The locking spring washer, code 06.16169-0004.2, is a critical safety element used to maintain the integrity of bolted joints in the MAN L21/31 engine. Its elastic design generates continuous preload, preventing loosening caused by vibration, thermal cycling, and dynamic mechanical loads typical for medium-speed diesel engines. By ensuring a constant clamping force and compensating for minor surface irregularities, it protects fasteners from self-rotation and preserves precise alignment of assembled components. This small but essential part significantly enhances operational reliability, reduces the risk of unplanned downtime, and supports long maintenance intervals.