EXHIBIT 5.1

                     [Weil, Gotshal & Manges LLP letterhead]

                                  May 7, 2007

Altra Industrial Motion, Inc.
American Enterprises MPT Corp.
American Enterprises MPT Holdings, LLC
Ameridrives International, LLC
Boston Gear LLC
Formsprag LLC
Inertia Dynamics, LLC
Kilian Manufacturing Corporation
Nuttall Gear L L C
Plant Engineering Consultants, LLC
TB Wood's Corporation
TB Wood's Enterprises, Inc.
TB Wood's Incorporated
Warner Electric LLC
Warner Electric Technology LLC
Warner Electric International Holding, Inc.
   c/o Altra Industrial Motion, Inc.
   14 Hayward Street
   Quincy, Massachusetts 02171

Ladies and Gentlemen:

          We have acted as counsel to Altra Industrial Motion, Inc., a Delaware
corporation (the "COMPANY"), the guarantors listed on Schedule I hereto
organized under the laws of the State of Delaware (the "DELAWARE GUARANTORS"),
the guarantors listed on Schedule I hereto not organized under the laws of the
State of Delaware (the "NON-DELAWARE GUARANTORS" and together with the Delaware
Guarantors, the "GUARANTORS"), in connection with the preparation and filing
with the Securities and Exchange Commission pursuant to the Securities Act of
1933, of a Registration Statement on Form S-4 (the "REGISTRATION STATEMENT"),
with respect to the issuance by the Company of $105,000,000 aggregate principal
amount of 9% Senior Secured Notes due 2011 (the "NOTES") under an Indenture,
dated as of November 30,



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Page 2


2004, as amended by the First Supplemental Indenture, dated as of February 7,
2006, the Second Supplemental Indenture, dated February 8, 2006, the Third
Supplemental Indenture, dated April 24, 2006, the Fourth Supplemental Indenture,
dated March 21, 2007 and the Fifth Supplemental Indenture, dated April 5, 2007
(the "INDENTURE"), among the Company, the Guarantors and The Bank of New York,
as trustee (the "TRUSTEE"). The Notes are to be unconditionally guaranteed on a
senior secured basis by each of the Guarantors pursuant to guarantees contained
in the Indenture (the "GUARANTEES").

          In so acting, we have examined originals or copies (certified or
otherwise identified to our satisfaction) of the Registration Statement, the
Indenture, the form of Note and Guarantees set forth in the Indenture and such
corporate and limited liability company records, agreements, documents and other
instruments, and such certificates or comparable documents of public officials
and of officers and representatives of the Company and Guarantors and have made
such inquiries of such officers and representatives, as we have deemed relevant
and necessary as a basis for the opinions hereinafter set forth.

          In such examination, we have assumed the genuineness of all
signatures, the legal capacity of all natural persons, the authenticity of all
documents submitted to us as originals, the conformity to original documents of
all documents submitted to us as certified, conformed or photostatic copies and
the authenticity of the originals of such latter documents. As to all questions
of fact material to these opinions that have not been independently established,
we have relied upon certificates or comparable documents of officers and
representatives of the Company and Guarantors. We have also assumed (i) the
valid existence and good standing of each Non-Delaware Guarantor and the
Trustee, (ii) that each Non-Delaware Guarantor and the Trustee has the requisite
limited liability company or corporate power and authority to enter into and
perform its obligations under the Indenture and (iii) the due authorization,
execution and delivery by each Non-Delaware Guarantor of its respective
Guarantee. In addition, we have assumed that the Notes and each Guarantee will
be executed and delivered by an authorized officer of the Company or respective
Guarantor, as the case may be, substantially in the form examined by us.

          Based on the foregoing, and subject to the qualifications stated
herein, we are of the opinion that:

          1. The execution, delivery and performance of the Notes by the Company
have been duly authorized by all necessary corporate action on the part of the
Company. The Notes, when duly and validly executed and delivered by or on behalf
of the Company in accordance with the terms of the Indenture and as contemplated
by the Registration Statement and duly authenticated by the Trustee, will
constitute the legal, valid and binding obligations of the Company entitled to
the benefit of the Indenture, and



May 7, 2007
Page 3


enforceable against the Company in accordance with their terms, subject to
applicable bankruptcy, insolvency, fraudulent conveyance, reorganization,
moratorium and similar laws affecting creditors' rights and remedies generally,
and subject, as to enforceability, to general principles of equity, including
principles of commercial reasonableness, good faith and fair dealing (regardless
of whether enforcement is sought in a proceeding at law or in equity).

          2. The execution, delivery and performance by each Delaware Guarantor
of its Guarantee of the Notes have been duly authorized by all necessary
corporate or limited liability company action, as applicable, on the part of
such Delaware Guarantor. The Guarantees of each of the Guarantors, when duly and
validly executed and delivered by or on behalf of such Guarantors in accordance
with the terms of the Indenture and as contemplated by the Registration
Statement, and duly authenticated by the Trustee, will constitute the legal,
valid and binding obligation of such Guarantor, enforceable against such
Guarantor in accordance with its terms, subject to applicable bankruptcy,
insolvency, fraudulent conveyance, reorganization, moratorium and similar laws
affecting creditors' rights and remedies generally, and subject, as to
enforceability, to general principles of equity, including principles of
commercial reasonableness, good faith and fair dealing (regardless of whether
enforcement is sought in a proceeding at law or in equity).

          The opinions expressed herein are limited to the corporate and limited
liability company laws of State of Delaware, the laws of the State of and New
York and the federal laws of the United States. We express no opinion as to the
effect on the matters covered by this letter of the laws of any other
jurisdiction.

          The opinions expressed herein are rendered solely for your benefit in
connection with the transactions described herein. Such opinions may not be used
or relied upon by any other person, nor may this letter or any copies hereof be
furnished to a third party, filed with a governmental agency, quoted, cited or
otherwise referred to without our prior written consent.

          We hereby consent to the use of this letter as an exhibit to the
Registration Statement and to any and all references to our firm in the
Prospectus which is a part of the Registration Statement.


                                        Very truly yours,

                                        /s/ Weil, Gotshal & Manges LLP


                                   SCHEDULE I



GUARANTOR                                     JURISDICTION OF INCORPORATION
- ---------                                     -----------------------------
                                           
American Enterprises MPT Corp.                           Delaware
American Enterprises MPT Holdings, LLC                   Delaware
Ameridrives International, LLC                           Delaware
Boston Gear LLC                                          Delaware
Formsprag LLC                                            Delaware
Inertia Dynamics, LLC                                    Delaware
Kilian Manufacturing Corporation                         Delaware
Nuttall Gear L L C                                       Delaware
Plant Engineering Consultants, LLC                      Tennessee
TB Wood's Corporation                                    Delaware
TB Wood's Enterprises, Inc.                              Delaware
TB Wood's Incorporated                                 Pennsylvania
Warner Electric International Holding, Inc.              Delaware
Warner Electric LLC                                      Delaware
Warner Electric Technology LLC                           Delaware