Engine crankshaft support structure

An engine crankshaft support structure, comprising:

• a crankshaft;
• a main bearing having a roller, an outer race press-fitted and fixed to a crankcase, and an inner race separated from the outer race and loosely fitted onto the periphery of the crankshaft;
• and
• a sprocket for driving a camshaft, the sprocket being press-fitted on the crankshaft and arranged at a position outside the main bearing, the sprocket having a outer diameter R1 which is smaller than an outer diameter R4 of the inner race;
• and
• an oil seal mounting flange press-fitted onto the crankshaft and pressed against the inner race of the main bearing, wherein the sprocket for driving the timing chain is press-fitted onto the flange.

A method for assembling an engine crankshaft support structure comprising the steps of:

• integrating a roller with an outer race of a main bearing;
• press-fitting the outer race onto one of a right or a left crankcase;
• press-fitting an oil seal onto a seal bearing surface of the same one of the right or the left crankcase;
• loosely fitting an inner race of the main bearing onto a bearing seat of a shaft;
• press-fitting an oil seal mounting flange onto the shaft so that it presses against the inner race;
• press-fitting a sprocket for driving a timing chain onto the flange;
• passing the shaft through the roller and fitting the inner race of the main bearing against the roller;
• and
• fitting and integrating the right and left crankcases to form an integral crankcase for supporting the shaft.