Michiel

Picture is from an old topic on lwn not my machine, not my picture (and now i notice it is not threaded right,so do not thread your machine this way! But check if the spring is working well)

The small spring in the middle of this picture was not working properly and that caused the under thread being pulled at the wrong moment and that was why the under thread went out of his designated place…(on my machine) It happened mostly when sewing backwards (and not always)

I have had similar issues with a adler 69 (which is very like your machine) in my case my check-spring which was not working properly , after i fixed that it was solved

No, sorry later i found an adler assembly and changed it. the paff assembly did fitt but i had to modify it a little bit

Adler 69 should be the same and i once made an tension assembly of an pfaff 145 fit onan adler 67 Adler 67 68 69 167 168 and 169 all have the same tension assembly

This class of machines i lift by hand. but for the heavier ones I sometimes use this device

I would try too see what’s happening when actualy sewing with tread and material (leather, canvas or what you are using) It can be hard to see, but if you can, and turn the machine by hand, you can see what is the problem if the machine forms a good loop in the thread the hook needle distance is not that important but if your thread is bad or the timing wrong you might get this. with some machines you can see it by sewing on the edge of your project and open the slide right of the needle sometimes you have to look from the underside. use a flashlight!

You can adjust the height of the presserfoot look into the manual or search on the internet Should be one or two screws on the back of the machine, you find them also if you follow the presserfoot bar into the head of the machine

I have seen adlers with a crack that stil worked. (For a long time) i would like to see a picture, but in generall i think: “if its not broken, don’t fix it” (if you have someone who thinks he can weld it, you might consider to buy it and start using it)

Just a guess: Have you tried pushing the button you use to set the stitch length?

Did you see this recent thread? Is contains find the service manual This looks fine to me

According to the manual they are both for foot pressure. i think the small one is ment for fine tuning

If it is sold as sewing machine oil your machine will be fine

I hope I am clear enough my (technical) English is not good

Here you find the partbooks https://www.college-sewing.co.uk/parts-books/durkopp-adler-sewing-machine-parts-books.html but i think you have a change your barrel hook race is threaded on the backside and you can make your adjustment by making turns anti clockwise