Lift That Engine...

Have you ever wondered?

A point pondered and drawn by Lanny

Some of us occasionally have
the need to lift an engine, possibly with the transmission attached.
How often have do we use a lifting plate that attaches to the
intake manifold by four 5/16th bolts? How about if that manifold
is made of aluminum? Have you ever thought about just how much
weight is riding on those four little bolts screwed into aluminum.
I know I think about it every time I do it.

Well, I guess someone else thought about it too. In the July
issue of Car Craft, 2002 there is a letter to the editor asking
this very question. The answer is pretty involved. For those
of you that are mathematically inclined the answer can be found
using the following equation:

As=0.7854(Dbsc-0.9743/n) 2

Got that? Now how about that in English?

First lets assume that you run the bolt in at least twice the
depth of its diameter. In the case of a 5/16" bolt that
would be 5/8". Lets also assume that you are using a grade
5 bolt, the most common type. When you torque the bolt you
add a certain amount of stress to it, lets say that is about
20%. The tensile strength of a grade 5 bolt is 120,000 lbs
psi. That means that if the bolt was 1 inch thick it should
hold 120,000 pounds. But, of course it is not. A 5/16" bolt
would hold “only” 6300 lbs. and if we subtract
the 20% torque load we place on it, only about 5000 lbs. That’s
one bolt, we have four. So, assuming that all is well, we should
be able to hold about 20,000 pounds before the bolts would
fail. According to the article that applies even in the case
of an aluminum manifold.

Most of the engines I work with weigh a lot less than that,
so I guess I will worry about something else.

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