MTD 640A thru 645A - Manual (Page 7)

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SHARPENING OR REPLACING CHIPPER BLADES
1. Disconnect spark plug wire and move it away
from spark plug.
2. Remove the flail screen as instructed in previous
section.
3. Remove the chipper chute by removing three hex
nuts and washers. A 1/2" wrench is required. See
figure 6.
NOTE: When reassembling, the cupped washer goes
on the bottom of the chipper chute with the cupped
side against the chute.
4. Rotate the impeller assembly by hand until you
locate one of the chipper blades in the chipper
chute opening. Remove the blade, using a 3/16"
alien wrench on the outside of the blade and 1/2"
wrench on the impeller assembly (inside the
housing). See figure 7.
5. Remove the other blade in the same manner.
FIGURE 7.
Replace or sharpen blades. If sharpening, make cer­
tain to remove an equal amount from each blade.
Reassemble in reverse order.
Make certain blades are reassembled with the sharp
edge facing the direction shown in figure 10 (sharp
edge is assembled toward the slotted opening in the
impeller assembly).
SHARPENING OR REPLACING SHREDDING BLADE
The shredding blade may be removed for sharpening
or replacement as follows.
1. Disconnect spark plug wire and move it away
from spark plug.
2. Remove the six hex lock nuts and flat washers
from the housing weld bolts using a 1/2" wrench.
Remove the hopper assembly
3. Remove the back-up plate.
NOTE: When reassembling, make certain the open­
ing on the back-up plate is toward the bottom of the
unit.
Allen
Screws
Torque
Wrench
Blade
FIGURE 8.
4. Loosen the two hand knobs and cupped washers
which secure the chute deflector, and raise the
chute deflector.
5. Keep the impeller assembly from turning by
inserting a 1/2" or 3/4" diameter pipe through the
flail screen, or remove the flail screen, and insert
a piece of wood (2 x 4) into the chute opening.
6. Remove the two outside screws on the blade,
using a 3/16" alien wrench and a 1/2" wrench.
7. Remove the blade by removing the center bolt,
lock washer and flat washer.
NOTE: Use caution when removing the blade to avoid
contacting the weld bolts on the housing.
When sharpening the blade, follow the original angle
of grind as a guide. It is extremely important that each
cutting edge receives an equal amount of grinding to
prevent an unbalanced blade. An unbalanced blade
will cause excessive vibration when rotating at high
speeds and may cause damage to the unit.
The blade can be tested for balance by balancing it
on a round shaft screwdriver or nail. Remove metal
from the heavy side until it is balanced evenly. See
figure 9.