2. Install the cylinder head core hole expansion plug. Core plug should be recessed 0.158 cm (0.062 in.) with the inside
chamfer of the cylinder head core hole on the aft end of cylinder head.
Core expansion plug installed in aft end
of head
a - Core expansion plug
Tube Ref No. Description Where Used Part No.
66
Loctite 242 Threadlocker Outside diameter of core expansion plug 92-809821
3. Repeat procedure on opposite head.
NOTE: Each head needs a core plug installed in the aft end of the cylinder head.
Inspection
Cylinder Head
1. Inspect the sealing surfaces for burrs, scratches, deep nicks, erosion, or other damage.
2. Inspect for cracks in exhaust ports, water jackets, and combustion chambers (especially around spark plug holes and valve
seats).
3. Replace the cylinder heads if necessary.
4. Inspect for rusted, damaged, or leaking core plugs. Replace core plugs if necessary.
5. Inspect for corrosion around cooling passages.
6. Check the flatness of cylinder head gasket surfaces—head, exhaust, and intake gaskets, using a machinist's straightedge
and feeler gauge. Take measurements diagonally across the cylinder head from all four corners and lengthwise straight
down the center of the cylinder head.
Head deck shown, exhaust and intake decks are similar
a - Cylinder head deck
b - Machinist's straightedge
c - Feeler gauge
Engine Inspection and Assembly
Page 3B-44 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015
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