REFINEMENTS IN MC ENGINE n DEVELOPMENT TOWARDS MCC

Feedback from MAN B&W MC engines in service has shown average liner wear rates as low as 0.05 mm/1000 hours and cylinder overhauling intervals of 6000–8000 hours. R&D targeting enhanced durability and extended mean times-between-overhauls (TBOs) has focused on:

Engine structure: experience has shown that the jacket cooling water around the lower part of the cylinder frame may in some cases result in a corrosion attack and thus lead to higher wear rates. Cooling water in the lower part of the liner has therefore been omitted, thus increasing the temperature of the liner surface. The modification has been introduced on the latest engine versions (Figure 10.19). Cracks were experienced in the horizontal support for the forward main bearing in the thrust bearing housing. Investigations revealed that, under special service conditions, the design seemed to leave too narrow a margin; improper welding quality was also a contributory factor. While such rib cracks do not imply any risk with respect to the service of the ship in the short term, they should be rectified at the first available opportunity. For engines in service, the designer has evolved a rectification method which, in addition to remedying the cracks, also increases the margins. Repairs have been successfully carried out using this procedure. The standard design has also been changed to address the above conditions.

Piston rings: Investigation showed that the overhauling interval could be prolonged by introducing approximately 30 per cent higher piston rings in the two uppermost ring grooves. Such rings of a special alloyed grey cast iron were therefore introduced as standard on new engines. A further extension of maintenance intervals can be secured by plasma (ceramic) coating or chrome plating the surface of the uppermost piston ring. These coated rings are available as options. Experience showed that in some cases the normal oblique-cut piston ring gap led to a high heat input to the liner when all cuts coincided. An improved design of S-seal ring (double-lap joint) was developed and tested to achieve a completely tight upper ring and then reduce the pressure drop across this ring by introducing a number of small oblique slots to secure a controlled leakage. The temperature distribution and pressure drop measured across the ring were promising and very clean ring lands resulted. Rings of vermicular iron have also shown promising results. The higher piston topland and higher top rings (the uppermost featuring a pressure-balanced design) were introduced on engines with higher mean effective pressures to enhance reliability and extend times between overhauls (Figure 10.5).

Cylinder liner: factors to be considered when designing cylinder liners include material composition, strength, ductility, heat transfer coefficient and wear properties. The original MC-type liners with cast in pipes unfortunately suffered from cracks but the introduction of the bore-cooled liner solved the problem (Figure 10.20). Such liners have been fitted to all new engines produced in recent years. The change to a bore-cooled liner made of grey cast iron for engines originally supplied with liners of the cast-in cooling pipe design, however, could not be easily effected. Various parallel developments were therefore initiated, based on the use of stronger materials, and improvements to the original design introduced. A modified design of the cast-in pipes, in combination with a tightening-up of the production and quality specifications, has led to considerably improved reliability from this type of liner. The modified liner is the standard spare part supply for older MC engines. The standard specification for new engines is a bore-cooled type made of Tarkalloy C grey cast iron.

The inside surface temperature of the liner greatly influences the general cylinder condition. Traditionally, the cooling system has been laid out to match the maximum continuous rating load but there is an advantage in controlling the inside liner surface temperature in relation to the load. MAN B&W has investigated and tested different solutions for load-dependent cylinder liner cooling. One system simply adjusted the cooling water flow through the original cooling ducts in the liner but the results were not promising. 

Another system features different sets of cooling ducts in the borecooled liner, the set deployed depending on the engine load. At nominal power and high loads the inner row of ducts is used to cool the liner, yielding the highest cooling intensity. In the intermediate load range the cooling function is shifted to the next set of ducts which are located further away from the inner surface; this means that the cooling intensity is reduced and the liner surface temperature is kept at the optimum level. At very low loads both rows of cooling ducts are bypassed in order to further reduce the cooling intensity. Tests showed that the optimum liner temperature could be maintained over a very wide load range and that this system was feasible but the added complexity had to be weighed against the service advantages.

The operating condition of cylinder liners and piston rings is to a great extent a function of the temperature along the liner. The upper part is particularly important and a triple-fuel valve configuration (see section below) reduces thermal load while, at the same time, the pressure-balanced piston ring and high topland ensure an appropriate pressure drop across the ring pack and control the temperature regime for the individual piston rings. For monitoring the temperature of the upper part of the liners MAN B&W offers embedded temperature sensors and a recorder.

