rebuild or replace engine??

Ive been having trouble for the last 12months with the crankshaft on my 300. The key that holds the crankshaft cambelt pulley on somehow became loose and has worn a groove away in the shaft. I replaced the crankshaft key and the pulley and used some liquid metal type stuff to build up the groove in the shaft. This has worked fine for the last 10 or so months but im starting to get problems again. Every time I start the engine there is a mass of white smoke coming out and the acceleration is very delayed, press pedal and nothing happens, once it starts to rev up and the turbo kicks in theres a nice cough of black smoke aswell. Im guessing whats happening is the crankshaft pulley has some movement in it which has knocked the timing out, but I dont know? . I've had the injectors tested and they are fine. What i'd like to know is whether it's going to be better to try and find a decent 2nd hand engine or to get a new crankshaft ? which probably means a full rebuild?? which I have never done before but would like to have a go

Replacing the crankshaft involves taking out the engine, which replcing it obviously does also. Can you not just reset or adjust the timing, and see where that takes you? It may well have just slipped a tooth, or your belt could be loose, and nothing serious? Just a though.

I might buy the broken one off you if you replace it though

well when i put the crankshaft pulley back on i noticed that it had a tiny amount of play in it around the actual shaft. The timing was off when i did the belt last time but is it not just going to jump a tooth again even if i reset it because of that play? Im a bit worried im gonna be driving along and its all going to go and cost me a lot more than if i sort it out now.

It shouldn't have jumped a tooth anyway, i would check your tensioner. It will always be something to check, so see if it fixes it. If the crankshaft wobbles that much it may have thrown it a tooth out though.