1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 170Get this manual
CYLINDER HEAD
Valve Guide inspection
1Measure the valve guide boreIf valve guide wear is out of specification, replace the valve guide55794
a-Valve Guide Bore Valve Guide Inside Diameter Intake Valve Exhaust Valve 0.21650.2170 in(5.5005.512 mm)
Valve Guide Replacement
1Heat the cylinder head in an oven to 390 (200 C)This will help to ease guide removal and installation and to maintain correct interference fit2Remove the valve guide using valve guide remover