What Is a Gudgeon Pin?
A gudgeon pin, also known as a wrist pin, is an important part of a car engine. It creates a connection between the connecting rod and the piston and provides a bearing for the connecting rod to pivot upon as the piston moves.
Gudgeon pins can also be used with connecting rods and wheels or cranks. In very early engine designs, including those driven by steam, and many very large stationary or marine engines, the gudgeon pin is located in a sliding crosshead that connects to the piston via a rod. A gudgeon is a pivot or journal.
Generally, the term “gudgeon pin” is used in the United Kingdom, while in the United States and Canada, the preferred term is “wrist pin.”
Construction of Gudgeon Pin
The gudgeon pin is typically a forged short hollow rod made of a steel alloy of high strength and hardness that may be physically separated from both the connecting rod and piston or crosshead.
The design of the gudgeon pin, especially in the case of small, high-revving automotive engines, is challenging.
The gudgeon pin has to operate under some of the highest temperatures experienced in the engine, with difficulties in lubrication due to its location, while remaining small and light so as to fit into the piston diameter and not unduly add to the reciprocating mass.
The requirements for lightness and compactness demand a small diameter rod that is subject to heavy shear and bending loads, with some of the highest-pressure loadings of any bearing in the whole engine.
To overcome these problems, the materials used to make the gudgeon pin and the way it is manufactured are amongst the most highly engineered of any mechanical component found in internal combustion engines.
Design Options
The gudgeon pin can be installed in a semi-floating or fully floating configuration, depending on the design of the engine. It acts as a bearing for the connecting rod, allowing for rotational movement while the engine is running.
Specialized versions are produced for applications like car racing, where engine components need to be especially strong because high-performance engines create some unique demands.
Semi-Floating
In the semi-floating configuration, the pin is usually fixed relative to the piston by an interference fit with the journal in the piston. The connecting rod’s small end bearing thus acts as the bearing alone.
In this configuration, only the small end bearing requires a bearing surface, if any. If needed, this is provided by either electroplating the small end bearing journal with a suitable metal, or more usually by inserting a sleeve bearing or needle bearing into the eye of the small end, which has an interference fit with the aperture of the small end.
Fully floating
In the fully floating configuration, a bearing surface is created both between the small end eye and gudgeon pin and the journal in the piston. The gudgeon pins are usually secured with circlips.
No interference fit is used in any instance and the pin ‘floats’ entirely on bearing surfaces. The average rubbing speed of each of the three bearings is halved and the load is shared across a bearing that is usually about three times the length of the semi-floating design with an interference fit with the piston.
How to Install a Wrist Pin (Piston) Super Easy
Conclusion
When engines are inspected, as is done during oil changes, tune-ups, and other routine visits to the mechanic, the mechanic will look for obvious signs of wear on engine components. If there is a problem with a component like a gudgeon pin, the mechanic may recommend a replacement.
Uneven or unusual wear will be remarked upon, as it may indicate that there is an underlying problem with the engine that needs to be addressed. It is important to take engine problems seriously, as they can lead to catastrophic failures of components or the engine itself.
While repairs may be costly, it is usually cheaper to fix a problem at the time it manifests than to wait for something else to break.
