Such early failures are usually some form of improper technique used to couple the chain.
It is common on diesels for the piston to valve collision to be so harsh that the piston drives the valve right through the cam without drastically affecting either the piston or valve, sort of like the "kung fu" hand through bricks affair.
You have to replace the damaged pieces which could easily include the head.
Bosch Master, ASE Master, L1
33 years MB technician