How  to deal with a publication having its own title (Sefer Sam  Hayim)  but consisting of part(s) of  a  larger work,
"Sefer  Tokhahat Hayim"?

The  rule  dealing  with  such  a situation is 25.6A1:
"If  a separately cataloged part of  a work has  a title of  its own, use the title of  the part by itself as the uniform title."
So the uniform title (240) in the bib record will be "Sam Hayim."

The fact that we know "Sam Hayim" is part of "Tokhahat Hayim" is brought out  in  the authority record for  the uniform title (not the  bib record).  As rule 25.6A1 goes on  to  say, "Make a *see* reference from the heading for  the whole work  and  the title of the part as a subheading of the title of the whole work."  So the NAR will look somewhat like this:
          Palache ...$tSam Hayim
          x  Palache ...$tTokhahat Hayim.$pSam Hayim

The tricky part in this example may  seem  to  be  the  fact that it was (presumably) not Palache himself who called this
particular "separately cataloged part of  the work" by  the  name  "Sam Hayim".  But that's irrelevant as  far  as  the application of  the rule is concerned.  Since the piece in hand is by Palache and  is called "Sam Hayim," the rule applies.

Based on the evidence so  far presented, LC  would make a 246 30 for this record for the "Sam Hayim" portion of  the title  proper.  This access  point  is required by  RI  21.30J,  p.  11:  "When  a  title  proper  begins  with  a  separable statement  of  responsibility that is omitted from the uniform title ...  , make  an additional added  entry  for  the  title without  the  initial  statement of responsibility."  Here, what we've omitted is not  a  statement of responsibility, but  the introductory word  "Sefer":  but the application of the RI  is  the same.  (Properly speaking,  we are not tracing "the uniform title"; we  are tracing something  that just happens to be identical with the uniform title.)