Honda CRF450R Owner's Manual page 33

Rotate the crankshaft by turning the primary drive gear
lock bolt (crankshaft) clockwise until aligning the "T"
mark on the primary drive gear with the index mark on
the right crankcase cover. In this position, the piston
may either be on the compression or exhaust stroke.
If the crankshaft passed the "T" mark, rotate the pri-
mary drive gear lock bolt clockwise again and align "T"
mark with the index mark.
The inspection must be made when the piston is at top
of the compression stroke when both the intake and
exhaust valves are closed.
This condition can be determined by moving the ex-
haust rocker arm. If it is free, it is an indication that the
valves are closed and that the piston is on the com-
pression stroke. If it is tight and the valves are open,
rotate the primary drive gear lock bolt 360° and realign
the "T" mark to the index mark.
1
2
(1) PRIMARY DRIVE GEAR LOCK BOLT
(2) "T" MARK
(3) INDEX MARK
(4) EXHAUST ROCKER ARM
Valve Clearance And Decompressor Arm Clearance In-
spection
Measure the intake valve clearance by inserting a feeler
gauge between the valve lifter and cam lobe.
3
(1) FEELER GAUGE
(2) INTAKE VALVES, VALVE LIFTERS
(3) CAMSHAFT
Measure the exhaust valve clearance by inserting a
feeler gauge between the exhaust rocker arm and shim.
(1) FEELER GAUGE
(2) EXHAUST ROCKER ARM
(3) EXHAUST VALVE SHIM
VALVE CLEARANCES:
IN: 0.006 ± 0.001 in (0.16 ± 0.03 mm)
EX: 0.011 ± 0.001 in (0.28 ± 0.03 mm)
If intake valve clearance and exhaust valve clearance
need adjustment, see Camshaft Holder Assembly Re-
moval (page 32) and select the collect shim in each
valve.
Measure the decompressor arm clearance by inserting
a feeler gauge between the decompressor arm adjust-
ing screw and right side rocker arm.
(1) FEELER GAUGE
(2) DECOMPRESSOR ARM ADJUSTING SCREW
(3) RIGHT SIDE ROCKER ARM
(4) RIGHT EXHAUST VALVE
DECOMPRESSOR CLEARANCE:
RIGHT EXHAUST VALVE CLEARANCE
0.014 in (0.35 mm)
ex)
If measured right exhaust valve clearance is 0.011 in
(0.28 mm), decompressor clearance is;
0.011 in (0.28 mm) + 0.014 in (0.35 mm) = 0.025 in (0.63 mm)
If only decompressor arm clearance needs adjustment,
see Decompressor Arm Clearance Adjustment (page
37).
If intake valve clearance, exhaust valve clearance and
decompressor arm clearance don't need adjustment,
see Spark Plug Installation (Page 38).
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