JUKI LG-158 Instruction Manual page 23

Problems
3. Stitching fl aw.
a. In case of stitching
fl aw due to change
of sewing speed.
4. On feed pitch error
a. In case feed pitch
is too big.
b. In case feed pitch
is too small.
5. Isolated idling loops
are produced
6. Even with the safety
device in action, good
stitching condition can
not be attained.
Causes
⑤ Height of needle bar is not matched.
⑥ When skip-stitches occur at step-sewing
part.
⑦ When the blade point of the sewing hook
is crushed.
⑧ When the needle is defective.
① The bobbin thread is not passing the
center of the thread tension spring of
bobbin case holder.
② The outer rim of the bobbin is not smooth.
③ When the thickness of the needle is not
matched with the using thread.
④ When the supply of oil to the sewing hook
is not adequate.
⑤ Bobbin thread tension is too weak.
① Pressure of take-up spring is too weak.
② Timing of bobbin case opening lever is
not matched.
③ Finish of thread paths of all parts are bad.
④ Sewing hook is defective.
① Pressing pressure of presser foot is too
weak.
① Feed dog is too low.
② Tension of needle thread and bobbin
thread is too strong.
① Tension of the needle threa is too weak.
② Timing of the bobbin case opening lever
is not matched.
(Pulling of the bobbin case opening lever
is insuffi cient)
① When the safety device has not returned
to the correct position.
② Due to the strong impact, sometimes the
timing belt slides by one pitch.
○ When the needle bar is at lowest point make
the distance between the bottom of needle
clamp and upper surface of throat plate to 21.
2 mm (53/64").
○ Increase the alternate lifting amount of the
presser foot.
○ Remove the sewing hook and repair with a fi ne
mesh oil whetstone or exchange the hook with
a new sewing hook.
○ Exchange with a new needle.
○ Make the bobbin thread to pass the center of
the tension spring.
○ Exchange the bobbin or polish the outer rim of
the bobbin with a fi ne mesh paper fi le. (sand
paper).
○ Exchange with an appropriate thick needle.
○ Refer to the chapter on "3. LUBRICATION".
○ Refer to the chapter on "8. THREAD
TENSION".
○ Make the strength of take-up spring stronger.
(Refer to the chapter on "8. THREAD
TENSION"
○ Refer to the chapter on "13. ADJUSTING THE
BOBBIN CASE OPENING LEVER".
○ Polish with a fi ne mesh paper fi le (sand paper)
or by buffi ng.
○ Exchange the sewing hook with a new hook.
○ Tighten the pressure regulating themb screw.
○ Refer to the chapter on "17. ADJUSTING THE
HEIGHT OF THE FEED DOG".
○ Refer to the chapter on "8. THREAD
TENSION".
○ Strengthen the tension of the needle thread.
○ Refer to the chapter on "11. ADJUSTING THE
WALKING FOOT AND PRESSER FOOT".
○ Bring the safety device to the correct position.
○ Refer to the chapter on the timing of the main
shaft and the hook shaft.
– 15 –
Corrective measures