Frame front crossmember

[g8t gr&dads A]

I have noticed the front frame crossmember on my '29 Tudor has bolts instead of rivets. Is this telling me that some type of repair/replacement has been made? Was there some common problem with this crossmember back in the day to cause removal of the crossmember? Did any frames come from the factory with bolts? Thanks for any responses.

[BillCNC]

Something was done. They should be rivets.

I removed my front crossmember to straighten the frame rails forward of the cowl. When finished with the repair, I replaced the rivets. Measure your frame out and if it's straight and they didn't redrill the holes larger, install the intended rivets.

Regards
Bill

[Joe K]

No factory bolts but the Model A was subject frequently to "rough" service and frames could and did get "twisted." Bolts were a solution "back in the day."

Rough service I should know. Mine has a slight twist to "port." (Obese drivers?)

Many have removed the bolts, disassembled and straightened the pieces, welded the holes shut, re-drilled (which re-establishes correct alignment) and re-riveted the connections. "How to Restore Your Model A" book I believe has drawings and diagrams showing not only a way to do it, but also the "dollies" and "buck-up" pieces necessary to perform a successful re-rivet.

This has been discussed on the forum ad-nauseam. It's not a task for weak of motivation. Check out https://www.fordbarn.com/forum/showthread.php?p=34921

As to using rivets over other methods? Well rivets work - but they are a LOT of work.

Its a lot easier to weld (and likely even stronger) than to rivet - plus you can do a lot of the work with body-on - although I think a more consistent result might be had if it were off and you can start fresh minus the bolts.

Previous commentary has fallen on both sides of this argument.

It is nice to "keep it original."

Joe K

[Bob Bidonde]

The front crossmember is vulnerable to cracking, and apparently the crossmember in your car was replaced. The factory used hole filling rivets to attach the crossmember, but line fitting bolts (no clearance of bolts in holes) Grade 8 will work as well. Do not weld the crossmember into place because the frame needs to be flexible.

[g8t gr&dads A]

Thanks Bob. Do you know where the cracks tend to be? I was looking at the bolts and do not see any markings on the head, so I'm figuring they are grade 2. Are grade 8 bolts similar in strength to what the rivets were? Installing rivets is something I have not ever attempted.

[rotorwrench]

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Cracks are generally around the center area where the spring load is concentrated. If I were to use bolts, I'd first make certain that the holes fit the bolts as tight as possible. High tensile strength flush head screws can be used for the six locations that had flush set rivets. Even with good fit, bolts tend to work loose faster than properly bucked rivets.

[nkaminar]

Rolls Royce of the same vintage used bolts but they were tapered and the holes were reamed tapered to match.

[Joe K]

The rivets as you buy them are quite soft by design. The action of riveting "cold works" them as you complete the rivet process and they slip below "transition temperature." (About 400F or more commonly taken as "dark")

The strength/hardness is thus a bit "indefinite" for driven rivets. I would guess them at about Grade 5. Meanwhile Grade 8 are designed, constructed, and tested around predictable strengths and defined "stretch." (Bolting holds by virtue of the "clamping" force which occurs during torquing - large bolts such as on turbine casings are typically "stretched" to a definite level by hydraulic machines and the nuts set "hand tight" and the stretch/compression is what results in clamping the casing.)

So, according to this evaluation, Grade 8 bolting is probably superior to riveting by virtue of CONSISTENCY.

Another commentary considered rivets superior because of an inherent flexibility introduced. Note that the purpose of the rivets is to ANCHOR the connection and not allow flexibility AT THE JOINT - as it would be for bolting - as it will be for welding.

Any flexibility of the assembly comes in the structure in its "assembled" form. The fastener system bringing the assembly together is not part of the consideration and would be considered detrimental to consistency of the structure.

As many rodders can attest, the Model A frame is altogether TOO flexible when confronted with the higher torques of a higher powered engine - which leads to "boxing" the frame in attempt to counter the flexibility.

My older brother used to tell tales of his friend "Scab" who rodded his aunt's 1929 Coupe by insertion of a high power V8, possibly a later Ford engine (Deuce Coupe?) One of the trials of that assembly was a tendency for ONE of the front wheels to leave the ground on acceleration - leading to loss of control and soiled underwear for the operator.

I.e. loss of consistency.

Joe K

[BillCNC]

Putting in new rivets is simple and painless.

Heat them until they are red, but not bright red then put it in the hole. Then use the bucking tools the suppliers have and have at it. I bought two sets of rivets just incase I messed one up, which I didn't.

With 2 people and an air hammer, it's a 20 minute process and that's with everyone drinking a couple of beers.

Regards
Bill

[abachman3]

Big Flats Rivets has all the sizes that you would need.

[g8t gr&dads A]

Thanks for all the comments. It will take some mental preparation to tackle any riveting. It is a process I have never approached. Bolting is more my style but as stated above it is not "original".

[rotorwrench]

Steel rivets are just plain steel rivets. Iron rivets are softer but will not hold up to the tension and shear needed for riveted automotive structure. In aviation, there was only one type of steel rivet and they were seldom used in aircraft design. Aircraft bolts are made to precision tolerance AN/MS/NAS standards and even with plating on them, they hold very close tolerance. Bolt holes are not drilled to size for bolts or high lock fasteners. They are reamed to size to get that close tolerance fit. Rivets are forgiving of a drilled hole and will fill that hole a lot tighter than any bolts. They are work hardened by the driving process too, much like forging whether set hot or cold. There are a lot of old building & bridge structures still around that were riveted up over a hundred years ago and are still in service.

[Bob C]

I would also use a rivet gun not an air hammer.
https://www.aircraftspruce.com/catal...onorivguns.php

[Bob Bidonde]

The stiffness of a frame with cross-members / X members is definitely a function of its member joints. Rivets and screws provide less joint stiffness than welding. The Model "A's" frame is designed to be flexible and that's why Ford put it together with rivets in lieu of welding.
Joint stiffness is important because of load distribution and joint stresses. inflexible stiff joints (welding) cause high load concentrations at joints, and reduces the fatigue life.