1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 204Get this manual
NOTE: If, while performing Step 11, the drive shaft splines will not align with the crankshaft splines, place propeller onto propeller shaft and turn it counterclockwise as the gear housing is being pushed toward drive shaft housingNOTE: During installation of gear housing, it may be necessary to move the shift block (located under cowl) slightly to align upper shift shaft splines with shift shaft coupler splines11Position gear housing so that the driveshaft is protruding into drive shaft housing12Move gear housing up toward drive shaft housing, while aligning upper shift shaft splines with shift shaft coupler splines, water tube with water tube seal, and crank shaft splines with drive shaft splines13Install bolts and washers (two each side)14Install locknut and washer15Torque bolts and locknut (or nuts only if applicable) to 40 lbsft(54 Nm) 16Check shift operation as follows: aPlace shift lever in forward gearGear housing should ratchet when propeller shaft is turned clockwise and resistance should be felt when propeller shaft is turned counterclockwisebPlace shift lever in neutralPropeller shaft should rotate freely in either directioncWhile rotating propeller shaft, place shift lever in reverse gearResistance should be felt when propeller shaft is rotated in either directionIMPORTANT: If shift operation is not as described, preceding, the gear housing must be removed and the cause corrected