Abstract: An engine comprises two counter rotating multilobate cams which are acted upon by a pair of diametrically opposed pistons which are rigidly interlinked by connecting rods. Differential gearing is provided to time the counter rotation of the cams.The following is an examiner's statement of reasons for allowance: The prior art fails to teach or fairly suggest the invention as a whole including a shaft having a first multilobate cam axially fixed to said shaft and an adjacent second multilobate cam differentially geared to said first multilobate cam for axial counter rotation about said shaft, at least one pair of cylinders, the cylinders of each pair being diametrically opposed with respect to said shaft with said multilobate cams interposed therebetween, and a piston in each said cylinder, said pistons of a pair of cylinders being rigidly interconnected.