Hitachi CG 25EUAP, Service Manual

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7. Cylinder, rocker arm and valve
(1) Disassembly
Loosen three Bolts M4 x 10 [27] , and then remove the Cylinder Head Cover [28] . If the Cylinder Head
Cover [28] cannot be easily removed, use a plastic hammer to lightly hit the side of the Cylinder Head
Cover [28] .
Use a wrench to fix the lower Nut M5 [29] onto the Shaft Bolt [35] . In this status, loosen the upper Nut
M5 [29] , and then loosen the lower Nut M5 [29] .
After removing the Nut M5 [29] , remove the Pivot Rocker Arm [30] and Rocker Arm [34] from the Shaft
Bolt [35] , and then pull out the Push Rod [31] from Cylinder (A) [38] .
Be sure to remove engine oil from Cylinder (A) [38] before removing it.
Loosen the five Bolts M5 x 20 [37] , and slowly pull out Cylinder (A) [38] .
To remove the Exhaust Valve [41] or Intake Valve [40] , hold the Exhaust Valve [41] or Intake Valve [40]
from the combustion chamber side of Cylinder (A) [38] , slide the Retainer Valve [12] sideways while
pushing it down, and then shift the head of Exhaust Valve [41] or Intake Valve [40] from the center of
the Retainer Valve [12] . Then remove the Exhaust Valve [41] or Intake Valve [40] .
(2) Reassembly
Before reassembly, remove any carbon accumulated in the combustion chamber of Cylinder (A) [38]
and clean the combustion chamber with gasoline, while being careful not to damage Cylinder (A) [38] .
Similarly, remove accumulated carbon from the Exhaust Valve [41] and Intake Valve [40] , and then
clean both parts with gasoline.
Apply four-cycle engine oil onto the shafts of the Exhaust Valve
[41] and Intake Valve [40] , and then
mount the Exhaust Valve [41] and Intake Valve [40] in Cylinder (A) [38] . When mounting, be careful not
to confuse the Exhaust Valve [41] with the Intake Valve [40] .
While holding the Exhaust Valve [41] or Intake Valve [40] from the combustion chamber side of
Cylinder (A) [38] to prevent either valve from falling, set the Stem Seal [15] (only for the Intake Valve
[40] ), Stem Seal Base [14] (only for the Intake Valve [40] ), and Valve Spring [13] , and then attach the
Retainer Valve [12] to the Exhaust Valve [41] or Intake Valve [40] by reversing the disassembly
procedure.
Before mounting the Retainer Valve
[12] , apply four-cycle engine oil along the circumference of the 1st
Ring [48] , 2nd Ring [49] , and Oil Ring [50] . Fit the Piston [51] into Cylinder (A) [38] , and then tighten
the five Bolts M5 x 20 [37] little by little alternately.
Insert the Push Rod [31] into Cylinder (A) [38] , attach the Rocker Arm [34] and Pivot Rocker Arm [30]
to the Shaft Bolt [35] , and then adjust the valve clearance (see section 5 on page 8) with the Nut M5
[29] . After reassembly, turn the crank shaft to check for valve operation.
Apply grease (MOLUB-ALLOY 777-1) to the sliding sections of the Pivot Rocker Arm [30] and Rocker
Arm [34] , and lubricate both with four-cycle engine oil. Apply four-cycle engine oil to the engaging
surfaces of the Retainer Valve [12] , Exhaust Valve [41] , and Intake Valve [40] .
Wipe off the liquid gasket previously applied to the Cylinder Head Cover [28] surface to be mated with
Cylinder (A) [38] , apply new liquid gasket (Three Bond 1207C) to the mating surfaces, and then mount
the Cylinder Head Cover [28] on Cylinder (A) [38] .
Valve head diameter
• Intake valve: 13.5 mm
• Exhaust valve: 11.5 mm