Alarm and slowdown temperature settings allow the operator to take proper action to restore proper running conditions if, for example, a piston ring or fuel valve is temporarily or permanently out of order. Other features, such as an uncooled cylinder frame, serve to increase slightly the wall temperature on the lower part of the cylinder liner while, at the same time, reducing production costs (Figure 10.19). The rise in wall temperature is aimed at counteracting the tendency towards cold corrosion in the lower part of the liner.

Exhaust valves: a high degree of reliability is claimed for the MC exhaust valve design, and the recommended mean TBOs have generally been achieved. The average time between seat grinding can also be considerably increased for a large number of engines. Examples of more than 25 000 running hours without overhaul have been logged with both conventional and Nimonic-type exhaust valves. The Nimonic spindle is now standard for the 600 mm bore engines and above; and a steel bottom piece with a surface-hardened seat is specified to match the greater hardness of the Nimonic spindle at high temperatures. The combination of spindle and bottom piece fosters a mean TBO of a minimum 14 000 hours.

Some cases of wear of the spindle stem chromium plating may be related to the sealing air arrangement. A new sealing air system was therefore designed, incorporating oil mist and air supply from the exhaust valves air spring (Figure 10.21). In-service testing gave promising results: completely clean sealing air chambers and virtually no wear of either the spindle stem or the sealing rings. The system is now standard for new engines and can be easily retrofitted to those in service.

Cold corrosion of the exhaust valve housing gas duct led to lowerthan-expected lifetimes for a number of valves, particularly those installed in large bore engines. The corrosion attack occurs adjacent to the spindle guide boss and in the duct areas at the cooling water inlet positions (Figure 10.22). The problem has been addressed by new housings designed with thicker gas walls which are now standard fitments for new engines and spares (Figure 10.23). For engines in service, the following repair methods and countermeasures have proved effective in dealing with corrosion attacks in the exhaust valve housing: high velocity sprayed Diamalloy 1005 coating in the gas duct; and repair welding with gas metal arc welding (MIG-type), preferably in conjunction with the sprayed coating. 

Bearings: there should be no problems related to production or materials since the manufacture of whitemetal-type main and crankpin bearings is well controlled (Figures 10.24 and 10.25). Some cases of production-related problems were traced to the use of copper- or lead-polluted whitemetal or the lack of proper surface treatment of the steel back before casting the whitemetal. Based on service feedback, the main bearing design has been modified to secure a wider safety margin. The modifications include a larger bore-relief in order to prevent the mating faces from acting as oil scraping edges in case of displacement, and an increase of the side and top clearances to raise the oil flow to the bearing, thus keeping the temperature at a level which sustains the fatigue strength of the whitemetal. The modified bearing design was introduced as the standard for new engines and also made available as spares for engines in service. It is fully interchangeable with existing bearings but the shells must always be replaced in pairs.

∑ Fuel injection system: the fuel valve used on MC engines operates without any external control of its function. The design has worked very well for many years but may be challenged by the desire to maintain effective performance at very low loads as the opening pressure has to be increased with increasing maximum combustion pressure to prevent the blow-back of gases into the fuel system at the end of the injection cycle. At low loads this high opening pressure might lead to irregular injection, speed variations and a risk of fouling of the engine gasways.

Various solutions have been investigated, among them a fuel valve with variable opening pressure (Figure 10.26) which allows low load operation to be improved by reducing the opening pressure in the relevant load range. The opening pressure is controlled by a spring and the actual fuel oil injection pressure. At low load the opening pressure is controlled by the spring alone but, when the injection pressure increases at higher loads, this higher pressure adds to the spring force and the opening pressure increases (a small amount of fuel oil enters the space between the upper spring guide and the slide; the spring that controls the opening pressure is thereby compressed and the spring force increased). Under decreasing load, the leakages will reduce the opening pressure to an appropriate level within the course of a few injections.

Burning of the neck of the fuel valve nozzle on engine types equipped with three fuel valves per cylinder (B&W 90GFCA and 90GB models) has been noted with nozzles made from standard precision-cast Stellite which, in other respects, has yielded excellent service and lifetimes well above 15 000 hours. Several improved production processes and new materials have been investigated. A promising alternative to casting was found in the hot isostatic pressure (HIP) method which delivers a more uniform material composition. Fuel nozzles produced by the process achieved a considerable reduction in the neck-burning rate when tested on the engines concerned

Research also produced a new patented material composition with the same excellent wear properties as those of Stellite but additionally offering an ability to withstand hot corrosion neck burning. A truly heavy duty fuel valve nozzle is thus available when required.

