Chassis stiffening question

[alexideways]

:icon2:OK, I have read somewhere that Japanese car builders like to use stainless rivets as their weapon of choice to stiffen a chassis, some others like to add more OEM style spot welds and many will use stitch welding...

 

:icon2:Now, I just saw an time attack S13, (prepared by a very well respected Japanese builder) which was stitch welded 1" every 3" and the guy also installed stainless rivets in between each stitch...

 

:Which approach would you consider the best between the tree???

 

:What are, if any, the advantages of one over the other??? (besides the fact that rivets must be excruciatingly time consuming...)

 

Thanks!!!

[boodlefoof]

Without adding triangulation to the chassis, just sewing up the seams in the frame rails isn't going to do anything unless the chassis is inadequately put together to begin with (i.e., if you're worried it might come apart on you).

 

I can't see any reason to use rivets to do this... except not having access to a welder...

[2126]

IIRC, stitch welding is a common practice for adding a bit more rigidity to the Z chassis. Using rivets is just as applicable and certainly more time consuming. A plus up on the use of rivets is....no heat affected areas from the welding process.

 

Tom

[johnc]

I don't understand the stainless rivet thing. A properly seam welded chassis will be as stiff as that monocoque structure could get. The seams won't be flexing against each other, the material itself will be flexing.

 

BTW... the whole point of seam welding is to keep the two sheets that make up the seam from moving independent of each other. That's the best you can hope for when making this modification.

[Pop N Wood]

I thought the point of rivets was to allow some flex between the two pieces.

 

Doesn't seem like what you should be after.

[alexideways]

...just sewing up the seams in the frame rails isn't going to do anything...

 

I'm not talking about only the rails, I'm talking about seem welding the whole shell...

 

BTW... the whole point of seam welding is to keep the two sheets that make up the seam from moving independent of each other. That's the best you can hope for when making this modification.

 

I know what's the whole point of it, that's exactly what I'm trying to do, stiffen up my 35 y/o chassis, before the RB goes in.

I was just wondering why some people (well respected Japanese race car builders) would go trough the painstaking process of riveting the whole thing, instead of just stitch weld the seams... In one particular case they did both!?!?!?!?!?!

 

(BTW, I'm not building a race car here, but I want it to last a long time, so I want to stiffen it up, without going all out on triangulation and roll cage and... What I'm planning to do is stitch weld the whole thing and cut apart a donor car and overlay a second layer of sheet metal at every point where the shell's main members joint and reinforce all susp. attachment points and frame rails...)

 

Thanks for your answers...

 

Alex.

[johnc]

Now, I just saw an time attack S13, (prepared by a very well respected Japanese builder) which was stitch welded 1" every 3" and the guy also installed stainless rivets in between each stitch...

 

Sometimes when you see something done to a car, its done by more then one builder. Maybe the car owner put the rivets in and the well respected Japanese builder came by later and seam welded the chassis? There may be a reason to do both, but I don't know what that reason might be.

[alexideways]

Well, it's clearly indicated in the article that THEY did both, so I'll try to find out more on this subject and I'll post my findings here...

[JMortensen]

Well, it's clearly indicated in the article that THEY did both, so I'll try to find out more on this subject and I'll post my findings here...

Sounds like Japanese bling stuff to me. They do lots of weird things. I remember one car that was posted that was supposed to be a really nice Japanese tuner car and the roll cage didn't have any bends in the hoop. It had welded CORNERS. Just because it's Japanese doesn't mean it's good, and just because a car is fast doesn't mean that everything about it is right.

[PSi]

Sounds like Japanese bling stuff to me. They do lots of weird things. I remember one car that was posted that was supposed to be a really nice Japanese tuner car and the roll cage didn't have any bends in the hoop. It had welded CORNERS. Just because it's Japanese doesn't mean it's good, and just because a car is fast doesn't mean that everything about it is right.

 

It is... I went to japan for about 2 years before my son was born just before the major drifting sweep came thru the U.S. and i saw a lot of guys doing this prepparing to go drifting, after a few questions about what drifting was and how to do it, i started asking questions about the cars.. I noticed a car that looked very nice with rivets and stitch welding i asked abut the rivets and was told this in a nutshell..

