Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 150Get this manual
CYLINDER BLOCK AND CRANKCASE
Measuring Depth of Oil Pump Body
Standard Value Out of the Limit
If 0.238 in(6.06 mm) or more requires replacement
0.236 in(6.0 mm)
Measuring Inside Diameter of Oil Pump Body