Tony,
Sometimes, the nut will come loose holding the impeller to the shaft & when that happens, the spring inside the seal will push the impeller forward, far enough that it will make contact with the thin defusser plate & will wear the ends of the impeller blades. It will take a while for it to wear like that because of the coolant being in the area.
Only thing about it, once the water pump is taken apart & say rebuilt, that worn impeller if used, wont sit as close to the thin tin defusser as it needs to & the pump cant push as much coolant up into the cylinder. Those impeller blades need to sit as close as they can to that defusser so that the coolant can only go one way & not slip past the blades.
I guess if you really think about it, how many times do we put an engine together & never think about the water pump, other than if the bearing is ok or the seal is in good shape.
Checking all things like some will do, the idea might be a bit over board, but would be a good thing to clay the clearance between those impeller blades & that defusser tin to be sure it is sitting close enough.
I dont know if Honda even list a spec on that clearance, not that I remember.
Neil
