Sewing Machine Repair

Sewing machine repair is the major factors now a day. We should assemble the sewing machine correctly. To prevent the overheat of needle point caused by the high speed sewing especially when it is made with synthetic threads and/or fabrics, HR unit is installed on the machine. Regular  sewing machine repair makes the stitch skipping, thread breakage and such troubles as burning or enlargement of stitch hole on the fabric can be prevented. Oil should be used it is most effective to use those of Silicone Line. Check the quantity of oil occasionally, opening Lid (B). And replenish with new oil when it is running short.

Sewing Machine Repairs  and Assemble SP Unit :

Like HR Unit, SP Unit is assembled and the sewing machine repairs as Standard Equipment, to prevent troubles resulting from heated needle.

Sewing Machine Repairs and Assemble SP Unit
SP Unit

We can expect an excellent effect by using HR and SP Units in combination. Oil those of Silicone Line is most effective as in the case of HR Unit. And check the quantity of oil in tank to sewing machine repairs occasionally and supply oil if necessary.

Overlocker Needle Setting :

There are many sizes of over locker needles, so select the suitable needle for sewing machine repair and maintenace. Basically speaking, No.8~11 should be used for light and medium materials and No.14 for heavy ones. Needle must be set correctly after confirming the direction, facing its scarf for the back side of machine as shown in the sketch.

Overlock Yamata Presser Foot:

The pressure of Presser Foot of overlock yamata will be strengthened by turning Adjusting Screw(A) to the right direction and weakened by turning it to the left.

Overlock Yamata Presser Foot
Presser Foot

The pressure of Presser Foot should be adjusted most weakly so far as Presser Foot can act properly.

Adjustment of Width of Overlock Yamata Edge Seam :

To widen the width: Loosen the Screw(A) for Upper Knife Holder of overlock yamata and move the Holder to the direction (X) so far as the case needs, and tighten Screw (A) again. Then, loosen Screw(B) for Lower Knife Holder to enable to move to the direction (X) by the pressure of the Spring inside. Thus, Lower Knife will touch closely to Upper Knife(D) with the suitable strength. Keeping this condition, tighten Screw(B) again.

Adjustment of Width of Overlock Yamata Edge Seam
Adjustment of Width

To narrow the width: Loosen the Screw(B) for Lower Knife Holder and move the Holder to the direction (Y) so far as the case needs, and tighten Screw(B) softly. Then loosen Screw(A) for Upper Knife Holder and move this Holder to the direction(Y) to touch closely to Lower Knife(C), and tighten Screw(A) again. And then, loosen Screw(B) again and make the Lower Knife (C) touch with Upper Knife(D) by pressure of the Spring, and re-tighten Screw(B).

Note: In the adjustment for width of coveredge seam, the blade of Upper Knife must be positioned at about 1mm higher than that of Lower Knife as shown in the sketch.

Adjustment & Repair of Stitch Length:

How to change Stitch Length of overlocking . Pressing the Push button (A) with left hand until its finger will feel that the point of Button touches machine parts inside, then turn Pulley with right hand until the Button is fallen in. At this moment, press the Button more strongly to release engagement of Feed Dog Regulating Gear and continue the turning of Pulley.

Adjustment Repair of Stitch Length
Stitch Length

Graduations on the circumference of Pulley shows a Stitch Length in mm. Set any of Graduations as you desire with Countermark of Belt Cover(B), and then take the left hand off. There may be a little difference in the length owing to kind, thickness and differential ratio, in which cases Graduation must be readjusted suitably. Stitch length can be adjusted continuously from 1.0mm to 3.2mm.

Repair and Adjustment of Differential Feeding of Overlocking MC:

Normal Differential Feeding(Shrink Sewing): Loosen Nut(C) and decide the suitable position of Lever(D) by its up-and-down handling, then tighten Nut(C). When countermark of Lever is set with “2.3” of graduation, the ratio of differential feeding to main feeding becomes 1 : 2.3, and when it is set with “1” there is no differential feeding because of equal momentum. When the graduation on pulley is set at less than “2”, the differential ratio is available up to 1 : 2.3, and more than “2”, the ratio is up to 1 : 1.4.

Reverse Differential Feeding(Stretch Sewing): The reverse momentum will be increased with the lifting of Lever(D) from “1” to “S” on Graduation Plate(E). When the Countermark is set with “S”, the ratio of differential feeding to main feeding becomes 1 : 0.8.

