Primary housing assembly for a motorcycle engine

A motorcycle comprising:

• a frame;
• a steering assembly including a front wheel supporting a forward portion of the frame;
• a rear wheel supporting a rearward portion of the frame;
• an engine assembly coupled to the frame, the engine assembly including:
• a crankshaft defining a crankshaft axis;
• a crankcase supporting the crankshaft for rotation about the crankshaft axis and defining a first surface, wherein the crankcase defines a plurality of threaded bores extending through the first surface and angularly spaced about the crankshaft axis;
• a transmission including an input shaft defining an input axis, the input axis extending substantially parallel to the crankshaft axis;
• a primary housing defining a crankshaft opening through which the crankshaft extends and an input shaft opening through which the input shaft extends, the primary housing defining a second surface that faces the first surface and housing a primary drive assembly that drivingly couples the crankshaft to the input shaft;
• wherein the primary housing includes an inner housing that defines the second surface and an outer housing coupled to the inner housing, the inner housing defining a plurality of external coupling apertures extending through the second surface and substantially aligned with some of the threaded bores, and the outer housing defining a plurality of outer coupling apertures substantially aligned with the external coupling apertures, wherein fasteners extend through the outer coupling apertures, through the external coupling apertures and into the threaded bores to couple the outer housing to the inner housing and to couple the inner housing to the crankcase.