Replacing cross-members

M

Martinbuilt

Senior Member
Hi.
I'm slowly reviving a '29 business coupe.
While prepping the frame for paint, I noticed that both the front and rear crossmembers are bolted in.
They're not new, but they have been swapped.
I could replace them with grade 8's, or maybe figure out rivets.
I don't need it to be perfectly restored, but I don't want it to come apart either.
Advice welcome.
 
I suppose you could use flat head bolts in places. The heads will be in the way of both fenders and body sills.
You’d be much better off riveting them. Imho
Rivets available various places including JayCee rivets (have to buy a box of 100 but relatively cheap)
 
If you remove the cross members to address the rust I suggest you do one at a time, hold the member in position with the bolts, removing one bolt at a time to rivet that hole. And prime before reinstalling. There will be rust you won't be able to remove any other way.
I think the frame was dipped originally.
 
Martinbuilt said:
Hi.
I'm slowly reviving a '29 business coupe.
While prepping the frame for paint, I noticed that both the front and rear crossmembers are bolted in.
They're not new, but they have been swapped.
I could replace them with grade 8's, or maybe figure out rivets.
I don't need it to be perfectly restored, but I don't want it to come apart either.
Advice welcome.
Click to expand...

I can tell you what I know about swapping crossmembers and let you decide from there. Bolts struggle to hold the crossmembers to the frame rigid enough.
All they manage to do is wallow-out the holes which lets the crossmember move even more.

If a crossmember has been replaced and bolts were used in lieu of rivets, likely you will need to use oversized rivets, -or do as we do and weld the holes solid and re-drill to the proper rivet size. Very time consuming to do that part correctly.

Replacing a crossmember and squaring the frame is not an easy task (...even for those who have done it before and have the proper tooling). And, -it really cannot be done properly with an air hammer. You must use a Rivet gun and a torch. I hope this helps. If you decide to proceed, I will walk you thru with procedures we use and pix to show the basic steps.
 
BRENT in 10-uh-C
I can tell you what I know about swapping crossmembers and let you decide from there.
I know this an old thread, but i have searched for a newer one. I have one frame rail that needs replacing on my 31 tudor. If i lived closer i would bring it to you.
I either need to get the proper tolls to rivet, fid a better frame, or pay someone to do it for me.
I am not afraid of the work, i am sure i could do it, but how much will i have into the tools for a one time use?
Anyway, i would love to hear the correct process.
Thanks
 
There are currently THREE stacked frames for sale on Facebook Marketplace. The pix looks good. All three for $300.


Joe K
 
I just found them sent him a message. thanks waiting to hear. its 300.00 each from the ad, but if they are good, it may be the answer
Thanks
 
What Brent is saying is that the rivets swell when installed and fill in any gaps between the rivets and the holes, thus keeping the parts from moving relative to each other.

He is also saying to use hot rivets. They are softer and deform to fill the holes easier.
 
benbuilder said:
I just found them sent him a message. thanks waiting to hear. its 300.00 each from the ad, but if they are good, it may be the answer
Thanks
Click to expand...

Where there is a significant amount of your labor involved in the transition, "The best is none too good."

I might say at $300 each, check carefully for "best." Nice to have three to compare.

I pick up opposite corners with my fingers across the joint. Thereby doing it "twists" the frame - if you feel ANY movement at $300 that is reason enough to choose the next one. Check all four corners.


Joe K
 
nkaminar said:
What Brent is saying is that the rivets swell when installed and fill in any gaps between the rivets and the holes, thus keeping the parts from moving relative to each other.

He is also saying to use hot rivets. They are softer and deform to fill the holes easier.
Click to expand...

Just to amplify, the rivets themselves are no different hot vs. cold. It’s the way they are installed.

In the little bit of hot riveting that I have attempted (some more successful than others) I’ve found that the quality and rigidity of the backing (aka “bucking”) is a critical part of the process. You MUST have adequate mass on the backing to prevent the riveted pieces from vibrating with the hammer blows. That force needs to be absorbed to deform the rivet, not to vibrate the pieces. I’ve used an old axle with the end sculpted to fit the rivet head standing on a concrete floor, a 6” cube block of steel, and a big anvil as backing.

I researched this a bit ago and found that Model A frames were cold and hot riveted, depending upon when they were built. And the frames were held in jigs. Either hot or cold, the factory used very high capacity, special purpose-built hydraulic “C” presses, not rivet guns, to deform the rivets. Not something your average home shop will have on hand.

There are plenty of frames out there. I’d be hesitant to buy one without inspecting it for frame rail straightness, for twist, and for symmetry (diamond). You can use a 6’ level to check rail straightness, a pair of winding sticks (I have a couple of 7’ lengths of 1x1 tubular steel) for twist, and a good tape measure or trammels to check diagonals for diamond. I needed a new frame this summer and inspected and rejected a lot of frogs before I found the prince.
 
