So I need a basic chain education. I'm solid on the whole x-ring, o-ring, standard debate but what's up with the 420,428,520's ? I've got a '99 YZ400, what was stock? Anychance a previous owner changed it up? The reason I need a new chain is because I over-shortened the previous one:banghead: . I was shortening it because after I installed a 13 tooth front sprocket the adjusters were maxed out and the play was too much. So I tell myself it was streched and probably needed to be replaced anyways. But I don't know enough about chains to pick out the correct new one.