1. MyLock 644D
Service Seminar

2. Face Plate Removal…………………………………………………………………..…………1
Table of Contents
644D
Face Plate Removal…………………………………………………………………..…………1
Belt Cover Removal……………………………………………………………..………………2
Top Cover Removal………………………………………………………… ……..3
Front Cover Removal……………….……………………………………..…………………4-6
Side Cover Removal.………………………………………………………………….…………7
Base Cover Removal……………………………………….……………...…...…… ………....8
Preparation for Service……………………………………………………………………...….9
Needle Bar Height Adjustment……………………………………………………………….10
Lower Looper Height Adjustment………………………………………………….…….11-12
Lower Looper Timing and Clearance…………………………………………………
Front Needle Guard Clearance……………………………………………………………...18
Upper Looper Timing………………………………………………………………………….19
Upper Looper Positioning…………………………………………………..………………..20
Upper and Lower Looper Timing………………………………………………………..…..21
Upper Looper Clearance…………………………………………………… …22
Upper and Lower Knife Adjustment………………………………………….………….23-25
Tension Adjustment……………………………………………………...…………………26-27
Front, Base and Top Cover Installation……………………………………………...…28-32
Belt Cover, Face Plate and Side Cover Installation…………………………………

3. Removing the Face Plate
1. Turn the sewing machine toward the back and remove the screw.
2. Remove the face plate. 1

4. Removing the Belt Cover
1. Turn the machine toward the back and loosen the screw.
2. Lay the machine on its back and remove the screw.
3. Pull out the back edge of the belt cover and remove it. 2

5. Removing the Top Cover 1. Turn the sewing machine toward the back.
2. Loosen the 2 screws.
3. Raise the back of the top cover and remove it. 3

6. Removing the Front Cover
1. Loosen the 2 screws by the needle bar.
2. Place the sewing machine on its back. Open the front door. Remove the 2 screws.
3. Remove the door. 4

7. Spreader holding plate
4. Remove the 2 screws that hold the front panel to the casting.
Spreader holding
plate
5. Bring the upper looper to its lowest position. Remove the screw and remove the spreader holding plate. 5

8. 6. Remove the 2 screws.
7. Remove the front panel. 6

9. Removing the Side Cover
1. Loosen (do not remove) the 2 screws.
2. Remove the side cover. 7

10. Removing the Base Unit
1. Lay the machine on its back. Remove the 2 screws and the cushions.
2. Remove the 3 silver screws. DO NOT REMOVE THE CUSHIONS. Remove the base unit. 8

11. Preparation For Service
1. Remove the screw and the entire presser foot
2. Raise the needle bar to its highest point. Remove the left needle. If the right needle is old or damaged, replace it with a new needle.
3. Use a 7 mm nut driver or a screwdriver to loosen and remove the hexagon bold. Remove the upper knife. 9

12. Adjusting the Needle Bar Height
1. Raise the upper looper to its highest position. Loosen the screw inside the top of the upper looper shaft(2.0 mm) and pull out the upper looper to the left.
2. Raise the needle bar to its highest position. Place the serger step gauge (part number 787G05) on the needle plate, as shown. The tip of the needle should be even with the first step of the gauge or slightly above it.
According to factory specifications, the tip of the needle should be 11.6 to 12.2 mm above the surface of the needle plate.
3. If an adjustment is needed, loosen the 2.0 mm hexagon screw and raise or lower the needle bar. Do not rotate the needle bar while adjusting the height. Tighten the screw. 10

13. Adjusting the Lower Looper Height
1. Push in the width cutting regulator knob and pull the red chaining finger toward you to the R position.
2. Remove the screw and the lower looper
Shoulders
3. Inspect the lower looper drive arm. Make sure that the 2 shoulders are not broken. If either shoulder is damaged or broken, replace the entire lower looper drive arm. 11

