the rs2000 in indeed a chain, they can snap but its very rare. most can cover well over 120k miles on the same chain altough its advised to change at 80k
the rs1800 is a zetec and we all know about the dodgey timing belt tesioner's on those dont we?
im sure every single one of us here know of at 1thats snapped.
the rs2000 i4 lump is pretty much bullet proof. mine regulary goes to 7000rpm, most days infact. has coverd 96k now with only a wheel bearing going from time to time