 

"The rivets look great and add a little more support to the stitch welds but its mainly to make the car look cool"

 

I'd say that the rivets were just a cosmetic thing unless this guy had no idea what he was talking about but guys that tune "laurels" out there tend to know what they're doing.

 

=)

 

-PSi

[J__]

i would think that they'd use both stitch welding and rivets to stiffen up the chasis from the weld, and stiffen but still alow some flex with the ss rivets. the car has to flex at some point so if u weld up all the seams, like johnc said, the material will then flex, so at soem point it will crack. so its best of both worlds using both, weld in places that doesnt require the flex and rivet in places that does.

[johnc]

There's no place on a monocoque (unibody) chassis where you want to see flex. Unfortunately, due to budget and manufacturing considerations, there will always be places where the chassis flexes if the loads are great enough.

 

Seam welding, chassis reinforcements (subframe connectors, gussets, additional material), and roll cages are used to reduce flex in a chassis as much as possible. Nobody designs in flex or uses rivets to allow flex in a monocoque chassis. Flex is an undesirable thing.

[bjhines]

You can get a good Idea of seam strengthening on an old chassis... Forget about the rivets.

 

Cut out 2 spot welded sections. "seam weld" one section and leave the other stock. Mount them in a vice and bend the weld joints like you were trying to tear them apart.

 

The spot welded joint will have quite a bit of give in the joint. You can easily fatigue the welds and tear them apart without having to fold or crease the metal.

 

The seam welded joint will not flex. It is harder than the surrounding metal. The parts will have to be creased and folded(away from the joint) to get them to crack apart. The seam welded joint itself will not fold at all.

[LLave]

When you seam weld up a chassis do you hit both sides of the seam? IE top seam and bottom seam? Or do you just weld one, or drill and plug weld? What is the proper technique?

[bjhines]

I weld both sides to ensure maximum leverage on the joint. You obviously cannot get to both sides of every joint.

 

You should pay attention to water retention problems when seam welding areas low in the car. There should be gaps in the bottom seams to allow moisture to escape.

 

The job of picking and cleaning the seams and then welding everything up tight was the biggest job I have ever done on a car... Ever!....

[Tony D]

One thing Corvair people would do is trim those pinchweld flanges. Working on the Z, you can see statistical designing and manufacturing processes firsthand in the small pinchweld flanges. On a Corvair it was not uncommon to cut 20-30# from the Unitbody by trimming the pinchweld flanges (Marc Natale said he cut 33# of metal out on his 67 Monza that he ran up at Willow Springs, black car if anybody ever saw it in the 90's)...some of them are 1" WIDE! Mmmmm, production variation. When they were welding the chassis with Oxy-Acetylene, you could see the guys using very little rod, and using the longer pieces of the flange to melt down and become filler for the shorter pieces in the stackup. Other places would grind down the pinchwelds until all pinchweld pieces are even, and no one component is higher or shorter then the other, then they weld them. I really didn't see them cut the Datsun flanges down that much if at all...maybe a mm or two. On the Corvairs some times you would use a Sawzall and cut 1/2 to 3/4" off a flange, and then go back and weld it because some of the spotwelds were out on the far edges of the flange---imagine that in regards to flex! Nothing irritated me more than to see spotwelds on the EDGE of the flange, half on the metal, and missing one,two, or three panels of a four panel sandwich! Argh!

[johnc]

There are different ways to do seam welding. The usual method is to weld the edge of the seam everywhere you can get to an edge. A more difficult method used when a racing class doesn't allow seam welding is to is use an abrasive wheel to cut a slot through the top sheet of the seam, exposing the the bottom sheet. Weld up the slot and grind it smooth. That method works very well and pretty much undetectable if the slots are placed so they do not overlap the existing spot welds. Its also very tedious and expensive to have done. I did a 1970 240Z this way once after the shell had been media blasted - 60 hours of work.

[Pop N Wood]

So you cheated?

[johnc]

Nope. I was the fabricator, not the car owner, entrant, or driver. Its not for me to decide what others want done with their race cars.

[karl]

WRC teams start off with stock body cars and completly seam weld the entire car before adding the roll cage. The video I have says they do this for maximum stiffness because they are not allowed to have full tube chassis cars.