Marine Auxiliary Engine Decarb Procedure: Inspection and Assembly

In our last blog of Auxiliary engine decarb routines, we have discussed in details, about the dismantling procedure of major parts of a shipboard auxiliary engine. Here in series of this major overhaul routine blog, we are going to focus on the major parts cleaning procedure, various measurements/ calibration, area of major concerns for trend analysis and troubleshooting procedures.

As we know that the basics of the maintenance and overhaul procedures are same but few measurements and calibrations may vary as per the makers. So before the disassembly, cleaning, and calibration we have to refer our own auxiliary engine maker’s manual and thoroughly understand the specific procedures.

Cleaning, Dismantling, measurements, and testing of the cylinder head and its Accessories 

  • Put the Cylinder head in the Cylinder head stand secure it and carry out inspection.
  • Secure the valve removing tool on the cylinder head and Compress the valve spring to few centimeters, valve cotters will be free and can be removed. Unscrew the tool and release the compression of spring and remove valve rotator, both springs and suction/discharge valves.

The suction and exhaust valves use two cotters, respectively. In reassembly, fit the two cotters as one pair to the valve to which the cotters have been previously fitted. If not used the cotters as each pair, an improper contact at the cotters may cause a breakage to the valves stem.

  • Now put the cylinder head in water filled (add appropriate chemical if required) half drums for at least 4-6 Hrs.
  • Remove from water, Check the state of carbon adherent in the combustion chamber and at the suction and exhaust ports and take it as a reference for determining the intervals for subsequent servicing as we discussed in our last blog.
  • Clean all the carbon and sludge. After clearing all the areas, carefully check for cracks and corrosion.
  • Check the state of scale in the water jacket part.
  • Check for flaws and foreign matters in the socket and spigot part of the cylinder head fitting surface. If this part has been flawed or contaminated by foreign matters, a blow-by occurs during a run.
  • Conduct the Pressure test and check whether water leaks

 Checks and measurements of the valve, valve seat, and guide:

  1. Check for Acidic and high-temperature corrosion of the valve poppet and bend of the suction/exhaust valve stem, and measure the dimensions.
  2. If the clearance between the suction/exhaust valve stem and the corresponding valve guide exceeds the usage limit value, replace the concerning part.
  3. Check the state of erosion, blow-bye and carbon biting-in at the valve seat part, and according to the state, grind the seat face.
  4. Use proper greet size and quantity of grinding compound to the valve to be ground, and elaborately grind the valve with the specified grinding tool. Finally, carry out the sealing test of valves.
  5. Check for cracks and corrosion of valve springs
  6. Measure the dimensions of the valve seat part as shown in fig. If the dimensions have reached the usage limit values, replace it.
  7. Valve rotor or Rotocap overhaul and checks:
  • Improper rotation of the valve rotator can cause meting the same point at every valve closing and same carbon to be bitten in the valve seat part. It can cause seat or valve damage and hence blow-bye at the seat part and affecting the service life of the valve and valve seat. Dismantle the valve rotor and check for wear, corrosion or deformation of the body groove, Belleville spring, coil spring, and balls.


Piston cleaning, dismantling, and checks:

 Put the piston in the stand and remove all the piston rings with the help of tool provided. Remove the piston pin circlip and Draw out the piston pin while holding the connecting rod. Clean the piston top and ring groove area. After cleaning carry out following checks:

  • Carry out piston dye penetrate test for crack detection on its top surface and ring groove area
  • Take out piston cooling case cover and check for the adherent scale formation and clean this area
  • Measure the piston ring groove all dimensions and record it.
  • Measure piston pin and gudgeon pin bearing dimensions.
  • Put piston rings as recommended for their direction and the angled difference of the position of ring cut part. Measurement must be taken and recorded as per maker’s instruction after putting the new piston rings.
  • If any of the piston measured dimension is not is the allowable limit, replace it with the new one and provide the same set mark on the new one like that on the removed one. 


