MARINE ENGINEERING PRACTICE Volume Part MARINE MEDIUM SPEED DIESEL ENGINES by S H HENSHALL, C.Eng., F.I.Mar.E., F.I.Mech.E THE INSTITUTE OF MARINE ENGINEERS Published by The Institute of Marine Engineers The Memorial Building 76 Mark Lane London EC3R 7JN UK First published 1973 Reprinted 1991, 1995, 1996 © 1973 Marine Management (Holdings) Ltd A catalogue record for this publication is available from the British Library ISBN 900976 09 All rights reserved No part of this publication may be reproduced, stored in a retrieval sytem, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher Printed in the United Kingdom by Hobbs the Printers Ltd, BruneI Road, Totton, Hampshire S040 3WX CONTENTS Page Definition of Medium Speed Diesel Engines Four Stroke Cycle Diesel Engines Two Stroke Cycle Diesel Engines Construction 11 Operation 50 57 Maintenance ACKNOWLEDGEMENTS The author acknowledges with gratitude the assistance of his colleagues at Mirrlees Blackstone Limited, a Hawker Siddeley Company, and the permission of the Directors of that Company to publish this work His thanks are also due to Bryce Berger Limited for their kindness in providing the figures illustrating fuel injection equipment, and to Turnbull Marine Design Co Ltd., for their help in drawing some of the original figures DEFINITION OF MEDIUM SPEED DIESEL ENGINES 1.1 Diesel engines operate on either a four stroke or a two stroke cycle The feature which distinguishes diesel engines from other reciprocating internal combustion engines is that the fuel is not introduced into the cylinder until just before the beginning of the expansion (or power) stroke and it is ignited by coming into contact with the air in the cylinder which is very hot as the result of compression For this reason, they are sometimes called compression ignition engines 1.2 Medium speed diesel engines may be defined as those having rated speeds within the range of 300 to 1000 rev / FOUR STROKE CYCLE DIESEL ENGINES 2.1 The essential parts of a four stroke cycle diesel engine are shown in Fig 1, and in Fig are depicted the events of each of the four strokes Starting with the piston at the top of the cylinder, the induction stroke is performed as the piston moves down During this stroke the inlet valve remains open and a charge of air is drawn into the cylinder The piston then returns to the top of the cylinder whilst both inlet and exhaust valves remain closed and the charge of air is compressed The compression raises the temperature of the air and as the piston reaches the end of this stroke, a controlled amount of fuel is injected into the cylinder in the form of a fine spray On coming into contact with the hot air the fuel ignites causing a rapid rise in pressure which drives the piston downwards on the expansion stroke As the piston reaches the bottom of the cylinder for the second time the exhaust valve is opened and during the upward and fourth stroke the hOt spent gases are expelled through it 2.2 If the charge of air entering the cylinder during the induction stroke is drawn in by the piston movement only without being assisted in any way, then the engine is said to be naturally aspirated 2.2.1 The power of any diesel engine is determined by the amount of fuel that can be burnt in each cylinder per cycle and the speed at which it can be run The rotational speed is limited by the forces arising from the inertia of the moving parts In the case of a naturally aspirated engine the amount of fuel that can be burnt is limited by the mass of air drawn into the cylinder during the induction stroke Diesel fuel requires about 14'5 times its own mass of air for complete combustion The time available for combustion in the diesel cycle is very short; if only the chemically correct amount of air were provided, the fuel would not have time to burn completely and, in practice, almost twice this quantity is found to be necessary 2.3 The cylinder can be charged with a greater mass of air by supplying it under pressure The air is pressurized in a compressor, sometimes termed a blower, and fed to the induction manifold of the engine The process is called pressure charging or supercharging 2.3.1 In some special cases the compressor is driven mechanically from the engine crankshaft More usually, some of the energy present in the exhaust gas is utilized by passing it through a turbine which is directly coupled to a centrifugal compressor The compressor- and turbine together form a free running unit, separate from the engine, known as a turbocharger Figure shows diagrammatically a turbocharger and a turbocharged engine 2.3.2 The pressure of the air in the inlet manifold to the cylinders of a turbocharged engine is termed tile boost pressure In engines having a high boost pressure the air leaving the compressor is hot and it is beneficial and sometimes necessary to cool it as this assists in increasing the mass of air filling the cylinders and in keeping the internal parts of the engine cool The air is cooled by passing it through an intercooler FOUR STROKE CYCLE DIESEL ENGINES 2.3.3 The quantity of air provided by turbocharging is so great that the amount of fuel that can be burnt in each cylinder per cycle (and hence the power) is not limited on this account but by the temperature which the exhaust valves, cylinder heads and pistons can withstand TWO STROKE CYCLE DIESEL ENGINES 3.1 