Chrysler 70, 75 and 85 HP Outboard Motors Service Manual OB 3438, Page 190Get this manual
Subsection
_ TWO-PIECE 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 two-piece gear housing they pass the outletAs they rotate and the volume (displacement) increasesthe pressure drops, forming vacuum When the volume (displacement) is the greatest and the vacuum highest, the leading vane goes past the inlet and the vacuum draws cooling water into the body and carries it to the outlet where it is pumped through the motor cooling system Figure 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 engine The 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 wellThe volume (displacement) between any two vanes is least as