Adjust the Differential Ratio of Over Lock Machine: To adjust the differential ratio while the machine is operating, connect the Chain to the Chain Hole on the Lever(D)

Tension of Overlocker Thread:

The standard position of Overlocker thread eyelet(A) is the position where the center of Screw(B) is aligned with Countermark(C). In case of stretchable thread chain, align the center with Countermark(D). When blind hemming work, raise Needle Thread Eyelet (A) to its highest point.

Tension of Overlocker Thread
Tension of Overlocker Thread

Tension of Looper Overlocker Thread:

  1. When turning Lower Looper Eyelet(A) to the direction (X), the lower looper thread slackens and to the direction(Y), it tightens.
  2. When turning Thread Pull-off (B) to the direction (X), both upper and lower looper thread slacken and to the direction(Y), they tighten.
  3. When moving Upper Looper overlocker thread Eyelet(C) to the direction(X) the upper looper thread slackens, and to the direction(Y) it tightens.
  4. When moving Looper overlocker thread Pull-off (D) to the direction(X), upper looper thread slackens, and moving to the direction(Y), it tightens.

Over Lock Sewing Machine Repair and Checklist:

Check point (s )Corrective action (s)
Check the lubrication system.


Oil filter.

Oil condition.

Oil level.

Amount of oil circulation.

Check all the oil pipes are not damaged. If damaged replace the oil pipes.


If the oil filter is clogged with heavy dust-clean it or replace it.

If the oil is dirty, change the oil & fill it up to a level between redlines.

Make sure that all the relevant parts are lubricated.

Check the feed system i.e. Feed dog, presser foot, needle plate.If the feed dog teeth is worn out. Replace the feed dog.


If the presser foot is scratched. Buff the presser foot or replaces it.

Check the needle bar, needle bar bush. Needle holder.If the play between needle bar and needle bar bush replace of repair them.


If needle holder is worn out, replace it.

Check the threading system i.e. Thread stand, thread tension post, different thread guides.If the thread path is scratched or damaged smooth it by buffing of replace the thread guides.
Over all cleanlinessClean the m/c by a soft bristle brush or a fabric (knitted / soft)
Check the electrical wiring, motor, etcTake necessary action.
Check the safety devices i.e. Belt cover, eeshild etc.Install the safety devices. If damaged by somehow.

Over Lock Machine Maintenance:    

Daily Maintenance:  

Done by : Operators

Supervised by: Maintenance Personnel

Needle Replacement: Check whether the needle is bent or blunt or not. If it is bent or blunt change the needle and install it under the supervision of maintenance personnel.

Looper:Clean the tail of thread, dust and lint in the looper.

Lubrication:Lubricate the machine parts where necessary.

Time required: 10 minutes.

Cleaning the looper case and other possible parts:Clean the lint, loose thread and other dirt from the shuttle of looper and looper case. Besides the table and other parts which cannot effect the setting must be cleaned.

Required time: 10 minute.

Weekly Maintenance:Done by : Maintenance Personnel

Supervised by: Maintenance Manager

Needle – Looper timing:Check whether the needle – looper timing is correct or not. If there lies miss-timing then adjust it.

The check points are

  1. Needle – looper clearance
  2. The height of needle from its lowest position of upward stroke when the looper reach at the center line of needle
  • At the same time the distance between the looper and the top end of the needle eye.

Required time: 10 minute.

The clearance between looper holder and looper case holder bracket: Check the clearance between the looper & looper case holder bracket (1-1.5mm). Make sure that the looper will not touch loooper case holder bracket.

Required time: 5 minute.

Presser foot pressure: Check whether the pressure of presser foot is proper or not. If not adjust it by adjusting the distance between the bottom washer and top of pressure bar guide bracket. And the bottom of work clamp must be kept parallel to the top of the work.

Required time: 5 minute.

Thread take-up amount: Check the amount of the thread take-up stroke, clearance between needle thread and thread take-up lever guide (0.5-1mm). Make sure that it is not more than necessary.

Required time: 5 minute.

Needle & looper thread tension adjustment: Check whether the standard operating range of thread take-up spring is accurate or not (6-8 mm). The tension at appropriate operating range must be checked.

Required time: 5 minute.

Needle installation: It must be remembered during needle installation that the long groove of the needle is on the left and tightened with the needle clamping screw. Adjust the needle clearance and lift amount.

Required time: 2 or 3 minute.

Stitch Length: Check whether the stitch length is appropriate or not. If not , slowly turn the hand wheel as you keep depressing  push button and a point is found at which the push button goes further. With this condition, align the desired scale on the hand wheel with mark on the belt and reset the push button.

Required time: 5 minute.

