The main bearing cap, code 102985, is a precision-machined and highly loaded structural component of the MAN L21/31 engine that securely retains the main bearing and helps maintain the crankshaft in its correct operating position. Working together with the corresponding bearing housing, the cap must withstand substantial forces transmitted through the crankshaft while preserving the precise bearing geometry and clearances required for effective lubrication and smooth rotation. Accurate seating surfaces, correct fastening preload, dimensional stability, and proper alignment are essential because even small deviations can influence bearing load distribution, oil-film formation, crankshaft alignment, and component wear. During maintenance, the cap and its associated fastening and bearing surfaces should therefore be carefully inspected for deformation, fretting, cracking, wear, or other deterioration. By securely supporting the crankshaft and maintaining correct main-bearing alignment, the main bearing cap contributes directly to reliable lubrication, reduced mechanical wear, smooth engine operation, and the long-term durability of the MAN L21/31 engine.