Specifications
the second dark link on the chain with the timing
mark on the camshaft sprocket. Third Align the final
dark link on the chain to the timing mark on the
injection pump sprocket. Last install the chain
around the vacuum pump. For injection pump timing
refer to Group 14, Fuel for the proper procedure.
VALVE AND SEAT REFACING
VALVE REFACING
(1) Use a valve refacing machine to reface the
intake and exhaust valves to the specified angle.
(2) After refacing, a margin of at least 4.52-4.49
mm (.178-.177 inch) must remain (Fig. 9). If the mar-
gin is less than 4.49 mm (.177 inch), the valve must
be replaced.
VALVE SEAT REFACING
(1) Install a pilot of the correct size in the valve
guide bore. Reface the valve seat to the specified
angle with a good dressing stone. Remove only
enough metal to provide a smooth finish.
(2) Use tapered stones to obtain the specified seat
width when required.
VALVE STAND DOWN
Valve stand down is to maintain the adequate com-
pression ratio.
(1) Invert cylinder head.
(2) Fit each valve to its respective valve guide.
(3) Using a straight edge and feeler gauge (Fig.
10), check valve head stand down: Inlet valve head
stand down .80 to 1.2 mm (.031 to .047 in.) and
exhaust valve stand down .79 to 1.19 mm (.031 to
.047 in).
(4) If valve head stand down is not in accordance
with above, discard original valves, check stand down
with new valves and recut valve seat inserts to
obtain correct stand down.
VALVE GUIDE HEIGHT
(1) Valve Guides height requirement.
(2) Measurement A (Fig. 11): 13.50 - 14.00 mm.
VALVE STEM-TO-GUIDE CLEARANCE
MEASUREMENT
(1) Measure and record internal diameter of valve
guides. Valve guide internal diameter is 8.0 to 8.015
mm (.3149 to .3155 in.).
(2) Measure valve stems and record diameters.
Intake valve stem diameter 7.94 to 7.96 mm (.3125 to
.3133 in). Exhaust valve stem diameter 7.92 to 7.94
mm (.3118 to .31215 in).
(3) Subtract diameter of valve stem from internal
diameter of its respective valve guide to obtain valve
stem clearance in valve guide. Clearance of inlet
valve stem in valve guide is .040 to .075 mm (.0015
to .0029 in). Clearance of exhaust valve stem in valve
guide is .060 to .095 mm (.0023 to .0037 in).
(4) If valve stem clearance in valve guide exceeds
tolerances, new valve guides must be installed.
Fig. 7 Alignment Timing Sprockets
Fig. 8 Timing Procedure
9 - 42 ENGINE NS/GS
SERVICE PROCEDURES (Continued)