Thank you for your answer. I say is the cassete because with other cassete is not do that problem. Now new chain and new cassete yes i know my bike need that. I try found 9 speed cassete with 16 sprocket and 18 sprocket i see most of 9 speeds cassete not have 16 or 18 sprocket. I want try do century and i try make my bike ready. I not know i cant deside what is good crank and cassete size for century. Before i see online one interesting think. Have sprockets for single tooth jump and double tooth jump. I not know if the cassete i put on my bike and skip gears i have do mix sprockets.