Help! Problem With Engine noise

[axvel]

Hi, i have a 1994 325is and have a rattling sound form the engine. I think i know that the problem is with the chain, since the car lost power and the sound comes from the front of the engine. Does anybody have a walkthrough on how to change the chain and around price i should pay if i choose not to do it myself, i got quated 1900$ for 18 hours of work 90$ an hour plus parts i think it's abit too high and i can get the M Engine for that much and not worry about the repaires. Any Ideas would be appreciated.