Constabulary

if not the safety clutch then IMO the NB is too high AND the hook is too far away from the needle scarf.

What diameter is the pulley on the servo? A small pulley will help too. The lowest setting on my JACK Servo is 500 but it actually starts at 200 and I have a 1:3 reducer + 40mm motor pulley. That lets my Singer 111G156 sew super slow

you could add a speed reducer. https://www.google.com/search?client=firefox-b-d&q=speed+reducer+site:leatherworker.net/forum/

Binder is too far away from the needle, bring it closer to the needle and if necessary cut down the inner foot.

For spacing between the needles. The bars seem to be fixed in space but the different needle holders (one for each NB) are available for different needle spaces. Split needle bar machines are a bit different compared with plain double needle machines.

loosen this screw and you can raise or lower the feed dog. Removing the front plate (held by 4 screws) makes it a bit easier. Yes, that´s the only mechanism. Have you checked the stitch length adjuster? Lever up is short lever down is longer. If the lever does not move then loosen the set screw on the front side

The days of OEM Singer parts are over (almost) and no one will offer the complete set I guess. So you most likely have to buy the single parts and assemble them. Also make sure your cam on the top shaft has the bevel gear mounted.

Often the main problem is a seized needle bar. I would loosen the the 2 clamping screws on the NB clamp and apply heat (maybe with gas blowtorch) on the bushings and oil them and try to free the NB with a piece of wood and gentle hammer strikes. Heat and oil will most likely loosen the top shaft too if it is seized. this was my ".45" project - pretty much the same machine :

I´d go with #3. Though I like the Durkopps very much cause they share a lot of parts with Singer 111 machines so presser feet sets are available fairly cheap.

Maybe the parts list of the Consew 255 or similar machines like Singer 211 / 212 give you an idea. If not helpful just oil the machine manually. I have a Singer 212 and so do I.

manual can be found here. https://manualzz.com/download/29222852 Parts list: https://www.manualslib.com/manual/483282/Brother-Lt2-B835.html looks like a machine with switchable needle bars. I do not know if it is possible to adjust the needle bar space. Other than that I´m sure the machine is using the the standard gauge sets as used for Singer 212 needle feed machines as well as for their Seiko, JUKI, Consew... equivalents. EDIT: looks like there are special gauge sets for this machine available. Apperas needle holder are different: https://www.ebay.com/itm/1SET-AUTO-THREAD-TRIMMER-GAUGE-SET-FIT-FOR-BROTHER-LT2-B835-LT2-B845-/163232435756

Please post pictures of your machine. There were 2 Types of 51w machines and early and and a later model. Maybe this helps a little bit:

The World was waiting for someone like you

175 yrs of sewing machines and they are still inventing new needles... I had to look up MR needles. See attachment. It may solve some issues but a properly set up machine and the right needle size is still mandatory. The_special_application_needle_MR.pdf

it may depend on the thread sock and how tight it is on the cone but I leave it on (the fine white ones) - no issues and no need for adjusting tension so far.

Posting pictures will help to figure your problem. Needle clamp screw should be parts number 201030 and should be available from a sewing machine dealers. But better check the parts list of your machine. Check the needle hook timing when the hook is not catching the thread. Most likely needle bar is a tiny bit too high.

When sewing patches on existing shoes then yes, the patcher will be the only machine. I though you probably want to produce the shoes from scratch.

Forgot - this is the screw for attaching the plates: https://www.college-sewing.co.uk/1381-needle-plate-screw-singer-132k.html

agree - visit a dealer and test different machines. Sewing through that plastic material may be quite challenging for certain machines. That may require a needle feed or triple feed machine. Maybe you end up with two more machines - a post bed + cylinder arm machine.

They are pretty much all the same. Singer, Seiko, Juki... were using this type of screws on basically all industrial sewing machines. They differ in length sometimes. I even use them for attaching presser feet to the needle bar on my 45D91 https://www.college-sewing.co.uk/50190-long-thumb-screw.html

I`m not a shoe guy. Do you sew on the patches during the manufacturing process or later when the shoe is finished (f.i. as a customers option)? If during the manufacturing process then a flat bed machine or post bed machine would probably be the better choice. Patchers are not the ideal machines for the manufacturing process. They are meant as repair machines. Of course patchers can do a thousand jobs that other machines can´t do but usually they are not involved in a manufacturing process of shoes. Check out some videos where people ares sewing shoe uppers. That may give you can idea what kind of sewing machines they are using.

when the machine is set up for 135x17 / 16 then shorter needles will not work - never ever - only when you lower the needle bar but better buy the right needle system.

agree! Really Impressive and it really looks cool. Any chance that you have a pattern for this jacket?

Its a tapered pin it only goes out one - you have to figure which way. If it was me I would leave it where it is. I would neither remove the top shaft nor the cams on the top shaft. Just wash out the gunk with brushes and kerosene or paint thinner or similar.

Not possible afaik. Let me guess the speed reducer makes it harder to turn the hand wheel by hand. If so I think the reduction is too big. I have the same issue on my Singer 45D91. The big reduction makes it hard to turn the hand wheel. I don´t have the problem on other machines with smaller reduction.