can anyone tell me what the difference is between a centre and rear thrust crankshaft??

and how can you tell the difference?

 

Have a look at the crank main bearing journal and you will see the thrust faces by each web.
The rear thrust crank (No.5 main bearing journal) uses a wider bearing shell and wont fit onto the Center thrust (No.3 Main bearing journal).

 

i dont get what you mean??

i need to buy a new crank but need to know what i need and what to look for when buying a new one