Abstract: An internal combustion engine includes a shaft and a multilobate central cam fixed to the shaft, the central cam having at least three lobes which define a central cam surface. There is at least one cylinder module, each cylinder module including a pair of cylinders. The cylinders are diametrically opposed with respect to the shaft with the central cam interposed therebetween. There is a piston in each cylinder, each piston including an associated engagement device for engaging the central cam surface and a connecting member connecting the pistons. The connecting member has an internal space through which the central cam extends. The reciprocating motion of the pistons in the cylinders in use imparts rotary motion to the shaft via engagement of the engagement device of the pistons with the central cam surface of the central cam.