It's possible that when the inner and outer rockers were replaced that the car might have bowed just a little bit if it wasn't put on a jig but with out a time machine we'll never know for sure.

Regardless these early cars are hand made and no two are alike. Take your time and get the door and gaps at a place you are happy with before you proceed with any paint prep. It's a compromise game with a handmade car. There is no perfect situation.

The door window frames have a lot of leeway for adjustment and fitting them is a bit of an art form. Take your time and learn all the idiosyncrasies. The results will be worth it. Some times a little grinding or drilling on the door shell is required so don't be afraid to make adjustments to get it right.

I would be curious if doing a total seam weld (no gaps between welds) vs. a stitched seam weld job would have any added benefit. The factory does a sticked job in order to facilitate easier panel replacement if the need arises. My assumption would be the added benefit would be minimal... anyone know for sure?

Another thought would be to take a look at what was done for the offroad rally 959's used for stiffening, besides a roll cage.

I think some solutions are already on this thread. Go back a few pages.

Sherwood

total seam welding is commonly done to mod these cars for more stiffness & racing

a wider center tunnel works well - look at a 964

TRE has also done some things along the rockers IIRC

also Tyson once looked at some stiffening up front, but IIRC he rejected the idea

What are the effects of doing a total seam weld as far as heat-affected zone (HAZ) compared to a spot weld? Could some of the perceived benefits of seam welding be lost without heat treating the final weld? Spot welding should preserve more of the original temper strength of the sheet metal. Maybe a better way to add structural reinforcement would be to spot weld and then use a bonding agent, like the one Louts uses on its Aluminum chassis in the Exige, to chemically seam weld.

As far as I know, heat treating any type of metal, is done only to increase is resistance to breakage. In a car, the metal would likely lose it's ability to bend without breaking.

Just a guess... I think a chemical bond or glue would need to be done at the time of assembly. I've have heard of metal to metal epoxies that are supposedly stronger than a weld.

I would just like to know if a total seam weld is any better than intermittent seam welds???

Do you mean making small sections of seam weld, then stiching them together to limit warpage compared with a single continuous bead at once? I think stiching is better for limiting warpage.

I consider "seam welding" to be a continuous bead of weld, whether it be made from sections connected together one at a time or a single long bead. I do not know if I am understanding your question.

Heat treatment should add stiffness but take away a little yield strength. This is not so bad, carbon fiber does not have much margin above its elastic deformation limit, where stiffness ends and permanent bending begins, before it shatters. Stiffness is really what racers want so that they can remove an unclassified spring from their dynamic calculations of suspension spring rates, etc. If the chassis bends enough, it is almost as bad as breaking, other than for safety reasons, of course.

I mean stitches of seam welding (stitches not touching other welds) kinda like an inch and a half or so between welds of the same length. There is a chart for a GT3 or something that shows what I mean. Not sure what page it was on. SOMEWHERE in this thread though.

LOL - so to revive a great thread - I offer this off the wall idea with absolutely no knowledge of what I'm talking about -

As I climbed out of my slant nose cab with BOXED ROCKERS it occurred to me that perhaps that might be one way to strengthen the torsion rigidity of my cab - using externally applied and more structural than cosmetic metal in the boxed rocker area....we've avoided the roll cage throughout this thread, and so in keeping with the idea that external support might just help the problem we're discussing - I offer up this nutty idea.

Am I totally off base with this thought? There has been a ton of discussion in this thread about beefing up the center tube - what if we went at the problem externally? Possible?

thanks for the education...

td

The reason it hasn't been covered is that some would say that a slant nose cab with boxed rockers is a bit, well...

I may not know art but I know what I like. ;)

That is because I just came across this thread...

I did installed a bolt on roll bar the same year I got the car.

Attached the wind screen to it.

Don't fell any flexing but since I don't have a coupe, how would I know ;)

http://forums.pelicanparts.com/uploa...1308648560.jpg

Max,

Sadly heat treatment doesn't really add any stiffness to a component as the Young's Modulus of the material will not change.

