Honda Z50A Manual page 14

12
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0.5mm
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0.020in)
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valve head)
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2. Inspecting the valve seat
The standard width of the valve contact
surface is 0.040-0.051 (1.0-1.3 mm) .
When the contact surface becomes wider
than 0.080 (2.0 mm). the valve seat
should be repaired with a seat cutter
(included in the special tools). Valve
seat is cut to the proper dimension using
the valve seat top and interior cutters.
The 90° seat cutter is used to repair
the valve seat contact surface.
©
Valve face contact area
®
Valve guide
@
Cylinder head body
Fig. 17
©
Valve seat cutter 90°
®
Valve seat cutter holder
Fig. 18A
©
Valve seat top cutter
®
Valve seat cutter holder
Fig. 188
©
Valve seat interior cutter
®
Valve seat cutter holder
Fig. 18C
Whenever the valve seat has been repaired or the valve replaced, the valve must
be lapped to the seat.
To lap the valve, apply a small amount of lapping compound to the valve contact
surface and rotate the valve back and forth against the seat using a suction cup
tool ; lifting the valve off the seat occasionally. After the valve lapping is completed,
wash off the lapping compound thoroughly from both the seat and face of the
valve. Finally, check the seating of the valve with Prussian blue or red lead to assure
that a good seat has been obtained.
Note:
1. Apply a small amount of oil to the valve stem when inserting the vaive into the
guide.
2. After the valve has been assembled into the cylinder head. check the sealing
of the valve by pouring a small quantity of engine oil into the combustion
chamber until the valve heads are covered and then apply compressed air at
28.4 psi (2 kg/cm
2 )
alternately into the inlet and exhaust ports and check for any
bubbles arising from around the valve seats. If there are no bubbles. the valves
are sealing properly.
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