Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 30Get this manual
GENERAL INFORMATION
Propeller RemovalInstallation
rotate,d ,hit,engine is in gear, there the engine will crank over and startTo prevent this type of accidental engine starting and possible serious injury caused from being struck by rotating propeller, always shift outboard to neutral position and remove spark plug leads when you are servicing the propeller