Constabulary

I have no 441 type machine but I know there are harness feet for them. Maybe you can shorten the toes a bit if needed. https://www.ebay.com/sch/14339/i.html?_from=R40&_nkw=441+foot Maybe the left toe foot does the trick

You did not say what machine you are using. If it is some sort of singer 111 machine then this foot set may help to sew closer to the hardware https://www.ebay.de/itm/224401640036 if it is a 441 type machine an inline foot set may help: https://leatherworker.net/forum/topic/76502-inline-cowboy-presser-feet-on-cowboy-cb4500/

These are my DIY winder - I also have one more for the large 132K6 bobbins. https://leatherworker.net/forum/topic/75580-diy-electric-bobbin-winder-singer-111-and-45k-type-bobbins/

I don´t know what they (still) produce in Bielefeld (Dürkopp-Adler) but the plant is still there. The new DA M-Type machines are build in the Czech republic by MInerva https://www.minerva-boskovice.com/

IMO timing belts are not really an issue, modern timing belts are quite long lasting. Old aged not well kept machines stored away in unfavorable conditions (dust, oil, heat, cold, moist, maybe sun or a combination of one or more) usually have problems with timing belts. Adler and Pfaff used some sort of brownish timing belts for a while (in the period when 67 or 167 and the like where en vogue) but they have learned and no longer so. So the issues with timing belts you read about are usually found on machines that have been stored away for many years or decades in unfavorable conditions. I would not worry about that when you buy a new machine.

Belts are a No? It does not matter if a machine is an "upholstery machine". Its sewing capabilities matter and you can easily sew heavy letter when the machine is equipped with a proper motor and maybe a speed reducer. The 267 usually sews with 138 thread and 207 (as mentioned earlier) when properly set up. And depending on the subclass I´m sure 10mm leather or maybe a little more should be possible but usually they can sew what ever fits under the foot. But without knowing more details about the machine (subclass f.i.) we only can guess. But belts are not a problem at all.

Thread guide is not original but should not be an issue cause they were used on the later 212 models as well. To start with he timing marks - when the timing marks line up the thread take up lever should be it is upper position - can you confirm that? Read page 21 in the manual I linked above. Your check spring is too low, there should be a curved rest behind the tension unit held by a screw which you can reach from the right side of the tension unit - see page 15 of the manual. Also make sure your safety clutch in engaged (if machine has one) - see page 22 Thats what I would start with.

check the the post #3 and the linked PDF in it https://leatherworker.net/forum/topic/84610-looking-for-a-manual-for-my-adler-467-fa-373-g2hp/?_fromLogin=1

I´m pretty sure this is an excellent machine - but IMO less is more on the long view. Of course if you have a large volume output all the bells and whistles makes the sewing live a lot easier but if not you have to ask your self when will it start earning money. And keep in mind this is not a "simple" patcher which you can service by your self (and some even struggle with this). I only can guess but I´m almost certain machines like this require to turn them in for service. So it´s not that you pay just the machine service and parts are cost factors too. You often see folks here and elsewhere who buy (even cheaper) machines and sell them soon again. Reasons may vary but I´m sure some just bought too much machine for what they really need. my 2 cents

Skipping stitches are of then the result of a too high set needle bar or hook too far away from the needle. Anyway - it may help when you post pictures of the situation on your machine or post a YT video with some explanations. Does this 111 manual (Single needle w reverse) help you - maybe? You find mechanics instruction from page 15 onward. I have the manual in better quality too but I had to compress it to upload it here. Manual Singer 111G156_compressed.pdf

I have an almost complete 7-32 or 7-33 (I guess) in very good shape that I could take apart - I wanted to set it up but most likely don´t have the time the next few month and it takes quite space... so... If you don´t mind please post some pictures of your machine and also the sub class.

needle bar height could be an issue too. Maybe it is set a little bit too high.

Haven´t yet seen a 42 in person but the machine looks like a beefed up Singer 16 so I would guess some sort of Singer 16 needle plate could fit but depends on what feed dog you have installed. Maybe worth checking with this seller and compare measures: https://www.ebay.com/itm/303485230634 Just a guess!

not sure if Singer 16 NB are still available - if not look for one from a different model with same diameter and similar length or longer length. I think a Singer 31 / 31K bar should work - maybe you have to shorten it. If you order a 31K bar (or similar) make sure you buy the needle holder with it. I replaced a NB on a 34K with a Singer 17 NB a few years ago. https://leatherworker.net/forum/topic/66729-singer-needle-bar-i-could-use-some-help/

not possible - when you look at the toothed presser foot and understand how the machine is feeding the material you will notice why.

why do you want to order sewing thread overseas? Ya have no thread in down under?

bending the hook tip is never a good idea. It may break and it does not solve the real problem. shifting the hook toward the needle usually requires loosening the bevel gear on the horizontal drive shaft and moving the hook saddle toward the needles. Should be approx the same as mentioned in the 227 manual. I`m not sure but IIRC the 345 hook saddle is held by 1 or 2 screws from the left or right side (really not sure)

I once owned a 345 but do not recall all details. So I would probably look into a Consew 227R manual. I´m sure you will find a lot of similarities. https://www.manualslib.com/manual/1231775/Consew-223.html#product-227

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THANK YOU VERY MUCH FOR THIS!!! Very helpful!!! I have my 307G2 for some years already but it is the only machine that never required any major adjustments. So you really dived into it and explained it very well. Thanks a lot for sharing this!!! Maybe a moderator can upload the pictures directly into the above thread so they are safe for the future

Maybe use use the cap part as bottom stud. Know what I mean? Other than that DOT makes this cap: https://www.dotfasteners.com/durabletm-caps-2267.html

I´m pretty sure I have the 453 screw but I have to dig for it. I also have an OEM Singer shuttle. Shipping from Germany to France is not crazy expensive. Send me a PM if interested.

are you using a leather needle instead round point - maybe?

$100 for both? So $50 each? Go back and buy the 2nd one too - asap!

The Adler 220 and SEIKO JW8BL are similar machines and they share parts with the Singer 144 / 145 - you can check for parts f.i. on the College Sewing website. https://www.college-sewing.co.uk But I´m sure you will find dealers for these parts in the US as well but the CS website gives you a good idea how much conversion parts would cost.