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
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