533 rescued on its way to the dumpster sews a wonderful straight stitch but clunks if asked to ZZ. My granddaughter has it and has been told to use it as it is unless her stepfather (my son) wants to deal with it. I don't. 639 Touch and Sew may become a Touch and Throw. The black metal spring that holds the bobbin holder in place isn't seating right and doing its job. I want this one to sew badly, but so far no luck. The 1978 MW (made by Juki) sews wonderfully, both SS and ZZ. So I'm batting 500 here. 1 1/2 out of three plastic machines are functional. All my metal machines do exactly what they are supposed to.