MTD YM26BC - Manual (Page 23)

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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. See Figure 51.
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. See
Figure 53. Remove the rocker arm cover and gasket.
3. Remove the screw behind the engine cover. See
Figure 52.
Rocker Arm Cover
Screw
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. See Figure 53.
• 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. See Figure 54. Measure
both the intake and exhaust valves.
Adjusting Nuts
Feeler Gauge
Rocker Arms
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 feeler gauge should slide between the rocker arm
and valve stem with a slight amount of resistance,
without binding. See Figure 54.
Feeler Gauge
Adjusting Nut
Rocker Arm
.003–.006 in.
(.076–.152 mm)
Valve Stem
10. If the clearance is not within specification:
a. Turn the adjusting nut using a 5/16 inch (8 mm)
wrench or nut driver. See Figure 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).
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 tabs until they snap
into place. See Figure 50.
14. Check the spark plug and reinstall. See Replacing
the Spark Plug.
15. Replace the spark plug wire.
INTAKE
EXHAUST
SECTION 7: MAINTENANCE AND REPAIR INSTRUCTIONS
Figure 55
Figure 54
Figure 53
Figure 52