Marine Crankshaft Main Bearings – Maintenance & Replacement  


Powerful rotation of the crankshaft is significant for regulating the propulsion system. The main bearings offer the structural support and connectivity of connecting rods to the crankshaft. Marine crankshaft main bearings transmit alternating loads of the main engine, eliminating frictional metal-to-metal contact.

In this guide to main bearings in marine vessels, we explain why regular maintenance and on-time replacement are essential for propeller and crankshaft performance.

Marine Crankshaft Main Bearings – An Overview

Bearings are absolutely crucial for all marine machinery, including the crankshaft. They are mounted at various points of the crankshaft, including the base of the connecting rod on the crankcase. Marine crankshaft main bearings are unsung heroes, serving multiple purposes within the engine block.

  • maintain accurate positioning of the entire equipment setup
  • regulate the rotation of the crankshaft
  • minimise surface-to-surface rubbing of the piston against the cylinder walls

Hence, these multi-functional parts support the crankshaft alignment, boost equipment efficiency, and prevent cylinder heating.

When Should You Consider Main Bearings Replacement

Inspection is mandatory at regular intervals to examine the condition of the bearings. Heavy fuel consumption, crankshaft misalignment, and heating are initial signs of bearing failure. However, the following are sure signs that it is time for the main bearing replacement:

Discoloured and Uneven Surface

Lubrication is a must to optimise the functioning of the marine crankshaft main bearings. However, poor quality and acidic lube oil can lead to bearing corrosion. Discolouring and roughness on the bearing surface are the prime symptoms to identify the problem.

Scratches and Cracks

Bearings exposed to contaminated oils and particulates go through severe abrasion. Deep scratches and cracks on the bearing surface are signs of abrasive wearing.

Stripped Overlay Layer

This happens due to heavy erosion in the main bearings. The failure to maintain the accurate oil supply pressure and faulty journal operation in medium-speed engines can lead to stripping.

Separation of the Bearing Lining

Fatigue happens when the bearings are exposed to excessively high engine load.

Excessive Wiping

Continued metal wiping happens due to high temperatures. It can trigger clearances and retard the bearing performance.

Check Product Attributes When Buying Crankshafts Bearings

Replacing decommissioned main bearings is inevitable to continue engine operation without any downtime. When buying OEM bearings, it is vital to ensure the quality and configuration of the parts concerning the crankshaft. Here is a checklist of essential points to consider during purchase to ensure it meets the quality standards:

  • Marine crankshaft main bearings are made of corrosion-resistant material to prevent frequent wearing of bearings, bearing keep, and the journal.
  • Friction between the journal and bearing means energy loss and poor fuel economy. Therefore, bearings must be resistive to friction to ensure energy efficiency and prevent heating.
  • Withstand the dynamic load.
  • Bear grinding-in and running-in during crankshaft operation.
  • Compatible with the hydrodynamic pressure and film of the of the oil film for uninterrupted journal rotation
  • Resistant to deleterious reactions with lube oil
  • Allow small particle embedding to the main bearing surface, but do not manipulate the journal pin.
  • Possesses superb tensile strength
  • Must be of high compressive strength
  • Excellent thermal resistance to perform in heated conditions

Buy Crankshaft Parts and Main Bearings Online 

Alfa Marine Spare Parts offers an extensive selection of crankshaft spare parts from Perkins, Yanmar, Caterpillar, Cummins, and many other brands. We ship marine engines and spare parts globally.

Following are popular Crankshaft main bearings on our product gallery and the compatible models.

Perkins KRP3122 –2306 / 2806 / 2506TAG3 / 2506C / 2506TAG4.

Yanmar YM-129001-02931 – 4TNV88-BDHQ / 4TNV88-BDHQ(T) / 4TNV88-BDSA (STD)

Perkins T427328 – 1204F-E44TTA / 1204E-E44TA / 1204F-E44TA (STANDARD)

Perkins T417566 – 1206E-E70TTA / 1206F-E70TTA (STANDARD)

Here are some crankshaft items in our product catalogue:

PerkinsKRP3022 – Connecting rod bearing for 2806 / 2506TAG3 / 2506C / 2506TAG4

Perkins U5MB0037C – Main bearing kit 1103

Perkins ZZ90242 – Crankshaft kit 1106D

Visit our crankshaft product category to view the entire range. Please feel free to contact us if you do not find the required part number. Our sales executives can arrange the OEM item in 2-3 business days.


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