Service Experience - marengine.commarengine.com/ufiles/MAN-Service_Experience_2002.pdf · Service...

Contents:

Service Experience

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Cylinder Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Alu-coating of piston rings and wave-cut in cylinder liners . . . . . . . . . . . . . . . . . . . . . . 3Alpha Lubricator, cylinder oil savings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Cylinder wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Main bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8- Thick shell bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8- Optimum Lemon Shape (OLS) bearing with flexible edges . . . . . . . . . . . . . . . . . . . 8- Thin shell bearing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9- Alignment and vertical offset of aft-end bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Crosshead bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Exhaust Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Sealing oil dosage unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Cooling water leaks/U-seal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Seat geometry/W-seat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Engines with Oros combustion chamber, hydraulic safety valve . . . . . . . . . . . . 11

Fuel Injection Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Fuel pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Fuel valve and atomisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Engine Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Crankshaft thrust bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Tools and lifting equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14- Wire ropes and wire locks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14- Other tools related to personal safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Oil mist detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

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Introduction

As a service to our customers, MANB&W Diesel have for many years, aspart of our open information policy, atregular intervals published papers underthe title ‘Service Experience’.

The present paper gives an update onhow the latest generation of MC andMC-C low speed engines, i.e. thosehaving entered service after 1997, areperforming. The major developmentsteps are shown in Fig.1, which in-cludes the engines of the recent newbreed of large container vessels thathave attracted special attention in themarine market, and therefore the largebore main engines of our range in thesevessels will be dealt with in this paper.

From the start of the service periods ofthese large engines, we have made inten-sive follow-ups, including many visits onboard the vessels. As a result, a numberof modifications have been introduced.

It is important to underline the fact that,irrespective of the great attention beinggiven to large engines, we are also care-fully following up on all other sizes ofMC/MC-C engines.

Hence, the full range of S-MC-C en-gines have been subject to the sameintensive follow-up, primarily in order todetect and cure any teething troublesas early as possible.

Cylinder Condition

The cylinder condition of the MC/MC-Cengines has developed in a most posi-tive direction in recent years. Contribu-ting to this are the Oros combustionchamber, high topland pistons, pistoncleaning (PC) ring, controlled pressurerelief (CPR) piston ring, alucoat, etc.See Fig. 2.

With the Oros configuration, the com-bustion air is concentrated around thefuel nozzles and the distance from thefuel nozzles to the piston top is increased.This has resulted in lower heat load onthe piston top and basically unchangedheat load on the cylinder cover andexhaust valve.

The higher topland and the introductionof the piston cleaning ring have provedto be very beneficial for avoiding a build-up of lube oil derived deposits on the

piston topland. Such deposits would,by hard face sponge effect, scrape offand absorb the oil film, leaving the na-ked liner wall vulnerable to extensivewear and/or scuffing.

The use of the high topland piston alsomeans that the mating surfaces betweenthe cylinder liner and the cylinder coverare lowered, thus reducing the thermalload on the cylinder liner and improvingthe conditions for lubricating the liner.This was taken into account before in-troducing the Oros configuration.

Years back a number of cracked cylin-der liners were reported and, conse-quently, countermeasures were intro-duced. Today, we can state that thesecountermeasures, in terms of bore-cooledliners, and for smaller engines, slim liners,have been successful, in that crackedliners are very rarely reported. For en-gines originally specified with cast-incooling pipes in the liners, the designwith oval pipes has stopped the crackoccurrence.

Alu-coating of piston rings andwave-cut in cylinder liners

Controlled breaking-in and subsequentrunning-in of piston rings and cylinderliners are considered very important inachieving good performance of a linerlater on in service.

New piston rings and a fresh liner surfacehave to adapt to each other in the break-ing-in period to optimise the surface forrunning-in. An ample amount of cylin-der lube oil is therefore needed initially.

However, besides providing the neces-sary lubrication, this high cylinder lubeoil amount will create deposits and thusa more difficult condition for piston ringperformance.

