Alfa Romeo Repair: alfa 2.4 jtd engine, alfa 2, cam sensor

Question
My car has done 71K miles, full service history. At about 69K it started rattling. The garage took the head off and raplaced valves....engine OK.
At 71K engine management light came on and a new mechanical noise started. he garage reported the fault code was injectors, synchronisation (cam to crank). Crank sensor changed but noise still there. (cam sensor changed on forst problem.
Do you have any ideas, the head off job cost me £850 and I can't afford to do this every couple of thousand miles.
Thanks

Answer
i am suspicious about what has been done. also, i am in the usa and that would be covered here under the warranty. i would suggest a second garages opinion if no dealership is available. a diesel engine is designed to go at least 250k miles before this kind of work is needed.