Have a look at this link, tells you everything you need to know, as its a very common issue. HOWEVER, it says to put in the tensioner in its compressed state and rev the engine to 3k rpm to pop it out, I would advise against that. Instead, Decompress the tensioner by placing it end down on a flat surface, turn slightly and carefully and the spring pressure will be released, it makes it a bit more of a faff to get it back in, but the engine is protected straight away. Its rarely the chain itself unless the car has been run for a long time with a worn tensioner.
http://www.esatclear.ie/~bpurcell/318isfaults.html#timingchaintensioner
EDIT, found you another link, this is the better one lol, nice bargain btw!
http://www.m42club.com/forums/showthread.php?t=2925
If you want to change the ATF in the sealed for life autobox, let me know ive done that aswell, what fun that job is!