Nay
@Bodgeitandscarper that hole is for a set screw that enters from the back for the thread tension assembly.
I've concluded that the spare screw is infact from something else. It's too new. No wear marks on it. It's black.
There is a spare washer though.........
Anyhoo, as Dr Frankenstein is rumoured to have shouted,
IT LIVES!
With the exception of the thread catch spring being mangled a bit and causing issues she's stitching beautifully.
There's a slight hollow sounding hum when doing so but I think that's a result of
1: the bearings being free of what I think was stale beer covering them for who knows how long and
2: scratches on the bearing surfaces from my Dremel wire brushes.
I'm hoping they'll quieten down once the oil works it's way into the nooks and crannies and hopefully the micro scratches will be polished out as time goes by.
A closer inspection of her guts leads me to believe they'll be fine and dandy if I leave as is. Minor dust particles and some blackening of the oil, perfectly normal. I'll not mess with the original Singer mechanics work. Clearly they knew what they were doing.
The thread catch spring is however royally p*****g me off. Mangled somewhat by a previous owner and then some more by me it's failing to keep the thread taught as the needle rises during stitching.
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The dimples on this plate are to allow the spring to move freely when the whole thingymajig is tightened up but because of mini bends in the spring that ain't happening. Sooooooooo, it's either hammer the hell out of the spring to flatten it (the neighbours will love that I'm sure
) orrrrrrrrr buy a new spring. I'll see what happens after annoying the neighbours first.
But yep, it's all looking good so far