Two stroke cycle diesel engines take several forms 3.1.1 One form, which is illustrated in a simple manner in Fig 4, has a 61 MAINTENANCE If the "nip" or the clearance is incorrect a new shell or pair of shells should be selected with the most advantageous dimensions within the manufacturing tolerances When fitting these shells in position it is essential to be sure that they are absolutely clean It is a mistake to use thick grease on the backs of the shells in order to secure them in position during assembly as this would be quite sufficient to distort their shape 6.4 CRANKSHAFT ALIGNMENT 6.4.1 Frequency of Inspection The crankshaft alignment should be checked at installation and then after the first 1000 hours of running have been completed Thereafter, a check should be made at annual overhauls These checks should be made with the engine and oil tanks warm, and with the ship in its most usual loaded condition Additionally, the alignment should be checked whenever a holding down bolt or a major part of the engine structure has been disturbed 6.4.2 Inspection Procedure and Criteria The cylinders should be put into open communication with the atmosphere by opening the indicator cocks or by removing the injectors or some equivalent action The deflexion gauge should be inserted between the webs of No crankshaft as shown in Fig 45, the crank being set as nearly as possible to bottom dead centre as indicated The dial gauge is adjusted to zero The first check is to make sure that the engine is firmly bolted down This is done by watching for a change of reading on the dial gauge whilst testing each foundation bolt adjacent to No crank for tightness If there is any change of the gauge reading the holding down bolt should be slackened off and shims inserted until the bolt can be pulled down tight without altering the dial gauge reading The procedure is repeated for all the other holding down bolts with the gauge in the appropriate crank It is preferable to fit new chocks rather than leave a number of shims on top of a chock when a correction has been made The next check is to ensure that the main journals are resting on the bottom half of each main bearing Each crank in turn is placed as nearly as possible on bottom dead centre with the dial gauge between its web and set to zero The main bearing caps adjacent to the crank are lifted and a strip of well oiled fibre is placed between the top half of the bearing shell and the journal The cap is replaced and pulled down; during this action the gauge is watched for any change in reading and if such a change takes place it means that the journal concerned is not resting on the bottom half of its main bearing The measurement is usually repeated at 180 past the bottom dead centre turning the crank in the normal direction of rotation and without resetting the gauge These checks should be made starting at No crank and No journal and repeated on all the other cranks and journals in turn 62 MARINE ENGINEERING PRACfICE If the dial gauge alters its reading by more than 0'006 mm (0'00025 in) it means that a journal is not resting on the bottom half bearings as it should A significant difference in the numerical value between readings taken with a crank pin at the bottom and at the top dead centre means that either the journal is not round or the crankshaft is permanently bent Permanent distortion of a crankshaft is most unusual but if a check on the diameters of the journals shows them to be round, then it must be assumed that bending of the crankshaft has somehow taken place In this case the crankshaft will have to be removed from the engine and returned to the manufacturers for a thorough check and possible correction More usually, the journal is prevented from resting on the bottom half of the bearing because either the bottom half bearing has failed or it is not of the correct thickness, or the bearing housings are not in correct alignment The bearing shell can be checked for thickness by direct measurement using a micrometer If there is a previous record of thickness of the bottom halves with the crank shaft in alignment (this will be available if a proper maintenance log book has been kept), then by measuring the thickness of the suspected bottom half shell it can be decided whether or not there has been excessive wear (when the bottom half shell would have to be replaced), MAINTENANCE 63 or whether the engine bearing housings are out of alignment If there is no previous record of thickness of the bottom halves and the crankshaft alignment readings are satisfactory, then it is necessary to measure the thickness of the adjacent bottom halves and to assess the correct thickness for the bottom half that is not supporting its journal After refitting replacement bottom half shells, a further check must be made of whether journals are resting on them When it has been ensured that the crankshaft is resting properly in the bottom halves of each main bearing then a check can be made on the alignment With the main bearings correctly assembled as for running the dial gauge is inserted between the webs of No crank with the latter as nearly as possible at bottom dead centre, as shown in Fig 45 The dial is set at zero The crankshaft is then turned round in the normal direction of rotation and a reading taken at 900, 1800, and 2700 past bottom dead centre The zero is then