Re: Bolting the Front Crossmember
There is WAY too much confusion here! Folks are trying to solve problems that aren't even problems! As I said initially it's no big deal. I'll attempt to clarify several points.
1. The top six holes (three on each side) are already countersunk in the frame rails so the rivet heads would be flush with the top surface of the rails. This is necessary whether it be rivets or bolts.
2. As mentioned but not explained, due to the flexing of the frame the load on those fasteners are shearing loads or pressures. That is simply the two adjoining parts wanting to slide in opposing directions. Clamping pressure from properly tightened grade 8 bolts cannot fully constrain that motion the way properly installed rivets do.
Ford went through several iterations in the design and methods early on. For the vast majority of production the punched rivet holes were considerably larger than the shank of the rivets used. However the rivets were red hot in their entirety when inserted and set so the shanks swelled and fully filled the pockets. This eliminated the possibility of lateral shifting at the joints.
3. With bolted joints, once there is circumstance where the shear force is strong enough for one or more fastening points to shift from their initial position (even a few thousandths) it/they will do so again. Each time it will require slightly less force to do so. that does not mean a bolt is loosening or stretching. The slight abrasion will begin to form a path for that motion which will increase over time. As one or more fastening points do this it places more pressure on other fastening points that had previously held steady and the issue begins to spread.
3. Nobody has suggested that good quality self locking nuts will back off so keep the darn Loctite on the shelf!
4. With all this said, there is no scenario where there will be any significant failure. Nothing is going to fall apart! There is not enough range of motion to actually shear a bolt. It's highly unlikely that you would EVER find a bolt that feels loose. All that will occur are subtle squeaks as noted in my first post. It SHOULD take years and/or many miles to reach any level of annoyance and even then, only if you keep other improper squeaks and rattles at bay so this one stands out.
Not a big deal.
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