Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 141Get this manual
Valve Springs 1Check each spring under load on spring testerReplace any weak springs55796
Cylinder Head Reassembly
Valve Installation
INTAKE AND EXHAUST VALVE COMPONENTS
bSpring Seal
cValve Seal
2Check free length limit of each springReplace valve springs jf not in specification55846
dValve Spring
eSpring RetainerValve Keepers
[Valve Spring Free Length 1.4911.569 in(37.85 39.85 mm)