the stock chain is junkThat is unquestionably true.any sprocket wear will ruin any new chain:naughty:That's not. It depends on the degree and nature of the wear present. A rear sprocket moderately worn by a chain that is less than 1% longer than it's original pitch won't do any harm to a chain at all. Even rear sprockets fairly well worn by a "stretched" chain are far more likely to be damaged by the new chain than to damage the chain. There is no advantage to running such a sprocket, of course because the new chain will fairly quickly finish it off, anyway. Fronts are different. The wear patterns induced by chains still in spec are entirely different than those caused by worn chains, but because the tooth shape is significantly changed, and because the specific load carried by each tooth is much greater at the front, the front sprocket should be changed with a new chain if it shows any significant wear.