With the introduction of the alu-coatedpiston rings, a thin layer of alu-coatingwill be worn off the rings during the first

3

Mk mep (bar) Cm (m/s)1982 Full L-MC programme 1 15.0 7.2 1251986 K-MC introduced 3 16.2 7.6 130

S-MC introduced 3 17.0 7.8 130L-MC upgraded 3 16.2 7.6 130

1988 K-MC-C introduced 3 16.2 8.0 1301991 MC programme upgraded 5 18.0 8.0 1401994 K98MC-C introduced 6 18.2 8.3 1401996 S70MC-C, S60MC-C, S50MC-C 7 19.0 8.5 150

and S46MC-C introduced 7 19.0 8.5 1501998 K98MC introduced 6 18.2 8.3 140

S80MC-C, S90MC-C, L90MC-C introduced 7 19.0 8.1 150S35MC upgraded 7 19.1 8.1 145

2001 L70MC-C introduced 7 19.0 8.5 150L60MC-C introduced 7 19.0 8.3 150

maxp

mep = mean effective pressure • Cm = mean piston speed • pmax = maximum firing pressure

Fig. 1: Major development steps

Service Experience


1,000 - 2,000 hours. This makes it possi-ble to reduce the breaking-in and run-ning-in time, as well as the cylinder oilfeed rate during most of the breaking-in period. This is beneficial not only tothe engine manufacturer, who can re-duce the time at engine delivery, but alsoto the operator who will receive an enginewith improved running-in conditions.

The surface of MAN B&W cylinder linersis specified as semi-honed. This semi-honed surface, together with alu-coatedpiston rings, ensures safe and stablerunning-in. The semi-honing processcuts off the tops of the wave-cut, thusreducing the necessary breaking-in be-tween piston rings and liner surface, whilestill having circumferential pockets for lubeoil. We apply semi-honing only, in thatthe alu coated piston rings, see Fig. 3,do the remaining removal of broken ordamaged cementite from the cylinderliner surface during the initial wear pe-riod, thereby performing a “free ofcharge” full honing.

Alpha Cylinder Lubricator, cylinderoil savings

One of the tools for optimising the cyl-inder condition is optimising the cylin-der lube oil dosage.

Examples show that over-lubrication(above 1.6 g/bhph) can be damagingto the cylinder condition, and by ana-lysing the correlation between the fuelsulphur level, the lube oil BN and thewear rate as measured from the com-position of the drain oil from the bottomof liners, we are able to recommendthe optimal feed rate for the engines.

In addition to being potentially detrimental,excessive cylinder lube oil consumptionrepresents a large expense for engineoperation. Therefore, the aim is to reducethe cylinder lube oil dosage while, atthe same time, retaining satisfactorypiston ring and liner wear rates and

4

Features:

Improvements:

Verification:

�

�

�

�

�

�

�

�

�

�

�

�

High toplandOros shape of piston topCPR top piston ringAlu-coat piston ringsBore cooled, forged piston ofheat resistant steelPiston cleaning (PC) ring

Approx. 100 °C lower temperatureon top compared with former typepistonElimination of Inconel coatingon piston topIncreased chrome layer thicknessin bottom of ring groovesAnti-erosion bushing in oil outletin piston rod foot

Extensive calculationsComprehensive tests on K90MC,K90MC-C and K98MC

Previous High topland

Fig. 2: Oros combustion chamber geometry

Wave-cut Semi-honedsurface

Alu-coated rings

The combination of:

Wave-cut, semi-honed liner

Alu-coated rings

Result in:

Unproblematicproduction ofcylinder liners

Safe and stablerunning-in

�

�

�

�

Fig. 3: Alu-coated piston rings + wave-cut


maintaining, or improving, the time be-tween overhauls. This can be done bymeans of the Alpha Lubricator systemwhich, by way of being computer con-trolled, provides means of feed ratecontrol based on e.g. the fuel oil sulphurcontent, referred to as “Alpha AdaptiveCylinder oil Control” (Alpha ACC).

The principle of the Alpha ACC is shownin Fig. 4. The cylinder oil amount is con-trolled so that it is proportional to theamount of sulphur entering the cylinderwith the fuel (the “Sulphur throughput”).

Two basic needs have to be catered for:

1. The cylinder oil dosage must not belower than the minimum needed forlubrication.

2. The additive amount suppliedthrough the BN (the “Alkalinitythroughput”) must be only sufficientfor neutralisation and for keepingthe piston ring pack clean.

As the second criterion usually over-rides the first one, the following twocriteria determine the control:

• The cylinder oil dosage shall beproportional to the engine load (i.e.amount of fuel entering the cylinders)

• The cylinder oil dosage shall be pro-portional to the sulphur percentagein the fuel.

The implementation of the above twocriteria will lead to an optimal cylinderoil dosage, proportional to the amountof sulphur entering the cylinders, butwith a low minimum setting to ensurelubrication.

