Seiko LLW8BL issues with stitch formation

[ZIIK]

I picked up a Seiko LLW8BL a while ago and are having some issues with it. The hook base was broken when I picked it up, so I have replaced that with a new Hirose hook. I have also found a bunch of settings to be out of specification and corrected that. The timing between upper and lower shaft is correct (matching marks, and the pick up lifts at the right time compared to the lower shaft). Despite this I am having some odd behavior when the thread is traveling around the bobbin, it is as if the tension is to high (despite normal thread tension). I have played around with the latch opener in case it was interfering and noticed that the thread is "out of sync" when forming the loop around the bobbin. It is as if the thread is to late to finish its cycle, getting to the latch opener later than what is normal.

The only thing I have not checked is the position of the rocker arm compared to the rear foot. The movement of the feed dog is fairly well centered in the needle plate, so it looks okay from a visual inspection. Though I have suspected that this could have some impact on my issue since it affects the angle of attack from thread to hook base/needle plate. On other machines, the thread slips right passed the finger early in the cycle, on this one the thread is dragged passed the finger at the stitch plate right at the end with no help from the latch opener.

I have noticed that the vertical space between the stitch plate and the hook "finger"  is tighter than I would like it. I have not found a way to adjust this since the hook sits on a bushing pressed into the machine chassis. I have checked if it is possible to change the position of the bushing but did not manage to move it on the first try. Would be great if someone could give some input on how to do this vertical setting of the hook in relation to the stitch plate.

I can get it to a point where it sews good in forward but makes a little noise in reverse when the thread is pulled through the tight space.

Any help would be much appreciated.

I don't have any documentation for the machine, but it is essentially a stretched Singer 211. So much of the settings are similar.

 

[ZIIK]

I have continued troubleshooting this evening and come to a couple of conclusions. I checked the position of the Rocker arm, it is correct according to the Singer 211 manual, so i will assume that it is correct for this "stretched" Seiko version as well.

I was to hard in my judgement on the thread timing around the hook and have achieved okay results with the latch opener and general timing of the machine so that the machine sews well in forward with normal thread movement around the hook.

Reverse works okay on shorter stitch lengths, the ticking sound increases with increased stitch length. I have also located the reason for the "ticking sound" towards the end of the stitch formation. My previous assumption was incorrect. The thread seams to pass between the hook "finger" and the stitch plate okay after all. What does happen is that the upper thread gets caught between the lower thread and the underside of the feed dog as it is being pulled up, causing a small "pop" when it is released.

Does anyone know how to remedy the issue? I am considering if it would help to chamfer the bottom edge of the feed dog, making it easier for the thread to slide "around". The edge is 90 degrees and rather sharp at this point.

[CowboyBob]

12 hours ago, ZIIK said:

I have noticed that the vertical space between the stitch plate and the hook "finger"  is tighter than I would like it. I have not found a way to adjust this since the hook sits on a bushing pressed into the machine chassis. I have checked if it is possible to change the position of the bushing but did not manage to move it on the first try. Would be great if someone could give some input on how to do this vertical setting of the hook in relation to the stitch plate.

The quickest way to test it is make a shim & put underneath the needle plate,loosen both screws but you can usually put it underneath the back screw.

It should help to smooth the feed dog hole too.

Edited December 16, 2019 by CowboyBob

[ZIIK]

Great input Bob, I should have thought of that! I will try that and see if it helps. 

I have a new feed dog for a Singer 111 laying around that should fit this machine. I will try swapping it and see if I get the same results with a different feed dog.