The connecting rod is a major link inside of a combustion engine. It connects the piston to the crankshaft and is responsible for transferring power from the piston to the crankshaft and sending it to the transmission. There are different types of materials and production methods used in the creation of connecting rods. The most common types of connecting rods are steel and aluminum. The most common type of manufacturing processes are casting, forging and powdered metallurgy.
The connecting rod is the most common cause of catastrophic engine failure. It is under an enormous amount of load pressure and is often the recipient of special care to ensure that it does not fail prematurely. The sharp edges are sanded smooth in an attempt to reduce stress risers on the rod. The connecting rod is also shot-peened, or hardened, to increase its strength against cracking. In most high-performance applications, the connecting rod is balanced to prevent unwanted harmonics from creating excessive wear.
The most common connecting rod found in production vehicle engines is a cast rod. This type of rod is created by pouring molten steel into a mold and then machining the finished product. This type of rod is reliable for lower horsepower-producing engines and is the least expensive to manufacture. The cast rod has been used in nearly every type of engine, from gasoline to diesel, with great success.
High-performance applications typically use a forged steel rod. This type of connecting rod is created by milling a solid block of steel into a finished product. The forged rod is able to withstand much greater loads and faster engine revolutions than a cast rod. The forged rods are often called billet rods due to the process of machining them from a block of billet steel. This is a much more costly way to manufacture the rod and the reason that these are typically only used in high-horsepower applications.
Another type of high-performance connecting rod is made of aluminum. The aluminum rod allows the engine to accelerate much faster due to the reduction of weight on the crankshaft. Aluminum also absorbs the harsh shock of acceleration and deceleration of a performance engine much better than steel rods. The aluminum is not as durable; however,and must be changed more frequently than its steel counterpart.
New technology has created the powdered metal rod. These rods are created by applying high pressure to metal powder as it is shaped into a rod. This is the rod of the future for most production engines. They are durable and cost effective to produce.