After taking out the bearing metal from the connecting rod bottom end clean it properly while paying attention on the serration area. After cleaning carry out the following tests:

  1. Check the contact area condition and looseness in the fit of piston-pin metal bearings.
  2. Measure the inner diameter of a piston-pin metal. If the measurement exceeds the usage limit value, replace the piston-pin metal. To incorporate the piston-pin metal, align oil holes and press fit the metal. After having press fitted, measure the inner diameter of the metal.
  3. Check for any cracks and wear on the serration mating surface of the connecting rod big end.
  4. Put the bottom half of the big end bearing and tight it with the rated torque/hydraulic pressure without the bearing metal and carry out ovality test.
  5. carry out bend test of connecting rod by inserting an optimum diameter rod in the lube oil hole turn the rod. If the connecting rod is bent, the rod cannot be inserted, or it can be inserted but cannot be turned.
  6. Connecting rod bolts are subjected to fatigue stress and very critical. So visual check for any damage, hit mark and plucking on the bearing surface and threaded part of each Connecting rod bolt must be carried out. Carry out die penetrant test and measure all other dimensions of con rod bolts as recommended by the makers and replace it if required. If the replaceable running hours as per makers have been reached, then renew all the con rod bolts irrespective of satisfactory results of visual or any shipboard non-destructive tests.
  7. Check the contact on the rear and mating surface of each crank pin metal on the crankshaft, and also check for cracks, seizure and embedded foreign matters on the sliding surface of each metal. 

Cylinder liner cleaning inspection and calibration

Generally, Cylinder liners are provided with heat- treated layer on the outer periphery so, do not use sandpaper, wire brush, or the like when cleaning the outer periphery of the cylinder liner. Otherwise, the heat-treated layer on the surface is removed to cause rusting or corrosion.

  1. Use the template and mark the points in forward-aft and Port-  Stbd direction at three vertical points and do liner calibration. Record the readings and compare with the last overhaul report and maximum permissible wear down and ovality value of makers. If the cylinder liner diameter or ovality exceeds the usage limit value or if the measurement is expected to reach the usage limit value before the next servicing, replace such a cylinder liner.
  2. Check for seizure, streak, erosion, and corrosion on the sliding surface of the cylinder liner.
  3. Carry out visual and dye Penetration check of the rounded part of the collar of cylinder liner for cracks.
  4. Check for corrosion and wear at the part of cylinder liner mated with the cylinder block.
  5. Clean and inspect the sealing O ring sitting area for any deposits or corrosion.
  6. Clean the water jacket and cylinder liner fitting part of the engine, and check for corrosion.

Reassembly of parts in sequence after overhaul and measurements:

 Reassembly of the cylinder liner

Clean the O ring sitting area of the cylinder liner and replace the O-rings. Apply the lubricating oil or silicone oil to new O-rings, and fit them. Then, eliminate torsion from the O-rings. (Before incorporating the O-rings, stretch them to check whether a crack has developed or not on their surface. If it is stored under the improper condition like high temperature and humidity or due to the aging, chances of such damage are more).

 Just before incorporating the cylinder liner, apply the silicone-based liquid packing to the upper section of the cylinder block. Moreover, apply the lubricating oil to the mating part of the cylinder liner and block.

Use the Liner mounting exclusive tools as discussed in our last blog and put the liner into the jacket while matching the mark provided on liner and cylinder block.

Incorporate the piston

Incorporate the piston can be done in the sequence reverse to drawing-out. While putting back the piston into the engine following important procedure must be followed:

  • Incorporate the perforated piston cooling case cover on the operating side, apply a proper screw lock agent on the bolts, and tighten them to fix the cover.
  • Incorporate the piston rings as per the sequence is given in the correct direction of their cuts shifted to the recommended angle from those of adjacent rings.
  • To reduce the possibility of opening and damage, Incorporate the oil ring with its coil joint shifted 180° from its cut.
  • Incorporate the piston and connecting rod, aligning their set marks with each other.
  • Apply plenty of lubricating oil to the piston, piston rings, cylinder liner, and crankshaft pin just before insertion. Make sure lubricating oil is not applied on the rear face of crankpin metal bearing which may cause slippage or small relative moment during operation.
  • Set the piston inserting guide on the liner and incorporate the piston. While tapping the piston with a resin hammer, drive the piston down.
  • Align the connecting rod bottom end with the crankshaft pin and then fit the connecting rod bolts, metal bearings, metal cap and tighten the nuts up to the specified torque/ hydraulic pressure as recommended by the manufacturer.
  • Check the connecting rod bottom end part free axial movement by pushing with a small bar. Make punch mark/ paint marking on the bolts and bottom casing for reference.

