[Kevin Sevcik]

Okay, followup question to help solve your problem. Mounting depends on how much load will be on the sprocket/gear. If there's a fairly light load on it and it's large enough, I'd just bolt it directly to the plastic coupler for the keyang motor. If it's not that big.... Well you might be able to remove the gear from the keyang and attach your sprocket directly to the shaft of the keyang with an ugly but possibly functional combination of JB Weld, a roll pin, and a hose clamp. Mostly it depends on the particular details of the mechanism.