I partially agree with Steve on this. Some of the shorter chains will go this long, but I have measured the old chains and sprockets against new ones, and have found significant wear at as little as 80k miles. The sprockets have to be taken off to do the rails. Why not do the chain and sprockets if you go that far? I'd do 'em while there. (This is the good thing about this site, you see more than one opinion.)