The frame, code HP1101, is a fundamental load-bearing structure of the MAN L21/31 engine, providing the rigid mechanical foundation required to support, connect, and accurately align major engine components. During operation, the frame must absorb and distribute substantial forces generated by combustion, rotating and reciprocating masses, vibration, and thermal expansion while maintaining the precise geometry required for reliable engine performance. Its robust construction and accurately machined mounting surfaces provide stable support for associated assemblies and help prevent excessive deformation or misalignment under changing operating loads. Proper inspection of the frame, particularly its mounting surfaces, fastening points, and highly stressed areas, is important during maintenance and overhaul. By maintaining structural rigidity and accurate component alignment, the frame contributes significantly to smooth engine operation, mechanical durability, operational safety, and the long service life of the MAN L21/31 engine.