Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 117Get this manual

Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 117

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CYLINDER HEAD
1 Clean the carbon deposits from the valveDiscard any cracked, warped, or burned valves2 Measure the valve stem diameter to check for wearReplace valves if not within specification