ENGINE
B1220, B1620, B1820, WSM
1-S39
(EU)
[4] SERVICING
(1) Cylinder Head and Valves
Top Clearance
1. Remove the cylinder head. (Do not attempt to remove the
cylinder head gasket.)
2. Move the piston up and stick a strip of fuse [1.5 mm dia. (0.059
in. dia.), 5.0 to 7.0 mm long (0.20 to 0.28 in. long)] on the piston
head at three positions with grease so as to avoid the intake and
exhaust valves and the combustion chamber ports.
3. Lower the piston, and install the cylinder head and tighten the
cylinder head screws to the specified torque.
4. Turn the flywheel until the piston exceeds top dead center.
5. Remove the cylinder head, and measure the thickness of the
squeezed fuses.
6. If the measurement is not within the factory specifications,
check the oil clearance between the crankpin and crankpin
bearing and between the piston pin and small end bushing.
• After checking the top clearance, be sure to assemble the
cylinder head with a new cylinder head gasket.
9Y1210272ENS0056US0
Cylinder Head Surface Flatness
1. Clean the cylinder head surface.
2. Place a straightedge on the cylinder head's four sides and two
diagonal as shown in the figure.
3. Measure the clearance with a thickness gauge.
4. If the measurement exceeds the allowable limit, correct it with a
surface grinder.
• Do not place the straightedge on the combustion chamber.
• Be sure to check the valve recessing after correcting.
9Y1210272ENS0057US0
Top clearance Factory specification
0.50 to 0.70 mm
0.020 to 0.027 in.
Tightening torque Cylinder head screw
38 to 42 N·m
3.8 to 4.3 kgf·m
28 to 31 lbf·ft
(1) Fuse
Cylinder head surface
flatness
Factory specification
0.05 mm
0.002 in.
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