Valve Guides; Valve Seat Reconditioning - Mercury FourStroke 2.5 Service Manual

Powerhead
NOTE: Check each spring on a flat surface using a square. Rotate spring and check space between the top coil and
square.
Valve Spring
Tilt limit

Valve Guides

Measure the valve guide inner diameter. If valve guide wear is out of specification, replace the cylinder head.
a
Valve Guide I.D.
Intake
Exhaust

Valve Seat Reconditioning

1. Clean the carbon deposits from the combustion chambers and valve seats. Check the valve seats for pitting.
2. Several different types of equipment are available for reseating valve seats. Follow the equipment manufacturers
instructions.
3. Apply a thin, even layer of mechanic's bluing dye (Dykem) onto the valve seat.
4. Insert the valve into the valve guide and lap the valve slowly on the valve seat.
5. Remove the valve and measure the valve seat contact pattern width. Resurface the valve seat if not in specification.
a
b
Valve Seat Contact Width
Intake and exhaust valve
6. To reface a valve seat, use a 30°, 45°, and 60° valve seat cutting tool.
a
b
NOTE: When twisting the cutter, keep an even downward pressure to prevent chatter marks.
NOTE: After refacing the valve seat or replacing the valve and valve guide, the valve seat and valve face should be
lapped.
Page 4A-32
c
c
20964
2.0 mm (0.0787 in.)
a - Valve guide I.D.
20975
5.51–5.55 mm (0.217–0.2185 in.)
5.51–5.57 mm (0.217–0.2193 in.)
a -
b -
d
c -
20969
d -
a - 30° angle
b - 45° angle
c - 60° angle
20974
Correct valve seat contact width
Valve seat too high
Valve seat too low
Valve seat too wide
1.0–2.0 mm (0.0393–0.0787 in.)
90-8M0065421 NOVEMBER 2012