1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 368Get this manual
2Apply marine sealer to shanks of mounting bolts (not threads) and secure engine to transom with bolts, flat washers and locknuts, as shownBe sure that installation is water-tight WARNING
Before operating, motor(s) MUST BE SECURED to boat transom with four 12 diameter bolts and locknuts, as follows: bolts must be installed thru upper mounting holes and bolts thru lower mounting holes, as shown in step 5Installation must be water-tight, and engine should be checked for tightness on the transom during operationFailure to bolt engine to transom (using bolts and locknuts, as shown in step 5) may result in damage to boat andor loss of motor and possible injury to occupants of boat