Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 108Get this manual
CYLINDER HEAD
3Rotate flywheel until raised mark on camshaft is visible through fuel pump hole and notched mark on flywheel aligns with TOC mark on block castingPiston is now at top dead center and valve clearance may now be checked with feeler gaugeaRaised Mark on Camshaft
bNotched Mark on FlywheelTDC Mark50 BTDC Mark on Block Casting25 BTDC Mark on Block Casting