checked by a reading as close to 3600 as is possible This procedure is then repeated on all other cranks The manufacturer's instruction book will give the permissible limits for crankshaft deflexions However, as a general guide for engines with cylinder bores between 203 and 406 mm (8 and 16 in) the following may be taken When the engines and bearings are new the deflexion should not exceed 0'00005 times the crankshaft diameter When the engine has been in use for some time deflexions of up to 0'00012 times the diameter of the crankshaft are acceptable and the engine may be allowed to continue to its next annual overhaul If the deflexions should exceed 0'00017 times the diameter of the crankshaft then immediate action to correct them should be taken 6.4.3 Remedies Worn bearings should be replaced so that the journals of the crankshaft rest on each bearing If this does not give true crankshaft alignment it may be necessary to re-chock the engine, first trying with shims at each holding down bolt to ensure that the bearing housings are in line It helps a good deal to make a rough sketch of the crankshaft and its main hearings in conjunction with a table of the crankshaft alignment readings, this when examined will indicate which bearings are likely to be low and in need of renewal in order to correct the crankshaft alignment Finally, in the maintenance log book, tabulate the dial gauge alignment readings for the reassembled engine both with the crank free and with the caps pulled down on to fibre strips 6.5 TORSIONAL VIBRATION DAMPERS 6.5.1 Frequency of Inspection At annual surveys Whenever the crankshaft is being examined or the damper is exposed to some other job 64 MARINE ENGINEERING PRACTICE 6.5.2 Inspection Procedure and Criteria The bolts and nuts or other fasteners securing the damper to the shaft should be examined for tightness If the damper is of the viscous fluid type it should be examined for discolouration and signs of leaks" for deformation and cracks Mechanical dampers should be examined in accordance with the maker's instructions 6.5.3 Remedies Any kind of damper must be securely fixed to the shaft and any loose fastenings should be renewed A viscous damper showing leakage or deformation must be replaced by a new damper Mechanical dampers should be maintained in accordance with the maker's instructions ,6.6 CONNECTING ROD, Top END BEARINGS, BOTTOM END BOLTS 6.6.1 Frequency At annual surveys If a piston seizure has occurred Any time a connecting rod is removed 6.6.2 Inspection Procedure and Criteria The rod and the bottom end bearing cap should be examined for fretting and cracks If they have visible defects they should be replaced If the piston has seized or if new bottom or top end bearings have been fitted, then the connecting rod alignment should be checked The connecting rod assembled with its bearings should be supported on rectangular ground steel blocks on a surface table as shown in Fig 46 Mandrels of a size that closely fit into the top end and bottom end bearings are used as shown By traversing a dial gauge over both ends of both mandrels, any twist in the rod can be detected By measuring the difference in the distance between the mandrels on either side of the connecting rod any lack of parallelism between the two bearings can be detected These measurements should be taken about 150 mm (approximately in) along the mandrel from either side of the connecting rod Misalignment in either sense should not exceed 0'130 mm (0'005 in) If it does, the bottom end bearing shells and the small end bush should be removed from the rod and larger diameter mandrels which fit the bores in the rod should be used to check whether the fault lies in the rod itself or in the bearing bush or shells In the case of a marine-type connecting rod, the fault may lie in the bottom end bearing housing or in -the rod If the assembled rod shows no misalignment from twist but does show lack of parallelism then the rod should be dismantled from the housing and placed perpendicularly on its palm end on the surface table and measurements shall then be taken up to the small end mandrel MAINTENANCE 65 6.6.3 Remedies If the fault is shown to lie in the bearings then new shells or a new small end bush should be fitted If the fault is not in the bearing shells then it is necessary to fit a new connecting rod except, perhaps in the case of a FIG 46.-Connecting rod alignment marine type rod where the fault may lie in the compression plate or in the housing and a rectification can be made by scraping or filing the incorrect component 6.6.4 Bottom End Bolts The bottom end bolts should be inspected before being replaced and 66 MARINE ENGINEERING PRACTICE tightened If a bolt has completed 15000 running hours it should be renewed whatever its condition Bolts should also be renewed if the engine has experienced a piston seizure or if there has been a failure of an overspeed trip such that the engine has unintentionally run at very high speeds Before replacing each bolt it should be inspected to see whether it is scored, bent or twisted It can be checked for straightness by rolling it on a surface plate using engineer's blue Twist is indicated by scribed lines on the bolt If no lines exist they should be scribed for use at the next inspection Note that these lines are scribed only on the raised shoulders not on