Craftsman 247.770990 Operator's Manual page 19

7. Carefully tilt and support the unit up to provide access underneath
to the nozzle mounting hardware and impeller. Remove the three
shoulder bolts securing the black plastic lower flail housing to the
lower housing. Refer to Figure 25.
8. Tilt top of black plastic lower flail housing toward the engine to
remove.
9. Using a 3/16" allen wrench, remove the flat head cap screws that
hold the chipper blade to the impeller. These screws are accessible
through the opening created when the chipper chute was removed
earlier. See Figure 26.
10. The nuts on the flat head cap screws can be reached from
underneath using a 1/2-inch socket, universal, and extension. See
Figure 27.
11. Replace or sharpen chipper blade. The blade can be sharpened
with a file or on a grinding wheel.
12. When sharpening blade, protect hands by using gloves and follow
the original angle of grind.
13. Reassemble by performing the previous steps in the opposite order
and manner of removal.
NOTE: Tighten blade screws to 210 - 250 in-lbs. Make certain chipper
blade is reassembled with the sharp edge facing upward.
SERVICE & ADJUSTMENTS
19
Black Plastic
lower flail
housing
Shoulder Screws
Figure 
Figure 6
Figure 7