Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 168Get this manual
4Inslall balance piston, secure with nut Exhaust Cover Installation
1Install exhaust cover, thermostat, and thermostat
coverNOTE: Always use new gaskets
55814Nut (30mm)
bPiston
Bolts (7)Exhaust CoverGasketThermostatGasketThermostat CoverBolts (2) e
Balance Piston Nut Torque
116 in(13 Nm) b
5Install O-ring and cover
2Tighten bolts in sequence and in two steps to the specified torque