This principle is founded on the obser-vation that the main part of cylinderliner wear is of a corrosive nature.Therefore, the amount of neutralisingalkalinic components needed in thecylinder should be proportional to theamount of sulphur (generating sulphu-

rous acids) entering the cylinders. Aminimum cylinder oil dosage is set inorder to account for other duties of thecylinder oil (securing sufficient oil filmdetergency, etc.). Thanks to its accu-racy, the Alpha Lubricator does just that.

Fig. 5 shows control of cylinder oil dos-age proportional to the sulphur percen-tage in the fuel. A minimum dosage of0.5 g/bhph is indicated, based on ex-perience so far. This minimum value ispreliminary and, given the efficient lubri-cation achievable with the Alpha Lubri-cator system, we expect to be able tofurther reduce this minimum value inthe future.

Alpha Lubricators can be retrofitted,and have a relatively short payback

time. Thus, Alpha Lubricators are cur-rently being retrofitted on a large num-ber of plants in service.

Cylinder wear

Wear of the liners is monitored on a largenumber of engines through visits byour engineers, because liner wear istraditionally considered an engine qualitycriterion.

As can be seen in Fig. 6 for cylinder linerwear, both K98MC/MC-C and S90MC-Cshow very convincing low wear perfor-mance data and good liner condition.

While initial wear is naturally higher, thewear rate is reduced to less than 0.05mm/1,000 hours after about 1,500 hours,which is considered very satisfactory.

Initial wear is part of the running-in ofcylinder liners and piston rings, andhigh wear is expected in this period.The wear study is based on cylinderfeed rates between 0.9 and 1.2 g/bhph.Experience with the Alpha Lubricatorindicates that there is a significantpotential for cylinder lube oil reductionwhile still having a fully acceptablecylinder wear rate and mean timebetween overhauls.

Fig. 7 shows extracts from our data-base regarding cylinder wear rates.

S-MC engines, S-MC-C engines andK-MC-C engines all experienced lowand uniform wear rates.

On the K98 engines, as mentionedabove, the cylinder condition has beengood, with very low wear rates and lowcylinder oil feed rates. However, onthese engines the good condition hasbeen temporarily overshadowed by anumber of failures of the top pistonring. Though there are strong indicationsof this being a production-related issue,the top ring design has been upgradedto increase the safety margin against

5

Cylinder oil amount

Sulphur amount

Fig. 4: Cylinder oil amount proportional tosulphur amount entering the cylinders(basic principle of Alpha ACC)

Cylinder oil dosage (g/bhph)

1.25

1

0.75

0.5

0.25

0

0 1 2 4 5 6Sulphur %

Fig. 5: Cylinder oil dosage proportional tosulphur percentage in the fuel


breakage. The production process atsubsuppliers has been changed in orderto reduce breakage incidents.

The design upgrading implies a num-ber of changes, including relocation ofthe controlled leakage (CL) grooves, re-duction of the number of grooves from6 to 4 (same leakage area is achievedby applying wider grooves), as well asa change in surface machining of thegrooves to avoid fine cracks from theoutset. See Fig. 8.

6

0 2000 4000 6000 8000 10000 12000 Running hours

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

Alpha Lubricator

0.05 mm/1000 h

0.1 mm/1000 h initial wear

1.02 g/bhph

1.1 g/bhph

1.02 g/bhph

1.02 g/bhph1.02 g/bhph1.1 g/bhph

1.1 g/bhph

1.0 g/bhph

1.0 g/bhph

0.9 g/bhph0.9 g/bhph

0.9 g/bhph0.9 g/bhph

Liner wear (mm)

7K98MC 2nd engine, cyl. 410K98MC-C prototype, cyl. 110K98MC-C prototype, cyl. 210K98MC-C prototype, cyl. 410K98MC-C prototype, cyl. 67K98MC 4th engine, cyl. 76S90MC-C prototype, cyl. 46S90MC-C prototype, cyl. 6

7K98MC prototype, cyl. 27K98MC prototype, cyl. 37K98MC prototype, cyl. 47K98MC prototype, cyl. 57K98MC prototype, cyl. 67K98MC prototype, cyl. 77K98MC 2nd engine, cyl. 77K98MC 2nd engine, cyl. 1

Fig. 6: K98MC-C, K98MC and S90MC-C cylinder liner wear


7

S26MC, S35MC, S42MC, S46MC-CTotal 199 cylindersAverage wear: 0.036 mm/1,000 hours

