..unfortunately Bastian is right about the oil consumption issue. My 4.2 also burns a lot of oil and i tried the same procedure last year. I removed the cylinder heads, took out all the valves, cleaned everything nice and shiny and put it all together with new valve seals. For a few thousand, the engine only took a litre on thousand km, put after that, same problem as usual...
Some people also make the valve guides responsible for that, most agree that clean / new piston rings lower oil consumption. Many discussions about that, besides that only those, who upgraded to the aec are happy now with the oil thing.
Downloading the Reperaturleitfaden also referred to as RLF will give you a hand changing the timing belt (if it needs to be changed)
Maintainance Guideline So long
Florian