After inserting all pistons and securing of connecting rod bolts turn the engine with the help of turning gear and check for free movement. If everything is satisfactory prepare for cylinder head assembling.


  • Clean all the packing ring and o ring sitting area and replace each packing and O-ring with new ones. If you cannot avoid using a packing or an O-ring again, sufficiently check it for no flaws, deformation, and deterioration before using it.
  • Put the stem seals on suction and exhaust valves guide with the help of special too provided.
  • Apply the lubricating oil on the suction and exhaust valves, put the valve mounting tool, valves, valves spring, valve rotor. Compress the spring and attach the same cotters as those used in the disassembly to the respective valves, and fit them while taking care not to damage the lip of a valve guide stem seal.
  • Use the correct thickness of new head packing, as that used previously, to maintain the same the top clearance.
  • Check for no foreign mattes in the suction and exhaust passages of the cylinder head, piston upper part and boost air chamber of the cylinder, and then incorporate the cylinder head.
  • Take care not to flaw the threaded part of a cylinder head bolt, when mounting the cylinder head on the cylinder liner
  • Tighten cylinder head nuts with hand, put hydraulic jacks and tighten as per the correct sequence at rated hydraulic pressure. After securing the nuts apply grease or lubricating oil on the hydraulic jack fitting threaded part of the cylinder head bolts to prevent the threaded part from being rusted.
  • Mount all the cylinder head mountings including 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, rocker arm, suction/exhaust valve guard and pushrod. Put the overhauled and pressure tested fuel valve and secure it. Renewed O rings and packing wherever required.

After overhauling and fitting back of the cylinder liner, piston and cylinder head, open jacket water and check for a water leakage from the O-ring part. Open preheating jacket water valve and ensure initial warming up of the engine.

Carry out following inspection and make sure there is no abnormality and all operational preparation has completed.

  • Make sure no rags, spare part or tools have been left in the crankcase.
  • Take fresh lube oil in the crankcase
  • Check for the tightness of all parts.
  • Check and adjust the suction/exhaust valve tappet clearance.
  • Open the pressure indicator cocks of all the cylinders and start the lubricating oil priming pump.
  • While turning the flywheel, make sure the optimum lubricating oil is dropping from each part of the valve rocker arm shafts, piston pins, crank pins, main bearings, and piston cooling arm.
  • Bleed the air from the fuel oil and lubricating oil strainer and pipings.
  • Manually lubricate the governor linkage, and make sure it moves smoothly.

Initial Running-in Operation

For the prevention of initial abnormal wear of piston rings and cylinder liner, most of the maker’s advice to run the engine on diesel oil and at very low load. It ensures the proper matching of piston rings and liner and then only gives proper sealing effect. Refer your maker’s manual and follow procedures as recommended for running in.

In general, we can follow the following procedure for the initial running:

  • Start the engine and run it for 5- 10 minutes.  Check all the surrounding for any abnormality and all other running parameters. Stop the engine, open crankcase doors and check for bearing temperatures and connecting rod bolt markings. If everything is in good condition again start the engine and run it for15 to 20 minutes and follow the same procedure of inspection. Run the engine for one hour without load and repeat the checks.
  • After no load running if everything is in order to run the engine for an hour each on 10%, 30%, 50% and on 75% load. During this trial operation increase the load slowly and keep continuous monitoring on all running parameters ie: Exhaust temp, scavenge air temp, Jacket water temp, lube oil inlet temp and pressure temp of all units, turbocharger inlet/Outlet exhaust and lube oil temperature.
  • After sufficient running in operation run the engine on 85% load and take performance and check all readings.
  • Nearly after 500 running hours, open the crankcase door once again and check for the tightness of connecting rod bolt, the axial freeness of bottom end and the markings made during the re-tightening of connecting rod bolts.

Do not open the side cover of crankcase for at least 10 minutes after having stopped the engine. Entry of fresh air into the engine may cause ignition of oil mist, resulting in an explosion. Crankcase Explosion: Cause, Action and Safety Arrangement

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Anurag Singh

He is working as an engineer in Synergy Marine Group. He is alumni of Marine Engineering & Research Institute(MERI) Mumbai. With his versatile talents, he loves to play cricket and write blogs. Speciality: Tanker operations

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