The O-ring K 34144 is an important sealing component designed for the cooling insert K 34133 within the operating piston assembly of the Adriadiesel/Jugoturbina/Zgoda/Sulzer ZV40/48 engine. Its principal function is to create a reliable fluid-tight seal around the cooling insert, helping prevent leakage of the cooling medium and ensuring that the designed cooling circuit remains effective during engine operation. Although relatively small, the O-ring performs a critical role because deterioration, hardening, deformation, or damage to the seal can lead to coolant leakage, reduced cooling efficiency, contamination of surrounding areas, and potentially increased thermal loading of associated components. The sealing material must therefore be compatible with the applicable cooling medium and capable of tolerating pressure, temperature variations, vibration, and repeated thermal cycles. Correct installation and replacement of the K 34144 O-ring during appropriate maintenance interventions help preserve the integrity of the cooling system, maintain efficient temperature control, and support reliable long-term operation of the cooling insert and operating piston assembly.