Troy-Bilt TB490BC Manual Del Operador página 22

MAINTENANCE AND REPAIR INSTRUCTIONS
3. Remove the screw behind the engine cover (Fig. 53).
4. Disconnect the spark plug wire.
5. Clean dirt from around the spark plug. Remove the
spark plug from the cylinder head by turning a 5/8 in.
socket counterclockwise.
6. Remove the engine cover (Fig. 52).
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 T-25 bit
(Fig. 54). Remove the rocker arm cover and gasket.
Rocker Arm Cover
Spark Plug Hole
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 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.
The recommended clearance for the intake is .003 – .006
in. (.076 – 0.152 mm). The recommended clearance for
the exhaust is .013 – .016 in. (.330 – 0.406 mm).
Use a standard automotive .005 in. (0.127 mm) feeler gauge.
The 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.
22
Screw
Fig. 53
Fig. 54
Rocker Arms
INTAKE
Feeler Gauge
Exhaust
Adjusting Nut
Exhaust
Clearance:
.013–.016 in.
(.330–0.406 mm)
Intake Valve
Stem
Intake Clearance:
.003–.006 in.
(.076–0.152 mm)
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. 56).
• 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
12. Reinstall the engine cover. Check alignment of the
cover before tightening the screws. Tighten screws.
13. Reinstall the muffler cover. Slip the rear tab on the
muffler cover into the engine cover rear slot. Then
slide the remaining slots into the taps until they snap
into place (Fig. 51).
14. Check the spark plug and reinstall. See Replacing
the Spark Plug.
15. Replace the spark plug wire.
Adjusting Nuts
EXHAUST
Fig. 55
Exhaust
Rocker Arm
Feeler Gauge
Exhaust
Valve Stem
Fig. 56
lb (2.2–3.4 N m).
• •