O-Ring for Rotax Kart Engine Gear Case components. This o-Ring further seals the internal crankcase of the engine from the gear case, helping to separate the gear oil from the internal crankcase.
This O-ring fits behind the main crankshaft-driven gear next to the wall of the gear case. A humble o-ring, this is a very, very crucial part of the gear case assembly.
This is part 7 in the diagram. The dimensions of the o-ring are 18mm diameter by 3.5mm thickness.