14. 4. Inspect the lower looper and replace it, if necessary
4. Inspect the lower looper and replace it, if necessary. Reinstall the lower looper and temporarily tighten the screw.
5. Adjust the height of the lower looper by loosening the screw and moving the looper up and down. Adjust the looper so the slot in the looper is completely covered by the screw. Then firmly tighten the screw. (Do not overtight the screw) 12

15. Adjusting Lower Looper Timing and Clearance
1. Locate the needle guard screws.
The top 2 screws (2.5 mm hexagon) hold the front needle guard.
The bottom 2 screws hold the rear needle guard.
2. Loosen the front needle guard by loosening the top 2 hexagon screws. Loosen the screws only enough to enable the needle guard to move. 13

16. Thickness Gauge Clamp Gauge
3. Turn the handwheel to bring the needle bar to its lowest position. Place the gauge clamp (part number 787G02) on the needle bar as shown. Insert and hold the thickness gauge (part number 787G03) above the gauge clamp.
Thickness
Gauge
Clamp
Gauge
4. Raise the clamp until clamp and thickness gauge stop. Tighten the screw. 14

17. 5. Remove the thickness gauge
5. Remove the thickness gauge. Turn the handwheel toward you to raise the needle bar until it stops.
6. At this point, the tip of the lower looper should be even with the left edge of the needle. 15

18. 7. In order to adjust the lower looper timing and clearance, locate the hexagon bolt (7 mm) at the back of the lower looper drive arm.
8. Carefully loosen the hexagon bolt, using a 7 mm open-end wrench or a hexagon driver. Loosen it only until you are able to move the lower looper drive arm and it will stay in the position where you set it. Adjust the lower looper timing, but do not tighten the hexagon bolt yet.
9. Move the lower looper to the right slightly until the tip of the lower looper is behind the needle. 16

19. 10. Check the clearance between the lower looper and the needle
10. Check the clearance between the lower looper and the needle. The clearance should be .05 mm. Use a small screwdriver to push against the needle from the front. The needle should move very slightly.
11. If an adjustment is needed, move the lower looper drive arm in or out until the clearance is .05 mm.
12. Tighten the hexagon bolt. To prevent breaking the lower looper drive arm, do not overtight the bolt. Remove the gauge clamp. 17

20. Front Needle Guard Clearance
1. Bring the tip of the lower looper behind the needle. Lightly push the front needle guard against the needle until there is no clearance between the needle and lower looper.
2. Tighten the 2 front needle guard hexagon screws. Using the handwheel, move the lower looper back and forth behind the needle. If you hear a loud scraping sound, readjust the front needle guard clearance. A very light rubbing sound is normal. 18

21. Upper Looper Timing
1. Raise the upper looper shaft to its highest position. Inspect and reinstall the upper looper so that the looper is in front of the needle and resting lightly against the needle. Temporarily tighten the screw inside the upper looper shaft(2.0 mm hexagon).
2. Bring the upper looper shaft to its lowest position. Check the clearance between the upper looper shank and the upper looper shaft guide. Use the tip of the serger step gauge to measure this clearance.
3. If an adjustment is needed, loosen the two screws(2.5 mm hexagon). 19

22. Upper Looper Position
1. Raise the upper looper to its highest point. Use the serger step gauge for this adjustment.
2. Place the first step of the gauge lightly against the needle. The second step of the gauge should be centered in the eye of the upper looper.
3. To make an adjustment, loosen the 2.0 mm hexagon screw inside the upper looper shaft. Move the upper looper to the left or right, then temporarily tighten the screw. 20

23. Upper and Lower Looper Timing
1. Bring the upper looper to its lowest position, than raise it until the tip of the looper is even with the bottom edge of the lower looper
Sample #1
Sample #2
Wrong
2. The tip of the upper looper should be between .2 to 1.2 mm to the left of the eye of the lower looper.
3. If an adjustment is needed, loosen the 2 hexagon screws( 2.0 mm) on the upper looper drive cam and turn the cam:
Away from you if the loopers look like sample#1.
Toward you if the loopers look like sample#2. 21

