chains stretch .. i have mks tensioners .properly installed and tracknuts tightened down as hard as you can. my chain has stretched in the past month..its a fact. i reset my chain tension about a month ago as i say and when i did i made it fairly tight(ish) as i like to not have any play when i trackstand.i ride without a handbrake so my chain gets stressed i guess you could say..but there is no denying that there is now slackness in my chain and hence a small amount of play in it when i trackstand..so..chains stretch!