The Role of Connecting Rods, and the Different Types - Samco

The Role of Connecting Rods, and the Different Types

How well do you the function of connecting rods? Here’s essential information to know.

Connecting rods – also referred to as ‘con rods’ – are one of the most vital parts of internal combustion engines. It is greatly used in steam engines but is now of the greatest importance in today’s engines.

This article highlights what a connecting rod is as well as its primary role or function. You will also discover the different types of connecting rods used extensively today.

Let’s dive in.

What is a Connecting Rod?

A connecting rod is a rod that connects a crankshaft (via the crankpin) to the piston (via the piston pin). The small end of a connecting rod connects to the piston pin, while the big end connects to the crank pin. The rod assists the conversion of the piston’s reciprocating motion into the rotation of the crankshaft.

In other words, the #1 or primary function of the connecting rod is to efficiently convert the piston’s linear motion into the crankshaft’s rotary motion.

Connecting rods, usually constructed from forged steel or aluminum alloy, comprise an I-beam cross-section. Con rods are often matched in sets of similar weights to maintain proper engine balance.

The lighter the piston and connecting rod, the lesser the vibration and the greater the resulting power. This is due to the fact that the reciprocating weight is also less.

A connecting rod transmits power thrust from the piston right to the crankpin. This is why connecting rods are made of highly durable and strong but lightweight materials like aluminum and forged steel.

Vital Parts of Connecting Rods

Every connecting rod comes with the following essential parts:

  • The big end
  • The small end
  • Bolt and nut
  • Bush bearing
  • Wrist pin
  • Bearing inserts
  • Piston
  • Shank
  • Bearing cap

Here’s a brief look at these parts:

The Big End

This is the part that is connected to the crankpin.

The Small End

This part is connected to the piston pin’s face.

Bolt and Nut

When connecting rods are fitted to the cranks at the bottoms, both sides of the rods’ big ends are usually fastened with a few bolts and nuts. After this, connecting rods are ready for use.

Bush Bearing

Connecting rods are often fixed at both ends using bush bearings. Phosphor bronze bush, fitted with a solid eye, is attached to the small ends of connecting rods.

But the big end, as stated earlier, is attached to the crankpin. This area is divided into two distinct parts and supported by the crank-bearing shell.

Wrist Pin

The wrist pin – called ‘gudgeon pin’ – is a hardened hollow steel tube connecting the piston to the connecting rod. This component moves through the short end of the con rod and then pivots on the engaged engine piston.

Bearing Insert

A bearing insert – found at the big end of a connecting rod – connects to the bearing cap. They usually come in two components that fit perfectly together on the crankshaft. At this position, the connecting rod travels conveniently in the reverse direction.


The piston is connected to the crankshaft via the connecting rod. The #1 purpose of the piston is to function as a movable plug within the cylinder which constitute the bottom of the combustion chamber.


As stated earlier, bolts and nuts connect the connecting rod to the bearing cap. A section beam called ‘shank’ is utilized here.

This section of the con rod comes in different shapes: it could be circular, tubular, or rectangular.

The length of the connecting rod relies heavily on the following ratio:



l = length of the beam or shank.

r = radius of the shank.

What Are The Different Types of Connecting Rods You Should Know?

Here are the different types of connecting rods you should know:

  • Plain type con rod

This type of connecting rod is used extensively in inline and opposed engines. The big end of a plain type connecting rod is usually attached to the crankpin. It is fitted with a bearing cap.

A stud or bolt mounts this bearing cap at the end of the con rod. In order to maintain adequate balance, the con rod must be placed in the same relative position and within the same cylinder.

  • Billet connecting rod

Billet con rods are made from aluminum or steel. This makes them stronger, lighter, and highly durable. They are usually employed in reducing stress risers as well as ease into the natural grains of billet material.

  • Master and slave connecting rod

Master and slave con rods are generally employed in radial engines. In this particular system, a piston consists of a master connecting rod directly attached to the crankshaft.

Other pistons connect their individual connecting rods to the rings that surround the edge of the master rod.

  • Forged connecting rod

A few connecting rods are created through forging. Manufacturers make this type of con rod by forcing grains of material in order to shape the end. This material could be aluminum or steel alloy, depending on the properties required.

The most common steel alloys used to make forged connecting rods are nickel and chrome. They help enhance the overall strength of the con rod.

  • Powered metal connecting rod

Some connecting rods are made of powered metal. This type of con rod is created using a metal powder mixture pressed into the mold and heated until it reaches an incredibly high temperature.

The final product usually comes out of a finished product mold and may need some light machining. Powered metal connecting rods are far less costly than steel con rods but much stronger than cast connecting rods.

  • Cast connecting rod

Cast connecting rods are designed to make them capable of handling loads from stock engines. Manufacturers love making them due to their low production cost, though they can’t be utilized in applications requiring high horsepower.


Connecting rods serve as the central connection between the crankshaft and the piston. Its primary function is to convert the piston’s linear motion into the crankshaft’s rotary motion.

Different types of connecting rods exist today. Each one is made or constructed using different materials and unique processes to fit specific uses.

From industry standards like Ariel compressor parts to Clark and Cooper Bessemer compressor parts, we carry compressor parts you can trust and the service you can count on.