the highly stressed waisted part of the bolt The free length of the bolt should be measured by the method specified by the engine manufacturer This will be a measurement of either the overall length or the length from the underside of the head to the screwed end of the bolt, or from the underside of the head to a mark made on a flat on one of the threads The nut should be inspected for distortion and cracks and it should be checked that it screws on the bolt by hand easily, but firmly Any unacceptable bolt or nut should be replaced When reassembling the bottom end bearing the bolt must be tightened to the correct tension using either a torque spanner or an extension gauge as advised by the engine maker The nut castellations should be brought in line with the split pin hole by careful filing of the nut face and not by slackening or further tightening of the nut 6.7 GUDGEON PINS, PISTON BOSSES AND SMALL END BEARINGS 6.7.1 Frequency of Inspection At annual overhauls or whenever a piston is removed 6.7.2 Inspection Procedure and Criteria The gudgeon pin should be removed from the piston (an aluminium piston should be heated in boiling water to free the gudgeon pin) and inspected for distortion by rolling it on a surface plate or table using engineer's blue It should also be examined for cracks and scores on its surface A pin showing any of these faults is unacceptable The gudgeon pin bosses in the piston and the small end bush in the connecting rod should also be inspected for scores or cracks The maximum and minimum diameters of the gudgeon pin should be measured and also the bores of the gudgeon pin bosses in the piston and the internal bore of the small end bush The correct clearances between these parts depends upon the size of engine, the piston material and whether four stroke cycle or two stroke cycle operation is used The manufacturer's criteria should be followed in judging when replacements are needed 6.7.3 Remedies If the gudgeon pin, the small end bush or the bushes in the piston are unacceptable then the component should be replaced After fitting a new MAINTENANCE 67 small end bush it should be reamed to the correct size If a new piston is fitted a new gudgeon pin should be used with it 6.8 PISTON, RINGS AND CYLINDER LINERS 6.8.1 Frequency of Inspection At annual surveys, whenever a piston is removed, or if a piston seizure has been experienced 6.8.2 Inspection Procedure and Criteria The piston should be inspected to see that it is free from cracks and that there are no ridges or grooves on bearing surfaces other than the ring grooves If scores cover more than per cent of the contact area with the liner the piston is unacceptable The axial clearance of each piston ring should be measured at about four places round its circumference, this is done by pressing the ring down on the bottom land of the groove and using feelers to measure the clearance between the top of the ring and the top of the groove This axial clearance should be between 0'00045 and 0'0015 of the piston diameter The rings should be inspected to see that they are free from ridges, cracks and grooves The gap clearance of the rings should be measured by inserting each ring in turn in a ring gauge or if none is available by placing it in the bottom unworn portion of a cylinder liner and using a depth gauge or a piston crown to make sure that is is positioned symmetrically The gap is measured by feeler gauges between the ends of the rings The top compression ring gap should be between 0'006 and 0'009 of the cylinder bore, the other rings between 0'004 and 0'006 The bores of cylinder liners should be inspected and measured They should be free from scores, cracks and ridges If the liner is chromium plated then patches where the chromium has worn off should be carefully examined If scoring of the surface is evident, the corresponding part of the piston should be examined to see if gas blow past is occurring A cylinder dial gauge should be used to measure the wear of the liner by taking readings parallel to and at right angles to the centre line of the crankshaft at the top of the top piston ring travel, half way down the liner bore, and at the bottom of the liner bore where it is probably not worn These readings should be entered in the maintenance log Any liner which is badly cracked or scored causing gas blow past should be replaced If the chromium plate on the bore of a liner is beginning to wear through, the liner should be replated The wear of a cylinder liner should not exceed 0'004 times the bore diameter If it is a chromium plated bore liner the permissible wear will depend on the thickness of the chromium plate and the makers should be consulted 6.8.3 Remedies A piston that is cracked or badly scored or ridged will have to be 68 MARINE ENGINEERING PRACTICE repewed; small scores and ridges can be smoothed by hand If the axial clearance of the piston rings is unacceptable, the ring should be measured to see whether it is the ring or the groove that is worn If it is the groove, then some manufacturers offer rings of oversize axial thickness and the groove can be re-machined to suit such a new ring If this facility is not available, then a replacement piston is necessary If the gap clearance of a piston ring is too large the thickness of the ring should be checked and the ring replaced if it is apparent that it is