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Pulling an engine from the rafters

To: shop-talk@Autox.Team.Net
Subject: Pulling an engine from the rafters
From: Lee Daniels <DANIELS@alchem.chem.tamu.edu>
Date: Tue, 11 Aug 1998 11:41:51 -0500
The recent talk about engine hoists prompted me to talk to a friend (who is
a civil engineer) concerning his use of his rafter+comealong method of
pulling engines (from his TR4 and MG Midgets).  I plan to "borrow" his 
garage to do a clutch job on an MGB.  Anyway, here's his description of 
how he designed the setup:

------------------------------------------------------------------------------
     I did a very interesting (only to a structural engineer)
     analysis of the rafter system, modelling it as a beam on
     elastic foundation... this allowed me to estimate how much
     load would be transferred to each rafter, which depends on
     the relative stiffness of the 2x6 tee-beam I bolted to the
     ceiling joists (they are not rafters).  It is a rather
     technical exercise, but was fun for me. 

     The essence of the problem is the relative stiffness of the
     joists (2x12x20ft or so, simply supported beams) to the load
     at the point in question, compared to the stiffness of the
     spreader beam (I used two 2x6, in a Tee section).  If the
     tee beam is very flexible, it does not do a very good job of
     transferring load to the adjacent joists.  So, you have to
     calculate the joist stiffness, then design an appropriately
     stiff spreader beam, then determine how it loads adjacent
     joists. 

     I was designing mine for safe load of 750 pounds, but had to
     cheat a bit. It might exceed allowable stress a bit if I
     pull my Chevy 350 engine, but should still hold up. 

     -------------------------------------
     Ray W. James, P.E., Ph.D.
     Texas Transportation Institute
     Civil Engineering Department
     Texas A&M University
     College Station, TX 77843
     Phone (409)845-7436; Fax (409)845-3410
     E-mail: r-james@tamu.edu
     Date: 8/11/98   Time: 9:26:23 AM
     -------------------------------------
------------------------------------------------------------------------------

 Lee M. Daniels             Laboratory for Molecular Structure and Bonding
 daniels@tamu.edu           Texas A&M University
 '74 TR6  '77 MGB           http://acs.tamu.edu/~lmd1191

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