0 0 0

11

22

33

44

55

66

77

88

99

110

121

4

8

12

16

20

24

28

32

36

40

44

0.001 0.001 0.0010.01 0.01 0.010.1 0.1 0.11 1 1

5

10

15

20

25

30

35Number of cylinders

S50MC, S60MCTotal 396 cylindersAverage wear: 0.055 mm/1,000 hours

S70MC, S80MCTotal 696 cylindersAverage wear: 0.073 mm/1,000 hours

Cylinder liner wear rate

0.010

0

1

2

3

5

4

0.100 1.0000.010

0

1

2

3

4

5

6

7

10

8

11

9

12

13

0.100 1.000

S50MC-C, S60MC-CTotal 58 cylindersAverage wear: 0.068 mm/1,000 hours

S70MC-C, S80MC-C, S90MC-CTotal 19 cylindersAverage wear: 0.067 mm/1,000 hours

0.0100.001

0

5

10

15

20

25

30

35

40

45

50

0.100 1.000

K80MC-C, K90MC-C, K98MC-C,Total 299 cylindersAverage wear: 0.056 mm/1,000 hours

Wear rate in mm/1,000 hours

Wear rate in mm/1,000 hours

Fig. 7: Extracts from our database regarding cylinder wear rates


Bearings

Main bearing

Thick shell bearingSince 1998, we have seen a decreasein the number of reported main bearingfailures. In 1998 a number of featureswere introduced in the design of thebearings, the adjustment of the bear-ings, and to the installation of the en-gine/shaftline.

The major updates can be summarisedas follows:

As an evolution of the Mark 5 bearingtype, the “Optimum Lemon Shape”type main bearing was introduced, seeFig. 9. This type features optimised (re-duced) top and side clearances. Serviceexperience has confirmed the efficiencyof this bearing type simply by the signifi-cantly reduced number of reporteddamage incidents.

A revised engine installation recommen-dation (available upon request), includ-ing an updated shaftline alignment pro-cedure together with differentiated bearingheight in the aft end of the engine, hasadded to the safety margin.

Optimum Lemon Shape (OLS)bearing with flexible edgesThere has been a significant reductionin the number of main bearing failures,as will appear from Fig. 10. However, itmust be acknowledged that main bear-ing damage sometimes still does oc-cur, e.g. due to poor bonding of thebearing metal.

8

90°45°

45°90°

45°

45°

60°30°

60°30°

-

60°

4 relocated CL-grooves(E4-type)

Width ofCL-groove: 2 mm


6 relocated CL-grooves(E-type from Jan. 2002)

Original location of grooves(6 CL-grooves)


Fig. 8: K98 CPR piston ring development

Side clearance

Top clearance

Future spare bearings will be of the reviseddesign and delivered as a set.The set is fully interchangeable withprevious designs

Oil film thickness in the highpressure areas of thebearings was not optimal

Optimised (reduced) side andtop-clearances introduced basedon good experience with theMC-Compact engines

Optimum ‘lemon-shape’ will givea minimum oil film thicknessincrease of 30-40%

Design update:

Fig. 9: Main bearing, thick shell design

80

60

40

20

01999

The graph shows the positive influence ofthe introduction of the “Optimum LemonShape” bearing and the aft endbearings of the engine. The statistics aremade based on attendances from theOperation dept.

offset of

No. of reported damage incidentsto MC/MC-C engines

2000 2001

Fig. 10: Bearings – statistics


In nearly all cases, main bearing dam-age is initiated from a fatigue crack atthe edge of the bearing, the aft edge/manoeuvring side being the most com-mon point of initiation. Often, geometri-cal non-conformities are involved in thesecases. Such non-conformities furtherincrease the damage frequency asmargins established during the designphase are reduced.

Calculations, combining the dynamicsof the complete crankshaft with the hy-drodynamic and elastic properties of

the bearing, have provided detailedinformation about the mechanismsleading to local loading of the main bear-ing edges. The calculations have indi-cated that a slight radial flexibility of thebearing edge will increase the overallminimum oil film thickness significantly.At the same time, the maximum oil filmpressure will be reduced.

A bearing design with flexible forwardand aft edges of the bearing shell hasbeen successfully tested.

The flexibility has been achieved by re-moving the contact between the shelland bedplate at the end portions of theshell. The unsupported width of theshell is equal to the shell thickness.Apart from the flexible edges, the prop-erties of the bearing are similar to thoseof the Optimum Lemon Shape type.This design provides a larger safetymargin in the event of geometricalnon-conformities.

Thin shell bearingThe thin shell bearing design has beenintroduced on our latest engine types.For the small and medium bore en-gines (S46MC-C to S70MC-C), themain bearings are lined with AlSn40and provided with a running-in coating

consisting of PTFE as standard. 9,000shells are now in service, many of whichhave been in service for more than adecade.

