Sewing Machine Upper Tension Regulator Overhaul

The check spring on my old 50's (or 60's?) vintage no-name Japanese sewing machine was bent and mangled. It took some research and experimentation to figure out how to replace it. I learned a lot about how my sewing machine works through this endeavor, and since I couldn't find out any information about this particular machine, I decided to write my first instructable on how I fixed it.

Screw driver
New check spring

Open the light bulb access cover to expose the tension regulator set screw, Loosen the tension regulator set screw just enough to remove the complete tension regulator assembly from the side of the machine.

1. Push the dial into the tension disk cowl to disengage the knob from the dial. This makes it possible to turn the knob as many rotations as necessary to unscrew it from the post.
2. Twist the knob counterclockwise to remove it from the post. Note that the threads aren't like a normal screw. When the regulator is assembled it takes only one turn to travel the full operational distance. It won't feel right when you are twisting it off the post, but that's normal.
3. Remove the dial.
4. Remove the finger washer. This washer is like an interface between the dial above it and the indexing washer below it. The dial has a post at the zero position. The finger on this washer works with the dial post to limit the dial to one complete turn in either direction.
5. Remove the indexing washer. The purpose of the indexing washer is to lock the finger washer and the resulting 0 and 9 positions on the dial to fixed positions around the post. This gives you the ability to set the stop position of the dial.
6. Remove the cone spring.
7. Remove the pressure disk.
8. Remove the tension release pin from the center of the post. FYI: There is a cam inside the machine which pushes on this pin at the proper time in the stitch cycle. The pin pushes the pressure disk away from the tension disk stack, releasing the tension on the thread allowing the take-up lever to pull more thread from the spool.
9. Remove the outer tension disk.
10. Remove the inner tension disk.
11. Remove the tension disk cowl.
12. Note the three indexing slots on the cowl. There is a post in the check spring housing which locks the angular position of the cowl to the housing. The three slots are provided to adjust the location of the dial pointer on the cowl.
13. Loosen the set screw on the check spring housing just enough to separate the post from the housing. Do not remove the set screw from the housing.
14. Remove the post from the check spring housing.
15. Remove the check spring from the post.
16. Congratulations, you just completely disassembled your upper tension regulator.

1. Slide the check spring over the back end of the post. Note that the tail of the spring inserts into one of the slots around the post. I don't think the orientation matters, but I align the loop that the string goes through with the slot in the threaded side of the post. (The check spring was the part I needed to replace)
2. Slide the check spring housing over the back end of the post. Rotate the housing so the shoulder stop just touches the back of the string loop exiting the housing.
3. Twist the post one quarter turn clockwise and tighten the set screw in the housing. This one quarter turn pushes the shoulder stop on the housing into the string loop. It pre-loads the check spring and gives a nice snap to the string loop.
4. Align the left most indexing slot on the tension disk cowl with the post on the check spring housing. This aligns the dial pointer on the cowl with the string loop protruding from the housing.
5. Insert the inner tension disk onto the post. The inner disk must point to the outside of the cowl.
6. Insert the outer tension disk onto the post. The outer disk must point to the inside of the cowl. When the two disks are installed properly, they only touch each other at their inside diameter.
7. Insert the tension release pin into the post.
8. Insert the pressure disk onto the post.
9. Insert the cone spring onto the post. The wide end of the cone must touch the pressure disk. The cone must point outward.
10. Insert the indexing washer onto the post.
11. Insert the finger washer onto the post. Note that the finger bends out of the plane of the washer. The bent finger needs to face the indexing washer to engage with one of the indexing slots. The finger should go into the slot just to the left of the dial pointer on the cowl.
12. Insert the dial onto the post. When the dial bottoms out on the finger washer, twist it clockwise until the post on the dial butts up against the stop finger. At this point the dial pointer on the cowl should be pointing to 9 or zero on the dial. The position isn't accurate because the dial isn't perfectly centered on the post.
13. (multiple steps in one photo)
    
    1. Push the dial against the force of the cone spring as far into the cowl as you can while maintaining the clockwise rotation against the stops. Simultaneously, twist the knob onto the post until it bottoms out on the dial.
    2. Release your pressure on the dial and allow the cone spring to push the dial towards the knob.
    3. Twist the knob counter clockwise until the indexing post on the back of the knob engages with a slot on the dial
14. Twist the knob counter clockwise until it stops. It should stop on or near zero. Twist the knob clockwise until it stops. It should stop on or near nine. In my case, it stopped -near- zero. It doesn't really matter, but I think the zero at the stop should be the one thing about this setup that should dead on. so I backed out the set screw on the check spring housing and twisted the entire post assembly until the dial pointer was centered on the zero. Then, of course, I tightened the set screw back up again.

Push the complete tension regulator assembly into the hole in the side of the machine and tighten the set screw. Congratulations. You just assembled a complete tension regulator assemebly.

The way that I showed how to assemble the upper tension regulator will result in the tension disks pressing pretty tightly against the thread even at the zero setting. For me that's okay because I'm messing around with canvas and using strong thread. If you are sewing something delicate and are using delicate thread, this setting is likely to break the thread. The adjustment is pretty simple for that.

1. Turn the dial counterclockwise to the zero stop.
2. Push the dial into the cowl to disengage the indexing post on the knob from the slot in the dial.
3. Twist the knob counterclockwise just a hair and stop.
4. Release the dial to allow the cone spring to push it against the knob. The knob indexing post is now between slots on the dial.
5. Twist the knob counterclockwise a little bit more until the indexing post falls into the next slot.

This procedure reduces the pressure on the string by one slot. Repeat adjustment sub-steps 2-5 until you find a range of tension that works for the thread and fabric you are using.