Seiko STW-8B needle bar rock mechanism

[Joanah08]

Hello all,
Does anybody enjoy technical challenges?
My Seiko STW-8B has developed some movement in needle bar. The needle bar, and the inner foot behind it, as well as the feed dog underneath, move backwards and forwards a couple of millimetres, and slight sideways movement too. It means that the needle is easily deflected and snapped in thick materials, so the timing has to be corrected more often.

With the side of the machine open, moving the needle bar by hand, I can see the needle bar rock mechanism moving forwards and backwards, hinging at the top (green arrow pic 2). 

With the machine tipped backwards, whilst slowing turning the hand wheel, the piece outlined in red (pic 3), I think it's called the 'feed driving eccentric connection', is the only section to be moving side to side as well as in the expected circular motions. I can wobble it left and right. The movement here seems to be at the joint with the blue arrows (pic 4), which is amplified at the other end of the component, resulting in sideways movement relative to the adjacent pieces, labelled with red arrows (pic 4). Looking at the feed driving eccentric connection from the LHS (pic 5), it sits around a grey circular piece, with a gold circular piece inside that. It appears that the grey piece moves left and right relative to the gold piece, at the yellow arrow. 

If I were to replace the feed drive eccentric connection, would that stop the excess movement in the needle bar, or are the 2 things unrelated (and therefore 2 problems?!). Has anyone done this particular fix before? In theory it looks like 5 or 6 screws could be loosened to release my proposed section, but if I mess it up then I am in trouble. I also haven't found where to source a spare part from yet.

Thank you very much for reading and if you would like to make a comment, I'd love to hear it.
Joanah

[Michiel]

Hello joanah,
This play is very common in old machines.
Usually it is due to play in different joints (which add up).
If you have the impression that there is one joint that has more play than the rest you might indeed consider addressing that one (but usually the play is in several places).
It is also a question of whether only the part you want to replace is worn, or also the shaft it rotates on. (Often one of the two parts is of a softer material, but how that is here I don't know).
I bought a lathe and milling machine to possibly fit new parts but haven't gotten around to it myself yet