Abstract: This invention relates to an Oscillating Drive Shaft (ODS) and related components that replaces the crankshaft of reciprocating piston engines. The ODS is positioned to the left and/or right of the piston/s line of travel. The distance of the ODS from the center line of the piston's direction of travel is determined by the design nee& of the engine. One or more arms/beams (depending on the number of pistons) are fixed on the ODS. These arms are then connected to the reciprocating pistons using a suitable medium (e.g. connecting rod or gears) so that the reciprocating travel of the piston imparts an oscillating or rocking motion to the ODS. The ODS then passes through ratcheted gears or ratcheted flywheel (depending on requirements), converting the oscillating/rocking motion into the desired rotary direction of travel.