Constabulary

hard soldering then drill the hole and polish it but new take up levers are available new. Should be this one but check parts list first: https://www.ebay.com/itm/196288462626 I´d buy a new one.

no one knows the history of this machine maybe one of the former owners had the same idea and change the NB some time ago. Who knows?

The Juki 562 / 563 manual is probably the closest for your SEIKO STW8. See attachment. Can you post pictures from the underside of your machine maybe the stitch length has been limited for what ever reason. Juki 563 562 Manual.pdf

You probably have to play with the needle bar height. Have you checked the NB height / needle - hook timing? Procedure should be mentioned in your manual. If it was me I´d probably try lo lower the NB a tiny bit so you will have a bit larger thread loop. But thats just me from a distance. Hard to tell what it going on when not in front of the machine.

looks good, hope you have fun with this machine and it suits your needs 😃

The Seiko STW-8B basically is a later / more modern clone of the Singer 111G156 with some differences but it basically is a very similar machine. How long is your maximum reverse stitch length? Usually when the reverse stitch is longer the forward is shorter (and vice versa). With other words, usually F & R are equal at approx 5mm at this type of machine (Singer 111 and later clones) so when the F is 3.5mm then usually the R is longer and I guess it is 6.5mm.

Good Lord 😲 - needles to say yours is bigger than mine. And I say this w/o any envy... 😁 $400 for sure is a good deal - money wise. But otherwise it pretty much is an overkill for most projects, Bigger is not always better. Maybe setting it up selling it and looking for something smaller would be a good idea. But due to its size it could take some time to find a customer. There is big $ in machines of this size.

looks good so far - how ever some fine tuning could be necessary. Little hint - the thread should run above the thread lever and not under it.

The check spring should rest in ~ the 9 o'clock position. There is a curved metal piece (A) underneath the tension unit that is secured by a screw (B). The end where the check spring rests on should be at approx 9 o'clock and the check spring needs a little pretension so when the thread lever goes down the spring goes back on the rest.

some Singer machines have a crazy thread path and an "odd" / unnecessary thread loop or hole - don´t know why. My 108w20 also has this path and I do not follow it and it works w/o problem. Beside that you have not instated the new tension unit correctly therefore the machine will not work properly. Not much time atm, have to run, more later....

But the machine has no needle positioner as it seem (see hand wheel) so in this case the white plastic nub has no purpose.

happens when you are not logged in, should be available when you are logged in.

My guess: The black internal lever with the magnet on it (on the inside of the accelerator unit) which is attached to the external lever where the pit man rod is attached to (other side is attached to the foot pedal) has shifted and the magnet no longer is aligned with the hall sensor. That probably happened due to the bumpy roads you drove. Just my guess. Assuming it looks similar on your motor - see pictures:

maybe this manual will help. According to this manual PD seems to be a "pedal warning" Servo Motor Technician User Manual(v3.7 L-Type 4-Bar for ShuangZheng).pdf

a personal comment suits better here I´d say. I never hit any like or dislike button - no matter where. But I´m Generation X and not very social media affine anyway.