a reciprocating piston machine , such as an internal combustion engine , is provided with a piston translator arrangement operated by a pair of oppositely rotatable crankshaft means disposed on opposed sides of the cylinder longitudinal axis such that the piston moves in a true straightline motion . this arrangement enhances ultimately possible compressions and improves operating efficiency since debilitating cylinder sidewall pressure by the piston is eliminated and forces are carried by two shaft systems , instead of one . an arrangement for removal of the piston from the cylinder , uniquely adapted for straightline motion piston running , is also disclosed .