Jump to content
HybridZ
280Z-LS3

Stitch welding question

Recommended Posts

I don't know honestly what is "correct practice" (you will get a bunch of opinions) but I did stitch weld this area, for whatever that's worth (not much).

 

There are many informed, intelligent car fabricators who will say that stitch welding itself is a waste of time.  At the end of the day you will have to do what seems correct (and worth the effort) to you.

Share this post


Link to post
Share on other sites

I stitch welded those areas. The middle of the wheelwell is easy if you have a rotisserie. The inside area where the wheel well hits the inside of the body is a huge PITA, because there are about 4 layers of metal with seam sealer jammed in between. I'd either skip it, or weld a plate that attaches to each side over the seam so that you don't have to dig all the sealer out. Took forever.

Share this post


Link to post
Share on other sites
1 hour ago, Ironhead said:

I don't know honestly what is "correct practice" (you will get a bunch of opinions) but I did stitch weld this area, for whatever that's worth (not much).

 

 

The one advantage is that you know the parts are now solid and not relying on 40 to 50 year old spot welds.  And if you do ever bend it you can pull it straight.  With just the spot welds they often shear and you can't pull the complete part.  I learned this from talking to a number of unibody racers and seeing first hand when they did pit repairs.  

 

Cary

Share this post


Link to post
Share on other sites

I do have the car is on rotisserie so I will weld them up and have already removed most of seam sealer while scrapping under coating off.  Being able to pull the body straight after damage is reason enough for me.  Let's hope it doesn't come to that...

Share this post


Link to post
Share on other sites
5 hours ago, JMortensen said:

The inside area where the wheel well hits the inside of the body is a huge PITA, because there are about 4 layers of metal with seam sealer jammed in between. I'd either skip it, or weld a plate that attaches to each side over the seam so that you don't have to dig all the sealer out. Took forever.

 

Boy is this the truth.  I did it, and just remembering doing it gives me PTSD.

 

Actually I would rank the entire stitch welding process, if one is fairly thorough about it, as very high on the PITA scale.  Probably the thing I hated doing most on my car.  Of course, it isn't the welding, it's removing the paint/primer/seam sealer so you can weld it.

Share this post


Link to post
Share on other sites

I just tore the wheel well apart as well, to do rust repair. The steel is super thin here, so be careful not to blow holes. This is where water and dirt will be flung at high speed, so use a flash light to check for pin holes when you are done welding. It would be better to fill the holes with a tack, but por-15 seam sealer will do the trick if they are hard to get a welding nozzle too. Personally, I have a hard time welding upside downs 
 

I wonder if there is a “top-10” list of sorts, for the most strategic places to add steel. My car has already been seam welded, but I still feel some flex, even with a full cage and strut bars. I suspect it is my failing/rusted floor pans which act as a shear wall, but I’d like to add more metal while I’m at it. 

Share this post


Link to post
Share on other sites
On 10/21/2020 at 9:02 PM, AydinZ71 said:

My car has already been seam welded, but I still feel some flex, even with a full cage and strut bars.

Wow, you still have flex with a full cage?!  Can you share a pic of cage design?

 

Do a search for "chassis stiffening" for everything you need to strengthen chassis.

 

 

Share this post


Link to post
Share on other sites

Wouldn't it be nice to see some actual testing? There are some basic ideas of how to do such a test in the book Think Fast, but requires making plates to bolt to the hubs and screwing to the slab. I suspect I could have gotten the rigidity gains I did with fewer tubes and less weight with some FEA prior to building too. All too technical for my little brain... 

Share this post


Link to post
Share on other sites

I imagine most of you have already seen them....but there are black and white photos floating around detailing the cage design on one of the later BRE Datsun Zs from back in the day.

 

A couple of things that stood out about them.  For one, they didn't "stitch weld" the OEM joints, they ran solid beads down the entire sheet metal joints.  The other thing that surprised me was that they used a hell of a lot of tubing.  My conclusion was that they were much more concerned with rigidity than weight, although I cannot tell from the photos if the tubing is chrome moly or mild steel.  The design would make entry and exit of the car difficult, to the point that it would be pretty much just like leaving the doors closed and climbing in/out of the window.

 

This was a long time ago, and I imagine cage design has advanced since then.  I suspect they could have had virtually identical rigidity with fewer tubes.  But, on the other hand they were certainly successful cars in their day. 

Edited by Ironhead

Share this post


Link to post
Share on other sites
On 10/24/2020 at 11:15 AM, 280Z-LS3 said:

Wow, you still have flex with a full cage?!  Can you share a pic of cage design?

 

Do a search for "chassis stiffening" for everything you need to strengthen chassis.

 

 


I will snap a few pictures in the morning. It could be my rusted-out floor pans. They act as a shear wall against the horizontal flex of the OEM unibody subframe. Even the full cage has no horizontal members at floor level, only vertical and longitudinal. Makes sense since the tranny tunnel is in the way.

 

its stiffer than my 71’ with no cage, but not as stiff as my 08’ 335i. I know... apples and oranges

 

i agree with Jmortensen that empirical testing is necessary. Beyond driving, I have lifted the car and each of the 4 corners and watched how the body reacts (flex). Like a 4 legged stool, a stiff frame will show a close relationship between the subframe member being lifted, and the change in angle at the opposite corner. The less you see a cause-effect at the remaining 3 corners, the more body flex you are experiencing. The body is essentially twisting/bending to compensate for the differential stress, vs. “tipping” the car. Extreme example is like picking up a paperback book from one corner and watching it bend. 

