<PAGE>

                                                                   EXHIBIT 10.52

                          AMENDMENT TO CREDIT AGREEMENT

         THIS Amendment to Credit Agreement (this "AMENDMENT") dated April 2,
2004, is between ALLIS CHALMERS CORPORATION, a Delaware corporation (hereinafter
referred to as "BORROWER") and WELLS FARGO ENERGY CAPITAL, INC. ("LENDER").

                                    RECITALS:

         A. Lender and Borrower entered into that certain Credit Agreement dated
as of February 1, 2002 (as amended, the "AGREEMENT), in conjunction with that
certain senior secured credit facility from Wells Fargo Credit Inc. ("SENIOR
LENDER") to STRATA Directional Technology, Inc. ("STRATA") and certain senior
secured credit facility from Senior Lender to Jens' Oil Field Service, Inc.
("JENS", Jens and Strata are herein sometimes collectively, "GUARANTORS") each
dated February 1, 2002, as same have been amended from time to time
(collectively, the "SENIOR CREDIT FACILITY").

         B. Senior Lender has agreed to enter into amendments under each Senior
Credit Facility with each of Jens and Strata dated as of the same effective date
of this Amendment (collectively, the "SENIOR LOAN AMENDMENTS").

         C. Borrower's defaults under the Senior Credit Facility as more
particularly described under the Senior Loan Amendments have caused an Event of
Default under the Agreement (the "DESIGNATED DEFAULT").

         D. Borrower has requested that Lender, among other things, waive the
Designated Default, agree to extend the Maturity Date under the Agreement and
consent to the amendments to the Senior Credit Facility as set forth in the
Senior Loan Amendments, including extending the maturity of the Senior Credit
Facility to February 1, 2006. Lender has agreed to do so, subject to the terms
and conditions contained herein.

         E. Borrower and Lender now desire to enter into this Amendment on the
terms set forth herein.

         NOW, THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto agree as follows:

                                    ARTICLE 1

                                  GENERAL TERMS

         Section 1.1 TERMS DEFINED IN AGREEMENT. Except as may otherwise be
provided herein, all capitalized terms which are defined in the Agreement, as
amended, have the same meaning herein as therein, all of such terms and their
definitions being incorporated herein by reference.

<PAGE>

         Section 1.2 CONFIRMATION AND EXTENT OF CHANGES. All terms set forth in
the Agreement shall remain unchanged except as otherwise specifically provided
in this Amendment. It is hereby confirmed that the term "AGREEMENT" includes the
Agreement as amended by this Amendment.

                                    ARTICLE 2

                              AMENDMENTS AND WAIVER

         Section 2.1 AMENDMENT TO SECTION 1.01. Effective as of the date hereof,
Section 1.01 of the Agreement is hereby amended to delete the existing
subsection (b) and insert in lieu thereof subsection (b) as follows:

                  "(b) VOLUNTARY REPAYMENT. Interest shall be due and payable as
                  provided in the Note. Notwithstanding any provisions in the
                  Term Note to the contrary, the outstanding principal under the
                  Term Note shall be due and payable in installments as follows:
                  (i) $400,000 on April ___, 2004, (ii) $25,000 on the first day
                  of each month until the Maturity Date, commencing May 1, 2004,
                  and (iii) the final payment shall be due and payable on
                  January 31, 2006 (the "MATURITY DATE"), in an amount equal to
                  the unpaid principal balance of the Term Note as of such date,
                  together with all accrued but unpaid interest and outstanding
                  expenses."

         Section 2.2 WAIVER OF DEFAULT. Borrower is in default of the following
provision of the Credit Agreement (the "DESIGNATED DEFAULT"): Subsection 6.01(i)
with respect to cross-default to the Senior Credit Facility. Upon the terms and
subject to the conditions set forth in this Amendment, Lender hereby waives the
Designated Default. This waiver shall be effective only in this specific
instance and for the specific purpose for which it is given, and this waiver
shall not entitle Borrower to any other or further waiver in any similar or
other circumstances.

         Section 2.3 NO WAIVER OF RIGHTS. Acceptance by Lender of any payments
or property hereunder or waiver by Lender of the Designated Default pursuant to
the terms of this Amendment shall not be construed to be a waiver of any other
default or a waiver of any rights of Lender against Borrower in accordance with
the Agreement, or any other Loan Documents. Borrower acknowledges and agrees
that Lender shall retain all remedies and rights of default and shall be
permitted to exercise and enforce such rights and remedies as provided in the
Agreement.

         Section 2.4 LIMITED SCOPE OF AGREEMENT. Except as otherwise expressly
set forth herein, all obligations of Borrower under the Agreement shall remain
in full force and effect as written and shall be enforceable in accordance with
their respective terms, subject to applicable bankruptcy, insolvency, fraudulent
conveyance, reorganization, moratorium and similar laws affecting creditors'
rights and remedies generally. Borrower acknowledges and agrees that, except as
specifically set forth in SECTION 2.2, Lender has not waived any defaults or
agreed to forbear from exercising or enforcing any rights or remedies it may
have as a result of any other failure by Borrower to comply fully with the
Agreement or the terms of this Amendment.

