An auxiliary engine or generator on a ship is very important machinery and provides all electrical power for the safe operation of the ship. For keeping the auxiliary engine always in a state of readiness it requires periodic maintenance. It includes daily checkups, weekly routines, and running hour based maintenance for major overhauls(Auxiliary Engine Decarb).
The period of inspection and overhaul cannot be fixed indiscriminately because it is influenced by various factors like- application of the engine, conditions of use, quality of fuel oil and lubricating oil used, and daily handling circumstance. So the first overhaul and servicing of the engine accessories and major parts to be carried out as the maker’s instruction and the amount of accumulation of carbon, Wear down, Corrosion, Lube oil condition must be assessed. Based on these first overall checks and results make the most economical checking schedule suitable for your engine, and conform to the specified schedule from the second overhaul.
As we said earlier that period of inspection and overhaul or even auxiliary engine decarb cannot be fixed and it varies from maker to maker. Here you can find the Table of Periodic maintenance of the Auxiliary engine parts of a Yanmar Engine-
|Part Name||Nature of Service||Servicing Frequency|
|Drawing-out check & adjustment||1500 to 2000 Hrs|
|Cylinder head||Check of valve spring||4000 to 5000 Hrs|
|Disassembly, check & cleaning||4000 to 5000 Hrs|
|Scale cleaning & hydraulic test of the water chamber||4000 to 5000 Hrs|
|Replacement of stem seal (Suc/Ehx. Valve)||8000 to 10000 Hrs|
|Piston||Drawing-out, cleaning, checking & measurement of piston||8000 to 10000 Hrs|
|Check & measurement of piston rings||8000 to 10000 Hrs|
|Check & measurement of the piston pin||8000 to 10000 Hrs|
|Connecting rod||Check & measurement of piston pin metal||8000 to 10000 Hrs|
|Check & measurement of crank-pin metal||8000 to 10000 Hrs|
|Check of connecting rod bolt tightening force||8000 to 10000 Hrs|
|Change of connecting rod bolts||8000 to 10000 Hrs|
|Cyl. liner||Inner Dia. checking, cleaning & measurement||8000 to 10000 Hrs|
|Drawing-out, check & cleaning of water jacket part||16000 to 20000 Hrs|
|Crankshaft||Measurement of crankpin outer dia. & journal||8000 to 10000 Hrs|
|Measurement & adjustment of the deflection||2000 to 2500 Hrs|
|Main bearing||Disassembly, metal checking & measurement||8000 to 10000 Hrs|
|Check on tightening force of main bearing clamping bolts & side bolts||8000 to 10000 Hrs|
|Camshaft||Check of cam & roller bearing||4000 to 5000 Hrs|
|Disassembly & check of fuel pump tappet||8000 to 10000 Hrs|
|Disassembly, check & measurement of the swing arm||8000 to 10000 Hrs|
|Fuel injection pump||Check of injection timing||2000 to 2500 Hrs|
|Check of deflector & replacement||4000 to 5000 Hrs|
|Disassembly, cleaning & check||4000 to 5000 Hrs|
In this blog we are going to discuss about the decarb routines carried out onboard. Decarb is a very major overhaul onboard a ship for the Auxiliary engine, So before doing this major overhaul make sure that you are ready in all aspects for the upcoming voyage. Things that must be keeping in mind before planning for auxiliary engine decarb routine-
- Carry out a risk assessment and toolbox meeting with all involved personnel and explain to them about their responsibilities and the safety procedures followed during the overhaul.
- Discuss the major overhaul plan with 2nd engineer and chief engineer and inform deck department.
- Check with the Manufacturer manual for all required tools for disassembly and overhaul. Refer the manufacturer manual and explain all working hands about the special precautions and safety measures followed during overhaul.
- All consumable spares like O rings, packing and Piston rings must be checked and kept ready.
- All major parts specified torques/ pressures for tightening & Clearances, Calibration/measurements procedure and data must be checked. Keep last overhaul reports for trend analysis.
- Make sure that all other auxiliary engines are in state of readiness for any emergency situation.
- Use the specified engine tools only to prevent the damage of the respective part of the engine. In advance of using exclusive tools, check the function of these tools. Carefully check for any damages to high pressure pipe and joints of hydraulic jacks. Use the specified lifting gear, hook, rope, etc.; and pay attention to safety when handling a critical or heavy engine parts particularly.
- During overhaul works with electrical tools, buffing, welding and grinding, be careful of any spark generation. Since there is the possibility of catching fire, try not to leave combustibles such as fuel, lubricating oil and used waste cloth in a working area.
Isolation of the auxiliary engine for the major overhaul/auxiliary engine decarb.
- Before stopping the AE for maintenance run it on DO for line flushing and shut all fuel valves after AE stops
- Shut air starting valve, Control air valve.
- Put the fuel lever in stop position and lock it.
- Shut all Jacket water, preheating and cooling water valves. Open vent valve and drain valve. Make sure that all the water has been drained before disassembly.
- Stop L.O. priming pump, ACB off, Locked and tagged.
- ACB must be in open position, properly locked and tagged.
- Engage turning gear
- Give sufficient time for cooling down the engine and then only stat the dismantling procedure.
Cross check the isolation procedure once more and if everything is in order then only start preparing for the disassembly of Cylinder head for auxiliary engine decarb.
Disassembly of Cylinder head mountings before removing the cylinder head
- Detach the exhaust manifold cover and Remove the exhaust manifold.
- Disconnect all the cylinder head mountings:
- Overflow oil pipe,
- Fuel injection pump pinion Lube oil pipe,
- Cooling water connection pipe,
- Pressure indicator cock,
- Fuel injection pipe joint,
- Fuel injection pipe cap nut and fuel injection pipe from the cylinder head.