Edited by AydinZ71

Share this post


Link to post
Share on other sites
On 10/25/2020 at 7:35 AM, JMortensen said:

Wouldn't it be nice to see some actual testing? There are some basic ideas of how to do such a test in the book Think Fast, but requires making plates to bolt to the hubs and screwing to the slab. I suspect I could have gotten the rigidity gains I did with fewer tubes and less weight with some FEA prior to building too. All too technical for my little brain... 

 

I have used solidworks with FEA when I was younger at a job. The software and license is just way to expensive for personal use. My dream would be to design an Al tube frame using FEA the whole way. I could laser check the dimensions between the body skinS, fenders etc. , and build a skeleton frame within its cavity. 
 

it would look like an S30 on the outside, but just below the surface there would be a matrix of AL tubes. 
 

carbon fiber is of course lighter, but no way I could cost effectively fabricate that. AL tube is relatively cheap here (less than $2 a pound).

 

I follow a guy on IG who has an all steel tube frame (I think AL frame is not allowed?) S30 designed to tackle pikes peak. 

Share this post


Link to post
Share on other sites
15 hours ago, Ironhead said:

black and white photos

 

Ironhead, The first thing i purchased for my Z after buying the car years ago were Bad Dog frame connectors.  Fun fact, the owner of Bad Dog came across an undeveloped film roll in a garage somewhere and that is where those pics came from.  Talk about hidden treasure, right?  I too noticed that every seam on the BRE was fully welded contrary to current advice of stitch welding.  John Coffey, famed Z car wizard, mentions that fully welding the seams relieves the forming strength/stress in the steel weakening the final product.  I don't know squat about metallurgy...

 

9 hours ago, AydinZ71 said:

I have used solidworks with FEA

 

 AydinZ71, I would love to have the ability to use Solidworks but for now I live vicariously through others like Noah Dropkin who designed my 2015 Mustang front spindle swap.  Completely amazed what he does with 3D scanners and Solidworks. 

 

Maybe new frame rails with tie-ins to cage can help strengthen up your 71.  Curious about location and extent of rust.

Share this post


Link to post
Share on other sites

Yeah, haven't seen a racing series where AL tubing is allowed. Mostly it's mild steel ERW (drag racing) or DOM (SCCA). Some allow chromoly, but it's harder to weld correctly so you have to be more careful with it and the tech inspectors will scrutinize it more closely. Re: Pike's Peak, the one thing that I think it's really hard to do on a Z is to protect the floor. It's already so low, and most of us want the car lower, that it's tough to get any protection on the floor. Heavy85 was talking about how to do it when he rolled his Z at a hillclimb into small boulders, luckily he walked away unscathed.

Share this post


Link to post
Share on other sites

Floor strength is something I want to enhance when installing my seat.  I will need to modify trans tunnel encroaching into the seat area anyway so may as well try to strengthen the floor.  The only idea I have so far is forming up some sheet metal like the original transmission mount and have it tie in the frame rails.  More ideas are welcome.

 

I was fired up to try hill climb racing until I saw Heavy85's video of his crash!

Share this post


Link to post
Share on other sites

Have you seen the Flying Miata butterfly brace? That's a good place to start. 

Hard to do on a Z with the exhaust hanging down. Reason number 486 for going with sidepipes. If I ever get around to doing a paneled floor, I'll incorporate some sort of bracing into the top side. For protecting the driver really needs to extend all the way to the rockers.
 

 

Share this post


Link to post
Share on other sites
3 hours ago, 280Z-LS3 said:

Floor strength is something I want to enhance when installing my seat.  I will need to modify trans tunnel encroaching into the seat area anyway so may as well try to strengthen the floor.  The only idea I have so far is forming up some sheet metal like the original transmission mount and have it tie in the frame rails.  More ideas are welcome.

 

I pondered the same thing, wondering if the floor is an adequately sturdy mount for seats.

 

If you think about it, a seat is most likely to break free in a crash if the impact occurs from the rear.  Then the entire weight of the driver will be slammed into the seatback, and the harness will do little/nothing to keep the driver/seat in place.  In a frontal impact, nearly all of the driver's momentum will be captured by the harness with very little strain on the seat.  Same with a roll-over.  A side impact will be somewhere in between.

 

This was my reasoning for installing a seat-back brace, this one specifically:  https://www.bkauto.com/R_9020_Seat_Brace_Fixed_Back_Composite_Seats_p/r-9020.htm  It bolts to brackets welded to the harness bar.

 

Other than that, I welded seat mounts from square tubing that tie fairly securely into the frame rails, which really is the only significant source of strength in the floor pan.

Share this post


Link to post
Share on other sites
3 hours ago, JMortensen said:

Yeah, haven't seen a racing series where AL tubing is allowed.

 

I know the factory Porsche 935s had an aluminum roll cage, but again, they were raced long ago.  I wonder if the ones still participating in vintage racing have been retrofitted with steel cages...?

Share this post


Link to post
Share on other sites

Don't think I could incorporated a Flying Miata type brace into my build but also have not given thought to side pipes.  I like the idea of anything under the car hugging the floor pan.  Building added structure inside the cabin is interesting too.

 

I have a Cobra Suzuka which the manufacturer states it does not require a back brace.  It's a fiberglass seat and don't know if they are compatible with rear bracing.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...