Internal combustion engine having crankshaft guide

An internal combustion engine having a horizontally opposed cylinder arrangement, including at least one pair of pistons associated with a respective pair of opposed cylinders of the cylinder arrangement, and an output shaft, wherein each of the pistons is arranged for reciprocating motion within a respective one of the cylinders, driven by combustion, and wherein the pistons are coupled to the output shaft by a coupling such that said reciprocating motion of the pistons drives rotation of the output shaft, wherein the coupling includes a connecting rod moveably coupled to a respective pair of pistons such that each piston is permitted to centre within its associated cylinder, a slider bearing located for reciprocating movement relative to the connecting rod, and a crankshaft that is rotatably mounted within the slider bearing, the crankshaft having a pair of guide shoulders for supporting axial location relative to the slider bearing, each of the guide shoulders having an inner surface that faces the slider bearing that is larger in radius than an outer surface of the guide shoulder.