They types of steel used for bodies of 911s don't really have any specific 'temper' and are quite different to modern Dual Phase and some of the other steels used.

The idea of 'seam welding' has been used since the early sixties and has never really been a continuous seam.

The expression simply means welding the seams of the car where the panels fit together.

This not only stiffens the basic structure it also stops the seam from popping open and makes the shell last longer.

The downside is that it can make the shell very difficult to repair as it is much harder to pull straight after a collision.

I would agree that using spot welds where appropriate is a good idea and we normally carry out this exercise around door and window apertures when MIG or TIG may be an issue.

The difference if the 'feel' of a car on a forest surface after it has been welded up is significant but I am not sure if anyone has good data concerning time differences other than if it feels better we tend to try harder.

I do find it interesting and perhaps counterintuitive that seam welding works. Is the implication then really that spot welds, even with the many that Porsche put into our cars, really allows for some degree of motion between panels and the seam welding really just removes that relative panel to panel motion?

I guess, based on what is obviously my faulty intuition, that there would be paint cracking or other signs of panels moving relative to each other which would go away when the chassis is seam welded.

I am looking at my '89 tub, wondering if I ought to bite the bullet and just seam weld it, even though I worry about increasing my chances of rust (interior of panels having their primer come off due to welding heat). It'd be a day or two with the MIG, and as Chris says...it makes for a nice feel if nothing else.

Much to ponder in this thread....

Dennis

I've learned a lot at university since 2010 when I made that post. Yep, I was dead wrong. Hardening heat treatments increase yield and decrease ultimate if it's too brittle. Modulus the same.

I have a similar question about the seam welding though. It seems the spots are in the same place the seam welds would be, so would not the seams merely add some strength but not stiffness?

Max - sorry - I didn't notice how long ago this was posted :o


With regard to the benefits of seam welding I think it all depends on how many spot welds there are in a particular seam.

If you bend and twist a shell at the same time the seams open up and the spot welds fatigue and crack and lose integrity.

Most of my early experience was with Fords and you could see gaps forming between panels as you competed on more and more events and eventually you had to carry out substantial repairs.

In a shell that has been aggressively used on rough surfaces you will see much more than cracks in the paint.

You will see cracks and ripples in the panels and often serious misalignment of suspension pick up points.

Clearly the stronger and stiffer the original structure the less the need for this type of preparation.


The other issue is that a spot weld in the centre of two plates does tend to allow some 'oil canning' and some buckling which is how they typically fail.

I am not sure how much benefit will be gained on a 911 but by the time we had enough budget to run one we had already been welding up Escorts for years and just followed the same practice.

Having had the strut towers crack and fail and rear damper mounts pull out of various Fords it just seemed like a good idea.

Time to update this thread with some practical experiments.
I've have had an idea to stiffen my targa for a few years that I implemented the last 2 days.


http://forums.pelicanparts.com/uploa...1419883516.jpg
http://forums.pelicanparts.com/uploa...1419883581.jpg
http://forums.pelicanparts.com/uploa...1419883759.jpg
http://forums.pelicanparts.com/uploa...1419883870.jpg
http://forums.pelicanparts.com/uploa...1419884049.jpg

Unfortunately its cold and snowy outside, so I can't drive the car to test it. But I did jack up the car ant put it on stands on the torsion bars.
Usually this results in a large gap between the targa bar and targa roof and a difficulty to open and close the doors.

With these bars the gap is significantly reduced, almost gone, and the doors open and close like on the ground.

As I do a lot of track days with the car, it also feels better to have a bit more impact protection.

This is a modification that only works (easily) for targas and cabs because they have reinforcements in the a and b pillar that I welded the plates to.
I also needed to lose the door pockets as the bar takes up that space.

Great Thread! Subscribed

John, I know this is old but did you ever find the SC/RS torsion tube pics?

andy

Is it spring in Sweden yet?

That looks great.