BMW Repair: Engine knock...Down low, rod bearing, definate answer

Question
Hello,
I was wondering if you could help try to diagnose a engine knock on my 93 525i(M50). In went to Florida with it and live in NJ. The car drove perfectly and it was about 18 hours down. I did notice once we had arrived a engine had developed a new sound. It knocks at idle and does not go away...We spent a week down and returned this past weekend. I drove the car home slowly and it made it fine....No high temp or any performance loss,dash lights or any thing like that? I know I hurt the motor somewhere but not sure how to evaluate...Rod? Bearing? where should I start with the repair shop with out getting taken....Thanks Very much for any light you may shed on the subject...

Respectfully,
Deane

Answer
The possibilites are endless, it could be anything.  The camshaft spins at 1/2 speed of the crank so you can sometimes figure it out just knowing that, however it could also be timing related or even carbon buildup.  It would be adviseable if the mechanic can't diagnose the problem to have the head taken off to take a look.  as far as not getting ripped off i can't give you a definate answer as to what the problem is it could be anything from $100-$4000. What you can do is ask the mechanic to see whatever parts he replaces (notify him before authorizeing the charges that you would like to see the broken part afterwards) and it's harder for him to decieve you.
-cheers