An interchangeable concrete cutting chainsaw cutting assembly adapted for installation upon a drive assembly in exchange for a removed, different type cutting head assembly, said chainsaw cutting assembly comprising: a housing (703; 502,504) having fasteners that releasably attach said housing (703; 502,504) to a drive assembly in an installed configuration; a ratio transmission (525; 526) comprising a plurality of interconnected rotatable members (533, 535; 530, 532, 534), each rotatable member (533, 535; 530, 532, 534) having a mounting shaft (641, 643; 538, 542, 546) positioned at a fixed location on said housing (703; 502, 504) by a bearing assembly (640, 642; 536, 540, 544); and said plurality of rotatable members (533, 535; 530, 532, 534) comprising a round, disk-shaped driven member (533; 530) and a round, disk-shaped cutting chain drive member (535; 534), characterized in that said driven member (533; 530) having a circumference at least twice as long as a circumference of the cutting chain drive member (535; 534); said driven member (533; 530) having a receiver that interconnects with a driveshaft of the drive assembly in the installed configuration whereby said driven member (533; 530) is rotated by the drive assembly; a chain bar attached to said housing (703; 502,504); drive sprocket (707; 566) and nose sprocket, at least one of which is rotatably mounted on said chain bar and a cutting chain suspended on said drive sprocket (707; 566) and nose sprocket for circulation about said chain bar; and said cutting chain drive member (535; 534) operatively interconnected with said drive sprocket (707; 566) whereby rotation of said cutting chain drive member (535; 534) rotates said drive sprocket (707; 566). a housing (703; 502,504) having fasteners that releasably attach said housing (703; 502,504) to a drive assembly in an installed configuration; a ratio transmission (525; 526) comprising a plurality of interconnected rotatable members (533, 535; 530, 532, 534), each rotatable member (533, 535; 530, 532, 534) having a mounting shaft (641, 643; 538, 542, 546) positioned at a fixed location on said housing (703; 502, 504) by a bearing assembly (640, 642; 536, 540, 544); and said plurality of rotatable members (533, 535; 530, 532, 534) comprising a round, disk-shaped driven member (533; 530) and a round, disk-shaped cutting chain drive member (535; 534), characterized in that said driven member (533; 530) having a circumference at least twice as long as a circumference of the cutting chain drive member (535; 534); said driven member (533; 530) having a receiver that interconnects with a driveshaft of the drive assembly in the installed configuration whereby said driven member (533; 530) is rotated by the drive assembly; a chain bar attached to said housing (703; 502,504); drive sprocket (707; 566) and nose sprocket, at least one of which is rotatably mounted on said chain bar and a cutting chain suspended on said drive sprocket (707; 566) and nose sprocket for circulation about said chain bar; and said cutting chain drive member (535; 534) operatively interconnected with said drive sprocket (707; 566) whereby rotation of said cutting chain drive member (535; 534) rotates said drive sprocket (707; 566).