Service experience with this configura-tion has been excellent, see Fig. 11.

On the large bore engines, the bearingsare lined with white metal, see Fig. 12.

In general, few damage incidents to ourthin shell main bearings have been re-ported:

• Following Q/A inspections, weldrectification of bearing saddles hasoccasionally been carried out duringthe production of the engine. In afew cases, these welds have beenintroduced at a late stage (after finalmachining). This has provided eitherhigh spots on the running surface ofthe bearing shell or areas with missingcontact. Both could disturb the oilfilm, leading to high local load, andthus fatigue damage, see Fig. 13.Countermeasures introduced havebeen either adaptation of the runningsurface of the bearing shell by meansof scraping or the introduction ofbearings with AlSn40 lining, offeringan increased margin against fatigue

• Deformed bearing housings of thethin shell design have been seen dueto the improper use of the triple anddouble hydraulic tightening jacks.Thishas occurred either prior to machin-ing of the bearing housing or duringmounting of the bearing shells. Suchdeformation changes the ratio be-tween the side and the top clearances.New instructions and Service LetterSL02-400/HMH highlighting the fea-tures and the proper use of the jackshave been issued. In addition, a QualitySpecification instruction has been is-sued, intended for use at the productionfacilities, thus assisting the licenseesin preventing similar incidents in thefuture.

9

No remarks – excellent condition

Thickness measurement of shell did notreveal indication of significant wear rate –less than 0.01 mm

S50MC-C main bearing lower shell –18,000 hours

Fig. 11: Thin shell AlSn40 main bearing

7K98MC main bearing No. 4 after 6,000 hours

No remarks – except for minor traces of dirt

Fig. 12: K98MC-C white metal main bearing


Alignment and vertical offsetof aft-end bearingsIn addition to other initiatives, attentionhas been paid to some cases of re-peated damage to the aft-end bearingsin the engine. This is, presumably, causedby missing static load, particularly in the

second aftmost main bearing duringnormal operating conditions.

On the basis of comprehensive investi-gations made together with a numberof licensees, shipyards and classificationsocieties, a new alignment procedure

has been introduced. The new procedureincludes precalculated bedplate saggingas well as vertical offsets to the mainbearing saddles. This has resulted in asignificant drop in the number of reporteddamage incidents to the aft-end bearingsin the engine.

Crosshead bearing

In general, the crosshead bearings in bothMC and MC-C engines perform verysatisfactorily, but cases of wiping havebeen observed. In itself, this wiping is ofa cosmetic nature, but it can some-times cause blockage of the oil-wedgesthat normally build up the oil film to the“pads” inside the bearing, see Fig. 14.Disturbance of the oil film build-up insidethe bearing could result in slight fatiguedamage just behind the blocked areaof the oil-wedge. If the phenomenon isobserved at an early stage during inspec-tions, the problem is solved by remov-ing the wiped lead from the oil-wedge.

Exhaust Valves

Nimonic spindles are well acceptednow that the operators have becomeacquainted with the long-lasting seatperformance despite dent marks, seeFig. 15. Nimonic spindles are standardfor 50MC and for 60MC/MC-C upwards,and Stellite spindles are standard forsmaller engines.

Corrosion in the valve housing is effec-tively minimised by the introduction ofthe optimised cooling water system,which raises the wall temperature in thehousing above the critical level for theformation of acid on the gas side of theduct. With the high temperature level, acast iron spindle guide bushing is nec-essary.

Wear of the previously chrome-platedspindle stem has been effectively re-duced by the introduction of the HVOF-

10

-0,7

-0,6

-0,5

-0,4

-0,3

-0,2

-0,10 100 200 300 400

Pos 4

Large rectified area – missingcontact between shell andsupport. Maximum depth ofrectified area 0.20 mm

Fig. 13: Weld-rectified bearing support

S90MC-C crosshead # 6 (3,500 hours)after dressing up

S90MC-C crosshead # 6 (3,500 hours)before dressing up. Note that the leadoverlay apparently has a tendency ofnon-conformity. In this case t

only cosmetiche

problem is

Fig. 14: S90MC-C crosshead bearing


based cermet coating. All spindles fromour Copenhagen works have been pro-vided with this coating since 1997, andapproximately 6,000 spindles havebeen produced. The very few claimsreceived were due to initial productionproblems. The licensees are graduallyalso using the HVOF process.