MAN B&W has addressed the potential for enhancing the reliability of combustion chamber components under increasing mean effective pressure conditions by rearranging the fuel valves in the cylinder cover. Originally, the 90-type large bore engine was provided with three fuel valves per cylinder. A number of tests were made in the early 1980s using only two valves which, with the contemporary mean effective pressures and maximum pressures, showed an advantage in the form of a slightly reduced specific fuel consumption and only a minor increase in the heat load. A two-valve configuration was consequently introduced. Rising mean effective pressures in the 1990s, however, encouraged further testing with three fuel valves per cylinder, the measurements showing a reduced temperature level as well as a more uniform temperature distribution. A three-valve configuration was subsequently introduced on the K80MC-C and K90MC/MC-C models to enhance engine reliability, while the S90MC-T and K98MCC models were designed from inception with such an arrangement.

Many owners today prefer to have their fuel equipment overhauled by a shoreside workshop but this means that engineroom staff lose familiarity with some vital components, particularly the fuel valves. In a number of cases MAN B&W has found that nozzles with different spray hole sizes and spray patterns have been mixed. Up to four different types have been found on the same engine and even different types on the same cylinder unit. Such mixing may have an adverse effect on the running condition. A problem noted on many ships is incorrect tightening of the fuel valve spring packs—in some cases caused by faulty spring packs. This can lead to malfunctioning of the fuel valve (such as sticking) due to deformation of the components inside the valve. The consequences have been jumpingfuel valves and cracked high pressure injection pipes. It is therefore important, MAN B&W Diesel warns, to follow instructions covering the correct tightening of the spring packs.

Fuel pumps: the lifetime of the MC fuel pump plunger and barrel has proved to exceed 50 000 hours. Only a few cases of sticking pump plungers have been reported, and these generally resulted from foreign particles entering the system. The introduction of puncture valves at the top of the pump improved crash stop performance and increased engine shutdown safety. Some problems were experienced with the sealing rings mounted around the plunger. The rings are intended to prevent fuel oil from leaking into the camshaft oil and lowering its flashpoint. Different sealing rings were tested after the introduction of the MC engine, the original ring—with an O-ring as a spring element—having been used on the previous engine type with relatively good results. Under attack from fuel oil, however, the O-rings became hard and lost their tension too quickly, making the sealing ring ineffective. Work on improving the material quality as well as the sealing ring design resulted in spring-loaded lip rings which are now standard. A new so-called umbrellatype fuel oil pump design (Figure 10.27) features a sealing arrangement which eliminates the risk of fuel oil penetrating the camshaft lube oil system (a separate camshaft lube oil system is therefore no longer necessary). The uni-lube oil system introduced as standard allows reductions in installation costs, maintenance and space over the separate systems previously used: tanks, filters, pumps and piping for the camshaft system are eliminated.
Chain drives: the chain drives for the camshaft and moment compensators have functioned well and, if the chains are kept tightened to MAN B&W instructions, the rubber guide bars will hardly ever need replacement. Since the chain tightening procedure on some ships might prove difficult for crews, automatic chain tightening was introduced as an aid to reducing the onboard maintenance workload. The tightening force is applied by a hydraulic piston to which oil is fed via the engines lubricating/ cooling oil system. The hydraulic chain tightener is also available for the front second-order moment compensator drive. Positive service experience encouraged the fitment of the automatic tightener as standard on 50–90 bore MC engines.

Installation refinements: a simplified type of hydraulically-adjustable top bracing introduced for vibration control in 1989 was designed to cope with hull deflections giving rise to excessive stresses in the traditional mechanical type of top bracing. The system features a hydraulic cylinder which is a self-contained and does not need an external pump station. Instead, a pneumatic accumulator is built into the piston. The hydraulic cylinder is pre-tightened by the air pressure in the accumulator. When the engine is started the oil pressure in the cylinder increases because of the influence of the guide force moments, and the hydraulic cylinder adjusts its length to cope with slow hull deflections and thermal influence (Figure 10.28).

