Abstract: The two-stroke engine includes at least one cylinder, a piston reciprocable within the cylinder and a cylinder head which contains at least one exhaust port which is controlled by a poppet valve and at least two inlet ports which are controlled by respective poppet valves and are connected to respective inlet ducts. The inlet ports are of directed type with the axes of the inlet ducts being convergent in the direction of flow whereby the air flowing through them into the cylinder flows preferentially generally towards the cylinder axis. The axes of the inlet ducts pass substantially through the cylinder axis where the air flows through the inlet ports merged to form a single air flow on or adjacent the cylinder axis.

Abstract: A two-stoke engine comprises a cylinder accommodating a piston and having an air inlet port and an exhaust port. The exhaust port communicates with an exhaust system which includes a reduction catalyst and an oxidation catalyst. The exhaust system includes two exhaust flow paths in parallel, the first of which includes the reduction catalyst and the second of which bypasses the reduction catalyst, the downstream ends of the two flow paths being connected together upstream of the oxidation catalyst. The exhaust port is controlled by the piston or by poppet valves so that as the piston performs its downstroke the initial flow of exhaust gas is substantially through the first flow path and the subsequent flow of exhaust gas is substantially through the second flow path.

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.