Furthermore, wear and corrosionproblems at the spindle guide/spindle/seal area, caused by combustion prod-ucts, have been minimised over the yearsby design changes on the sealing airsystem. However, the stem seal hasdifficulties in reaching lifetimes similarto those of the valve seats. Tests haveshown that improvement can be ob-tained by lubrication. It has, therefore,been decided to replace the sealing airsystem by a lubricating device, whichhas been long-term service tested withgood results.

Sealing oil dosage unit

Good results have been obtained re-garding the reduction of wear of thespindle stem (HVOF coating) and of the

long spindle guide (grey cast iron).However, the lifetime of the stem sealitself is still sometimes too short.

Tests with oil as the sealing medium,instead of air, have shown very low wearrates on the seals. At the same time, ahigh cleanliness level is obtained on thesurfaces of the spindle stem and spin-dle guide.

A system delivering the necessary dos-age of only approximately 1 kg/cyl./dayhas been developed for medium andlarge bore engines. It is located in thetop of the exhaust valve and is fed byoil from the hydraulic system of the ex-haust valve. The oil is fed to the spindleguide via a small pipe. The sealing oil istaken from the circulating oil and is therebypart of the necessary minimum oil con-sumption for keeping the system oilviscosity and BN-level at the prescribedequilibrium.

Cooling water leaks/U-seal

The latest design of exhaust valve onsmall and medium bore engines occa-sionally suffers from cooling water leaksat the lowermost O-ring between bottompiece and cylinder cover. Investigationsresulted in replacing the lowermostO-ring with a special Teflon seal with springback-up (U-seal). This was communicatedby Service Letter SL01-389/PGK.

Seat geometry/W-seat

During our test work, results have shownthat the best way to increase the seat

lifetime was by altering the seat geometryof the bottom piece to the patentedW-seat, see Fig. 16. On a few S50MC-Cengines with Al50 spindles, the resultswere remarkably better using the W-seat,which is now standard on all MC/MC-Cengines. When using the new type ofslide fuel valves as well, the result iseven better.

Seat material standards for MC/MC-CEngines are summarised in Table 1.

Engines with Oros combustionchamber, hydraulic safety valve

Engines equipped with the so-calledOros combustion chamber leave littledistance between the piston top andthe underside of the exhaust valve spindle.Therefore, the usual extended lift systemfor release of high hydraulic pressure can-not be utilised. A safety valve located inthe actuator is used instead.

Unfortunately, a few cases of damagedexhaust valves and camshaft sectionshave been reported, due to differentexternal factors, including insufficientrelease action of the safety valve. Con-sequently, the safety valve has been re-designed. Once activated, it implements aspecial function to keep it open for about20 seconds. Furthermore, a disc springhas been introduced in the exhaust valveon top of the spindle guide to avoiddamage to the air piston in the event of‘over-shoot’/extended lift of the valvespindle. This has eliminated the problem.Fig. 17 shows the various design detailsmentioned.

11

Fig. 16: W-seat, exhaust valve

Engine type Spindle Bottom piece26-42MC SNCrW/Al50 * Cooled/hardened steel/W-shape

46-50MC-C SNCrW/Al50 * Semi-cooled/hardened steel/W-shape

50-98MC60-98MC-C

Fully forged Nimonic 80A Semi-cooled/hardened steel/W-shape

* Nimonic can be delivered on request

Table 1: Seat material standards

Fig. 15: Nimonic valve normal condition,after 11,500 running hours


Fuel Injection Gear

Fuel pump

In general, the fuel pumps work welland without difficulties. However, a fewincidents have been experienced.

On the S60MC-C, S70MC-C,S90MC-C and K98MC/MC-C engines,a combined puncture and suction valveis used. This design originally involveda bellow as substitute for the conven-tional sealing rings, in order to have acomponent needing no or very littlemaintenance. However, the reliabilityof the bellow was not satisfactory, anda new design without the bellow hasbeen introduced on the above-men-tioned engine types.

As a cost-down measure, fuel pumpswithout shock absorbers were intro-duced on the S60MC-C, S70MC-C,S90MC-C and K98MC/MC-C, but this

resulted in annoying, but not damag-ing, pressure fluctuations in the fuelsupply system.

Even though the pressure fluctuationsmeasured were within our design limits,as well as within the classification societies’limits, shipowners experienced problemswith shipyard-installed equipment suchas pumps, filters and preheaters. In orderto avoid such problems, a shock absorberhas been re-introduced on each fuelpump on the above-mentioned engines.