badly worn The new ring should also be checked for gap clearance and filed on the butts to the correct minimum dimension Chromium plated rings must not be fitted in chromium plated cylinder liner bores A cylinder liner will have to be replaced if it is cracked or if there is excessive wear or scoring of the bore, or pitting and corrosion on the outside A ridge will have formed in the liner bore at the top of the piston ring travel, this should be removed by stoning if the top ring is renewed 6.8.4 Reassembly When the connecting rod assembly has been checked for alignment, as described in Section 6.6.2., it should be assembled, with the piston, in the engine as for running With the piston at the top of its stroke a check should be made, using feeler gauges at the top of the crown and the bottom of the skirt, to see that its axis is parallel with the liner bore This check should be repeated with the piston, halfway down and again at the bottom of its stroke If the alignment is wrong, withdraw the assembly and recheck the connecting rod alignment If the fault does not lie in the rod set the piston on a surface table and check that the gudgeon pin bore is square with the outer surface If the piston is satisfactory check the liner for symmetry 6.9 COMBUSTION CHAMBER AND VALVES 6.9.1 Frequency of Inspection The intervals at which the exhaust valves will require attention will depend on the duty of the engine and on the fuel which is used When running on heavy fuel it may be necessary to inspect exhaust valves between 500 and 1500 hours but an installation running on light fuel will probably be satisfactory if left to run for 2000 hours and may be as long as 8000 hours between inspections When the engine is equipped with caged exhaust valves, only the cage assembly need be removed at this interval of time By using reconditioned units which can be replaced immediately the time out of service for the engine may be kept to a minimum Removal of cylinder heads may be left until the annual overhaul If the exhaust valves are fitted directly in the cylinder head then the 69 MAINTENANCE cylinder head itself must be removed at the inspection period required to keep the exhaust valves in good condition 6.9.2 Inspection Procedure and Criteria The combustion chamber sutiaces should have a light coating of sooty carbon Any heavy deposit of carbon or sludge indicates faulty combustion After noting the extent of the carbon deposits the internal parts of the combustion chamber should be cleaned thoroughly; they should then be examined for cracks and scores and the valves and valve seats for pitting, burning or abrasions The valve seat and valve should be examined together to ensure that "pocketting" has not taken place as a result of excessive wear or frequent regrinding The diameter of the valve stem and the bore of the valve guide should be measured and entered in the log book The valve stem should be tested for straightness by rolling on a surface table The valve springs should be examined to see that they are free from pitting, cracking, scoring and corrosion The free length of each spring should be checked against the length of a new spring or compared to the minimum stipulated by the engine manufacturer 6.9.3 Remedies and Reassembly Any part which is cracked should be replaced by a new part A new part should also be used to replace a valve which is bent in the stem or too badly burned to be reground, a valve cage seat which is too badly pocketted, pitted or burned to permit recutting and regrinding, a valve or guide which has too much clearance and a valve spring which is pitted, cracked, scored or corroded or is less than the minimum allowable free length Valves and valve seats should be recut and reground using the appropriate machines where these are available to remove all pits and signs of burning Each valve should then be ground into its seat by hand until it makes contact all the way round its circumference 6.1 O VALVE GEAR, CAMS AND CAM SHAFT DRIVE 6.10.1 Frequency of Inspection At annual surveys 6.10.2 Inspection Procedure and Criteria The cams, cam followers, tappets and all the valve operating gear parts should be inspected to see that there are no cracks, flaking, scores or burrs, and to see that wear has not reached a stage which would prevent the accurate setting of clearances or satisfactory operation of the engine Push rods should be checked on a sutiace table to indicate whether they are straight If the earn shaft drive is by gears the teeth should be checked for 70 MARINEENGINEERING PRACTICE pitting, abrasion and deformation and the back lash checked by feeler gauge or dial indicator This check should be made at 90° intervals around each wheel The amount of backlash depends on the design of the gears and the maximum allowable figure should be obtained from the engine builders If the camshaft drive is by chain, the rollers and links' should be inspected for pitting and abrasion With the chain removed the alignment of the chain wheels should be checked by means of a straight edge across the end faces of each pair of wheels The chain stretch should be measured by laying it on a flat surface and stretching it by applying a known force measured by means of a spring balance The engine makers will provide a figure for this stretching force The length of the chain should then be measured over a known