Nice to know | gudgeon pin

The piston pin is an underestimated component in your engine. So that you know what's behind it and you can understand your engine better, in this article we will focus on the small but extremely important component.


The piston pin is the link between the piston and the connecting rod. Due to the linear movement of the piston and the superimposition of gas and mass inertia forces, it is exposed to high loads in alternating directions. At the bearing points of the piston, in the piston boss and the small connecting rod eye, the rotary movement of the connecting rod must be compensated for by the piston pin.


Piston pins must meet the following requirements:

  • They should have sufficient strength and toughness to withstand the high loads without damage.
  • In order to achieve favorable wear behavior, piston pins should have a high surface hardness.
  • Piston pins should have a high shape and position tolerance in order to achieve optimal adaptation to the contact surfaces of the piston and connecting rod.
  • The weight of the piston pin should be as low as possible in order to keep mass inertia low.
  • To avoid overstressing in the piston boss, piston pins should also have high rigidity (high resistance to an external load).

Here are some additional facts about the above requirements:


Due to the forces acting on it, the piston pin is subject to bending, ovalization and shearing. As a result, there is a requirement that the piston pin should be as stiff and light as possible.


The critical component of the piston joint is not the gudgeon pin but the piston. An ovalization (= elastic deformation) of the piston pin must therefore be as small as possible, otherwise the already heavily loaded piston boss would be overloaded and the boss could crack. The ovalization can be minimized by larger piston pin diameters and an increase in wall thickness, which contributes to an increase in mass.


Due to the minimal lubrication of 2-stroke engines, the use of needle bearings is preferred for the piston pin bearings. In 4-stroke engines, the use of plain bearings has prevailed due to the existing splash oil and the higher gas forces. Oil pockets as a reservoir are possible to improve the build-up of a lubricating film.


Piston pins are made from case-hardened and nitrided steels. With good toughness in the core, hardening results in high surface hardness with good wear behavior.

BARIKIT wrist pin

BARIKIT piston pins are available in two versions. One with a cylindrical bore and a weight-optimized bolt with a conical bore. Here it is important to choose a compromise between the piston pins, since both variants offer advantages. With its reduced weight, the conical bolt is ideal for engines that are designed for higher speeds. However, these piston pins tend to become more oval than piston pins with a cylindrical bore. With higher gas forces, the piston boss can be heavily loaded and, in the worst case, lead to the piston breaking. Piston pins with a cylindrical bore are therefore suitable for engines with higher gas forces and torques. If you are unsure, please contact us via WhatsApp or email. You can find our contact details below. We are happy to advise you.

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