Big hammer said:
Rivets shouldn’t have to fill a hole, they should be snug in the hole, then you just buck the tail !
Click to expand...
For hot riveting applications the holes start out a bit oversized, that way the externally heated (expanded) rivet will fit. For cold application yes the holes can be snug. At least on the frame I installed running board brackets on last weekend the holes were a bit larger than the 5/16” rivets we used. The rivets on the chowdered-up brackets I removed to install the good ones were very tight in the holes, indicating that they had been expanded. I also riveted the actuating arms to the brake cross-shaft, same deal, oversized holes.
 
benbuilder said:
BRENT in 10-uh-C
I can tell you what I know about swapping crossmembers and let you decide from there.
I know this an old thread, but i have searched for a newer one. I have one frame rail that needs replacing on my 31 tudor. If i lived closer i would bring it to you.
I either need to get the proper tolls to rivet, fid a better frame, or pay someone to do it for me.
I am not afraid of the work, i am sure i could do it, but how much will i have into the tools for a one time use?
Anyway, i would love to hear the correct process.
Thanks
Click to expand...

Buy the tooling used, -and then sell it afterwards to recover your investment.



I guess my thoughts on this process are different than others here. I will offer my thoughts on some of this and you can do what seems the best for you;

I feel the hole diameters in both the Frame and Crossmember should be very close to the diameter of the Rivet. In this case, 3/16" or 01875". You don't want a hole size that requires the need of a hammer to get the Rivet pounded into the hole however you should have very negligible 'sloppiness' in the hole. Think of it this way, if you are attaching two structural steel pieces together that have a 1/2" hole, most would agree that you should use a 1/2" bolt, -and not a 3/8" or 7/16" bolt as this will allow the pieces of metal to shift.

In your situation, I would NOT recommend replacing one Rivet at a time. As mentioned above, the hole size in the Crossmember and Frame are supposed to be 3/16 in diameter. Most people that installed bolts generally enlarge the holes to install a 1/4" bolt. That means that hypothetically the Crossmember can move 0.060" in any direction. A 3/16" Rivet will not swell enough (-even when installed hot) to fully fill the oversized hole.

Our method for repairing the hole and installing the Rivet correctly is to use a metal ruler and a scribe, and mark the centerline of the hole in 2 directions extending the scribe line at least an inch outward. Then fill the hole with weld. Grind & metalfinish smooth. Now you should still have the outer scribe lines still remaining on the piece you are working on. Use the ruler to align beside the existing scribe line and remark the scribe line where you now know exactly where the center of the Rivet hole should be. We drill the new hole using an 1/8th drill in the Crossmember holes, and a 3/16th drill in the Frame Rails. Once the Crossmember has been reinstalled in the proper place and clamped securely, use the 3/16th drill to make the corresponding hole in the Crossmember align perfectly with the new hole in the Frame. The benefit is that if you happened to miss-drill a hole in the Frame that is off by a small amount, it can be corrected and no one will likely ever know.


See what you can find used in the way of a 3X or 4X Rivet gun. Most of the bucking bars are pieces that we have made over the years. All that is needed is the mass to cause the Rivet to collapse. It is also worth noting that while a Rivet Gun looks like an air hammer, the Rivet Gun hits much slower, and much harder. The Rivet Gun can be substituted for an air hammer, but the Air Hammer cannot be substituted for a Rivet Gun.
 
The connection of frame members need to be structurally sound. The frame is riveted together and rivets completely fill their holes that makes them efficient fasteners in shear but not so good in tension. Bolts used to replace rivets should have a line fit or slight interference fit in their frame holes to be efficient shear connections. Unlike rivets, bolts can carry tension forces efficiently. So properly fitted Grade 8 bolts are superior to rivets.
 
If you are going to use bolts, do as Bob said and make them a tight fit in the hole. Use grade 8 bolts and nuts and tighten them tight. Consult the recommended maximum torque for the size grade 8 bolts you are using.

My structural engineering class in college discussed bolted connections. The theory is that the shear load is carried by the static friction between the two members. We were tasked with calculating how much shear force could be obtained by a given bolt that was tightened to a given value. The shear value of the bolt itself was not considered.

I suspect that Ford used riveted connections for two reasons. First was the strength of the connection and second was cost.
 
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My dad did rivet work at Kaiser Steel. He riveted several early Ford front crossmembers at home. I've done one, a '34 pickup crossmember awhile back. A second person would have made it a lot easier. Those small rivets cool off really quick so the more hands the better. I don't recommend just jumping in on your crossmembers. Practice first, start off with a rivet that's 1 1/2 times the thickness you need on some spare metal and adjust the length of the rivet until you end up with nice looking rivet heads. The worst thing is not having a straight shot at driving the rivet. A straight shot on a rivet was easy to do not so much on a rivet you could barely get at. I'd screwed up a couple of them on the front and had to redo them until I was happy with them. Hopefully when they ground and drilled the old rivets out, they didn't destroy their original sized holes. I grind the original rivet heads down until they were turning red, just before I reached the frame metal. Then I center punched the rivet with and drill it with a slightly smaller diameter, but don't drill clean through it, drill it just the thickness of the frame and crossmember. That gives the punch something to hammer against without expanding the rivet where it's been drilled. The rivet pops right out leaving the perfect original hole.
 
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Can someone post pictures of installed rivet heads? I assume that they aren't completely flush with the top of the frame rails but protrude a bit. What do properly installed rivets look like? Thanks, everybody!
 
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