Alex
Your 535i should have a cam chain which is capable of incredible longevity. They do stretch, and the crank and cam sprockets do wear. Each time the valve cover is off for checking the banjo & head bolts/adjusting the valves, you can check the chain for looseness with a coat-hangar. Turn the engine by the crank, or the nut on the front of the alternator, just enough to start to move the cam. Now all the looseness is on the passenger side which is where the tension shoe is located. This shoe can only move so far, then any additional looseness is just slop and it can endanger the well-being of the engine as they can hop the teeth of the sprockets, sending the valves into the pistons. If you can wiggle the chain and it's other than "stiff" movement, it's time to change the chain.

These usually out-last the condition of the valves and it's quite easy to change the chain while the head is off for a valve job. My wife's chain lasted 350k miles and could have made it more but I was there so I did the right thing.

Dan Patzer
The CyberWrench
from Bimmers Only