1995 Mariner Mercury Outboards Service Manual 50HP 4-Stroke, Page 104Get this manual
Valve Clearance Adjustment NOTE: Valves should be adjusted when engine is cold
Adjusting Valves NO.1 AND NO.2 INTAKE VALVES NO.1 AND NO.3 EXHAUST VALVES 1Disconnect spark plug leads2Turn the driven gear and align the "1" mark on the gear with the the cylinder head 3Adjust the valve clearance for No1 and No.2 intake valves and No1 and No.3 exhaust valves
Engine could possibly start when turning flywheel during adjustmentTo prevent this type of accidental engine starting and possible serious injury, always remove spark plug leads from spark plugs