Case member attachment structure

A case member attachment structure comprising:

• a first case member;
• a second case member attached to a first surface of the first case member;
• a third case member attached to a second surface of the first case member that is opposite to the first surface;
• a bolt;
• and
• an oil filter, wherein
• the first case member and the third case member are fastened by the bolt,
• the second surface and a position where the bolt is attached are located on an inner side with respect to the first surface in an extending direction of the first surface,
• the first case member includes a first oil passage,
• the second case member includes a second oil passage,
• the third case member includes a third oil passage,
• the first oil passage, the second oil passage, and the third oil passage constitute a single oil passage,
• a first portion of the first case member surrounds a head of the bolt, the head and the first portion of the first case member being disposed within the first oil passage outside a main flow of oil in the first oil passage to avoid interfering with the main flow,
• the oil filter is provided upstream of the single oil passage,
• the bolt is located downstream of the oil filter, and
• the first case member is a first chain case and the second case member is a second chain case, and the third case member is a crankcase of an internal combustion engine.