Marine decarb - To free the auxiliary generator engine of carbon deposits and much more

Marine decarb - To free the auxiliary generator engine of carbon deposits and much more
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D’carb of auxiliary engine is nothing but the carrying out of certain routines at intervals prescribed by the manufacturer or experience. Normally the following should be done during a marine decarb to free the engine from anomalies

  • Every 3000hrs take out cylinder head, take the worn out mountings and/or over haul the mountings
  • All units cylinder head, piston, connecting rod, and turbocharger to be overhauled
  • Clean sump tank and fill with fresh lube oil
  • Take crank shaft deflection before and after removal of bearings
  • What ever actions taken should be recorded in the maintenance record book

D’carb preparation

  1. Make sure the all stand by auxiliary engines are ready
  2. Keep all the special tools and other tools ready
  3. Go through the previous records/manual for clearance and adjustments
  4. Put the display card “MEN AT WORK”, “DON’T START”
  5. Close air bottle valve to auxiliary engine and engine start and stop valve
  6. See that the turning bar is not in the flywheel and should be in place
  7. Open the indicator cocks
  8. If the main bearing is to be removed, check crank shaft deflections
  9. Close lube oil, fuel oil, fresh water inlet/outlet valve, drain the cooling water line and remove connections

Cylinder head of generator engine before cleaning

exhaust valve before cleaning

Removal of cylinder head

  1. Scavenge manifold, exhaust manifold rocker arm, lube oil drain connection from rocker arm, rocker arm tank and cover connection to be removed
  2. Fuel oil high pressure connection from fuel pump to the injector, fuel valve cooling connections in and out (either diesel or water) to be removed
  3. Remove the rocker arm assembly and the push rod. Remove all the mountings such as starting valve, indicator cock, relief valve and exhaust valve assembly
  4. Remove the rocker cover and check any marking on cylinder head nuts and studs. If no torque spanner is available, note down the markings.
  5. Open the cylinder head nut with box spanner and extension rod. Never use the torque spanner. With box spanner available note down the marking .
  6. Put the cylinder head lifting tool and before lifting make sure all the connections are removed. Also ensure that the liner is not removed along with the cylinder head
  7. Take out the copper joint between the head and the liner

Piston removal pictures

piston with rings before cleaning

piston with out rings before cleaning

piston after cleaning

connecting rod removal

Removal of piston and connecting rod

  1. After lifting the head, check the liner surface for score marks, blow past etc. Crack remove the ridges or deposits if any on the top surface to avoid the lifting of liner along with the piston and breakage of piston rings while lifting piston
  2. Open the crank case door and remove the bottom end bearing bolts after removing the lock arrangement and the remove the bolts
  3. Remove the bottom half of the bottom end bearing
  4. Bring the piston to TDC. Make sure the bolt holes on the piston top, lifting tool holes must be cleared from carbon deposits. Threads should also be checked and cleared
  5. Put the piston lifting tools and tighten the bolts
  6. Lift the piston and remove top shell of bottom end bearing
  7. Place the piston on the piston stand and cover the crankcase pin to avoid the foreign material damaging the crank-pin.

Cylinder liner and other parts d’carb

liner before cleaning

cooling water space after liner removal

cooling water side of liner

liner after honing process

piston pin removal

connecting rod cleaning

bottom end bearing before cleaning

bottom end bearing after cleaning

Cleaning the carbon content on all the parts of engine

  1. Clean the piston rings, measure dimensions and keep them in order
  2. Clean the piston ring grooves thoroughly and measure the groove thickness at 3 different points
  3. Check for the deposits on piston crown (Sulphur, carbon or thick vanadium deposits) and measure the dimensions
  4. Remove the gudgeon pin and clean the gudgeon lube oil holes as well as the bush or small end bearing
  5. Check the bolts of connection rod for any cracks
  6. Every 20,000 hrs engine connecting rod bolt must be replaced
  7. If new piston rings are going to be replaced, then there is no need for measurement
  8. Calibrate the liner thickness by using template

Assembly of the engine parts

  1. First put the piston rings one by one and measure the butt clearance for all the rings
  2. Then measure the axial clearance between piston rings & grooves
  3. Place the piston guide on top of the liner and bring the particular crank shaft to TDC. Apply sufficient lube oil and start lowering the piston. Make sure that butt gap should not be in line it may cause blow past
  4. Before engaging check the crankpin for any cracks or scratch
  5. Check the bottom end bearing clearance and if needed measure the main bearing clearance as well
  6. Taper clearance is checked
  7. Check for any cracks in the water jacket and in the cylinder head
  8. Replace all rubber joints and copper gasket to be put on the cylinder cover
  9. Put the cylinder head gasket in the top of the cylinder
  10. Anti-seizure coating or powder like molycote, copper slip should be used. It is applied to avoid any seizure mainly on the threads or joints and it will be easier while removal
  11. Tighten the cylinder mounting according to torque specified as in manual and make all connection like lube oil, fuel, jacket cooling water connections etc
  12. Fit the rocker arm back


A Paper on HFO Gensets by C.P. Ships (UK) Ltd.

This post is part of the series: Diesel Generator Set - Used On Board.

This series will help you in understanding the overhauling procedure of the diesel generator set i.e. D’carb of generator and checks to be made before starting it.

  1. D’carb Process Of Auxiliary Generators Explained In Detail
  2. Marine Generators - Starting Checks & Procedure