Adjusting The Upper Shaft Timing Belt; Adjusting The Rotary Hook Lubrication - Brother LH4-B800E Service Manual

4-21. Adjusting the upper shaft timing belt

1. Loosen the screws q, and then use a spring gauge to push the notch in the tension pulley plate w with a force of
98 N.
2. Tighten the screws q.
If you do not have a spring gauge, adjust the tension so that the amount of belt deflection is approximately 5 mm when
a force of 5 N is applied in the middle of the belt span between timing pulley U e and the idle pulley r in the place
indicated by arrow A.

4-22. Adjusting the rotary hook lubrication

1. Remove the rubber stopper q.
2. Turn the adjusting screw w to adjust the lubrication amount.
* Adjust so that approximately 10 drops of oil are released when the sewing machine is run at a speed of 4000 rpm
for three cycles to sew about 114 stitches. Use Kraft paper e or similar to catch the oil drops. As a guide, the
optimum position can be obtained if the adjusting screw is tightened as much as possible and then loosened about
two turns.
* If the lubrication amount has been reduced, run the machine for 200—300 sewing cycles and then check it again.
If lubrication stops, it will cause problems such as rotary hook seizure and thread breakages.
e
w
A
F = 98 N (10 kgf)
q
r
q
w
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Less
e
LH4-B800E
To oil tank
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4. Adjustment
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