Mercury Mariner 4, 5, and 6HP 4-Stroke Factory Service Manual, Page 31Get this manual
GENERAL INFORMATION
Propeller RemovalInstallation
WARNING
If the propeller shaft is rotated while the engine is in gear, there is the possibility that 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 1Remove the spark plug leads to prevent engine from starting