Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 193Get this manual
GEAR HOUSING
Drive Shaft
IMPORTANT: Retain shim(s) (a) for reassembly
1Remove shim(s) (a)2Remove drive shaft assembly (b) and pinion gear (c)
Forward Gear and Bearing
1To remove forward gear, strike open end of gear housing (a) on block of wood as shown, dislodging gear from bearingMake sure to retain shim(s) found behind gear for reassembly