Any Ford Flathead gurus here???
 

I have posted this on a Flatheaf formum at Yahoo! groups, but I have disappointed by the quality of the replies.
I am helping a friend restore a '38 Ford pick up. The original front crossmember was broken, and since it had been previously patched, it seemed prudent to replace it. He has located a NOS crossmember. The question I have is, "How should it be attached?
The oem method was rivets. Some peole weld them in, and others prefer bolts with some sort of locking nuts. What I am seeking is some discussion of the relative merits of these various methods. Opinions are OK,( "weld it", or "grade 8 bolts") but the discussion is required to understand the "why" of each method.

Michael
Bel Air, MD

In my opinion Ford used rivets so the frame had a certain amount of flex, much like a ship's riveted hull. If it is welded (I have seen welded ones that broke) it won't flex at those points over uneven terrain and will likely break. On semi trucks there is usually a tag on the frame that says No Welding. They use bolts and or rivets.

Thanks for starting off the discussion. I think many late model frames are made of heat-treated steel, and the heat of welding would compromise the strength. I am not sure if early V8s had any heat reatment of their frames, so that caution may not apply.
AFAIK, rivets are very strong when properly installed--If the rivet is at a red heat, then it has stretched a bit--just due to its temperature. If it is installed and peened while still stretched, it will shrink as it cools and become VERY tight. I am not convinced that you can tighten even a grade 8 bolt to provide that same clamping force. But thats what this thread is for. I am looking for comments on the relative merits.

Should be able to get at the HAMB - it's a hot rod forum, but they should know what's up.

http://www.jalopyjournal.com/forum/

Click on 'Hokey Ass Message Board'. Let us know how it works out.

PaulC
Part of the problem is that my friend, still can't make up his mind. One day he's talking about an authentic restoration, the next, he's thinking about boxing the frame and installing a SBF with Air and power steering. Then, he has mentioned just putting the '39 body on a late model frame. I don't know what he really wants; he doesn't know what he really wants, but when I discovered that the original crossmember was beyond repair, he didn't hesitate to buy a new cross member. I think if we get the frame done as per original, and it is stable, he might stay with the restore idea. I believe part of his reservation is due to how much the frame rolled. Stepping on the running board would cause the body to roll a lot. That was due ( I think) to the broken crossmember. So if we get that fixed, it should be OK.

I agree with the comments regarding grade 8 bolts.

I have over the years restored and otherwise maintained countless early vehicles,chiefly pre-29, and chassis rivetting was done of a purpose.

My Vauxhall is a prime example,in all essentials it is an Edwardian design,deriving from the Prince Henry 3 litre,with a correspondingly flexible chassis.

While the Vauxhalls could not be beat in straight sprints and hill climbing their somewhat flexible chassis robbed them of any easy handling above 75-80 MPH.

many have tried welded members but the penalty was cracked joints as if in rebellion to the welding.

I have found that grade 8 bolts,welded at the nut-bolt joint are more than sufficient for durability and flexibility,my InterState being a prime example.

I thought rivets were used only in shear, and bolts in either shear or tension according to the application. Please correct me if I'm wrong.
regards,
Mark

In automotive chassis application,at least before the advent of flexible engine mountings and independent suspension rivets were subjected to tension,not compression and the ideal bolts chosen to replace worn rivets should have a non-threaded shoulder where it fits through the frame members.

Difference between rivets and bolts,

Hot rivets are HOLE FILLING and bolts are not generally. So, when you put a bolt in the open hole, locally you have 3 times the stress level as a filled rivet. Not good for fatigue life especially since holes are generally where cracks start.
Rivets are a shear fastener, bolts can be either tension or shear.

It was stated correctly, you want no threads in the shear joint. Ideally, you know the thicknesses of the 2 metal piece, and you find a grip length so there is no threads in the metal. You can use a washer under the nut, so it doesn't bottom on the threas. The shank (unthread portion of the bolt) should be available in 0.062 increments if you stay with aircraft bolts (160 ksi is a grade 8) or 0.125 for grade 8 bolts.

What size holes do you have approximately? You could find some surplus hi-locks and carefully match ream the holes. Install them with paint to prevent rust or some MIL-s-8802. You can use self-locking nuts and install with red loktite. No lock washers. I can give you some good torque values to use for the bolts once I know the diameter.

Michael