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TedSlick TedSlick is offline
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Join Date: Apr 2002
Location: So.Cal
Posts: 266
Garage
Quote:
Originally posted by 125shifter
I'll second the comealong idea. Just make sure your rafters can handle it, most can. There should be a lifting lug near the rear of the engine and use the mustache bar at the front to run a chain or strap through so you can lift it level.
Can the rafters handle it? Try a quick calculation as a sanity check?...

The worst place to hang the engine (point load) would be at the center point of the span, so do the calc at that (worst case) point. Formula would be:

PxL/4

P=load (say 500lbs. for a 911 engine)
L=span of joist in inches

For a 20 ft. span (240 inches)...assuming the rafter has no other vertical loads on it:

(500 lb x 240 in)/4 = 120,000/4 = 30,000 in-lb

Divide this result by 'S' value for the joist size:

2x6 = 7.56 cu. in.
2X8 = 13.14
2X10 = 21.39
2x12 = 31.64

For a 2x8 for example: 30,000/13.14 = 2,283 psi (max. bending stress on the joist created by the engine load)

Once this value is known, look at the wood quality to see if it can handle this amount of stress. Assume for a garage rafter you have decent No. 2 wood which has an allowable bending stress of ~1,450 psi. Beam WON'T hold, in theory, since 2,283 > 1,450.

However, if it were a 2x10: 30,000/21.39 = 1,402 psi
Beam WILL hold, in theory, provided there are no other loads on the beam. If you hang the engine closer to either support point, the situation improves as you get closer to the support.

This is likely simplifying your actual conditions, but try it as a sanity check. In my case, my wimpy 2x6x20ft rafters are useless. I do the HF hydraulic cart thing.
Old 01-28-2004, 08:57 AM
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