I've got the frame for the '51 disassembled and I'm finshing up the welding and prep work before I start blasting it. After I already had the engine mounts welded up, I remembered something that didn't occur to me when I was buzzing it together. I remembered reading here awhile back that it's a no no to weld vertically on a frame and that you should only weld horizontally tp prevent cracking. Well, it's too late now if that's the case. The mounts are in the first pic. So my first question is am I going to have trouble with this? The second question is regarding my transmission mount pads. I had to cut out the original trans. crossmember for clearance. Since it was the major midship crossmember that kept everything in the cab area tied together, I built a beefy new one and welded plates to the edges of the rails to bolt it to. Now that I'm looking at it again, I'm concerned that either the welds will break or the 3/16" plate will bend if the chassis twists much. I devised a neat, attractive way to stiffen it up, but I'm not sure if I should for the above reasons regarding proper frame welding. The frame rails are in the second pic - one as-is and one with the proposed gussets. To serve any useful pupose, they are going to have to be welded vertically to the frame rail. Can I do this? Do those rules only apply to frame splices and fish plates or is it in any case? Is the sky blue? How many licks does it take to get to the center of a Tootsie Pop? HELP!!

 

Joe

While it may not be best to weld vertically, sometimes you have to take the lesser of two evils. From what I saw of your suspension kit and frame, what you are doing here is necessary. I am certain a 351W built to your specs, is going to eat that F1 frame alive with out the mods you are decribing. The mid mount support is needed. I would proceed.

In any case, your frame is not going to disintegrate during one evening of Camaro hunting. If a crack starts, you can address it with box plates or other methods. Not something you look forward to of course, but not the end of the world either.

 

'Rage,

Not sure how much my opinion is worth in this case (or any case for that matter) since I have no metalurgical background - hell I have to teach myself to weld in a couple of weeks, but;

I like your motor mounts (visually and structurally) but I would have designed them to attach to the top as well as the bottom and sides as you have done or boxed the frame first and then attached them. (no offense intended)

I cut one half of that same crossmember out this past week end, stood on the other half hoping to pop it out (this is after all the rivets were removed) and almost freaked when I saw the the flex in the frame - and I weigh in at a svelt 165 lbs.). I'm thinking about boxing from behind where the steering box will fit in all the way back near the rear of the cab......

I'd like to hear from that other lad that put in the Cordoba set up to see what he did and how his has held up.

Your mileage may vary, the opinions expressed here do not represent the vies of management....

Later,

 

OK Joe, I'll try to keep this short. I've learned the practical part from the great folks here and other places and the high-falutin' engineering part in school and at work.

The main forces on the frame rails are normally in the vertical direction. Things like spring perches, engine/tranny and cab mounts, etc. all put essentially vertical forces on the frame rail. If you pull straight down or push straight up on a frame rail they are stiff and strong because that's the direction they see the biggest forces and they were designed to resist those big forces.

When a vertical force is applied to a frame rail, the rail bends and the biggest stresses are actually along the long axis of the rail - that is, the bottom and top of the rail want to either get longer or shorter depending on whether the vertical force is up or down on the rail. This is the reason you don't want weld repairs to be vertical on a frame. The big stresses from vertical forces will be along the axis of the rail and will tend to push the material in the vertical repair line together or pull it apart (again, depending on the direction of the vertical force on the frame rail).

Imagine cutting through the lower flange on a rail and continuing the cut three-quarters of the way up the rail web. If you stand on that frame rail over the cut, it's going to be a LOT weaker, the cut will tend to open up, the rail will sag a LOT, and the stresses at the end of the cut will be sky-high. The cut is called a stress concentration becuase the stresses can be VERY high at the end of the cut compared to stresses in a rail with the same force but without the cut. Stepping on-and-off the cut rail will increase and decrease the forces (cycle the forces) and cause crack initiation and growth at the tip of the cut where the stresses are really high. Your frame sees similar cyclic forces every time you go over bumps, tromp on the gas, get in/out of the truck, etc.

In your case, the vertical welds are where the vertical forces are actually applied (engine/tranny and cab weight loads). In this case, the stresses from bending I talked about above are not as important as the shear stress caused by supporting the weight.

An additional problem is that the cross members are what keep the rails from seeing big twisting torques. As RMF pointed out, cutting a cross member and standing on the cut end puts a heck of a torque on the frame rail which it is NOT designed to withstand. That's why the cross members are there - to keep the frame rails from seeing large twisting torques (among other things).