24. Upper Looper Clearance
1. Turn the handwheel to bring the upper looper behind the lower looper, as shown.
2. The clearance between the upper looper and lower looper should be as zero as possible but no more than 0.2mm, without the loopers hitting each other as they pass.
3. To adjust the clearance, loosen the screw inside the upper looper shaft(2.0 mm) and rotate the upper looper forward or backward. Then firmly tighten the screw. 22

25. Knife Position
1. Reinstall the needle plate. Remove the two silver screws and remove the looper cover guide.
2. The top edge of the lower knife should be level with the surface of the needle plate.
The lower knife is replaced by removing the 2 screws.
3. To adjust the lower knife height, first loosen the silver screw located to the left of the cutting width regulator dial. 23

26. 4. Locate the eccentric shaft
4. Locate the eccentric shaft. Insert a flat screwdriver and turn the shaft until the top edge of the lower knife is level with the surface of the needle plate.
Eccentric
shaft
5. Tighten the silver screw by the left side of the cutting width regulator dial making sure that the eccentric shaft does not rotate (use a flat driver as show).
6. Install the upper knife with a 7 mm hexagon bolt. 24

27. 7. Turn the handwheel toward you to bring the upper knife to its lowest position.
8. The front lower corner of the upper knife should be 0.8 to 1.5 mm below the top edge of the lower knife. To make this adjustment, loosen the hexagon bolt and move the upper knife up or down. Tighten the hexagon bolt.
9. Reinstall the looper cover guide. Inset and tighten the 2 screws. 25

28. Tension Adjustment Adjusting plate
1. Observe the tension unit and locate the adjusting plate. The tension dials are calibrated by first sewing a sample and turning the dials until the stitch looks correct. Then, if any of the dials are not on number 3, the following adjustment is made.
Adjusting
plate
2. Use a small screwdriver to raise the adjusting plate, then rotate the tension dial as needed and lower the plate.
3. When serger tension is adjusted correctly, the upper and lower looper threads meet at the edge of the fabric and both needle threads are tight in the fabric. 26

29. 4. When the left needle tension is loose, you will notice these loops on the bottom of the fabric. To correct loose left needle tension, turn the left needle tension to a higher number.
5. When the right needle tension is loose, you will notice these loops on the bottom of the fabric. To correct loose right needle tension, turn the right needle tension to a higher number.
6. When either upper looper tension is too loose or the lower looper tension is too tight, or both, the upper looper thread is pulled to the bottom of the fabric. To correct this, turn the upper looper tension dial to a higher number or turn the lower tension dial to a lower number, or both. 27

30. Reinstalling the Front Cover
1. Turn the handwheel to bring the upper looper to its lowest position. Reinstall the front cover.
2. Insert and tighten the 2 silver screws that hold the cover to the casting.
3. Insert and tighten the 2 silver screws on the right side of the cover. 28

31. 4. Insert and tighten the 2 screws by the needle bar.
5. Reinstall the spreader holding plate. Insert and tighten the screw. 29

32. Reinstalling the Base Unit
1. Lay the machine on its back. Reattach the base unit, install the 2 cushions on the top and tighten the screws.
2. Insert and tighten the 3 screws on the bottom. 30

33. Reinstalling the Base Unit
3. Reinstall the front door , insert and tighten the 2 screws.
4. Make sure the front door moves freely and adjust if necessary. 31

34. Reinstalling the Top Cover
Locking Tabs
1. When reinstalling the top cover, be sure that the tabs on the front edge of the cover fit inside the top of the front cover.
2. Insert and tighten the 2 screws. 32

35. Reinstalling the Belt Cover
1. Reinstall the belt cover. Gently push in the belt cover making sure the locking tabs are positioned properly.
2. Tighten the silver screw.
3. Lay the machine on its back. Install and tighten the screw. 33

36. Reinstalling the Face Plate
1. Reinstall the face plate, making sure it fits properly with the front, top and rear covers.
2. Insert and tighten the silver screw. 34

37. Reinstalling the Side Cover
1. Reinstall the side cover.
2. Tighten the 2 silver screw.
*Install the presser foot unit and the left needle. 35