The main bearing cap, code 102985, is a precision-machined and highly loaded structural component of the MAN L21/31 engine designed to securely retain the main bearing and maintain the crankshaft in its correct operating position. Together with the corresponding bearing housing, the cap forms a rigid support around the main bearing and must withstand substantial dynamic and combustion-related forces transmitted through the crankshaft while preserving the precise geometry and bearing clearances required for effective lubrication and smooth rotation. Accurate seating surfaces, dimensional stability, correct alignment, and the specified tightening and preload of the fastening elements are essential because deviations can adversely affect bearing load distribution, lubricating-oil film formation, crankshaft alignment, and component wear. During maintenance and overhaul, the cap and associated contact surfaces should be carefully inspected for wear, fretting, deformation, cracking, or other damage. By maintaining stable crankshaft support and correct main-bearing alignment, the main bearing cap contributes significantly to reliable lubrication, reduced mechanical wear, smooth operation, and the long-term durability of the MAN L21/31 engine.