It is simple, but tricky to figure out. There are index marks on the rotors, whcih should be aligned on both sides when the halves are assembled. Make sure there is a little oil film in these rotors when assembling, too. Then, with all of them aligned, lightly close the screws and rotate the gear to see if it 'feels' smooth, then keep turning it while you sngu the screws closed. I've had to do this several times in some cases, but eventually the pins in the shaft settlie into their happy position (sounds Japanese?) as the cover is tightened, and it will spin again.
Sometimes I have screwed them together once and it worked!
The hardest part now: getting oil back into the dry pump. It's messy, so plan on that: turn the pump (sans the lower plate, do this, if you can, before putting the bottom on for ease, but otherwise it still works, just clumsy) upside-down in the oil and turn ti until th ebubbles stop, both directions. It WILL harbor a bubble in both sides, and if it is bigger than a certain size (that you can see thru the aluminum?) the pump will NOT prime when you put it back into the engine with the tank filled. Been there, sadly too often: now I immerse the pump and turn till the bubbles quit, then turn it upright and go drink some tea, or something. Then I come back, invert it and do it some more. Then I screw the bottom back on, using a NEW paper gasket: that silly thing is real important!
