Water Pump Indmar Ford 351

Can anyone help me out?? I just purchased my first boat and noticed the water pump impellar cover was missing a screw. I pulled it off to look at the impellar and the impellar is not centered. On one side the "veins" are expanded out while the other side the veins have little or no room. My question is this...isn't the impellar suppose to be centered within the water pump? Please help.. Thanks

The VANES should be compressed on one side by a CAM. The SHAFT that the IMPELLER rides on should be centered in the housing. Without the CAM, the pump wouldn't work very well.

Sounds like buying a factory manual would be a good investment.

Thanks for the insight. I have the factory manual, but unfortunatley only gives information concerning regular maintenance and very little other info.

That's a bummer. I think Jabsco's (ITT's) www site may have more details.

The cam causes the vane compartments to expand and contract. When they come off the cam, the expansion of the compartment creates suction and draws water thru the inlet. The filled compartments spin around until they get to the other side of the cam. The cam starts to squeeze them at the same time the outlet port is exposed to the compartments. Since the water doesn't compress, it is forced out thru the outlet port, to the engine.

The suction created by the movement over the cam is what allows the pump to prime and maintain a constant flow of water as the boat moves forward. The edges of the vanes have a lot of surface area. Since they spin pretty fast, there is a lot of friction. That friction is what burns the impeller if it is run dry. The last bit of pump knowledge is that it works fine as long as the cover is smooth and tight....if not, that suction is lost and the pump's functions are impaired.