Sorry to bring this up again. (I know there's been lot of posts as I've spent the last two nights researching them) . I'm changing a friends wr400 to 426 due to big end rattle/scored bore/worn piston. I am using the same crank with 400 crank pin, 426brg +rod, + 426 piston + cylinder. The problem arises with the piston part number, some say use 5NG-11631-10-00. Others use 5JG-11631-10-00. Does anyone know the difference, or what the 5NG and 5JG Denotes? And can anyone confirm the cam chain part number. I need to get the parts right as am ordering from thumper store and shipping to England. (Returns are going to cost time and agro). Thanks in advance.