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                                                                   EXHIBIT 99(a)



         FOURTH AMENDMENT (this "Amendment"), dated as of July 23, 2001, between
NEWCOR, INC., a Delaware corporation (the "Company"), and MELLON INVESTOR
SERVICES LLC, a New Jersey limited liability company, formerly known as
CHASEMELLON SHAREHOLDER SERVICES, L.L.C., (the "Rights Agent"), to the RIGHTS
AGREEMENT, dated as of January 12, 2000, between the Company and the Rights
Agent (as amended, the "Rights Agreement").

         A. Reference is made to the Rights Agreement. Capitalized terms used
but not otherwise defined herein have the meaning assigned to them in the Rights
Agreement.

         B. The Company and the Rights Agent have agreed to amend certain
provisions of the Rights Agreement.

         Accordingly, the parties hereto agree as follows:

         Section 1. Amendment to Section 1(a). Section 1(a) of the Rights
Agreement is hereby amended by replacing the parenthetical language immediately
after "outstanding" in the third line thereof with the following:

         "(or with respect to Exx Inc. and David A. Segal, together with all
         their Affiliates and Associates, more than 34.9% of the shares of
         Common Stock then outstanding)".

         Section 2. Rights Agreement. Except as specifically stated herein, the
Rights Agreement shall continue in full force and effect in accordance with the
provisions thereof. As used therein, the terms "Agreement", "herein",
"hereunder", "hereto", "hereof" and words of similar import shall, unless the
context otherwise requires, refer to the Rights Agreement as modified hereby.

         Section 3. Governing Law. This Amendment shall be deemed to be a
contract made under the laws of the State of Delaware and for all purposes shall
be governed by and construed in accordance with the laws of such state
applicable to contracts made and to be performed entirely within such state.

         Section 4. Counterparts. This Amendment may be executed in any number
of counterparts and each of such counterparts shall for all purposes be deemed
to be an original, and all such counterparts shall together constitute but one
and the same instrument.



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         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the day and year first above written.

                               NEWCOR, INC.


                               By:      /s/ James J. Connor
                                   ---------------------------------------------
                               Name:    James J. Connor
                               Title:   President & CEO


                               MELLON INVESTOR
                               SERVICES LLC, as Rights Agent


                               By:      /s/ Kathryn M. Gallagher
                                   ---------------------------------------------
                               Name:    Kathryn M. Gallagher
                               Title:   Vice President