The system worked satisfactorily after teething problems were solved but a drawback of the hydraulically-adjustable top bracing is its higher first cost over the traditional mechanical bracing. An improved mechanical top bracing, incorporating two beams, was designed and tested in service from early 1997 (Figure 10.29). This is rigid in the athwartship direction and sufficiently flexible in the longitudinal direction to adapt to movements between engine and hull.

Simplification has also benefited engine seating arrangements. Feedback from shipyards indicated a preference for epoxy supporting chocks; epoxy chocks therefore became the standard in an effort to reduce installation costs, with the previously used cast iron supporting chocks as an option. Normal holding-down bolts are used in association with epoxy chocks but with the tightening force substantially reduced. The lower force is due to the higher coefficient of friction as well as the need to comply with the permissible specific surface pressure of epoxy. The general application of epoxy thus permits the use of thinner bolts which—following successful testing in service—have been introduced as standard. Larger engines (L42MC and upwards) have had one side chock per crossgirder per side. Investigations and experience showed that this number could be halved without any problems. An even simpler solution proposed features a side chock design that allows epoxy to be used as a liner. Installation man-hours are saved since the location of the side chock itself is much less demanding in terms of accuracy (Figure 10.30).

POST-1997 SERVICE EXPERIENCE

A service experience report covering mainly larger bore MC and MCC engines commissioned after 1997 indicated that a significant increase in reliability and longer times-between-overhauls had resulted from continuous development and updating. The following contributions were highlighted: Cylinder condition
A number of measures have contributed to positive developments in the cylinder condition in recent years, notably the Oros combustion chamber,  high topland pistons, the piston cleaning (PC) ring, controlled pressure relief (CPR) piston rings, alu-coating of piston rings and wave-cut cylinder liners.
 With the Oros configuration, the combustion air is concentrated around the fuel nozzles and the distance from the nozzles to the piston top is increased. This results in a lower heat load on the piston top and a basically unchanged heat load on the cylinder cover and exhaust valve. The higher topland and the PC ring have proved very beneficial in avoiding a build-up of lube oil-derived deposits on the topland. Such deposits (via the hard face sponge effect) scrape off and absorb the oil film, leaving the naked liner wall vulnerable to extensive wear and/or scuffing. A high topland piston also means that the mating surfaces between the cylinder liner and the cover are lowered, thus reducing the thermal load on the liner and improving the conditions for lubricating the liner. (This was taken into account before introducing the Oros configuration.)
 Cracked cylinder liners are now rarely reported thanks to the successful introduction of countermeasures, such as bore-cooled liners and (for smaller bore engines) slim liners. For engines originally specified with cast-in cooling pipes in the liners, the later design with oval pipes has stopped the occurrence of cracks.
 Safe and stable running-in is secured by the semi-honed surface of the liner in conjunction with alu-coated piston rings. A thin layer of alu-coating is worn  off the rings during the first 1000–2000 hours, making it possible to reduce the breaking-in and running-in time as well as the cylinder oil feed rate during most of the breaking-in period. This benefits the enginebuilder, who can cut the delivery time of an engine, and the operator, who receives an engine with improved running-in conditions.
 The surface of MAN B&W cylinder liners is described as semihoned. The semi-honing process cuts off the tops of the wave-cut,thus reducing the necessary breaking-in between rings and liner surface, while still retaining circumferential pockets for lube oil. The alu-coated piston rings remove the remaining broken or damaged cementite from the liner surface during the initial wear period (effectively performing a "free of charge" full honing).
 Low and uniform cylinder wear rates and a good liner condition are revealed by inspections of S-MC, S-MC-C, K-MC and K-MC-C engines. While initial (running-in) wear is naturally higher, the wear rate of the largest bore (90 and 98) models is reduced to less than 0.05 mm/ 1000 hours after around 1500 hoursrunning, which is considered very satisfactory.  Initial wear is part of the running-in of liners and piston rings, and high wear is expected during this period. Experience with the Alpha Lubricator (see above) indicated that there was significant potential for cylinder lube oil reduction while retaining a fully acceptable wear rate and mean time-between-overhauls.
 The top ring design of the K98 engine was upgraded to increase the safety margin against breakage in response to a number of failures. The production process at the sub-suppliers was also changed to reduce such incidents. The upgrading involved a number of changes, including relocation of the controlled leakage grooves, reduction of the number of grooves from six to four (the same leakage area is achieved by applying wider grooves) and modified surface machining of the grooves to avoid fine cracks from the outset (Figure 10.31).

