1980 Johnson 4HP Service Manual, Page 68Get this manual
Observe location of keyway in impeller and driveshaftSlide water pump assembIy key down driveshaft and engage keyImpeller housing cover will contact spacer in water pump cavity before cover flange contacts face of gearcase leaving space of about 0.010" (0.25 mm) See Figure 6-9Slight finger pressure will seat cover face of gearcase This fit is necessary for proper operation of the water pumpAttach pump to gearcase with screws dipped in Gasket Sealing Compound, Part No317201 Torque to specifications
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Water tube grommet Screws Impeller housing cover Impeller plate Impeller Impeller drive key Impeller housing cup Spacer 1About 0.010" (0.25 mm) press to gearcase face