Valve Springs; Cylinder Head Resurfacing - Mercury 25 EFI Service Manual

Cylinder Head

Valve Springs

1. Check the free length of each valve spring. Replace the valve springs if out of specification.
Valve Spring
Free length
2. Measure the valve spring tilt. Replace the valve springs if out of specification.
NOTE: Check each spring on a flat surface using a square. Rotate spring and check the space between the top coil and
the square.
Valve Spring
Tilt limit

Cylinder Head Resurfacing

NOTE: The following procedure should only be attempted for minor scratches and minor warpage. Severe scratches or severe
warpage cannot be corrected with resurfacing the head.
1. Place a sheet of 400 ‑ 600 grit wet sandpaper on a flat surface.
2. Apply a light downward pressure on the head. Move the head in the pattern shown.
3. Rotate the head several times during the resurfacing procedure to avoid removing material from one side.
4. Thoroughly clean all sanding grit from the cylinder head.
Page 4B-14 © 2016 Mercury Marine
20973
33.5–35 mm (1.32–1.38 in.)
20974
1.1 mm (0.043 in.) maximum
3007
90-8M0105568 eng MARCH 2016