large number of pitches If the length when stretched exceeds by more than 1/ 50th the length obtained by multiplying the number of links by the chain pitch then it should be discarded With the chain assembled on the wheels in the engine the tension should be adjusted so that it is just sufficient to prevent any appreciable backlash The correct tension is frequently judged by moving the centre of the longest free span of chain inwards by hand and checking that the movement is between and per cent of the length of the span This should be checked at each 90° interval of movement of the wheels 6.10.3 Remedies and Reassembly Any slight burrs can be removed by hand; any other sort of damage requires replacement of the unacceptable part After reassembling the camshaft drive, camshaft and valve gear, the tappet clearances should be set to the figures recommended by the engine maker 6.11 FUEL INJECTION EQUIPMENT 6.11.1 Frequency of Inspection The fuel injectors will need replacing by reconditioned units at intervals of 500 to 1500 hours according to the duty of the engine and the type of fuel used Smoke in the exhaust gas or a rise in exhaust temperature at full load is an indication that perhaps an injector requires attention Experience of the particular installation will be the best guide in settling down to a regular reconditioning of injectors at definite periods The fuel control mechanism between the governor and the fuel pumps should be examined at intervals of every 500 running hours The fuel pump, including the delivery valve, should be inspected at annual overhauls Any imbalance in exhaust temperatures or unsatisfactory combustion which cannot be cured by changing fuel injectors should be the occasion for close examination of the fuel pump control mechanism and perhaps for the replacement of a fuel pump by a reconditioned or a new one 6.11.2 Inspection Procedure and Criteria Fuel injection equipment is very precisely and accurately made and MAINTENANCE 71 a number of parts have exceptionally small clearances between them The overhaul and general repair of this equipment should be approached only by an operator who has satisfied himself that he has the proper tools and test equipment as well as the required specialised skills If complete facilities are not available it is better to have the work done by qualified specialists A scrupulously clean bench covered with linoleum or zinc should be used in a dust free atmosphere together with clean tools and receptacles for the parts The most that can be done with the critical components such as needle valves and nozzles, fuel pump elements and delivery valves is to clean them thoroughly, reassemble and adjust; they can rarely be serviced in any way and any work performed with the intention of improving performance almost invariably destroys the important design characteristics of the component 6.11.3 Reconditioning Injectors Before dismantling an injector it should be cleaned thoroughly and carbon deposits removed from the nozzle taking care not to damage the tip The sequence of dismantling may vary with the type and make of injector and the manufacturer's instructions should be followed If the nozzle is held in the nozzle nut by a formation of carbon it may be necessary to push it out using a tubular drift made of copper or brass, as in Fig 47 It should certainly not be driven out by striking the nozzle end As the parts of the injector are dismantled they should be placed in a bowl in clean paraffin and left to soak It is necessary to have a separate bowl for each injector being dismantled as the parts from different injectors are not interchangeable Carbon and lacquer should be cleaned from the parts using a nozzle fuel chamber scraper, a nozzle hole pricker, a seat cleaning tool and a brass wire brush as supplied by the injector manufacturer Care must be taken not to scratch a needle valve, its seat in the nozzle or any mating surfaces which are intended to seal fuel oil pressure If any of these mating surfaces show signs of damage such as pitting, scores or grooves when examined under a magnifying glass, they are not acceptable and they should be replaced with new parts or parts that have been reconditioned by the makers 6.11.4 Reassembly and Testing of Injectors Before assembling the parts of an injector they should be thoroughly washed in light fuel oil and assembled whilst wet Before replacing a fuel injector in the engine, whether it is a new or reconditioned unit, it should be checked by connecting it to a test pump fitted with a pressure gauge and the injection pressure measured and set, whilst the spray is inspected for quality, pattern and absence of dribble' The test pump may be a unit on the bench of the type shown in Fig 48, or if such is not available then the engine injection pump can be used with a special test pipe connected to it so that the injector is held where it can be seen whilst the pump is operated by a special lever 72 MARINE ENGINEERING PRACTICE MAINTENANCE 73 Spraying should be set to commence at the pressure recommended by the engine builder, and there should be no sign of leakage or dribble at any lower pressure The spray should be in the form of fine mist free from streaks of unatomized fuel, each jet should be symmetrical about the centre line of the nozzle hole A reconditioned injector which is not required