MacDon 922 - Manual (Page 50)

Form # 46620 Issue 01/06 48
MAINTENANCE/SERVICE
Sickle Timing (Double Sickle Headers)
To prevent excessive vibration, the left and right sickles must be accurately timed to move in opposite
directions. Timing is achieved by rotating the wobble box pulley as required when installing the wobble box
drive belts.
To time the sickles:
1. Install the left hand wobble box drive
belt and tension as described (next
page). Check that the belt is properly
seated in the grooves on both driver
and driven pulleys.
2. Rotate the left hand wobble box driven
pulley clockwise until the left hand
sickle (A) is at the center of the
inboard stroke (moving towards the
center of the header).
NOTE: Center stroke is when the
sickle sections are centered between the guard points as shown.
3. Remove the right hand drive belt from the wobble box pulley and rotate the pulley counter-clockwise until
the right hand sickle (B) is also at the center of the inboard stroke.
IMPORTANT: It is critical that sickles are centered at guard points while both are moving towards the
center of the header, not one moving inboard and one moving outboard.
4. Install the right hand wobble box drive belt and tension as described (next page).
NOTE: To maintain timing, wobble box driver and driven pulleys must not rotate as the belt is tightened.
Tighten all hardware and check that the belt is properly seated in the grooves on both driver and driven
pulleys.
5. Check for correct sickle timing by rotating the rear cross-shaft slowly. Observe sickles where they over-lap
at the center of the header.
IMPORTANT: At the start of each stroke, sickles must move in opposite directions and must begin to move
at exactly the same time. If timing is slightly off, loosen right hand belt just enough to allow skipping the belt
one or more teeth as required: If R/H sickle "leads" L/H, rotate right hand driven pulley clockwise. If R/H
sickle "lags" L/H, rotate pulley counter-clockwise. Tighten right hand belt.
Changing Double Sickle Speed
Sickle drive is factory assembled for sickle speed
of 1875 strokes per minute (S.P.M.). By
exchanging pulleys (A) and (B) sickle speed can
be decreased to 1450 S.P.M.
To change sickle speed:
1. Loosen auger drive belt. See "Auger Drive Belt
Tension”.
2. Loosen and remove L/H sickle drive timing belt
and cross shaft drive belt. See “Tightening
Double Sickle Drive Belts”, next page.
3. Remove taper lock bushing (C) and remove
pulleys. Remove three nuts (D) and separate
the timing belt pulley from the inner “double B”
pulley (B).
4. Remove three nuts (F) and separate “double B”
pulley (A) from auger drive pulley.
5. Exchange positions of pulleys (A) and (B) and
reassemble.
6. Tension all belts and time the sickles as
described above.
\ CHANGING SICKLE SPEED
C
A
D
B
F