Dodgeman.
I feel to disagree with you.
Me and my dad overhauled the engine 20 000 to 30 000km ago.
I know we did it the right way as we used a datsun manual.Page by page.
The crank was not removed.Only head and pistons and conrods.
I feel 80 to 90% sure it is the engine's harmonic frequency that we talked about and that the flywheel is maybe out of balance.
If it was the engine it would have made rattles and noises.
I had the window down to make sure it did'nt make noises.
No noises were heard.
I am going to sort out the flywheel and then see if it helps.
I will also ask the mechanic to make sure everything is 100% correct and that I want to come and check things out first before it is assembled.
Thanks for the replies.
It helped me to look at the problem from all angles.