Chrysler 75 and 85 HP Outboards Service Manual OB 3646, Page 170Get this manual
Subsection _ GEAR HOUSING
GENERAL
The information in this section concerns the removal, repair and installation of the water pump, gear train and shift mechanism of the single piece gear housing they pass the outletAs they rotate and the volume (displacement) increasesthe pressure dropsforming vacuum When the volume (displacement) is the greatest and the vacuum highest, the leading vane goes past the inlet and the vacuum draws coo ling water into the body and carries it to the outlet where it is pumped through the motor cooling systemFigure 1
WATER PUMP
DescriptionThe water pump is located on top of the gear housing An impeller inside the pump body is attached to the driveshaft and is propelled directly by the engineThe center of the pump housing is offset, causing the impeller vanes to flex as they rotate The impeller is sandwiched between the water pump body and water pump backplate creating sealAt low speedthe impeller vanes push tightly against the outside circumference of the pump body forming seal there as well The volume (displacement) between any two vanes is least as