Troy-Bilt TB490BC Operator's Manual page 23

3. Remove the screw on back of the engine cover
(Fig. 53).
Fig. 53
4. Clean dirt from around the spark plug. Remove the
spark plug from the cylinder head by turning a 5/8 in.
socket counterclockwise.
5. Disconnect the spark plug wire.
6. Remove the engine cover.
7. Clean dirt from around the rocker arm cover.
Remove the screw holding the rocker arm cover with
a large flat blade screwdriver or Torx T25 bit
(Fig. 54). Remove the rocker arm cover and gasket.
Rocker Arm Cover
Spark Plug Hole
Fig. 54
8. Pull the starter rope slowly to bring the piston to the
top of its travel, (known as top dead center). Check
that:
', The 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 not, 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),
Do both intake and exhaust valves.
The recommended clearance for both intake and
exhaust is .003- .006 in. (,076- 0.152 mm). Use a
standard automotive .005 in. (0,127 mm) feeler gauge,
The fee_er gauge should sl{de between the rocker arm
and valve stem with a slight amount of resistance,
without binding (Fig. 56),
Rocker Arms
Nuts
Feeler Gauge
Gasket
Fig, 55 .............
Adjustinl
.003-,006 in.
(,076-0.152 ram)
J
Rooker Arm
Valve Stem
Fig. 56
10. If the clearance is not within specification:
a. Turn the adjusting nut using a 5/16 inch (8 mm)
wrench or nut driver (Fig. 55).
To increase clearance, turn the adjusting nut
counterclockwise,
• To decrease clearance, turn the adjusting nut
clockwise.
b. Recheck both clearances, and adjust as necessary.
11. Reinstall the rocker arm cover using a new gasket.
Torque the screw to 20-30 in.lb (2.2-3.4 N.m).
NOTE: A rocker arm cover gasket, Part # 182099 can be
purchased from your local authorized dealer.
12. Reinstall the engine cover, Check alignment of the
cover before tightening the screws. Tighten screws.
13. Replace the muffler cover. Slip the long tabs on the
muffler cover into the engine cover. Stide the
notches on the side of the muffler cover over the
tabs on the engine cover and snap into place
(Fig. 51).
14. Check the spark plug and reinstall See Replacing
the Spark Plug,
15. Replace the spark plug wire.
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