I am working on a 6bt cummins engine with the VE pump, I tore the pump apart, replaced the head and rotor. I am trying to get the correct shim for behind rotor. So far I have the pump together and I am getting port closure at 1.75mm on the cummins its supposed to be 1.35. by that math I need a .4mm shim and that just doesn't seem to be correct. Any suggestions?