CB 4500 Lower thread mess

[Hockeymender]

After years of trouble free use, this is what greets me on the underside of anything I sew with my  CB 4500. Using the same thread I always have (207 top and bottom). Top stitch is fine. Does not seem to matter what I sew the result is the same. Have checked and double checked the thread tension top and bottom and it seems right  (did not change that either before this started). Did some research on this and have checked the items mentioned, still the same. I do notice when I go into reverse there seems to be a "clunk" sound and the upper thread appears to pull. Stumped, all helpful thoughts welcome. 

[Sonydaze]

You might try cleaning out the bobbin tensioner.  After awhile things build up under it.

[Wizcrafts]

4 hours ago, Hockeymender said:

After years of trouble free use, this is what greets me on the underside of anything I sew with my  CB 4500. Using the same thread I always have (207 top and bottom). Top stitch is fine. Does not seem to matter what I sew the result is the same. Have checked and double checked the thread tension top and bottom and it seems right  (did not change that either before this started). Did some research on this and have checked the items mentioned, still the same. I do notice when I go into reverse there seems to be a "clunk" sound and the upper thread appears to pull. Stumped, all helpful thoughts welcome. 

If you are holding back the starting threads and still have a nest on the bottom, and a clunking sound in reverse, something may have changed with the timing between the top and bottom main shafts. There is an access port on the right front of the machine that exposes an large hex head bolt on an eccentric bearing that drives the shuttle and feeder.

Before you explore that opportunity to throw the machine completely out of time (or get it back in time), verify that the needle' to hook position is close to specs. That is, when the needle has risen about 3/16" above BDC, the hook should intersect the needle in the scarf area, about 1/8" above the top of the eye. This is set or checked with the stitch lever set to zero feed. If you find that the hook is crossing the needle too close to the eye and loop, it could have been caused by forced upward movement of the needle bar. That usually happens when the needle gets deflected into the feeder or throat plate under power.

Also, replace the needle, just in case it is at fault.

[Uwe]

My Cowboy CB-4500 also had some adjustment issues which caused the top thread to occasionally be pulled into the hook's race and snagged enough to cause hang-ups and loops at the bottom in reverse. You troubles may have a different cause, but it may be worth checking hook timing movements.

There was a detailed thread a few weeks ago about this and it prompted me to make an adjustment video for the Cowboy CB-4500. On my machine it was a few very subtle adjustments that made the machine cooperate again. 

Here's the thread: 

Here's the video that shows the problem on my machine (at the 2:17 mark): 

Here's the adjustment video I ended up making:

 

[Yetibelle]

Thanks for making those video Uwe they are excellent!