Do you have to replace the whole engine if the valve train moves?

Answer 1

I am not certain what is meant by 'valve train moves' but I will try to help.

If none of the valves has struck a piston only the cylinder head should require work.

If the above has occurred prepare for a large bill. The engine must be removed from the car. It may be a one piston replacement for a quick fix, but having got that far most people will do a complete overhaul.