PURPOSE: To realize a low vibration and a low noise by providing a viscous shaft in which viscous disks furnishing eccentric cam grooves fixed concentrically as an output shaft, and fitting arms fixed to pistons to the eccentric cam grooves in the offset condition.

CONSTITUTION: When the contrivance is applied to a horizontally opposing 4-cylinder reciprocating engine, cylinder heads 9 furnishing suction and exhaust valves 5 and 7 opened and closed by valve operating mechanisms 8 are linked to cylinder blocks 3 of one side two-cylinder incorporated to a crankcase 1. And to the skirts 11a of pistons 11 installed in cylinder liners 12 of the cylinder blocks 3, one ends of a pair of arms 13 are fastened with bolts, and bearings 15 arranged oppositely are provided to the other ends of them. These bearings 15 are geared to eccentric cam grooves 19a formed at both side surfaces of viscous disks 19 incorporated with a viscous shaft 16. The two disks 19 and 19 are provided by setting the difference of phase of the eccentric cam grooves 19a at 180°.