Mercury Mariner 4, 5, and 6HP 4-Stroke Factory Service Manual, Page 124Get this manual
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CYLINDER HEAD
Standard Value "a" Intake Valve Exhaust Valve 0.031 in(0.8 mm) 0.031 in(0.8 mm)
Limit that needs Repair 0.0708 in(1.8 mm) or greater 0.0708 in(1.8 mm) or greater