We just traded into two 158-17xxx Kenmore ZZ with cam machines. One really used, dirty and gummed up, the other in much nicer cosmetic condition and less used. Both are now cleaned, serviced and initially tested. Both are soooooooo very quiet compared to the same vintage ( early 70s ) Singers. Both are all metal, no plastic 'cept the cams.
I'm also testing a Kenmore 158-15000 cam machine with some additional cams that we also got during the trade. This machine isn't quite as good as the others, but it's still all metal and far better than the same vintage Singers.
We've got several more and now comes the hard part ........ Deciding which "ONE" to keep. All the others must be adopted out.
(( Wifie just read this and snickered .... think she knows something I don't? ))