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Marine diesel engine main bearing shells are precision sliding components that support the crankshaft within the engine block. Positioned in the main bearing journals of the crankcase, these semi-circular shells form a cylindrical bearing surface that allows the crankshaft to rotate under radial loads generated by piston combustion. Each main bearing position consists of an upper shell and a lower shell, fitted together within the bearing cap and housing.
The primary functions of main bearing shells include supporting the crankshaft weight and combustion forces, maintaining correct shaft alignment, reducing friction through hydrodynamic lubrication, and conducting heat away from the crankshaft journal. These components are critical to engine reliability, as bearing failure can lead to catastrophic engine damage and loss of propulsion at sea. Main bearings are subject to replacement during major engine overhauls and whenever crankshaft regrinding is performed.
Heavy-duty marine main bearings typically use a tri-metal construction. The steel back provides structural rigidity and ensures proper seating in the engine housing. Bonded to the steel is a copper-lead alloy interlayer, approximately 0.3 mm thick, which provides fatigue strength and load-carrying capacity. The top layer consists of a tin-lead overlay, approximately 0.02 mm to 0.03 mm thick, which provides conformability, embeddability, and anti-seizure properties. This tri-metal structure is suitable for high-load two-stroke and four-stroke marine diesel engines operating under continuous heavy conditions.
For medium-load applications, bi-metal bearing shells with an aluminum-tin alloy lining bonded directly to the steel back are available. The aluminum-tin layer, typically containing 6 percent to 20 percent tin, provides both load-carrying capacity and wear resistance without requiring a separate overlay. This construction is commonly used in auxiliary engines and smaller propulsion units where load conditions are less severe.
Parameter | Specification Range |
Wall thickness tolerance | ±0.005 mm to ±0.008 mm |
Bore diameter range | 80 mm to 980 mm (varies by engine model) |
Wall thickness range | 2.5 mm to 8 mm (varies by engine model) |
Surface roughness (bearing surface) | Ra 0.4 μm to Ra 0.8 μm |
Half-length spread | 0.5 mm to 1.5 mm above half circumference |
Oil groove width | Varies per engine specification |
The wall thickness is measured at multiple points around the bearing circumference using calibrated gauges during the manufacturing process. Each shell is marked with its size grade to facilitate correct matching with crankshaft journal dimensions.
The copper-lead interlayer in tri-metal bearings provides resistance to fatigue failure caused by the cyclic loading of combustion pressure. Each power stroke applies an impact load to the bearing surface, and over thousands of operating hours these repeated loads can cause fatigue cracking in the lining material. The alloy composition and thickness are specified according to each engine model's peak cylinder pressure requirements.
The soft tin overlay allows the bearing surface to conform to minor misalignments in the crankshaft journal and housing bore. This conformability helps distribute the load evenly across the bearing surface. The overlay also traps small abrasive particles that may circulate in the lubricating oil, preventing them from scoring the crankshaft journal surface. This embeddability characteristic is particularly important during the initial running-in period after engine overhaul.
Bearing materials are selected for their thermal conductivity properties, which allow frictional heat to transfer from the bearing surface through the steel back to the engine block and cooling system. Effective heat dissipation prevents localized overheating that could cause bearing wiping or seizure, especially during sustained high-load operation.
MAIN ENGINE | MAN B&W | S26MC,L/S35MC,L/S42MC,L/S50MC,L/S60MC,L/S70MC,L/S80MC,L/S90MC,S46MC-C,S50MC-C,S60MC-C,S70MC-C,S80MC-C,S90MC-C,K90MC-C,K98MC-C,K/L45GF(CA),55GF(CA),67GF(CA),80GF(CA),90GF(CA) |
WARTSILA | 6L20,9L20,8L32,R22,R32,L20,L32 | |
PIELSTICK | PC2-2,PC2-5,PC2-5L,PC2-5V,PC2-6,PA4,PA5,PA6 | |
HANSHIN | EL30-44,ELS-35,44,LH-28G,LU24-54,LUN28AR(G),LUS24-58,LF46-58 | |
NIIGATA | 16HS,16X,18CX,19HX,20AX,25BX,25CX,26AFTE,26KGHS,28AFTE,28BX,28KGHS,31EZ,31X,32CLX,34AFTE | |
SULZER | RTA38,RTA48,RTA52,RTA58,RTA62,RTA68,RTA72,RTA76,RTA84,RL(A/B)56,RL(A/B)66,RL(A/B)76, RL(A/B)90,RND68,RND76 | |
AKASAKA | A31,A34,A38,A41,A45,AH25,AH27,AH28,AH30,AH38,AH40,K28,K31,DM28FD,DM38FD,DM40FD,DM51SS | |
MITSUBISHI | UEC33LSE,UEC37LA,UEC45LA,UEC50LS,UEC52LA,UEC52LS,UEC60LS,UET45/75C,UET45/80D, UET52/90D,UET52/105H | |
AUX.ENGINE | MITSUBISHI | S6A,S6B,S6R,S6N,S16N,S16R,S12R,SA2 |
MAN B&W | 16/24,20/27,21/31,23/30,25/33,28/32,32/40,48/60,58/64 | |
YANMAR | HAL,KL,KDL,KFL,RAL,MAL,S165,S185,M200,M220,T220,T240,T260,Z280,N165,N18,N21,N165,N260,N280, N330,NY16,EY18,EY22,EY26,4CHL,6CHL | |
DAIHATSU | DK20,DK26,DK28,DK32,DL16,DL19,DL20,DL22,DL24,DL26,DL28,DL32,DS18,DS19,DS22,DS26,DS28,DS32, DS40,PK14,PK16,PL24,PL26,PS18,PS20,PS22,PS26,PS30 |
Each production batch undergoes multiple inspection stages, including ultrasonic bonding verification to ensure proper adhesion between the lining material and steel back, spectral analysis to confirm alloy composition, and dimensional measurement using coordinate measuring equipment. Bearings supplied for commercial procurement can be provided with CCS Type Approval certificates and individual material test reports upon request.
The correct specification is determined by the engine model, crankshaft journal diameter, and required undersize grade. Engine manufacturers specify standard and undersize bearing thicknesses to match different crankshaft regrind dimensions. You will need to provide the engine type, model number, and current crankshaft journal measurement to identify the appropriate bearing grade. Our technical team can cross-reference these details against manufacturer specifications.
Recommended clearance varies by engine model and is specified by the engine manufacturer. As a general guideline, main bearing clearances typically range from 0.1 percent to 0.15 percent of the journal diameter for large-bore two-stroke engines. The exact value is stated in the engine service manual and should be verified during assembly using plastigage or dial indicator measurement.
Main bearings are routinely replaced during major engine overhauls, typically at 12,000 to 24,000 operating hours depending on the engine type and operating conditions. They should also be replaced whenever the crankshaft journals require regrinding due to wear or damage, and whenever bearing inspection reveals scoring, pitting, fatigue cracking, or lining displacement. Routine oil analysis can also indicate bearing wear through elevated metal particle content.
Standard supply includes material test reports and dimensional inspection records. For vessels requiring class documentation, CCS Type Approval certificates can be provided for applicable models. For other classification societies such as DNV, LR, or ABS, third-party inspection can be arranged at the time of order to meet specific vessel class requirements.