On K98MC/MC-C and S90MC-C, leak-age has been seen between fuel pumphousing and top cover. One problemwas related to production tolerances,as a gap of up to 0.5 mm was foundbetween the pump housing and thetop cover, see Fig. 18. However, leak-age has been experienced even incases where the machining was correct.Therefore, a new type of gasket hasbeen introduced. The primary sealing is

obtained with a viton ring, protectedagainst erosion attack by a steel bushing.A soft iron plate of the same shape asthe original seal forms the “groove” forthe square viton ring.

Fuel pump top cover fractures have beenexperienced on small and medium boreengines. The fractures were initiated atthe position where the inclined drillingsfor the high-pressure pipes intersectwith the central bore, see Fig. 19. Thecause of the failure has in all casesbeen related to roundings which didnot fulfil our specification. However, toimprove the safety margin against fail-ures we have changed the design asper Fig. 19, which has made the designeasier to manufacture and less sensitiveto minor tolerance deviations.

Fuel valve and atomisation

Fractured fuel valve nozzles have beenfound on large bore engines whereslide type fuel valves have been stan-dard for some years. The main reasonfor the cracks was residual stress frommachining. However, the high temper-ature of the valve nozzle itself contrib-uted to the fractures because of theconsequential high mean stress. Thishas been cured by optimising the pro-duction parameters.

As for pressure testing of conventionalfuel valves, it must be noted, however,that the testing device is only capableof supplying 1-2 % of the normal fuelflow rate on the engine, which is notsufficient to ensure proper atomisation.If the remaining test items in the proce-dure are fulfilled, the fuel valve nozzlewill work perfectly. As the atomisationtest can be omitted, it is not describedin new testing procedures, so verifica-tion of a humming sound as earlier isno longer possible, nor necessary.

Pressure testing procedures for slidefuel valves are quite different fromthose for conventional valves and have,

12

Quick acting safety valve with“stay open function”

Single wall housing

W-Seat

High spindle guide

Disc springSingle seat

Sealing oil dosage unit

Fig. 17: Exhaust valve, 80-90MC


probably because of the difference, insome cases been misinterpreted by theoperators. Slide fuel valves must bedisassembled and cleaned beforepressure testing, and an atomisationtest must not be performed on slidefuel valves. The cleaning is necessarybecause the cold and sticky heavy fueloil, in combination with the very smallclearance between the cut-off shaft

and the fuel valve nozzle, would signifi-cantly restrict the movement of the spin-dle. An atomisation test is not accep-table, because the very small needle liftobtained during such a test would re-sult in an unequal pressure distributionon the cut-off shaft, resulting in a rela-tively hard contact in a small area, seeFig. 20. This, together with the highfrequency oscillations during an

atomisation test, and the low lubricityof the test oil, would increase the riskof seizure significantly. The full lift of theneedle, and the very good lubricity ofheavy fuel oil, completely eliminates thisrisk during normal operation of the engine.

During scavenge port inspections onengines with slide fuel valves, we oftenfind wet spots under each fuel valve. Inthe conventional valve, the sac volumeis emptied after each injection. In theslide valve, the fuel stays in the fuelnozzle until the next injection. However,when turning the engine and after somehours of engine standstill, the nozzlewill empty and fuel will drip down onthe relatively cold piston crown, shownas wet spots of up to 300 mm diame-ter. After some hours the drops willmore or less evaporate, depending onthe actual position of the piston in rela-tion to the scavenge ports, leaving onlysome ash on the piston top. This is notnormally an indication of malfunction.

13

Fuel inlet pressure

Leakage Gasket

0.5 mm gap

Fig. 18: Fuel pump top cover leakage

Previous

Sharp edges tobe removed:Radius:min. 0.5 mm

Crack initiation area

New

Fig. 19: Drillings in fuel pump top cover

Risk of seizure

3-5

4

1-2

Avoid atomisation testbecause of:1. Small lift2. Large pressure drop3. High contact

pressure4. High frequency5. Thin oil

Fig. 20: Slide valve pressure testing


Engine Structure

Crankshaft thrust bearing

The thrust bearing introduced on Mark5 engines has completely solved theprevious problem of cracks in the hori-zontal support plates. No cracks havebeen reported on engines with theso-called Calliper design of the thrustbearing.

The bearing saddles have remainedtotally free of cracks, in compliancewith precalculated stress levels.

Safety Precautions

Tools and lifting equipment

During recent years, there have beenexamples of lifting tools that have notbeen manufactured according to ourspecifications.

