Knocking is never a good thing, I have a timing problem and I am in over $1000 in just parts and tools and the problem is still kicking my butt. If it is a rattle you may have broken guide rails, knocking sounds like valves. I'm not an expert but unless you are willing to replace the engine or rebuild it is not worth it. I got a super great deal on my 2000 740i but it has been sitting for 3months and it's not because I have not worked on it, from what I have seen and heard the timing wil run you a couple thousand to fix. I am a DIYer so I am comfortable doing the work, but the special tool needed to do the timing will run you about $350- $420 + the parts. I would suggest getting one that is in better runnig shape, I promise you will be happier, you may have to spend a thousand or so more but it will be worth it. It is an awesome ride you will fall in love with it.
Last edited by awright1412; 12-01-2012 at 03:30 PM.