the exact procedure depends heavily on engine construction. Modern engines may have forged/semi-built crankshafts, and maker-approved lifting and alignment procedures must be followed.
Step 1 — Planning
Before starting:
- Consult engine maker's manual.
- Inform:
- company
- superintendent
- class
- maker/service engineer.
- Prepare detailed job specification.
- Obtain class approval where required.
- Arrange:
- dry dock/repair berth as necessary
- cranes
- hydraulic tools
- lifting beams
- chain blocks
- calibrated measuring tools.
Prepare:
- risk assessment
- toolbox meeting
- lifting plan
- permit to work
- enclosed-space/hot-work permits if relevant.
Main Engine Crankshaft Removal Procedure
1.Immobilization, Safety & Preparations:
Inform Master, Port Authorities, and Class. Obtain hot work / heavy lift permits, immobilize engine, engage turning gear with local lockout, isolate starting air, fuel lines, and lubricating oil pumps. Rig temporary overhead lifting beams and eye bolts tested to certified Safe Working Load (SWL).
2.Dismantling Upper Engine Components:
Remove cylinder covers, exhaust valves, fuel injectors, crosshead assemblies, pistons, and connecting rods. Store them safely on designated deck stands with proper securing.
3.Dismantling Frame Structure & Drive Mechanisms:
Disconnect and remove camshaft drive gearwheel/chain, intermediate shafts, and fuel pump drive mechanism. Hydraulic-slacken and extract tie rods in the reverse sequence specified by the engine manufacturer. Unbolt and remove entablature/A-frames if required by engine design.
4.Main Bearing Removal:
Hydraulically slacken main bearing stud nuts. Remove upper main bearing keeps using special jack-up tools. Roll out lower main bearing shells using turning gear and shell removal tools. Record all web deflection readings and bearing clearances prior to lifting.
5.Rigging, Jacking & Crankshaft Extraction:
Disconnect flywheel, turning gear, intermediate shaft coupling, and thrust bearing assembly. Position specialized synchronized hydraulic jacks beneath journal webs. Rig lifting beams with protective leather/brass slings around main journals (never on crankpins). Carefully balance and hoist the crankshaft clear of the bedplate, guiding it through the crankcase side doors or hull cutout casing.
6.Post-Removal Inspection:
Inspect bedplate cross-girders and pocket housings for micro-fractures (using Dye Penetrant / MPI), fretting corrosion, and alignment. Protect exposed journal surfaces on the removed crankshaft with anti-corrosive grease and heavy protective wrapping.