Wire ropes and wire locksIn some cases, experience has shownthat the length of wire ropes differs fromthe specified length. Often, this is accep-table, because the tool is designed toadapt to these minor variations. How-ever, in some situations (e.g. liftingtools for cylinder liners), the tool musthave the specified wire rope length, asthe lift would be dangerous if not per-formed straight.

The use of wire rope types other thanthose specified has been seen, for ex-ample, wire ropes with fibre-core in-stead of steel-core, which results in asignificant reduction in the safety marginof the lifting gear.

In connection with aluminium wire-locks,there have been examples where wireropes have not been cut to the correctlength before clamping the wire-lockaround the wire rope, thereby creatinga risk of injury to the hands of the crew,

service personnel, etc. An example isshown in Fig. 21.

Regarding the new lifting tool for mainbearing cap for the 60 - 98MC-C, ex-perience has shown, in some cases,that the wire-lock used was not in ac-cordance with the specification.

As seen in Fig. 22a, the wire-lock to theright does not have the correct insideshape. The specified lock (which isshown to the left and as No. 2 in Fig.22b) is wave-shaped inside to furthersecure the wire rope. In the wire-lock tothe right, there is a risk that the wire ropewill be pulled straight through the lock.

Furthermore, the centre hole in the lockto the right is oversized, which makes itpossible to tighten the two halves ofthe lock completely together, giving toolow a clamping force on the wire rope.The result was that the wire rope couldslide inside the wire-lock. The correctlock, on the left, leaves a gap betweenthe two halves after tightening.

Other tools related to personal safetyHydraulic tools: The hydraulic hosesand couplings are sometimes not of anadequate quality which, according tothe operators, means that they canonly be used a few times before a re-placement is necessary, and others areleaky from the start.

Chain tackles: There have been caseswhere the chain tackles do not havesufficient dimensions for the carryingout of normal as well as special overhau-ling tasks on board, e.g. when remov-ing a connecting rod from the engine.

Oil mist detection

Besides applying an oil mist detector,our efforts to prevent crankcase explo-sions have, so far, been concentratedon designing the engine with amplemargins in order to prevent overheatingof the components. However, we have

realised that when rare explosions oc-cur, they originate from other causes,such as factors related to production,installation, or incorrect maintenance ofcomponents or the lubricating systems.

Thus, it is recommended that:

• The oil mist detector is connected tothe slow down function

• The oil mist detector has remote moni-toring from the engine control room

• The relief valves are made with ap-proved flame arrester function.

14

Fig. 21: Wire ends with strands of wiresticking out

Fig. 22: Wire-locks

2

1

b

a


In the past, reliance was placed onspecifying safety equipment that hadbeen type approved by the classifica-tion societies. However, type approvalis not sufficient as it only comprises thechecking of the opening pressure ofthe relief valve.

In the event of a crankcase explosion,the pressure wave will send a largeamount of oil mist out of the crankcaseand into the engine room, where it willbe moved around by the ventilation.A major part of this could be sucked upinto the turbocharger air inlet.

If the oil mist meets a hot spot, it canbe ignited. Therefore, it is important tokeep the insulation around the exhaustpipes in good condition. Of course, thelargest risk of igniting the oil mist wouldbe if the flame arrester on the reliefvalve does not function properly.

Therefore, updates to the relief valvespecification have been made. Only re-lief valves approved according to thisspecification are accepted on enginesordered after 1st May 1999. A draft ofthis specification was sent to IACS inNovember 1998. Regrettably, so far,no new rules have been introduced.

Fig. 23 shows the result when testing anon-functioning relief valve, and Fig. 24

shows an approved type. So far, wehave approved two types of crankcaserelief valves:

• Hoerbiger type EVN

• Mt. Halla type HCSG-N.

There have been cases of fire after anexplosion in crankcases equipped withapproved relief valves where the func-tioning of the flame arrester had beenprevented by a local deformation, seeFig. 25. Thus, in the event of deforma-tions, the flame arrester must be renewed.

Concluding Remarks

On the basis of service experience, itcan be concluded that the continuousdevelopment and updating of the de-sign and production of the MC andMC-C engines have clearly resulted ina significant increase in reliability andlonger time intervals between over-hauls. At the same time, the engines’unit outputs have been increased whilethe physical dimensions have been de-creased, thus demonstrating the inde-pendence of the three parameters,reliability, power and size.

15

Fig. 23: Testing of a non-functioningcrankcase relief valve

Fig. 24: Testing of an approved type ofcrankcase relief valve

Fig. 25: Deformation of flame arrester


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