for immediate use should be carefully stored, having been covered with preservative grease, the pipe connection plugged and the complete unit wrapped in greaseproof paper When the injector is replaced in the cylinder head, the holding studs must be tightened evenly to the correct amount 6.11.5 Reconditioning Fuel Injection Pumps The delivery valve should be removed from the fuel pump, inspected and its seat checked for wear, scores or pitting, none of which is acceptable The fuel pump performance can be checked by connecting a new or reconditioned fuel injector to the outlet and, with the fuel control rack in the full fuel position, operating the pump and observing the spray and comparing it with that from an injector connected to a new pump Operating the pump by hand often gives an indication by feel of whether the clearances are maintained and the pump operating correctly Pumps should be dismantled, following the makers instructions, and the parts washed in paraffin and placed in bowls, each bowl containing the parts only from one pump The contact surfaces of the plunger and barrel and the sealing face of the barrel should be inspected with a magnifying glass for evidence of possible leakage which will show as fine irregular radial tracks on the surface If any blemishes are found they can seldom be rectified and it is safer to replace the element assembly Damaged or flattened sealing rings should be renewed Any washers removed should be discarded and new ones fitted 6.11.6 Reassembly of Fuel Pumps Prior to assembly all parts must be thoroughly cleaned and oiled and assembled whilst still wet Careful attention should be paid to the manufacturer's instructions When a pump is replaced on an engine it will require retiming and adjusting to carry its correct share of the load The procedure is described in Section 5.4 6.11.7 The fuel control racks and mechanism should move freely when operated by hand but without excessive play Check that all lock nuts on control rods and links are tight and that pins and joints are properly lubricated 6.12 GOVERNOR 6.12.1 Frequency of Inspection At annual overhauls 74 MARINE ENGINEERING PRACTICE 6.12.2 Procedure and Criteria When dismantling an hydraulic governor the manufacturer's instructions should be followed closely On all governors when dismantled the parts should be cleaned and examined for cracks, rust, scoring, pitting or distortion Any parts, showing deterioration of this kind should be replaced Pins and bushes may show wear, if this is excessive the parts should be replaced Neither undue stiffness between mating parts nor undue play is acceptable The free length of each spring in the governor should be measured and compared with the maker's limits In general the free length of these springs should not differ from that of a new one by more than per cent 6.12.3 Reassembly The governor should be reassembled, replaced on the engine and the links adjusted in accordance with the maker's instructions When carrying out these checks and adjustments it is necessary to move the start, run and stop controls and the speed control, consequently great care must be taken to ensure that there is no danger of starting the engine accidentally; all valves controlling the supply of compressed air for starting should be turned off and the fuel also should be turned off, except when required for adjustments The maximum fuel position of the fuel pump racks when up against the limit stop should correspond with settings taken before the governor was dismantled 6.13 TURBOCHARGER 6.13.1 Frequency of Inspection At annual overhauls 6.13.2 Inspection Procedure and Criteria Turbochargers are high speed machines requiring very careful handlin~ in maintenance Unless skilled labour is available it is advisable to fit replacement turbochargers and return the removed unit to the manufacturer for reconditioning If skilled labour is available and maintenance is undertaken then it should be in accordance with the turbocharger maker's instructions When cleaning the turbine blades and the compressor impeller it is essential to ensure that all deposits are removed so as to maintain the rotor balance Scale and sludge should be removed from the water spaces and ducts if the turbocharger is of the water-cooled variety All clearances and wear should be checked to see that they are within the manufacturer's recommended limits If ball and roller bearings are used then these should be renewed If any part of the rotating assembly such as a turbine blade or an impeller requires replacement the whole assembly should be returned to the MAINTENANCE 75 manufacturers for replacement of unacceptable parts and rebalancing of the assembly When the turbocharger has been reassembled, check that the rotor turns freely ...Published by The Institute of Marine Engineers The Memorial Building 76 Mark Lane London EC3R 7JN UK First published 19 73 Reprinted 19 91, 19 95, 19 96 © 19 73 Marine Management (Holdings) Ltd... valves, cylinder heads and pistons can withstand 3 TWO STROKE CYCLE DIESEL ENGINES 3 .1 Two stroke cycle diesel engines take several forms 3 .1. 1 One form, which is illustrated in a simple manner... ignition engines 1. 2 Medium speed diesel engines may be defined as those having rated speeds within the range of 30 0 to 10 00 rev / FOUR STROKE CYCLE DIESEL ENGINES 2 .1 The essential parts of a four