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                                                                    EXHIBIT 3.21

                     Name changed to McCOLPIN-CHRISTIE CORP.

                         CERTIFICATE OF AMENDMENT OF THE

                            ARTICLES OF INCORPORATION

                                       OF

                       McCOLPIN-CHRISTIE CORPORATION, LTD.

                   [To change name to McColpin-Christie Corp.]

     The undersigned, S. L. CHRISTIE and D. G. DINSMORE, hereby do certify that
they are, and at all times herein mentioned have been, respectively, the duly
elected, qualified, and acting president and secretary of McCOLPIN-CHRISTIE
CORPORATION, LTD., a California corporation; and, further, they do certify as
follows:

     FIRST: At a meeting of the board of directors of McColpin-Christie
Corporation, Ltd., duly held on February 20, 1952, at the principal office of
the corporation at 3410 West 67th Street, Los Angeles, California, at which
meeting a quorum consisting of two of the three directors of this corporation
was present and acting, the following resolutions duly were adopted by unanimous
vote:

          "WHEREAS, the board of directors of this corporation deems it to be
     for the best interests of this corporation and of its shareholders that its
     corporate name be changed to McColpin-Christie Corp.,

          "NOW, THEREFORE, IT HEREBY IS RESOLVED, that Article FIRST of the
     articles of incorporation of this corporation hereby is amended to read as
     follows:

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          "'FIRST: That the name of this corporation shall be

               McCOLPIN-CHRISTIE CORP.'

          "RESOLVED, FURTHER, that the board of directors hereby adopts and
     approves said amendment to the articles of incorporation;

          "RESOLVED, FURTHER, that the president and secretary of this
     corporation be, and they hereby are, and each of them hereby is, authorized
     to procure the adoption and approval of said amendment by the vote or
     written consent of the shareholders of this corporation;

          "RESOLVED, FURTHER, that the president and secretary be, and they
     hereby are, authorized and directed to sign, verify, and cause to be filed
     a certificate of the amendment of the articles of incorporation of this
     corporation, all in conformity with the laws of the State of California;

          "RESOLVED, FURTHER, that the president and secretary of this
     corporation be, and they hereby are, and each of them hereby is, authorized
     and directed to perform such acts and to execute such instruments as may be
     necessary or convenient to make the foregoing resolutions fully effective."

     SECOND: Shareholders of McColpin-Christie Corporation, Ltd. holding at
least a majority of the voting power of said corporation consented in writing
that the articles of incorporation of said corporation should be amended in the
manner stated in said resolutions adopted by the board of directors of said
corporation. The following is a copy of the form of written consent signed by
said shareholders of said corporation:

                                       -2-
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                    "CONSENT OF SHAREHOLDERS TO THE AMENDMENT

                       OF THE ARTICLES OF INCORPORATION OF

                       McCOLPIN-CHRISTIE CORPORATION, LTD.

          "WHEREAS, at a meeting of the board of directors of McColpin-Christie
     Corporation, Ltd., a California corporation, duly held on February 20,
     1952, at the principal office for the transaction of the business of said
     corporation at 3410 West 67th Street, Los Angeles, California, at which
     meeting a quorum consisting of two of the three directors of said
     corporation was at all times present and acting, an amendment of the
     articles of incorporation of said corporation was adopted and approved by
     resolutions of said board of directors amending Article FIRST of said
     articles of incorporation to read as follows:

          'FIRST: That the name of this corporation shall be

               McCOLPIN-CHRISTIE CORP.'

          "NOW, THEREFORE, each of the undersigned, being the owner of the
     number of shares of stock of said corporation set down opposite his or her
     signature at the end of this certificate, hereby does adopt, approve, and
     consent to the foregoing amendment of said articles of incorporation, and
     hereby does consent that Article FIRST of said articles of incorporation be
     amended to read as follows:

          'FIRST: That the name of this corporation shall be

               McCOLPIN-CHRISTIE CORP.'

          "Witness the signature of each of the undersigned, and following the
     signature, the date of signing and the number of shares of said corporation
     held of

                                       -3-
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record on the date of signing, all of which shares are entitled to vote upon
amendments of said articles of incorporation of the character of the foregoing
amendment.

<Table>
<Caption>
     "Signatures of Share-                         Date of          Number of
     Holders                                       Signing          Shares Owned
     ----------------------                        -------          ------------
                                                                  
     /s/ S. L. CHRISTIE                                May 3, 1952      2,276
     -------------------------------
     S. L. Christie

     /s/ S. L. CHRISTIE               )                May 3, 1952
     -------------------------------  )
     S. L. Christie                   )                                   800
           and                        )
     /s/ SIGRID CHRISTIE              )                May 3, 1952
     -------------------------------  )
     Sigrid Christie                  )

     /s/ E. E. HUGHES                 )                May 5, 1952
     -------------------------------  )
     E. E. Hughes                     )                                   660
           and                        )
     /s/ FLORA HUGHES                 )                May 6, 1952
     -------------------------------  )
     Flora Hughes                     )

     /s/ GLENFORD J. FOSTER           )                May 2, 1952
     -------------------------------  )
     Glenford J. Foster               )
           and                        )                                   324
     /s/ MARGARET J. FOSTER           )                May 7, 1952
     -------------------------------  )
     Margaret J. Foster               )

     /s/ D. G. DINSMORE                                May 2, 1952        128"
     -------------------------------
     D. G. Dinsmore
</Table>

     THIRD: The total number of shares of McColpin-Christie Corporation, Ltd.
adopting and approving said resolutions of the board of directors that the
articles of incorporation should be amended as stated in said resolutions, and
consenting to the amendment of the articles of incorporation of said
corporation, all as stated and set forth above, is 4,188.

     FOURTH: The total number of shares of McColpin-Christie Corporation, Ltd.
entitled to adopt and approve resolutions of the board of directors that the
articles of incorporation be

                                       -4-
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amended as set forth herein, and entitled to consent to the amendment of the
articles of incorporation as set forth herein is 4,842.

     Dated:  May 22, 1952.


                                             /s/ S. L. Christie
                                             -----------------------------------
                                             S. L. Christie, President


                                             /s/ D. G. Dinsmore
                                             -----------------------------------
                                             D. G. Dinsmore, Secretary

                                       -5-
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STATE OF CALIFORNIA     )
                        )  ss.
County of Los Angeles   )

     S. L. CHRISTIE and. D. G. DINSMORE, first being duly sworn, each for
himself deposes and says: S. L. Christie is, and at all tines mentioned in the
foregoing certificate of amendment was, the president of McColpin-Christie
Corporation, Ltd., the California corporation therein named. D. G. Dinsmore is,
and at all times mentioned in the foregoing certificate of amendment was, the
secretary of said corporation. Each of us has read said certificate of
amendment. The statements contained in said certificate are true of our own
knowledge. The signatures of S. L. Christie and D. G. Dinsmore affixed to said
certificate of amendment are the genuine signatures of the president and the
secretary, respectively, of said corporation.

                                             /s/ S. L. Christie
                                             -----------------------------------
                                             S. L. Christie, President


                                             /s/ D. G. Dinsmore
                                             -----------------------------------
                                             D. G. Dinsmore, Secretary

Subscribed and sworn to before me
me this 22nd day of May, 1952.

/s/ Harold S. Nutter
- --------------------------------------------
Notary Public in and for the County
of Los Angeles, State of California.
     NOTARY PUBLIC
        (SEAL)
My Commission Expires Mar. 20, 1995

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