Chain gear and crank mounting assembly

A chain gear and crank assembly for a bicycle comprising a crank arm having a shaft, a larger and a smaller diameter chain gear, said larger and smaller diameter chain gears having a different number of peripheral teeth, and an adapter for mounting said chain gears to said crank arm, each of said chain gears being formed in an annular shape and having at an inner periphery thereof engaging projections extending radially inwardly which function as first mounting means for mounting each said chain gear to said adapter, said adapter comprising a boss having a bore insertably engageable with said shaft of said crank arm, a plurality of legs extending radially outwardly from said boss, and at least one annular member connecting the radially distal ends of said legs, each of said legs having respective mounting portions for each of said chain gears, said respective mounting portions being axially offset for the respective chain gears and each containing a second mounting means comprising grooves respectively insertably engageable with said engaging projections of said first mounting means of said chain gears for fixing said chain gears axially offset from one another to said adapter, said annular member having a larger diameter than the diameter of said larger diameter chain gear and being displaced axially from said larger diameter chain gear to function as a chain guide.