- Detach the rocker arm chamber cover, and remove the rocker arm shaft pedestal, suction/exhaust valve guard and pushrod.
- Remove the fuel valve tightening the nut, put the fuel valve drawing tool and jack it out.
- Remove the protective cap of a cylinder head bolt and clean the threaded area.
- Follow the maker’s instruction for opening the Cyl head bolts in the correct sequence. It can be either of manual opening or by the use of the Hydraulic jack. Whenever using hydraulic jack, following cares must be followed
- When assembling the hydraulic jack inspect threaded part for any oil leakage. Use correct grade of hydraulic oil.
- Attach the hydraulic jack to the cylinder head bolt, and screw in the jack until it adheres to the spacer and then loosen the hydraulic jack by one full turn or a bit more as recommended. It ensures that it will not get struck once the Cyl head stud loose tension and it comes to its original length.
- When attaching the hydraulic jack to a cylinder head, make sure to check that the notch of the spacer fitting surface does not make a contact with the adjacent cylinder head. Otherwise, the spacer and the cylinder head will be damaged. Only then, raise the hydraulic pressure.
- When a hydraulic jack is used for the first time, the rubber hose is filled with the hydraulic fluid. Therefore, when the hydraulic pressure begins to rise, loosen the air vent plug of the hydraulic pump, and then checking the oil volume; replenish the hydraulic fluid if required.
- Close the relief valve of the hydraulic pump, and operate the pump lever to raise the hydraulic pressure to the specified limit and then by using tommy bar open the nuts as per the sequence recommended. If the nut to be removed could not be turned with use of the handle, slowly raise the hydraulic pressure( within the manufacturer limit) and then turn the nut.
- Remove all Cylinder head nuts and then put Cyl head lifting tool and take out all heads one at a time.
Piston drawing out procedure
While drawing out the piston, the crankshaft may turn spontaneously due to the unbalance. Securely lock the flywheel and do not allow the crankshaft to turn spontaneously, and then only proceed to a work.
- Set the piston at a position of about 80° to 90° before the T.D.C.
- Place the protection ring drawing-out tool on the piston with tapered face upward as shown in fig. If it is not provided, an old Piston ring can be also used.
- Attach the liner retaining Tool and spacer and lock them with the cylinder head tightening nut.
- Turn the flywheel, piston top will push the protection ring outward from the liner.
- After taking out protection ring remove the disassembling tools and protection ring.
- Eliminate the carbon from the upper part of cylinder liner which may cause inconvenience during piston withdraw.
- Set the crankshaft in approx. 75° passed T.D.C and applies hydraulic tools as shown in fig.
- Clean the piston top land threaded part with correct die and put the lifting eye bolt and connects it with the lifting chain block.
- Loosen the connecting rod bolts with the specified disassembling tool with the recommended hydraulic pressure, and then remove the bolts and the connecting rod bearing bottom half with special care.
- Lift the piston few centimeters and remove the upper metal bearing just by pushing with fingers.
- Take out the piston along with the connecting rod slowly with the help of lifting chain block. Take care to prevent the connecting rod from making a contact with the crankshaft pin or cylinder liner while drawing out the piston.
Cylinder liner removal
- Attach the exclusive liner removing tools in the order as recommended by the makers. Mostly it will be in two parts upper and lower half, connected by a long stud.
- Fit both the tools with the help of long stud as per the maker’s instruction and adjust the stud length.
- Initially jack up the liner with the help of tightening nut for few millimeters and then pull it out with the help of wire attached to the upper tool, while supporting the cylinder liner to prevent it from making contact with the cylinder head tightening stud.
Here you can see an arrangement of liner withdrawal for a YANMAR engine.
Main bearing removal for inspection
Here we are going to discuss the removal of under slug bearing with the help of hydraulic jack, which is most common nowadays in the shipboard auxiliary engine.
- Fit a hydraulic jack on the lower part of bearing.
- Adjust the hydraulic piping to facilitate the work.
- Here you can find the fitting procedure of hydraulic jack for a Yanmar engine.
Hydraulic Jack Fitting Procedures
- Start with removing the side bolts from the main bearing to be disassembled. This will allow the lower half casing to come down.
- Loosen the main bearing cap clamping nuts, applying the hydraulic pressure to the hydraulic jack. If the main bearing cap cannot be drawn out due to its own weight: O Loosen the side bolts of the adjacent main bearing caps.
- Loosen the main bearing cap tightening nuts to few turns, and then draw out the main bearing cap using the drawing-out tools.
- Fit the drawing-out tool body to the main bearing cap bolts with the bolts and then, screw the bolt to the main bearing cap, and turn the nut to draw out the main bearing cap as shown in fig.
- Remove the main bearing cap tightening nuts, and attach the main bearing cap holding implement to the main bearing cap clamping bolts as shown in fig.
- Do not remove both tightening nuts simultaneously. Otherwise, the main bearing cap may fall, resulting in injury. Screw each circular nut into the corresponding holding bolt to lock the holding bolt with the corresponding main bearing cap clamping bolt.
Remove the main bearing lower metal.
- Fit the attaching/ detaching tool to the crankshaft oil hole from the no-operating side, so that the head of attaching/detaching pin lies along the outer periphery of the crankshaft).
- Slowly turn the flywheel in the direction of engine rotation, and draw out the upper metal to the operating side as shown in fig
We will discuss all the above major parts cleaning procedure, various measurements/ calibration, area of major concerns for trend analysis and troubleshooting procedure in our next series of Marine Auxiliary Engine decarb blog.