Troy-Bilt TB490BC Operator's Manual page 22

3. Remove t hescrewbehind theengine cover(Fig.53).
Adjusting Huts
Rocker Arms
"- INTAKE
Screw
Figi 53
4. Disconnect the spark plug wire.
5. Clean dirt from around the spark plug. I,Zemove the
spark plug from the cylinder head by turning a 5/8 in.
socket counterclockwise.
,
7.
Remove the engine cover (Fig. 52).
Clean dirt from around the rocker arm cover.
Remove the screw holding the rocker arm cover with
a large flat blade screwdriver or Iorx 1-25 bit
(Fig. 54). Remove the rocker arm cover and gasket.
Rocker Arm Cover
Feeler Gauge
Exhaust
Clearance:
.013-,016in.
Spark Plug Hole
8. Pull the starter rope slowly to bring the pis!on to the top
of its travel, (known as tol_ dead center). Check that:
* Ihe piston is at the top of its travel while looking in
the spark plug hole (Fig. 54)
Both rocker arms move freely, and both valves are
closed
If these statements are not true, repeat this step.
9. Slide the feeler gauge between the rocker arm and
the valve return spring. Measure the clearance
between the valve stem and rocker arm (Fig. 55).
Measure both the intake and exhaust valves.
I he recommended clearance for the intake is .003 - .006
in. (.076 -0.152 mm). I he recommended clearance for
the exhaust is .013 - .016 in. (.330 - 0.406 mm).
Use a standard automotive .005 in. (0.127 mm) feeler gauge.
I he feeler gauge should slide between the rocker arm and
valve stem with a slight amount of resistance, without
binding. Figure 55 shows how to measure the intake
clearance, while Figure 56 shows the exhaust clearance.
Intake Valve Feeler Gauge
Stem
Intake Clearance:
T003--T006 inT
(.076-0.152 mm) Exhaust
Valve Stem
F!g! 8
10. If the clearance is not within specification:
a. lurn the adjusting nut using a 5116 inch (8 mm)
wrench or nut driver (Fig. 56).
* I o increase clearance, turn the adjusting nut
counterclockwise.
* Io decrease clearance turn the adjusting nut
clockwise.
b. Recheck both clearances, and adjust as necessary.
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151
11. I,Zeinstall the rocker arm cover using a new gasket.
Iorque the screw to 20-30 in,lb (2.2-3.4 N,m).
12. I,Zeinstall the engine cover. Check alignment of the
cover before tightening the screws. Iighten screws.
13. I,Zeinstall the muffler cover. Slip the rear tab on the
muffler cover into the engine cover rear slot. I hen
slide the remaining slots into the taps until they snap
into place (Fig. 51).
Check the spark plug and reinstall. See Replacinq
the 5park Plug.
I,Zeplace the spark plug wire.