Piston pin
The gudgeon pin connects the piston to the connecting rod. This component ensures that the piston's up-and-down motion is transferred to the connecting rod, which then transmits the resulting energy to the crankshaft. The gudgeon pin is located inside the piston, in the gudgeon pin bore, and is usually secured with retaining rings (circlips) to keep it in place. It passes through the piston and the eyelet on the upper part of the connecting rod. Its material is typically hardened steel, as it needs to be very durable due to high mechanical stress and high temperatures. A crucial function of the gudgeon pin is to allow movement between the piston and the connecting rod while minimizing friction. In terms of design, some gudgeon pins are fixed to the piston and rotate around the connecting rod's eyelet. However, there are also gudgeon pins that rotate not only in the connecting rod's eyelet but also in the piston, with circlips providing the fixation.