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8. TROUBLES IN SEWING AND CORRECTIVE MEASURES
Troubles Causes Corrective measures
1. Thread breakage
(Thread frays or is
worn out.)
(Needle thread trails
2 to 3 cm from the
wrong side of the
fabric.)
Thread path, needle point, hook blade point
or bobbin case resting groove on the throat
plate has sharp edges or burrs.
Needle thread tension is too high.
Bobbin case opening lever provides an
excessive clearance at the bobbin case.
Needle comes in contact with the blade point
of hook.
Amount of oil in the hook is too small.
Needle thread tension is too low.
Thread take-up spring works excessively or
the stroke of the spring is too small.
Timing between the needle and the hook is
excessively advanced or retarded.
○ Remove the sharp edges or burrs on the blade
point of hook using a ne emery paper. Buff up the
bobbin case resting groove on the throat plate.
○ Decrease the needle thread tension.
○ Decrease the clearance provided between the
bobbin case opening lever and the bobbin. Refer
to "4-6. Adjusting the bobbin case opening
lever" p.31 .
○ Refer to "4-4. Needle-to-hook relation" p.30 .
○ Adjust the amount of oil in the hook properly. Refer
to "3-5. Lubrication" p.17.
○ Increase the needle thread tension.
○ Decrease the tension of the spring and increase
the stroke of the spring.
○ Refer to "4-4. Needle-to-hook relation" p.30 .
2. Stitch skipping
Timing between the needle and the hook is
excessively advanced or retarded.
Pressure of the presser foot is too low.
The clearance provided between the top end
of the needle eyelet and the blade point of
hook is not correct.
Hook needle guard is not functional.
Improper type of needle is used.
○ Refer to "4-4. Needle-to-hook relation" p.30 .
○ Tighten the presser spring regulator.
○ Refer to "4-4. Needle-to-hook relation" p.30 .
○ Refer to "4-5. Adjusting the hook needle guard"
p.31 .
○ Replace the needle with one which is thicker than
the current needle by one count.
3. Loose stitches
Bobbin thread does not pass through the
tension spring of the inner hook.
Thread path has been poorly nished.
Bobbin fails to move smoothly.
Bobbin case opening lever provides too
much clearance at the bobbin.
Bobbin thread tension is too low.
Bobbin has been wound too tightly.
○ Thread the bobbin thread correctly.
○ Remove rough parts with a ne emery paper or
buff it up.
○ Replace the bobbin or hook with a new one.
○ Refer to "4-6. Adjusting the bobbin case
opening lever" p.31 .
○ Increase the bobbin thread tension.
○ Decrease the tension applied to the bobbin winder.
4. Thread slips off
the needle eyelet
simultaneously with
thread trimming.
Thread tension given by the tension
controller No. 1 is too high.
○ Decrease the thread tension given by the tension
controller No. 1.
5. Thread slips off the
needle eyelet at the
start of sewing.
Thread tension given by the tension
controller No. 1 is too high.
Clamp spring has improper shape.
Bobbin thread tension is too low.
○ Decrease the thread tension given by the tension
controller No. 1.
○ Replace the clamp spring with a new one or
correct the current one.
○ Increase the bobbin thread tension.
6. Thread is not cut
sharply.
The blades of moving knife and counter knife
have been improperly adjusted.
The knives have blunt blades.
Bobbin thread tension is too low.
○ Refer to "4-7. Position of the counter knife and
adjustment of the knife pressure" p.32 .
○ Replace the moving knife and counter knife with
new ones, or correct the current ones.
○ Increase the bobbin thread tension.
7. Thread remains uncut
after thread trimming.
(Bobbin thread
trimming failure
when stitch length is
comparatively short.)
Initial position of the moving knife has been
improperly adjusted.
Bobbin thread tension is too low.
○ Refer to the Engineer’s Manual.
○ Increase the bobbin thread tension.
8. Thread breaks at the
start of sewing after
thread trimming.
The needle thread is caught in the hook. ○ Shorten the length of thread remaining on the
needle after thread trimming.
Refer to "4-2. Thread tension" p.28 .
9. When a heave-weight
material is sewn, the
material warps.
The feed amount of the top feed is
inadequate.
○ Decrease the feed dog height and reduce the
feed amount of the bottom feed. (Refer to the
Engineer's Manual for the adjustment procedure.)
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