A Guide to Engine Connecting Rods
Engines nowadays are more complex than ever before with there being components that have always been part of an engine and some that have been added recently. The former more essential parts are needed for every piston engine and one of them are the connecting rods.
As you might expect by the name, a conrod is what connects the piston to the crankshaft. The piston is what pushes down in the cylinder to create compression so that fuel ignites and combustion happens. The crankshaft is what makes that mini explosion useful as it transfers the power from it, onto the wheels. Hence why automotive connecting rods are so important as their role of connecting parts is not the only one.
Parts of a Connecting Rod
Small & Big End
Even a conrod isn't as simple as it may sound. For starters, it has a small end and a big end with the former being the one connecting the rod to the face of the piston. The bigger end of an engine connecting rod is attached to one side of the crank pin.
Bearing & Bearing Insert
Bush bearings are found on both ends of a conrod. The small end has a phosphor bronze bearing while the big end has one that helps it sit on the crank bearing shell better. The bearing insert is found at the big end of the conrod which connects to the bearing cap. The bearing insert is made in two parts that go over the crankshaft.
Shank
Since both sides of a conrod have bearings, they also have bolts and nuts and for that, they make use of a section beam known as a shank. This part can be circular, tubular or rectangular.
Wrist Pin
The wrist pin is what connects the piston to the conrod. This hollow hardened steel tube is also known as a gudgeon pin.
Piston
The piston, as you already know is the main driver in which fuel together with air and a spark are compressed to make a combustion engine run.
Types of Connecting Rod Designs
Forged
Made by forcing a grain of material to the shape of the conrod's bigger end, forged connecting rods are usually made of steel alloy or aluminium. There are other materials that can be used when forging engine rods such as chrome and nickel alloy.
Billet
A billet connecting rod is one that's made from either aluminium or steel. These are made by a machine and are one whole piece which is quite light but also strong and durable when compared to other types of connecting engine rods. Hence why billet conrods are used in high-speed vehicles so that the stress being put on the rod is not going to damage it.
Cast
Cast conrods are favoured more by manufacturers themselves since they are able to handle the load of a stock engine quite well. This type of manufacturing also makes for an affordable component but one that can't be used in high HP engines. Usually, cast connecting rods are found in engines that can go up to 6000 RPM.
Connecting Rod Materials
Steel
When you have a high-torque engine, steel automotive connecting rods are the best solution since they are quite strong and thus can withstand the tensile force being put on them. But keep in mind that steel conrods are heavy and are not meant to be used in engines with a high RPM range.
Aluminium
Talking about high RPM applications, aluminium conrods are the best solution in this case. Why? Because they are lighter than steel ones but also quite strong. They're not stronger than steel conrods, but this balance is what makes them the ideal solution in this case.
Titanium
A titanium engine connecting rod has all the benefits of both steel and aluminium rods. They are the strongest but also the lightest connecting rods you can find which is what makes them so versatile. But you'll have to invest quite a big sum if you go for titanium conrods.
I-Beam vs H-Beam Connecting Rods
The main styles of conrods are I-beam and H-beam rods. I-beam conrods are found on most stock engines since their design allows them to handle more than 400 HP and around 6,500 RPM. If your vehicle goes over that level of performance you can always go for I-beam automotive connecting rods made of a different material to bear even more pressure. Or you can also go with an H-beam connecting rod.
This type of connecting rod is much stronger than an I-beam conrod when it comes to bending stress. But because H-beam conrods are more difficult to manufacture they're also more expensive than I-beam conrods. Although the overall reliability and strength of both I-beam and H-beam conrods depend on more than just one factor, usually, the material which they're made of plays a huge role.