How to Replace the Check Spring on a Gammill White Rotary Tension Assembly

If your Gammill machine is having thread control issues, inconsistent top tension, or the check spring has broken, replacing the check spring on the rotary tension assembly is a fairly straightforward repair. Gammill notes that this spring is pulled and released on every stitch, so over time the thin material can fatigue and break. They also recommend keeping spare rotary tension check springs on hand.

This guide walks through the replacement process for the white rotary tension assembly in a clean step-by-step format. One important note before you start: Gammill says the white knob should be flush with the post and should not be turned, because the spring tension is set during installation rather than by spinning that knob.

You can Find New Checksprings HERE

What the rotary check spring does

On a Gammill, the rotary check spring assembly helps control the top thread and remove slack as the machine forms a stitch. In the normal thread path, the thread goes over the first post, wraps around the rotary wheel, passes over the check spring, and then under the second post. Gammill specifies that the thread should be wrapped around the rotary check spring assembly 1 3/4 times.

If this spring is broken, grooved, or no longer moving correctly, you can see symptoms like poor thread control, unstable tension, or thread wrapping around the spring after a thread break. Gammill’s maintenance schedule also says to inspect the check spring for grooves and replace it if needed.

Tools and parts you’ll need

You will need:

• A replacement rotary tension check spring
• A .5mm Allen wrench
• A small Flat head
• Good lighting
• A clean work area so you do not lose small parts

Gammill’s procedure specifically calls for a 1/16 Allen wrench to loosen the set screw in the black tension ring.

Before you begin

Turn the machine off and remove the thread from the rotary check spring area so you can work cleanly. It also helps to look at how the assembly is sitting before removal so you can reinstall it in the correct position. Gammill’s threading guide notes that after thread breaks, thread can sometimes wrap itself around the check spring, so check for wrapped thread before rethreading or diagnosing the spring.

Step 1: Loosen the rotary assembly from the tension ring

Using your .5mm Allen wrench, loosen the small set screw located on the edge of the black tension ring at about the 3:30 position. Once loosened, remove the entire rotary check spring assembly from the ring. Gammill states that you do not need to disassemble the entire device just to replace the check spring.

Step 2: Loosen the tension shaft set screw

With the assembly removed, locate the set screw on the back side of the housing that holds the tension shaft in place. Loosen that set screw so you can remove the shaft and the broken or worn check spring.

Step 3: Install the new check spring

Take the new check spring and thread its end through the slot in the housing. Then press the coil portion of the spring back into the housing. After that, reinstall the tension shaft through the center of the spring coil. Rotate the shaft until part of the check spring fits into the groove in the tension shaft. Gammill says that when this is seated correctly, the spring arm will move as you rock the shaft back and forth.

Step 4: Set the spring strength correctly

This is the most important part of the job. Gammill’s procedure says to rotate the shaft clockwise until the spring arm rests against the right side of the slot or notch. Then continue rotating the shaft clockwise until the spring passes three spokes on the side of the rotary wheel, which Gammill describes as about 1/6 of a revolution. That added preload sets the proper spring strength.

Once the preload is set, tighten the shaft set screw on the housing to lock it in place.

Step 5: Reinstall the assembly in the black ring

Put the housing back into the black tension ring. Gammill says the radial position should be set so the bottom of the hoop of the check spring sits at about 10:30 o’clock, halfway between 9:00 and 12:00. After positioning it, tighten the Allen set screw.

There is one important caution here: do not push the housing so far into the ring that the check spring arm touches the black ring. If the arm contacts the ring, the spring will not move correctly.

Step 6: Confirm the tension assembly position

After reinstalling the assembly, verify that the white knob is still flush with the post. Gammill’s machine-head documentation says the white knob should be flush and should not be turned. Their threading guide also notes that turning the knob does not adjust the tension in the way many users assume.

Step 7: Rethread and test the machine

Rethread the rotary check spring path correctly: over the first post, clockwise around the rotary wheel 1 3/4 times, over the check spring, and under the second post. Then sew a test sample and watch that the spring arm moves smoothly with thread pull and returns cleanly without binding.

If your thread still behaves poorly after replacement, check the rest of the thread path and the intermittent tension assembly, because Gammill identifies the intermittent tension as the main top-thread tension adjustment point.

Signs the check spring should be replaced

You should inspect or replace the rotary check spring if:

• The spring is broken
• The spring has visible grooves or wear
• Thread control becomes inconsistent
• The machine repeatedly has top-thread slack issues
• Thread wraps around the spring after a break

Gammill’s maintenance schedule specifically says to inspect the check spring for grooves quarterly and replace it if needed.

Pro tips

A smart move is to keep at least one or two spare check springs in your shop. Gammill explicitly recommends having extra check springs on hand because they are wear items.

While you are in this area, it is also worth checking for lint, wrapped thread, or other thread-path issues. Gammill’s maintenance schedule recommends regular inspection and cleaning of related tension and bobbin components as part of routine upkeep.

Final Thoughts

Replacing the check spring on a Gammill white rotary tension assembly is a manageable repair if you follow the factory setup carefully. The two details that matter most are setting the spring preload correctly and reinstalling the housing so the bottom of the spring hoop sits at about the 10:30 position. Done right, the spring should move freely, control slack properly, and restore smooth thread handling.