Seam Welding Floor

[AdamP 0]

I'm going to seam weld in the floor of my RG in, probably in 1-1.5" bursts every few inches as I have been informed that it is only held in by a few spot welds and lots of seam sealer.

 

Anyone have any tips, anywhere I should seam weld for any reason?

 

Adam

[Beastie 1]

I'm going to seam weld in the floor of my RG in, probably in 1-1.5" bursts every few inches as I have been informed that it is only held in by a few spot welds and lots of seam sealer.

 

Anyone have any tips, anywhere I should seam weld for any reason?

 

Adam

 

In my experience there is only one reason to seam weld: To increase stiffness of the original assembly if you are using it beyond it's original design specification. Stiffness and strength are quite different terms. The original construction was made that way for a very good reason - and it wasn't just to save money: Firstly the seams were treated very thoroughly against rust before they were welded; welding heat destroys this treatment so it was considered good practice to keep such heat to a minimum by using the few spot welds and seam sealer which you mention. Secondly welding weakens the surrounding metal in the heat effected zone - keeping welds to a minimum increases the strength of the joint. A properly seam welded joint is usually stiffer than the original spot welded item but it is also usually weaker and has less durability.

 

If you are only considering keeping your car in the short term and you need the shell to be stiffer than original then I would advise seam welding in the 1 - 1.5 inch runs which you suggest.

 

If you intend keeping your car in the long term and you are going to do so within the design limits intended by the original manufacturer then I would advise repairing it painstakingly to the original construction because it has the following advantages: Maximum strength and durability, maximum corrosion resistance and least time consuming repairs. The last point is particularly important: I see cars of all ages (the oldest in my workshop at the moment is 92 years old) and the most costly cars to repair by a very long margin are the ones which have had their original construction modified by misguided enthusiasts: It's far cheaper to restore an original car dragged out of a field than it is to restore a tidy looking car which has been kept going with seam welded repairs.

[Rippthrough 98]

Use etch-weld primer before welding.

 

Or braze it, almost as stiff as welded but without the durability problems.

 

Or glue it.

Edited August 21, 2007 by Rippthrough

[Grahamrally 0]

Beastie has pointed out some good points there! Consider how long you want the shell to last, I've only ever seam welded shells used them for a few years then changed so I've not seen the long term effects that ageing does to seam welding. However, that said, the only places on the 205 that you can't then treat after you have welded would be inside the sill on the edges of the main floor pan.

If you're going to seam weld the shell, make sure you do it thoroughly and properly. Clean as much of the seam sealer that you can out of the seams on the boot floor, main cabinfloor and engine bay up to the level of the strut tops. People like to use a grinder with a wire wheel on it, but be warned it creates a lot of stringy mess! I prefer to use a blow torch and dig it out with a flat blade of some sort. The reason you only need to do up to the level of the strut tops in the engine bay is because if you crash the car there will still be a good crumple zone, that reduces the risk of the strut tops being bent inwards consequently meaning the shell is written off.

The only other thing to consider is it you run a non servo assisted pedal box. The bulkhead flexs a lot so it's wise to weld in a strengthening plate.

Shoot me an email and I'll send you some pics of a seam welded shell if you want?

 

Graham

[Rik 0]

Would fancy those pics as well Grahamrally!

 

Would it make a difference if the shell was seam welded and had a roll cage? As it has more stiffness then so i'm guessing it would take up some of the strain etc.

 

Rik

[Grahamrally 0]

Would fancy those pics as well Grahamrally!

 

Not a problem Rik, chuck me your email and I'll send them to you!

 

Would it make a difference if the shell was seam welded and had a roll cage? As it has more stiffness then so i'm guessing it would take up some of the strain etc.

 

Every little helps as Tesco say! I only really recommend seam welding a shell for motorsport use and most, if not all cars being used for motorsport will have a roll cage. Depending on the type of roll cage depends on how you go about your seam welding.

 

The best ideal is to have a weld in cage that connects the front and rear suspension mounting points together and is well triangulated. It's pretty much a space frame in the shell and all suspension energy is then transferred to the cage instead of the shell. In this situation it is almost redundant to seam weld a shell as it won't help handling or suspension geometry, (if the cage has been designed correctly), and absorbs all the energy the shell usually would.

However in reality, there are few cages like this that are able to completely remove the stress/flex from the shell, so seam welding is warranted.

 

The second best option is to have as best a cage as you can afford, make sure the shell is seam welded correctly and then weld both A+B pillars to the front and rear legs of the cage. This helps to remove top body movement and makes the cage more integral to the shell.

 

But think about seam welding carefully before you do it, because what you gain in rigidity on a seam or joint from welding, you loose in reliability and longevity of that metal or joint as beastie has pointed out. When you weld a seam you are stopping two pieces of metal from moving against each other. This transfers the stress to other parts of that metal which weren't originally designed to take it, causing undue stress and potential fatigue failures on surrounding parts of the material. Where you've seam welded is also more brittle, so although will have a higher maximum stress, it will also not be as flexible. After years of expanding and contracting and twisting it will eventually crack.

 

Bear in mind, all of the above is designed to keep suspension geometry aligned and you will only see the best results you can by making sure the suspension and steering components are in excellent condition.

Yes it does make that bigger difference if done correctly!

 

Graham

[SwedishBob 23 1 Cars]

Grahamrally: Would be highly appreciated if you could send some pictures to my email. robert@eventbilder.se

 

Thanks in advance.