1978 Johnson 4HP outboards Service Manual, Page 70Get this manual
REMOVAL OF GEARCASE It is possible to remove the gearcase without removing the powerhead or exhaust housingaRemove the screws attaching the gearcase to the exhaust housingSee Figure 6-3bWithdraw the gearcase carefully to avoid damaging the driveshaft and water tube
bRemove plate from impeller housing coverRemove impeller from impeller housing cup Remove spacer and washer from inside of water pump cavitySee Figures 6-7 and 6-12Remove and discard water tube grommet from impeller housing coverSee Figures 6-4 and 6-7 Inspect components for wear and deterioration, and replace as necessarycReassemble impeller into cup with blades positioned as shown in Figure 6-6