The connecting rod is the connecting piece between the crankshaft and the piston, the main purpose of which is to convert the translational motion of the piston inside the cylinder into the rotational motion of the crankshaft, from which the rotation is transmitted to the wheels of the car through the transmission. If you have an accident that causes the machine to have far fewer working parts than non-working parts, the machine should be recycled:

Connecting Rod Design

Features of the design of connecting rods directly depend on the type of engine and the scheme of its layout. For gasoline engines use light connecting rods, while diesel engines use heavy connecting rods.

The main parts of the connecting rod are the rod, the upper piston head, and the lower crank head.

The piston head is connected to the rod with a piston pin and the crank head to the crankshaft pin.


This connecting rod can have various types of cross-sections, which can be rectangular, circular, cross-like, or can be H-shaped. Some engine types are equipped with connecting rods that have a small oil groove for timely oil delivery to the piston head.

In most cases, the top section of the crank head is equipped with a small hole for splashing oil into the inner cavities of the piston and cylinder.

Piston head

The piston head is placed at the top and is a non-removable connecting rod element, the design of which depends directly on the method of mounting the piston pin.

In engines with a fixed pin, the piston head has a special cylindrical hole for its installation. In internal combustion engines with a floating pin, this head is fitted with a bronze or bimetallic sleeve.

In those models of engines that use a floating pin, but no bushing is provided, the rotary motion of the pin is performed in the corresponding head bore.

In order to reduce the significant stresses on the pin, some engine models are equipped with trapezoidal piston heads.

Crank Head

The connecting rod head below has a split design with the primary purpose of connecting the two mechanisms – the crankshaft and the connecting rod itself.

The head consists of a top and a cap that is bolted to the connecting rod. Among other things, this head can have two types of joints in relation to the rod axis – oblique (made at an angle) and straight (made perpendicularly).

The length of the cylinder block depends on the thickness of the lower head. Thin plain bearing shells are installed in the head, which can have from 2 to 5 layers, made of steel strips, the inner part of which is covered with a protective antifriction composition, corresponding to a certain type of engine.

Modern internal combustion engines commonly use 2-layer and 3-layer liners. The 2-layer liner is simply a layer of sliding compound on the metal liner, and the insulating layer is added in the 3-layer liner.

To reduce engine vibration and noise, all installed connecting rods, as well as their component parts, should have equal weight. This means that in one connecting rod, the weight of the individual parts must be the same relative to the weight of the same part in the other connecting rod.

For example, if the rod mass for one connecting rod is 50 g, then all other connecting rods must have the same mass.

The weight of the connecting rods is adjusted by removing a thin layer of metal from the bosses that are located on the top heads of the connecting rods. In some cases, such bosses are on the connecting rod or bottom of the piston head.

Materials for connecting rod manufacturing

Connecting rods can be made in two ways – by forging from high strength steel, or by casting from cast iron. Alloy steel connecting rods forged or hot forged are used in diesel engines.

Some gasoline engines are fitted with connecting rods made of powdered metals by sintering.

Because of the stressful conditions under which it is used, this connecting rod must be robust, durable, and wear-resistant.

Particular attention is paid not only to the manufacturing of connecting rods, but also to the bolts of attachment. Alloy steels with a high yield strength, which is several times higher than that of high-carbon steels, are used for bolt production.

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