In the end, 'fenders summed it up pretty well. Since you removed the rear cross member you HAVE to provide some way of keeping the rails from seeing the twisting torques. You also need to keep the local shear stresses at your engine/tranny and cab mount locations reasonable. I think you've got a very workable and sound design and I doubt you'll have problems with cracks at the vertical welds. Even if you do, they will be relatively easy to see since they should be visible on the outside of the frame web without too much effort.

One last point - by FAR the most important thing is to have welds with a minimum of voids, pits, or notches in them. Small pits and voids will start cracks as much as 100 times faster in these steels than unpitted material. If you'd like the fatigue crack initiation and growth and Charpy fracture toughness data I can post it for you.

Keep going! I want to see that thing movin'!

 

RMF

You should see his motor mounts in the installed position. They are the sweetest I have ever seen. They are strong as I-beams. Problem is they are so long heading all the way into the back of the frame rail. They have tremendous leverage on the frame with no additional support.

My Volare has no flex there due to the extensive boxing. I am STILL going to replace the mid crossmember support in some way, shape or form. I waited until the end because I moved my driveline around on almost a daily basis trying to make everything work out. It's like building a house on 30 inch centers. The sheathing and drywall might make the wall seem sound, but it just can't be.

 

'Rage
Don't poke fun at Harley riders. I have a job, pay my bills, drink very little, don't do drugs, and dislike being compared the Hollywood image of a biker.

 

'fenders - I'm glad you weighed in. Your opinion matters as you have actually seen what I'm attempting to do up close and personal. I'm just paranoid about all this for a couple reasons - 1. Although I've got a good grasp of what is structurally strong and what ain't, I've never done this before and don't want to screw it up. 2. After the front crossmember cracked when I tried to straighten a cupped rivet hole, I'm petrified of doing much to these frame components now. This stuff is brittle! I also share your concern about the length of the engine mounts and their leverage on the frame. I've got a plan there, too, but I can't proceed until the frame is reassembled. Trust me, it'll be beautiful.

RMF - Thanks for the kind words on my mount design. I agree that it would have been preferable to extend the mount to the bottom flange or box it, but the bottom flange is moving up at an angle in that area and I couldn't box it because the steering gear is inset in the rail directly in front of it. You really can't see either in the pic. The mounts are actually more complex than they appear. They sweep forward from behind the steering gear. I'll post another pic in my gallery to give you a better idea of what I'm trying to acomplish. As for the mid crossmember, I had a very similar experience. After I removed it, I put my foot on the adjacent running board mount to survey my work and the rail twisted about 45 degrees. AAGHH! The new crossmember that I've built will be a more than adequate replacement, but only if the attached portion of the frame is sound, hence this post. When you see the chassis and suspension/steering all back together, this will make a lot more sense.

George - I appreciate the logistical explanation. I knew I could count on you to spell it out. I believe it was the memory of your comments in a previous post that got me thinking about this in the first place. If you approve, then I definitely feel better. I wish we had a mechanical engineer at work like you with your thought process. We'd spend a lot less time doing rework when the engineer's design failed!

52F2 - Don't be offended. I only feel qualified to poke fun of Harley riders because I have a job, pay my bills, drink very little, don't do drugs, and the F-1 shares my shop with an '03 Lowrider. It's all in good fun! I ride because it completes me. I never did really give a damn what the neighbors or anybody else thought.


Thanks for all the replies, guys. I feel better now. I will proceed as planned. Now if I could only get this @#!$&% sandblaster to work right, I'd be in good shape.

 

"Now if I could only get this @#!$&% sandblaster to work right, I'd be in good shape."

Write it down when you figure it out. Aren't they a pain? Only ones I have ever used that didn't clog in the Iowa humidity were ones I could only afford to rent. You can't put enough water traps on them.

 

Beautiful work Joe and excellent comments from the assembled multitude.
In the future NEVER weld completely around a piece, be it a bracket or a fishplate.
Instead leave a small gap, 1/2" is OK, at ALL corners in all planes.
Look at some frames and rear ends for examples. These gaps were not intended to save money or provide drain holes but to stop stress from transferring to the other plane.
George has a good command of the pointy head lingo, I'll let him do the fancy stepping; I never made it to pocket protector status.

 

I have a 351 W/ Borg Warner T-10 4 speed with about 20,000 miles on it. The engine and trans mounts are bolted in (both custom made) and I have had no movement of either since I installed the drive train over a year ago. I don't drive like A NASCAR super racer but I don't exaclty baby the truck either. My point is, if you put your mounts in and make sure they are tight, I don't see how you should have a problem. Good Luck