Constabulary

Threading industrial sewing machines is basically the same. If your manual is bad look for a manual for similar machines with a similar thread tension unit. It´s not crazy different - really. Once you understood the threading you basically can thread all machines. The problem also could be the needle hook timing.

I have a 212 (112 predecessor) and I never use left twist thread (IMO that only is necessary for decorative reasons on visible seams - if wanted) and I would not recommend any bonded thread at all. I mainly sew heavy canvas. Polyester or Poly-Cotton thread is what IMO works best. Look for Aman SERAFIL for leather or for Jeans look for Aman RASANT or SABA ( I prefer RASANT). Look for fine burs or worn in groves in your thread path and the hook and polish them. Also check the needle hook distance and needle height. The needle could be a tad to high.

afaik the "counter hook tip" is meant for thinner thread at higher sewing speed. But I do not know how thin and how fast. So if the problem is solved w/o the tip then take it off al long as it does not cause other problems.

as far as I can tell the OEM Singer hinge screws work for the new Chinese made BCL´s but Adler 30´s have different hinge screws (different threading). But you probably have to rework the "ring" of the new BCL to make it work for older 29K´s (older than 29K71 and the like) I did that some years ago with a 29K1

looks like screw # 200054E is loose or missing

here is a 112w manual but the machine in the manual has a different stitch length mechanism everything else should be the same. Have you threaded both needle from the correct? 112W139-inst.pdf

its actually 111w155 - I doubt there is a mechanical difference, maybe its a different plating on the metal parts (chrome vs nickel or vs blueing or something) either of the parts will work, I´m very sure about that.

I may have an original one - will check in the days to come.

I´d say this new fancy Pfaff machine range is not wide spread already. I doubt there is much experience with this type of machine yet. But why should a top class manufacturer like Pfaff have needle bar issues? Well, you never know but I seriously doubt this cause they for sure have experience from the older models and why should a simple part like a needle bar cause issues? If there was / is a known issue then your Pfaff dealer should know about it and should provide a replacement.

Adler 20 And Singer 7 are "quite equal" if that helps... A modern variant of the Singer 7 is the SEIKO SLH-2B (kind of) https://www.college-sewing.co.uk/parts-by-machine/seiko-sewing-machine-parts/seiko-slh-2b-2b-1-2b-fh1-parts.html?p=2

But you can print it out 😆 may take a few moments... 😉

what parts do you have?

thanks, did not know what to look for 😉

Posting an AliExpress link may help 😉

Try the "tension release disc" from the old tensioner (the one with he small bar across the center hole) - just a guess. Looks like this one: https://armastore.eu/32572-singer-tension-release-disk