Mercury Mariner 8/9.9HP 4-Stroke Factory Service Manual, Page 130Get this manual
Valves 1Clean the carbon deposits from the valveDiscard any cracked, warped, or burned valves2Measure the valve stem to check for wearReplace if out of specificationa
Valve Springs
Check each spring under load on spring testerReplace any weak spring
Valve Stem Diameter "a" Intake Valve Exhaust Valve 0.21560.2161 in(5.4755.490 mm) 0.21500.2156 in(5.4605.475 mm) Valve Spring Compression Specification Compressed Length 0.96 in(24.4 mm) Compression Force 19.8 -22.0 lbft(90100 N)
3Check the valve face for pittingValves faces that are pitted must be refaced
NOTE: Several different types of equipment are available for refacing valvesFollow the equipment manufacturer's instructionsIMPORTANT: Do not lap the valves4Check the margin thickness of the valves after the valves have been groundAny valve with margin thickness of less than the specification should be replaced