Constabulary

I would assume your V-belt and / or hand wheel is too tight. Just a guess w/o sitting in front of your machine. If you bought the machine from a dealer just check with the dealer. Where in Germany have you bought a Cobra 26?

You get a good motor overview on the KEYSEW website - they have all kind of motors from clutch motors and low end servo to high end servo: https://store.keysew.com/parts/industrial-sewing-machine-motors this one could probably be an option: https://store.keysew.com/sp-1100-npfl

880€? Thats a quite good price I´d say. I have no experience with "modern" machines but considering its a Mitsubishi clone (probably just rebranded?) and seems it has a higher class servo (not sure though) with 5 buttons for making settings... I´d say not a bad deal. Looks like 9mm stitch length Guessing this comes from a dealer, right?

Mitsubishi LU something clone I guess

On my side of the pond you find 3 different measures for V-belts - abbreviation are: LI, LW and LA LI = length inner side of the belt (German: Länge innnen) LW= datum length of the belt (not sure if this is the correct translation) (German: Wirklänge) LA= length outer side of the belt (A = außen = outer suide) (German: Länge außen) So there can be a difference, but not sure how the official measuring on your side of the pond is. Just wanted to give this as a hint.

It depends on the foot lift mechanism, some are push types, some are pull types and and some have a kind of bell crank lever installed on the underside of the flt bed where the roller pushes against (like my 307G2 Singer) So sometimes knee lifters come with a roller installed or a roller is installed on end of the lifter rod on the machine - they look like this.

I think we already talked about it a while ago but forgot about it. So the device replaces the hex screw, right? Internally I guess the "T handle" thing is spring loaded so that is stays in place while darning , right? Or does it "click" into a certain position? Can´t be too difficult to make if the Hex screw has a standard threading... will check that...

For $200 most likely not - the HoHsing are more expensive. I have no experience with higher class motors as I´m rather a low tech fan. Maybe their website gives you an idea of what their motors can do or not http://www.hohsing.com/index.php/en/ac-servo-motor-en

Don´t know what you mean - you have to post pictures - there are literately dozens if not hundreds of different motors on the market...

Guessing you mean the fuse, right? Or what else could pop? Suggestions: New fuse / new circuit breaker / new switch or new motor. If you know nothing about electricity ask someone who is qualified. Not kidding, I mean that!

if he can make them and they do work then let him make a few more (like 5 or 10) - I´m sure these parts could rescue some nice vintage Dürkopp patchers

I understand that these bells and whistle motors are tempting to have them up and running but trust me - they can be a pain if they need support. I have tried it twice some years ago - no luck. Honestly - get rid of it an buy a new Servo motor! I think the higher class HoShing Servos can control some of the "Bells & Whistles" if you really need them. If not buy a plain Servo motor + speed reducer from one of the well known dealers. Its most likely cheaper than buying (probably importing) some of the parts and question remains - will they run? I also haven´t yet heard of anyone who was able to "revitalize" these od electronic clunkers for reasonable money. If you run a factory it´s probably a different story but as a hobbyist or small business these things are dead and not worth investing time & money. My 2 cents

I haven´t darned anything yet I´m using ZZ for repairs. However, I think I will try my 34K for darning. I think for darning you need the momentum in that the presser foot is holding down the material or you have to put the material in a embroidery / darning frame (or what ever it is called). BTW - there was a darning attachment for Singer 29K and Adler 30 patcher machines - not sure if there ever has been one for CLAES patchers. AFAIK WIZ has one

the regulator spring is a 2 piece spring. Your pics show the inner spring but there is a 2nd outer spring - do you have the 2nd spring too or just the one you have shown?

THAT is a tricky part! You have to braze it or look for a 2nd machine. Spare parts are no longer available. It is pinned and you have to drive out the pin in the right direction otherwise you damage more parts. I have been looking for a 2nd machine for approx 1 year! Check with LW member Shoepatcher - he has tons of patcher machines and probably some extra parts. The part in German is called Herzkurve ("heart curve")

Or try shrink hose on the presser foot. Regarding Teflon - you can buy Teflon sheets with an adhesive side - not sure if this helps you. https://www.college-sewing.co.uk/?s=teflon (scroll down a bit - they have different thicknesses)

Original Singer parts are a lot nicer but you no longer can buy OEM Singer parts - some dealers may have old stock parts but good luck finding them. I have ordered one of the above mentioned sets for my 45D91 and the parts do work. They are as expected - functional but not beautiful. Well, they work and are well worth the money. I cannot speak for all Chinese parts but he above mentioned parts have good value for money ratio. I would buy them again.

The Singer 45K92 is a flat bed machine - so feed dog and needle plate from the above set do not work but the presser foot will fit. Keep in mind that the 45K came as flat bed machines (like yours) and cylinder Army machines like the 45K91, 45K25 and so forth - that's a big difference! College Sewing in the UK has 45K flat bed needle plate and feed dog for a reasonable price: https://www.college-sewing.co.uk/store/Singer45KSewingMachineParts

You need a lap seam folder that suits the leather you are using and your machine needs an changeable attachment plate or screw hole in front of the needle plate or you make a custom bracket for attaching it to the screw holes right of the needle plate Not sure if this one works but thats basically the design of a lap seam folder https://armastore.eu/a31-xh-lap-seam-folder They have lots of different lap seam folder, some are described ad "Heavy Duty" guessing they could work for leather too. https://armastore.eu/sewing/folders-binders/?guide_machine=534 But there are for sure suppliers in the US - just wanted to give you an idea. Lap seam folder are usually used with double needle machine but they come for different needle spaces so I`m sure you can use the for single needle machines as well. Or check with an attachment mfg. Co. like Atlanta Attachment Co. for custom making one that suits your needs but they are pricey I guess.

looks like a tension issue or the thread is occasionally hanging somewhere. Check you thread patch and how the thread is coming off the spool. Post some pictures of your threaded machine please. It also could be that the check spring on the needle bar is worn.

Either System 332 LONG needles or System 88 but 332 LONG has a slightly sticker shaft. So both systems are possible, both are ~ 55mm long in total. I have underlined 332 LONG because there is a system 332 as well (not long) which is 45mm long. Nice machine by the way - yet the Class 17 is one of the few patchers I have not sewn with. What is the max stitch length this machine can do? My Class 18 was babel to sew phenomenal 8.5mm long stitches.

No idea - I´m sorry!

Hope you know what I mean Some Adler 4 / 5 / 104 / 105 and I´m sure some Singer 45K also have a roller on the cam for controlling the jump foot system on certain machines

There is a tappet or roller on the cam that drives the needle bar and thread lever. This tappet / roller controls the up an down movement of the presser foot. Note the piece that is attached to the presser foot bar and to the "plunger" that goes up in and down in the large hole on top of the machine. I think I can shoot a picture of my 34K machine as it has the similar system ... give me a few minutes...