Michiel

Great posts, thank you very much!

Good news! looking forward for your pictures.. regards michiel

As far as i know the bobins of my pfaff 138 fit in my adler 69

Or post a picture of your hook/bobbin

Thread size 20 shouldnot be a problem for your machine make some stitches by hand on a smal strip of leather without the lid right of the neelde (so you can see the upperthread pass the bobin) my gues is ther is too less space for the tread to pass the underside of the needle plate maybe the bobbincase lifter is not adjusted for bigger thead (or it is missing at all)

I mean the trhread guide pin:

When i thread a machine i usualy take one or two turns trough / around the thread pin on top of the machine most of the times i do not see much difference in the way i make the turns. but with some thread, when it starts to un-twist in the needle it helps to make turns the right way (in one direction it will make the thread loser and in the other way more thight) this works for me….

When i buy an used machine i always try to get an service manual and follow all the steps in it (Even if it seems to make normal stitches)

Have you seen this video? (and some other ones on his channel)

I do have an service manual but its too big to upload for me if you sent me an DM iwill mail it to you regards, michiel

Here you find parts lists for the adler 120 https://www.duerkopp-adler.com/en/main/Support/downloads/index.html?action=search&prop0=%2Fcommons%2Fdownload%2Fpublic%2F120%2F&prop1=

This looks like a fine machine for what you want to do

The sewing machine on your picture has only one foot (so it has not “triple transport”)

But that said that Adler 68FD62S looks like an nice machine and if the price is right you should be able to use it for some leather topstitching (but still are better of with an other machine for the rest of the work)