help with boxing frame

[ozzie]

Hello all, this may have been covered before and if so please excuse my redundancy but here goes any way. Ive rescued a gt6 and begun the resto process. My question is this: While ive got the frame stripped of all components, are there some things that need to be done in the way of strengthening? I am a welder by trade and material and welding know how are not a problem. Just need a little guidance on what to weld where /ubbthreads/images/graemlins/confused.gif
Thanks in advance,
Ozzie in Sapulpa

 

[Andrew Mace]

For most any normal street use, I'm not aware of any deficiencies in the GT6 chassis, with the possible exception of the front sway bar mounts. Beyond that, rust is a possible enemy...but I'm sure you've already spotted that if present!

 

[Alan_Myers]

Hi Ozzie,

I can't help much with specifics for GT6 (cause I don't have one... yet!). But I think you'll find most of the possible reinforcements are pretty easily identified. It's mostly just a matter of inspecting for any cracks or signs of weakness and considering what areas might take the most stress or be most important to the structural rigidity of the frame. From there, I'd just suggest a common sense approach using a minimum of additional metal (i.e., weight).

If any of the frame rails are "3-sided" or "U-shaped" (like a box or rectangle with one side open), it's relatively easy to shape up some sheet metal to make those stronger. This is a common fix on many body-on-frame cars. Manufacturers all over the world tended to use easily/inexpensively produced three-sided rails that can be strenghtened pretty easily. I'd generally use sheet metal the same thickness as the existing frame and roll flanges on either side that make for a snug fit inside the , then a close series of spot welds similar to what the factory did.

Also look closely around all suspension mounting points. There some gusseting or flitch plates or a second layer of metal might be really good to add. Especially check spring mounting points, since they are under constant stress and get hammered pretty hard when driving.

In many cases it's just a matter of increasing the length of a weld that the factory started, or carefully seam welding where spot welding was used originally. For example, the top pocket for many coil springs is often a spot welded assembly, might be far stronger welded all the way around.

The corners where frame rails join are also a point that can flex, and another place that flitch plates and gussets can help.

Look at all body mounting points, too. These often have internal supports of some sort, to keep the frame from collapsing when the body is bolted on. Check the integrety of those and beef them up as needed.

Hope this helps.

/ubbthreads/images/graemlins/cheers.gif

 

[ozzie]

Thanks guys. I am surprised at how thin some of these frame members are, but then again theres not alot of weight either. Anyway thanks again.
Ozzie in Sapulpa

 

[Alan_Myers]

Hi again Ozzie,

Yes, a lot of the frame structure gets it's strength and rigidity from the shapes of the sheet metal, rather than its thickness.

Another thing... as an experienced welder you probably already know this better than most... When doing this type of work it's important to be careful not to warp the frame. That usually results from too much heat on one section or area at a time. So, working on several areas, each a little at a time, is a better technique. A spot or short stitch weld here, then one on the opposite side, gradually filling things in and allowing things to cool between short welds is a wise precaution.

Most ideal would be some sort of jig to keep the frame squared up while working on it, but that's not a luxury most of us have to work with. Some frame repair shops and custom frame builders use large work surfaces and support structures with various adjustable clamps and vises to try to keep everything straight and square. But, even with it all clamped down tight, overheating one area while welding can still warp or twist things as it cools down.

Even the car's body itself can add to rigidity and is worth checking carefully. Most are also spot welded and seam welding is sometimes used to stiffen things up and strengthen the car.

If you are installing a rollbar or roll cage, careful design and construction of that can really help with frame/body strength and rigidity, too. I'm planning a roll cage for my TR4 that will bolt to the frame in 6 places (maybe more) and also tie to the body at several points.

How much is needed on your car is up to you, depends on how you plan to use the car ( street only? vintage racing? maybe some autocross?) and there are still some very different theories about chassis setup. A really stiff, rigid frame/body assembly might make for a rougher and more uncomfortable ride, but may be like "riding on rails" through fast corners. Some cars are instead designed to flex a bit and have their chassis "tuned" with that in mind (Lotus, for example).

/ubbthreads/images/graemlins/cheers.gif

 

[trfourtune]

if you are looking to stiffen, look at any portion that is not triangulated. if you can add a member to create a triangle where a rectangle is or trapeziod then do it. if you are going to add a roll bar, you can make a big difference with a 6-point or more. if you can triangulate the front suspension towers across the front of the engine then do it.As allan says, don't warp the frame.you are trying to tie the front suspension mounting points to the rear suspension mounting points as stiffly as possible. there is twist and bending to eliminate. if you can anchor the front or rear of the frame then take a 20ft long stiff member (4" round or hss or i-beam)to try and twist the frame from the opposite end (you will need a couple of stands in the middle)you can see where and how much it moves. tack in your possible braces to see if it helps reduce this. if it doesn't, take it out. weight is the big trade off.
rob

 

[ozzie]

Great advice guys!! I have done resto on tractors and one other vintage car (67 cougar) but have never been this excited about a car!