2012 RT 998 Water Pump Gear install - How is it driven?

[Tarzan]

I am reassembling my motor and the water pump gear and intermediate gear don't seem to be driven by the balance shaft that the driven gear is on. can't figure out how it works. As far as the schematics go it appears I am assembling them correct. the weird part is that the water pump gear has a key way, but the gear slides down past the key on the shaft. And the gear aligns perfectly with the intermediate gear. I'll post some pics for reference. Both gears are in mesh with each other and spin together while the shaft is stationary. Maybe when the next gear, washer , and nut are torqued they figure that's enough to drive the water pump? No key needed for that?
Please let me know if anyone knows.