So the OP (Christoff aka mcvn) which is a friend of mine, still haven't been able to get his 540 back running.
Today he sent me this, I seems like finally at least the problem has been identified:
"The sleeve of one piston is damaged. Suspect a ‘nut’ got through the intake manifold and damaged the sleeve and piston. I have to 're-sleeve' the sleeve and replace the piston. Or I have to buy another engine somewhere, but I'm not sure since you never know what you are going to get with a second hand engine. Or I need to get another block, just the engine block itself, where the sleeves are still fine. Not really sure where to start, could you asked on the BMWFanatics forum for me?"
Any advice to give?
Thx:thumbs: