I know you have explained these concepts repeatedly on the Barn and I am sure you are correct; but for present purposes can you briefly explain how these concepts are reconciled with the warnings we see in the
Bulletins that chassis parts should be straightened while cold, not heated,,,,
First let me start by offering that someone suggesting
it took the frame 80-odd years to sag is like seeing a flat tire on a Model-A wheel and suggesting it took 80-odd years for the tire to go flat!
In real world some of us live in, we know that just isn't the case is it?
Now you refer to the Service Bulletins as warning against using heat on chassis parts. I fail to recall it specifically mentioning using heat on a frame rail but maybe if you have time, you can PM me the page number(s) where I can read it in the proper context.
To answer specifically about the frame rails, we need to start from the very beginning. The frame rail was stamped cold however it was formed in a specific way through known engineering techniques. The frame rail steel is much like a rubber band that has been allowed to normalize. You can stretch the rubber band however when you do, it
will get thinner during the process. The thinner area is always weaker than a non-stretched area. This same mindset applies to the steel in a frame rail too. Unlike the rubber band, the metal does not have the ability to return to its' former state. Therefore when someone tries to bend the metal back to the original shape, the metal can only stretch in another area. Now we have created two structurally weaker areas. Now I will quickly agree that our Model-A's will likely never see the same adverse conditions they once did however isn't that a lame excuse to perform a substandard repair, ...especially when doing it correctly involves the same amount of labor with a superior end result?
The comment about using heat likely comes from "He said / She said" mindset where someone who was uneducated about the process made a comment that seemed believable, and now others have accepted it as fact. I have listened for years about some saying Ford parts have Vanadium in the steel and so it cannot be heated. When the truth is known, there is only trace amounts of Vanadium and the reason it was used was as a rust-prevention method, --not as a strength enhancer. The percentage of the Vanadium used is not of enough quantity to add any significant amount of extra strength.
Next, using heat on many parts can be compared to doing bodywork. Just because you purchased a gallon can of Bondo does not mean you must use the entire can on the body in one application. It is meant to be used in moderation and by only the amount that is truly needed. The same mindset applies about shrinking metal. There is not any need to heat the frame rail any hotter than it takes to make steam rise when water is placed on the hot surface. Just like using too much Bondo to fill a dent, turning the frame metal "red hot" is only abusing the metal and serves no useful purpose. Only an unskilled craftsman would do such a thing solely due to ignorance about the task he is trying to accomplish. One of the main reasons why we are involved in this type of forum is to gain knowledge on how to do something better and expand our abilities. For the folks who have tried the method of heat shrinking a bent frame (--or wheel, or sheetmetal), I have yet to hear anything but positive feedback from their results.
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