Mercury 250 XS OptiMax Operation, Maintenance & Installation Manual page 110

FASTENING THE OUTBOARD TO THE TRANSOM
IMPORTANT: The transom mounting surface must be flat within 3.17 mm
(0.125 in.). No step in the transom mounting surface is allowed. The inside
transom mounting bolt washer surface must be flat within 3.17 mm (0.125 in.).
a - Step (not allowed)
b - Gap between transom clamp and boat transom (not allowed)
OUTBOARD INSTALLATION
a
b
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eng