Originally Posted by steihy

As you can see there are differences.
I now have tested both machines with the other's bobbin system. Carefully, hand wheel only at first, then gradually to full speed ss, all lengths. Back to hand wheel, same procedure for zz. I ran them as hard as I could, changing direction and width at full speed. I did some specials, including the satin stitch, full width, full speed. No mechanical misgivings that I could detect. No visual damage to needles, bobbins, cases or needle plates.
Comparing stitch quality in all these modes was not part of this test, to many parameters, but they both sewed without glitches.
Are there other tests you want me to do?
To Rodney: Yeah, gadgetry is grossly underrated.
Stein