Abstract: A multi cylinder two stroke cycle internal combustion engine of known construction having an individual crankcase compartment for each cylinder 11 formed in a crankcase 12, the crankcase 12 including a wall 25,25 separating two adjacent crankcase compartments. A crankshaft 13 extends through the wall 25,26 with a journal 29 thereof supported in a bearing assembly 30 has an outer bearing ring 32 non-rotatably mounted in the wall 25,26. The outer bearing ring 32 has an axial extent greater than the thickness of the wall 25,26 to provide an internal annular surface co-axial with a shoulder 36 on the crankshaft that presents an opposing external annular surface to the internal annular surface of the bearing ring 32. A fluid seal is provided between the internal and external annular surfaces to prevent the passage of gas between the crankcase cavities.