Bearings
 A decrease in the number of reported main bearing failures has been noted since 1998, when a number of features were introduced to the bearing design, bearing adjustment and engine/shaftline installation. These major updates included the introduction of the Optimum Lemon Shape (OLS)-type main bearing as an evolution of the Mark 5 bearing type, featuring reduced top and side clearances. Service experience has confirmed the efficiency of the new bearing type, reflected in a significantly reduced number of reported failures. Main bearing damage can sometimes still occur, however: for example, due to poor bonding of the bearing metal. In almost all cases, main bearing damage is initiated from a fatigue crack at the edge of the bearing, the aft edge/manoeuvring side being the most common point of initiation. Geometrical non-conformities, often involved in these cases, further increase the damage frequency as margins established during the design phase are reduced. Calculations, combining the dynamics of the complete crankshaft with the hydrodynamic and elastic properties of the bearing, have provided detailed information on the mechanisms leading to local loading of the main bearing edges. The calculations have indicated that a slight radial flexibility of the bearing edge will significantly increase the overall minimum oil film thickness. At the same time, the maximum oil film pressure will be reduced. A bearing design with flexible forward and aft edges of the bearing shell was successfully tested, the flexibility achieved by removing the contact between the shell and bedplate at the end portions of the shell. The unsupported width of the shell is equal to the shell thickness. Apart from the flexible edges, the properties of the bearing are similar to those of the OLS-type and the design provides a larger safety margin in the event of geometrical non-conformities. A thin shell bearing design has been introduced to the latest engine types. The main bearings of the small and medium bore models (S46MCC to S70MC-C) are lined with AlSn40 and provided with a PTFE runningin coating as standard. The bearings of the large bore models are lined with white metal. Few damage incidents to the thin shell main bearings have been reported. A revised engine installation recommendation—including an updated shaftline alignment procedure and a differentiated bearing height in the aft end of the engine—resolved cases of repeated damage to the aft-end bearings. This was presumably caused by missing static load, particularly in the second aftmost main bearing during normal operating conditions. The new alignment procedure, exploiting pre-calculated bedplate sagging as well as vertical offsets to the main bearing saddles, achieved a significant drop in the number of reported damage incidents to the aft-end bearings. The crosshead bearings of both MC and MC-C engines generally perform very satisfactorily, but cases of wiping have been observed. Such wiping is of a cosmetic nature but can sometimes cause blockage of the oil-wedges that normally build up the oil film to the padsinside the bearing. Disturbance of this oil film build-up could result in slight fatigue damage just behind the blocked area of the oil-wedge. If observed at an early stage during inspections, however, the problem can be solved by removing the wiped lead from the oil-wedge. The crankshaft thrust bearing introduced on Mark 5 engines has solved the problem of cracks in the horizontal support plates. By making this plate (which connects the fore and aft thrust bearing supports) in one piece, and shaping it like a calliper, a significantly wider design margin is derived even though engine outputs (and hence propeller thrust) have been increased. No cracks have been reported on engines with this so-called Calliper design thrust bearing (Figure 10.32). The bearing saddles have remained free of cracks, in compliance with pre-calculated stress levels.
 Exhaust valves
 Nimonic exhaust valve spindles are well accepted now that operators have become acquainted with the long-lasting seat performance, despite dent marks. Nimonic spindles are standard for 50MC and 60MC/MCC engine models upwards; and Stellite spindles are standard for smaller models. Corrosion in the valve housing was effectively minimized by introducing the optimized cooling water system; this raises the wall temperature in the housing above the critical level for the formation of acid on the gas side of the duct. The high temperature level dictates a cast iron spindle guide bushing.

Wear of the previously chrome-plated spindle stem has been effectively reduced by the HVOF-based cermet coating introduced in 1997. Furthermore, wear and corrosion problems at the spindle guide/ spindle/seal area, caused by combustion products, have been minimized over the years by design changes to the sealing air system. Since the stem seal had difficulty in reaching lifetimes similar to those of the valve seats, however, it was decided to replace the sealing air system by a lubricating device tested with good results in long term service. Reduced wear of the spindle stem (HVOF coating) and of the long spindle guide (grey cast iron) has been achieved but the lifetime of the stem seal itself is still sometimes too short. Tests with oil as the sealing medium instead of air showed very low wear rates on the seals, along with a high cleanliness level on the surfaces of the spindle stem and spindle guide. A system delivering the necessary dosage of only approximately 1 kg/cylinder/day was developed for the medium and large bore engines. It is located in the top of the exhaust valve and fed with oil from the valves hydraulic system; oil is fed to the spindle guide via a small pipe. The sealing oil is taken from the circulating oil and is therefore part of the necessary minimum oil consumption for keeping the system oil viscosity and base number (BN) level at the prescribed equilibrium. The latest design of exhaust valve on the small and medium bore engines occasionally suffered from cooling water leaks at the lowermost O-ring between the bottom piece and cylinder cover. Investigations resulted in this O-ring being replaced by a special Teflon seal with spring back-up (U-seal).

