snatch

I have recently purchased an audi a8 2.8 2001 but on tick over as she was stood it started juddering and then cut out??? After investigation it shows that the tensioner nylon support against the chain had failed also, we have since found out that the valves have bent and sadly a hole in the piston so, has anybody experienced this before and i also need some advice/help on finding a piston? A chain tensioner for chain for both heads. Any advice given will be much appreciated.