Structural integrity

[thebmw1200gsa]

This should open up a few debates!

Interestingly having looked at a few Roof chops and cut up Saloons to Convertibles on a well known auction site.

I ask the following, when does a car become structurally corrupt?

If you cut a saloon up to make a convertible which seems common practice how does the car retain its strength?
Having seen a properly restored convertible it has strengthening pillars in the screen and other bits.

If you have a cut up saloon pretending it to be a convertible is this as strong?

Likewise I saw a few beautifully done roof chops up to 4 inches being cut out, does this change the strength of the car? Does welding it back to the C pillars and A pillars weaken it or strengthen it?

Does it become a cut and shut? By cutting the roof in 3 places does it weaken the whole thing?

But then look at this one which has quite clearly been cut in two and then rejoined.

http://www.powervampracing.com/news/pow ... -attention
I'd love to hear people's views on both the above and the link.

[ianmack]

The original convertibles have extra strengthening plates to make up for the lack of a roof, on the a post, b post and sills each side, so six plates in all. These can be purchased and should be used on a conversion and if welded soundly they should be as good as an original.

In the case of the cut in half car I suppose it will depend on good alignment and sound welding, after all that's how stretch limos are made. I have replaced cross members but never needed to cut the car in two. Nnot sure about the strength of roof chops.

I suspect the greatest risk for the strength of any model is more likely to be rot than modifications.

[MrIan]

There are two trains of thought in regards to welded mods. The main key word is "correctly" as in a correctly welded joint will be as strong if not stronger than a plain panel. Obviously no good if the joint isn't good. I posted on a jaguar forum when I was making and replacing the rear section of the chassis on an XJS, they were up in arms and saying the car should be scrapped !! Scrap a series 1 XJS ? Convertible conversions do need a lot of bracing and strengthening. As for roof chops if the welds for the 2 / 3 or 4 sections of roof and to the posts are all good I'm sure the bodyshell would be just as strong if not stronger due to the angle change of the pillars. Only my thoughts on it mind you.

[MrIan]

After a very quick look at that link yes the car was cut in two but from what I can see (on my small phone screen) is they put the two halves back together but with new inner and outer sills which I'd assume would span the joint. In any remaining body sections. If they then added floor pans really it's not a lot different than a normal restoration. All lined up and fully welded correctly to me would be fine.

[kennatt]

like all repairs body or mech. it depends on the skill of the person doing the work,so its pointless giving any advice as to how good ,unless you know the guy or can see some of his work. A number of years ago there was a guy who had a unit next to our family garage,who made a living doing cut and shut accident damaged repairs, (before the category system came into force).He had a caroliner jig and I saw most of his work. He used to basically put two crashed cars together by using the undamaged halves. But he used to go back to the original joints.As he pointed out all cars are built using sections on the production line,so if you unpick the car you can actually get to the stage where the sections ,be it a roof or front quarter etc, are at the same stage of build as in the factory. Then when you slide the bits together,on a jig of course,you are at the same stage.He was of the opinion that with his jig and more time than on a production line he could get the alignment truer,than the tolerance built into the production robots. I used to watch him and many times saw him slide halves and quarters together and was always surprised when I saw holes where he had unpicked factory spot welds line up with original spot weld marks on the other bit .He then fiddled with the jig and put the bits back to a more accurate aligment,the originals were always a few thou out. But he was a true master coachbuilder of the old school I learned a lot from him but would never claim to be capable of his standard of work.