Sea Water Pump Impeller
The instructions probably state that you should not pull the shaft out so that you don''t cause potential damage to the lip seal on the engine side of the pump. You should have two seals in the body of the pump, one oriented toward the engine to keep oil from leaking out, the other oriented toward the raw water side to prevent sea water from getting into the engine. When you pull the shaft and impeller out of the pump, you''re actually pushing the shaft against the engine side seal in the wrong direction. If you do happen to pull the shaft out just put a little lithium grease on the end of the shaft, if you''re careful you won''t damage the seal.
Sometimes they also have a slinger on the shaft, you can potentially drop this if you pull the shaft out. This is supposed to keep contaminates from getting to close to the two seals. When I rebuilt my water pump a few years ago I did not put the slinger on even though it came with the rebuild kit. The slinger is more useful on engines that run in an open unprotected environment such as for power generation.
I can''t tell you it''s OK, your engine could blow up any minute but, when I get to the east coast on business you''d better offer me a ride.