Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 109Get this manual
CYLINDER HEAD
5If valve clearance adjustment is necessaryhold pivot and loosen lock nut6Insert feeler gauge between rocker arm and valve7 Adjust the valve clearance by turning the pivot
SWhen proper clearance is achievedhold pivot and tighten lock nutTorque lock nut to
90 Ib-in(10 Nm)
9Recheck valve clearance