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Types of Gudgeon / Piston Pins (Explained)

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Last Updated on: 7th September 2023, 12:37 am

Piston pins, also known as wrist pins or gudgeon pins, are crucial parts of engines that transmit the reciprocating motion of the piston to the connecting rod.

Various types of piston pins have been developed to cater to different engine designs, such as the following.

  • Fully-floating
  • Semi-floating
  • Non-floating

In this article, we will explore the different types of gudgeon pins and their differences, advantages and disadvantages.

gudgeon pin different types

Full-Floating Piston Pins

The full-floating piston pin design is one of the most common types used. In this design, the pin is free to move within both the piston and the connecting rod.

Caps, plugs, and snap rings, or spring clips are used to secure the piston pin’s position and prevent it from coming out.

full floating piston pin diagram

Advantages

  • Reduced friction and wear: The free-floating movement of the gudgeon pin reduces friction between the piston, pin, and connecting rod, contributing to better engine efficiency.
  • Improved heat distribution: This design allows for more even distribution of heat within the piston assembly, leading to reduced thermal stress.
  • Quieter operation: The ability of the pin to move slightly helps in dampening noise during engine operation.

Disadvantages

  • Increased complexity: The use of circlips or retaining rings adds complexity to the assembly and maintenance processes.

Semi-Floating Gudgeon Pins

Semi-floating piston pins, also known as press-fit pins, strike a balance between the full-floating and fixed-pin designs.

In this design, the pin is fixed to the connecting rod and can only move within the piston.

semi floating piston pin diagram

Advantages

  • Simplicity: Compared to full-floating, semi-floating pins are easier to assemble and require fewer components, reducing their complexity.
  • Controlled movement: The limited movement of the pin reduces the risk of unwanted instability.

Disadvantages

  • Increased friction: The fixed connection between the piston pin and the connecting rod can lead to higher friction compared to full-floating designs.
  • Potential for uneven heat distribution: The restricted movement may lead to uneven heat distribution within the piston assembly.

Fixed (Non-Floating) Pins

Fixed or non-floating piston pins are directly attached to either the piston or the connecting rod, with no movement allowed in either direction.

This design is less common in modern engines but can still be found in certain applications.

fixed piston pin diagram

Advantages

  • Simplified design: Fixed pins eliminate the need for circlips, retaining rings, or complex assembly procedures.

Disadvantages

  • Increased friction and uneven wear: The lack of movement can result in higher friction and uneven wear between the pin, piston, and connecting rod assembly.
  • Limited heat dissipation: Without the ability to move, heat distribution within the assembly might be less efficient.

Coatings and Materials

In addition to different pin designs, advancements in materials and coatings have further improved piston pin performance.

High-strength materials like forged steel, titanium, and even special alloys are used to withstand the high stresses and temperatures present in the engine.

Coatings, such as DLC (Diamond-Like Carbon) coatings, are applied to piston pins to reduce friction and wear. These coatings enhance the overall efficiency and durability of the pin assembly.

Conclusion

Gudgeon pins are small components with a big impact on engine performance and longevity.

The choice of piston pin design depends on a combination of factors, including engine type, desired performance characteristics, and manufacturing considerations.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer. He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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