Tests showed that the best way of increasing valve seat lifetime was by altering the seat geometry of the bottom piece to the patented Wseat configuration, now standard on all MC/MC-C engines (Figure 10.33). Results are even better when used with the new type of slide fuel valves.

 Engines featuring the Oros combustion chamber (see section above) leave little distance between the piston top and the underside of the exhaust valve spindle. The usual extended lift system for releasing high hydraulic pressure cannot therefore be applied. A safety valve located in the actuator is used instead. Unfortunately, a few cases of damaged exhaust valves and camshaft sections were experienced due to different external factors, including an insufficient release action of the safety valve. The valve was subsequently redesigned so that, once activated, it implements a special function to keep it open for around 20 seconds. In addition, a disc spring was introduced in the exhaust valve on top of the spindle guide to avoid damage to the air piston in the event of over-shoot/extended lift of the valve spindle. Fuel injection system In general, the fuel pumps work well and without difficulties, although a few incidents have been experienced and addressed: 

 A combined puncture and suction valve used on the S60MC-C, S70MC-C, S90MC-C and K98MC-C engines originally featured a bellow as a substitute for the conventional sealing rings in order to benefit from a component needing little or no maintenance. The reliability of the bellow was not satisfactory,  however, and a new design eliminating this element was introduced for the above engine models.

Fuel pumps without shock absorbers were introduced on these same engine types as a cost reduction measure but this resulted in annoying (although not damaging) pressure fluctuations in the fuel supply system. Even though these measured fluctuations were within MAN B&Ws and the classification societiesdesign limits, shipowners experienced problems with shipyard-installed equipment such as pumps, filters and pre-heaters. The problems were avoided by re-introducing a shock absorber on the fuel pumps of these engines.

A new type of gasket between the fuel pump housing and the top cover was introduced to cure leakage experienced on some K98MC/MC-C and S90MC-C engines. The primary sealing is secured with a viton ring, protected against corrosion attack by a steel bushing. A soft iron plate of the same shape as the original seal forms the groovefor the square viton ring.

Fuel pump top cover fractures were experienced on small and medium bore engines, initiated at the position where the inclined drillings for the high pressure pipes intersect with the central bore. The cause of the failure in all cases was related to roundings that did not fulfil the MAN B&W specification. A design change has improved the safety margin against failures, simplified manufacture and made the component less sensitive to minor tolerance deviations (Figure 10.34).

Fractured fuel valve nozzles were found on large bore engines where slide-type valves had been standard for some years. The main reason for the cracks was residual stress from machining, but the high temperature of the valve nozzle itself also contributed to fracturing because of the consequential high mean stress. The problem was cured by optimizing the production parameters.

MC	MCC
Wt	Weight reduced by 10%
Power to weight ratio increased
Long stroke 3.8:1	Super long stroke 4.2:1, obtain high prop eff
Sfoc 167gm/bhp/hr	171
Mep 18	19
Peak pr 140	150
Mean piston speed 8.02m/sec	8.46
Governor mech	Epectro mechanical
Starting air distr axial	Radial type
Holding down bolt access from db tank	Easy access
T/c eff low	High
Chain smaller	Bigger
Emissioms	Appreciabke emissioms
Single stay bolt	Twin stay bolts without pinching screw
Thck shell brg	Thin shell brg
Journal dia less	Increased
Crosshead heavy and telescopic pipe connected to pin	Simple n telescopic pipe connected on guide shoe.
Liner thick	Slim
Piston top with Inconel coating	No
Bottom ring grooves thin chrome layer	Incr by 0.5mm
Top piston ring	Cpr ring, alu coat
Pistom land low	High top land with oros piston and the interface btw liner n head is lowered.
Fuel pump dia Smaller	Adjusted larger as per the more fuel reqd