My 431G came with a messed up zigzag needle plate. Someone had drilled it to accommodate a flat-head screw.
Replacement needle plates for Singer 431G machines are extremely hard to find.
I successfully modified a needle plate from a Singer 700 series machine to fit my 431G.
I ordered a Singer 174198 needle plate from eBay. The ad said it fit models: 750, 756, 758, School 417, 611, 719, 775, and 776.
The plate is very similar to the 431G plate. The holes are in different locations and there is additional material on the back side of the plate. The feed dog slots are also just slightly smaller than the 431G plate.
431G plate (left), 174198 plate (right):
Here is a picture of the plates stacked together.
Stacked Plates
Here is the new plate with changes marked in black.
Marked Plate
I drilled the new plate and sanded the extra material from the rear edge. I used a small diamond grinding bit to expand the feed dog slots and to make a few final adjustments.
The following pictures show the modified plate which fit into the 431G with the new magnetic mount. This is a hand-made prototype so it has a few imperfections but it worked very well. I intend to use this instead of the zigzag plate that came with my machine.
What about the bobbin cover / slide plate?
I compared a slide plate from a Singer 750 series machine to the plate on my 431G. The plate fits the slot in the 431G but the spring hold down is a different length.
The following image is of a 750 slide plate on my 431G sewing machine. It nearly matches the 431G needle plate curve. The 750 slide plate could be ground to fit better.
The following image shows the underside of a 431G slide plate vs. a 750 slide plate. You would need to use a wider hold-down spring to keep the 750 plate down.
The next two images show the profiles for the two different plates. If you trim the 750 plate to fit the 431G, you will lose most of the finger slot.
My 431G Bobbin Cover Spring is difficult to remove without removing the hook. I laid the 750 spring on the outside to determine the relative position to the 431G spring screw. This indicates it may be possible to use a 750 spring and cover plate on a 431G.
The tab on the 750 slide plate must be modified or it won’t slide backward in the 431G slot. You can set it in from the top but the tab is not deep enough to clear the 431G casting when you try to slide it back.
I found a 421 in the trash last night. It works great but it is missing the slide plate that covers the bobbin case. Do you think the 700 series part would fit? Or any other?? I know it wouldn’t have the curve but I believe I could sand it… thanks!
I think the size and the front curve is the same but the slots in the bottom may be in a different place. If it does fit, I think it may be a little too long. I will check my spare parts and see if I have a 700 series slide plate to try.
I found my parts and tested the fit. I added some photos and descriptions to the original post. You would need a different spring to hold the plate down or find another solution (like magnets or tape). I don’t know if a plate spring from a 700 series machine would fit on a 421 or 431 machine.
You may need to refresh the page at http://midcenturysinger.com/431g/431g-adapting-a-700-series-needle-p/ to see the additional photos.
Let me know if you are able to get it to work. I think you made an amazing find!
I didn’t realize I had a slide plate spring from a 750. I just added some photos to show the potential for using this in the 421 431 machines.