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         Section 2.5 COMPLIANCE WITH EXISTING LOAN DOCUMENTS; ADDITIONAL
COVENANTS. Unless expressly modified or amended herein, Borrower shall comply
with, and shall continue to be bound by, each of the terms and provisions
contained in the Agreement. In addition, Borrower shall comply with, and shall
be bound by, each of the terms and provisions contained herein.

                                    ARTICLE 3

                         REPRESENTATIONS AND WARRANTIES

         In order to induce Lender to enter into this Amendment Borrower
represents and warrants (which representations and warranties will survive the
execution and delivery hereof and will be deemed for all purposes to be
additional representations and warranties of the Agreement) that:

         Section 3.1 REPRESENTATIONS AND WARRANTIES OF THE AGREEMENT AND THE
LOAN DOCUMENTS. The representations and warranties of Borrower contained in the
Agreement and the Loan Documents and otherwise made in writing by or on behalf
of Borrower pursuant to the Agreement and the Loan Documents were true and
correct when made, and are true and correct in all material respects at and as
of the time of delivery of this Amendment, except for such changes in the facts
represented and warranted, waived or amended by this Amendment.

         Section 3.2 ACKNOWLEDGMENT OF INDEBTEDNESS. Borrower acknowledges that
it is indebted to Lender under the Term Note. The Indebtedness is due and owing
by Borrower pursuant to the terms of the Agreement as amended by this Amendment
without offset, defense or counterclaim.

         Section 3.3 COMPLIANCE WITH OBLIGATIONS. Except for the Designated
Default, Borrower has performed and complied with all agreements and conditions
contained in the Agreement and the Loan Documents required to be performed or
complied with by Borrower prior to or at the time of delivery of this Amendment.

Section 3.4 DEFAULTS. Except for the Designated Default, there exists, and after
giving effect to this Amendment, will exist, no default or Event of Default, or
any condition, or act which constitutes, or with notice or lapse of time (or
both) would constitute an event of default under either the Agreement or the
Senior Credit Facility, Seller's Indebtedness, or any loan agreement, note
agreement, or trust indenture to which Borrower is a party.

                                    ARTICLE 4

                                   CONDITIONS

         Lender has relied upon the representations and warranties contained in
this Amendment in agreeing to the amendments to the Agreement set forth herein
and the amendments to the Agreement set forth herein are conditioned upon and
subject to the accuracy of each and every representation and warranty of
Borrower made or referred to herein, to the performance by Borrower of its
obligations to be performed under the Agreement and the Loan Documents on or
before the date of this Amendment, except to the extent waived herein, and to
the following further conditions:

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         Section 4.1 AMENDMENT DOCUMENTS. This Amendment shall be fully
executed. Senior Lender shall have entered into a consent to this Amendment
consenting to the terms as provided under this Amendment. Guarantors shall have
executed the Acknowledgement and Agreement of Guarantors set forth at the end of
this Amendment.

         Section 4.2 PAYMENT OF OUTSTANDING INTEREST. Borrower shall pay
contemporaneously herewith a principal prepayment in the amount of $400,000,
plus all outstanding interest due and payable plus all of Lender's reasonable
legal fees up through execution hereof associated with the Agreement and the
preparation of this Amendment.

         Section 4.3 OFFICER'S CERTIFICATE. Lender shall have received a
certificate of the officers of Borrower setting forth (i) resolutions of its
board of directors in form and substance satisfactory Lender authorizing
Borrower to execute this Amendment and such other documents to which it is a
party, and (ii) specimen signatures of the officers so authorized.

         Section 4.4 EQUITY INVESTMENT. Lender shall have received satisfactory
evidence of the sale of new equity in Borrower and receipt of an aggregate sales
price of $2,000,000.

         Section 4.5 SENIOR LOAN AMENDMENTS. Senior Lender, Jens and Strata
shall have entered into the Senior Loan Amendments on terms satisfactory to
Lender and all conditions precedent to effectiveness thereunder shall be
completed.

         Section 4.6 AMENDED SECURITY DOCUMENTS. On or before October 1, 2004,
Borrower shall cause Jens to enter into an amendment to the Pledge of Machinery
and Equipment with Lender and Senior Lender to reflect the new maturity date of
obligations under the Senior Loan Agreements and of this Agreement and take such
further action as may be necessary to file and perfect such amendments with the
proper authorities in Mexico.

         Section 4.7 ADDITIONAL DOCUMENTATION. Borrower shall deliver to Lender
such additional approvals, opinions or documents as Lender may reasonably
require.

                                    ARTICLE 5

                                  MISCELLANEOUS

         Section 5.1 LOAN DOCUMENTS. All Loan Documents shall secure the
indebtedness and obligations previously secured by such Loan Documents, as such
indebtedness and obligations are affected by this Amendment (including, without
limitation, the Term Note), whether or not such Loan Documents shall be
expressly amended or supplemented in connection with this Amendment.

