Marine connecting rod for transferring power from piston to crankshaft in 2-stroke and 4-stroke engines

Marine Connecting Rods

Marine Connecting Rods for 4-Stroke Engines

Marine connecting rods are critical mechanical components in 4-stroke marine engines, responsible for transferring forces between the piston and the crankshaft. Their design accuracy, material quality and correct assembly directly influence engine reliability, service life and operational safety.
We have supplied marine connecting rods multiple times for major overhauls of medium-speed 4-stroke engines, supporting both scheduled maintenance and repair yard projects. Our delivery scope covers a wide range of engine types, including MAN, Daihatsu, YANMAR, MAK engines, as well as many other widely used 4-stroke marine engines.

Function of the Connecting Rod in a 4-Stroke Marine Engine

In a 4-stroke engine, the connecting rod converts the linear movement of the piston into rotational motion of the crankshaft. During each operating cycle, the rod is exposed to alternating tensile and compressive forces combined with high thermal and mechanical loads.
A properly specified marine connecting rod must:

  • Transfer combustion forces without deformation
  • Maintain correct piston and crankshaft alignment
  • Withstand cyclic fatigue over long operating hours
  • Support stable engine operation under constant load

4-Stroke Engine Types Supported

We support connecting rod supply for a wide range of medium-speed 4-stroke marine engines commonly used in propulsion and auxiliary applications, including:

  • MAN L16/24
  • MAN L23/30
  • Daihatsu DK28
  • Daihatsu DK20
  • Daihatsu DE18
  • Daihatsu DC17
  • YANMAR N21
  • YANMAR N18
  • YANMAR EY18
  • MAK majority of the engines types

and many other 4-stroke marine engines used worldwide.

This flexible scope reflects real overhaul practice, where shipowners operate mixed engine fleets across different vessel types.

Construction of a Marine Connecting Rod

A marine connecting rod is a precision-engineered component consisting of several key elements, each with a specific function.

Rod Body
The rod body is typically forged from high-strength alloy steel, designed to provide high fatigue resistance while maintaining rigidity under continuous dynamic loading.

Small End
The small end connects the rod to the piston pin and is fitted with a small end bearing or bush, allowing controlled oscillating movement and reducing wear.

Big End
The big end connects to the crankshaft journal and houses the big end bearing shells, ensuring correct load distribution and stable oil film formation.

Big End and Small End Bearings Supply
Alongside marine connecting rods, we supply big end and small end bearings as part of complete overhaul packages or as individual components.

Our supply scope includes:

  • Big end bearing shells matched to crankshaft journals
  • Small end bearings or bushes for piston pin applications
  • OEM and genuine bearing solutions
  • Bearings supplied separately or together with connecting rods

Correct matching of rods and bearings is essential to ensure proper clearances, lubrication and long-term engine reliability.

Connecting Rod Bolts

Connecting rod bolts are among the most highly stressed components in a 4-stroke marine engine. Their integrity and correct tightening method are critical for safe operation.
We supply marine connecting rods with:

  • OEM and genuine connecting rod bolts
  • Defined tightening and elongation procedures
  • Compatibility with hydraulic tightening systems

Hydraulically Clamped Connecting Rods

Many medium-speed 4-stroke engines, including MAN, Daihatsu, Yanmar and MAK designs, use hydraulically clamped connecting rods. Hydraulic tensioning ensures precise and uniform bolt preload during assembly.
This method provides:

  • Consistent bolt tension
  • Improved big end geometry
  • Reduced risk of bolt fatigue
  • Increased assembly safety during overhauls

OEM and Genuine Marine Connecting Rods

We supply OEM and genuine marine connecting rods in accordance with original engine manufacturer specifications. These components are intended for professional engine overhauls where reliability, traceability and dimensional accuracy are required.
Using OEM and genuine parts helps minimize operational risk and supports long-term engine performance.

Support for Engine Overhauls and Repair Yards

Marine connecting rods and bearings are typically inspected or replaced during major overhauls of 4-stroke engines. We support shipowners, technical managers and repair yards by supplying:

  • Marine connecting rods
  • Big end and small end bearings
  • OEM and genuine bolts
  • Technical verification of specifications

This approach helps keep overhaul schedules under control and reduces the risk of rework or unexpected delays.

+48 505 186 795parts@alfamarine.pl