1975 Johnson 4HP 4R75, 4W75 Outboards Service Manual, Page 49Get this manual
DRIVE SHAFT
CLEANING, INSPECTION, AND REPAIR
aVVash all parts in clean solvent such as Solvasol and dry with compressed airbDiscard all gaskets, oil seals, and "0" rings, as new ones should be used during reassemblyCheck flatness of gasket surfaces as described in Section 5, Power HeadRemove dried cement and particles of gasket with trichlorethyleneCheck parallelism of 'TIachined faces of exhaust housing and gearcase_ extension, if useo, on surface plate, using surface gage and scriber or dial indicatorSee Figure 6-8A drill press table with spindle locked to top of housing can also be usedDO NOT attempt to straighten bent housing; replace it
IMPELLER
GROMMET IMPELLER GEARCASE HEAD""-
FLAT SPOT TOP PROPELLER SHAFT ASSEMBLY,
cInspect propeller shaft assembly, pinion gear, and driveshaft splines for wearA bent exhaust housing will cause excessive crankshaft spline weardInspect bushings and thrust bearingeInspect impeller for wear or deteriorationCheck impeller pin on driveshaftInspect impeller housing and plate for scoring which reduces water outputREFERENCE PICTURE