Needle Bar height:  It is remembered that when the needle bar is in its lowest position the reference line on the must be at the lower end of the containing the needle bar. If it is not so, remove the needle plate, loosen the needle bar connecting stud clamping screw and adjust by raising or lowering the needle bar.

Required time: 5 minute.

Adjustment of Pressure on the material (fabric): The pressure on the material during sewing must be as weak as possible, but strong enough so that the material does not slip. Adjust the pressure through loosing the adjustment nut.

Required time: 5 minute.

Feed Dog Height: The standard height of the feed dog for sewing thin material is 0.8 mm, and for medium material is .00 mm and for thick material is 1.2 mm (when the stitch length is set to the maximum).

Adjust the feed dog height by loosening the screw when the feed dog is above the needle plate surface and move the feed lifting arm up and down.

Rquired time: 5 minute.

Feed dog angle: In order to prevent puckering, material from slipping the feed dog is to be raised or lowered downward at standard angle.

When the feed dog angle has been adjusted, check to confirm that the height of feed dog has not changed.

Required time: 5 minute.

Presser foot height: The standard height of the presser foot is 6 mm when the presser foot is raised with presser foot lifter lever. To adjust the presser foot height, loosen the nut of the adjustment screw and then the presser foot adjustment screw so that no pressure will be applied to the presser foot, then loosen the set screw and adjust the presser foot height by raising or lowering the presser bar.

Required time: 5 minute.

Lubrication: Change oil when it contains contaminants. If the pointer bar of the oil gauge comes down under the lower marker line when the observing the sideward, supply oil. Change oil when one month has passed after the first set-up of machine. Apply two or three drops of oil to the needle bar and upper looper guide when operating the machine for the first time after set-up of after along time of disuse.

Caution: Be careful not to exceed the upper red marker line, or else troubles due to excessive lubrication may result.

Required time:5 minute.

Height of the lower knife: Loosening the set screw adjust the height of lower knife so that its edge is flush with the throat plate surface.

Height of the upper knife: Loosening the set screw perform the adjustment so that upper knife overlaps the lower knife 0.5-1 mm when the upper knife is at its lowest position.


  • Be sure to tighten screw before operating machine.
  • After completion of adjustment, make the knives cut a thread to check sharpness of the knives.

Required time: 10 minute.

Sharpening the lower knife: When the lower knife has become dull, sharpen it.

Required time: 15 minute.

Monthly Maintenance:  

Oil replacement and other interrelated checks:

  1. Check lubricant or oil whether that is to replace.
  2. Check bush leakage, oil seal leakage or age, vibration of oil and the flow of oil pump more or less than setting.
  • Check rubber cushion seats, four corners of machine tool groove on which oil pan stands.

Required time: 10 minute.

Rotary hook: Check rotary hook wear whether it is need to replace.

Required time: 10 minute.

Presser foot canal: Check its canal wear. If necessary replace it.

Required time: 5 minute.

Quarterly Maintenance:

Cleaning the filter and pump-net: Clean the filter and pump net to lengthen the machine life. If these are clogged with dust, the machine components may be seized or worn out extraordinarily.

Half yearly Maintenance:

Lubrication: Change oil of the machine every six month.

Adjustment Overlocker Knives for Fabric Cutting:

Different types of overlocker knives are described below shortly-

Lover Knife : The blade of Lover Knife (A) must be even with the top face of Stitch Plate or a little lower (0-‘-‘0.3 mm). To make this adjustment, loosen Screw(B).

Flat Upper Knife : As for the height of Flat Upper Knife, when this Knife reaches the bottom of its movement, make the engagement with Lower Knife be 0.5~1.0min. To make this adjustment, loosen Screw(C).

Over Lock Flat Upper Knife
Over Lock Flat Upper Knife

Angled Upper Knife: Height of Angled Upper Knife is impossible to adjust as it is decided by Stopper(D) naturally. To set this Knife, loosen Screw(E) and insert the Knife to Upper Knife Holder until it will touch with Stopper(D), then tighten Screw(E) again.

Overlocking Angled Upper Knife
Overlocking Angled Upper Knife

Sharpness of Knives: Turning the Pulley manually, after adjusting width of overedge seam, check the sharpness of Knives with a thread put between both Knives.

Re Sharpening Overlocker Knives: It is unnecessary to re sharpen Upper Knife for about one year as this Knife is made of Super Hard Alloy. During this period, if the cutting becomes blunt, Lower Knife must be sharpned as the sketch shows. As stated above, the Upper Knife cannot be re-sharpened by the ordinary grinder, abd the provisional one must be prepared always. For overlocker sewing machine repair and adjustment of parameters, please contact us directly or the dealer who sold the machine to you.