Product Manual

4. Thoroughly clean all sanding grit from the cylinder head.
3007
Valve Guides
Measure the valve guide inner diameter. Replace the cylinder head if the valve guide inner diameter is out of specification.
a - Valve guide inside diameter
Valve Guide Inside Diameter
Intake 5.51–5.55 mm (0.217–0.218 in.)
Exhaust 5.51–5.57 mm (0.217–0.219 in.)
Rocker Arm and Rocker Arm Shaft Inspection
1.
Measure the rocker arm inside diameter. Replace if out of specification.
2. Measure the rocker arm shaft outside diameter. Replace if out of specification.
a - Rocker arm inside diameter
b - Rocker arm shaft outside diameter
Rocker Arm
Rocker arm inside diameter 13.01–13.05 mm (0.5122‑ 0.514 in.)
Rocker arm shaft outside diameter 12.94–12.99 mm (0.5094–0.5114 in.)
Clearance 0.006–0.035 mm (0.0003–0.0014 in.)
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 - Correct valve seat contact width
b - Valve seat too high
c - Valve seat too low
d - Valve seat too wide
Valve Seat Contact Width
Intake and exhaust valve 1.0–2.0 mm (0.0393–0.0787 in.)
20975
a
a
b
3306
20969
a
b
c
d
Cylinder Head
90-8M0125265 eng NOVEMBER 2017 © 2018 Mercury Marine Page 4B-17