I think it may be an urban myth, possibly based on somebodies experience of laying down a welded up crank and then retreiving it some time later only to find it was "bent".
I say this because I welded on a cast iron head and it warped .230". I laid it on a shelf and ten years later looked at it and all the warpage had disappeared. Had I not seen that I would have never believed it possible.
A welded crank may have behaved the same way, lending credence to the theorey.
If somebody with another experience to show it DOES cause the crank to bend I'm willing to be educated.
As a point of fact I now store my cranks vertically, hanging by the snout bolt. This takes up much less floor space. Another benefit may be that corrosive particles in the air are less likely to cover the tops of the journals, promoting rusting.