         Section 5.2 EXTENT OF AMENDMENTS. Except as otherwise expressly
provided herein, the Agreement, the Loan Documents and the other instruments and
agreements referred to therein are not amended, modified or affected by this
Amendment.

         Section 5.3 RELEASE. Borrower and each Guarantor, by signing the
Acknowledgment and Agreement of Guarantors set forth below, each hereby
absolutely and unconditionally releases and forever discharges Lender, and any
and all participants, parent corporation, subsidiary corporations, affiliated


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<PAGE>

corporations, insurers, indemnitors, successors and assigns thereof, together
with all present and former directors, officers agents and employees of any of
the foregoing, from any and all claims, demands or causes of actions of any
kind, nature or description, whether arising in law or equity or upon contract
or tort or under any state or federal law or otherwise, which Borrower or such
Guarantor has had, now has or has made claim to have against any such person for
or by reason of any act, omission, matter or cause whatsoever arising prior to
and including the date of this Amendment, whether such claims, demands and
causes of action are matured or unmatured, or known or unknown.

         Section 5.4 TITLES OF ARTICLES, SECTIONS AND SUBSECTIONS. All titles or
headings to articles, sections, subsections or other divisions of this Amendment
are only for the convenience of the parties and shall not be construed to have
any effect or meaning with respect to the other content of such articles,
sections, subsections, or other divisions, such other content being controlling
as to the Agreement among the parties hereto.

         Section 5.5 COUNTERPARTS. This Amendment may be executed in two or more
counterparts. It will not be necessary that the signatures of all parties hereto
be contained on any one counterpart hereof; each counterpart shall be deemed an
original, but all of which together shall constitute one and the same
instrument.

         Section 5.6 ENTIRE AGREEMENT. THIS AMENDMENT AND ALL OTHER INSTRUMENTS,
DOCUMENTS, AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH THIS
AMENDMENT EMBODY THE FINAL, ENTIRE AGREEMENT AMONG THE PARTIES HERETO WITH
RESPECT TO THE SUBJECT MATTER HEREOF AND THEREOF AND SUPERSEDE ANY AND ALL PRIOR
COMMITMENTS, AGREEMENTS, REPRESENTATIONS AND UNDERSTANDINGS, WHETHER WRITTEN OR
ORAL, RELATING TO THIS AMENDMENT AND THE OTHER INSTRUMENTS, DOCUMENTS AND
AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH THIS AMENDMENT, AND MAY NOT
BE CONTRADICTED OR VARIED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT
ORAL AGREEMENTS OR DISCUSSIONS OF THE PARTIES HERETO. THERE ARE NO ORAL
AGREEMENTS AMONG THE PARTIES HERETO.


        [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK. SIGNATURE
                               PAGES TO FOLLOW.]



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         IN WITNESS WHEREOF, the parties hereto have caused this instrument to
be duly executed as of the 2ND day of April, 2004.


                                          LENDER:

                                          WELLS FARGO ENERGY CAPITAL, INC.,


                                          By:    /S/ CLAYTON TAYLOR
                                                 ------------------------------
                                          Name:  Clayton Taylor
                                          Title: Assistant Vice President






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<PAGE>

                                      BORROWER:

                                      ALLIS-CHALMERS CORPORATION


                                      By:   /S/ MUNAWAR H. HIDAYATALLAH
                                            ---------------------------
                                            Munawar H. Hidayatallah
                                            Chairman and Chief Executive Officer



                                      S-2
<PAGE>


                   ACKNOWLEDGEMENT AND AGREEMENT OF GUARANTORS

         The undersigned, each a guarantor of the indebtedness of Allis
Chalmers, Inc. ("Borrower") to Wells Fargo Energy Capital, Inc. ("Lender")
pursuant to separate Guaranties each dated as of February 1, 2002 (each a
"Guaranty"), hereby (i) acknowledges receipt of the foregoing Amendment, (ii)
consents to the terms (including without limitation the extension of maturity of
the Term Note and obligation to file amendments to the Pledge of Machinery and
Equipment set forth in the Amendment) and execution thereof; (iii) reaffirms its
obligations to Lender pursuant to the terms of its Guaranty; and (iv)
acknowledges that Lender may amend, restate, extend renew or otherwise modify
the Agreement and any indebtedness or agreement of Borrower, or enter into any
agreement or extend additional or other credit accommodations, without notifying
or obtaining the consent of the undersigned and without impairing the liability
of the undersigned under its Guaranty for all of Borrower's present and future
indebtedness to the Lender.

                                    STRATA Directional Technology, Inc.,
                                    a Texas corporation


                                    By:   /S/ MUNAWAR H. HIDAYATALLAH
                                          ---------------------------
                                          Munawar H. Hidayatallah
                                          Chairman and Chief Executive Officer



                                    GUARANTOR:
                                    Jens' Oil Field Service, Inc.,
                                    a Texas corporation


                                    By:   /S/ MUNAWAR H. HIDAYATALLAH
                                          ---------------------------
                                          Munawar H. Hidayatallah
                                          Chairman and Chief Executive Officer


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