Abstract: A reciprocating-piston i.c. engine is supported on a supporting structure by means of mountings which are attached, not to the crankcase wall, but to the main bearing structure of the engine, by means of rigid support members which extend through flexibly-sealed apertures in the crankcase wall and are rigidly secured to the main bearing blocks. The crankcase wall is thus isolated from vibrations generated by internal moving parts of the engine, and the deformations of the crankcase by such vibrations, and hence the level of noise generated by the crankcase wall, are reduced. Where a longitudinal stiffening beam is secured to the bottom bearing blocks of the main bearing structure, some of the rigid supports of the mountings may be attached to the stiffening beam.