Leaded repairs to a rusty panel.

Any chance of some Pix posted somewhere Dave?...

I did do some pics for the SD1 club - but sadly neither my cheap camera or phone would focus properly on the shiny bits. But then that could be down to me.

In article , Dave Plowman (News) scribeth thus

OK would have been nice to have seem the before and after!...

Here you go - but they're only a guide. Not all pics are of exactly the same spot.

In article , Dave Plowman (News) scribeth thus

Interesting that, thanks:)...

How much distortion was there when you surface tinned and patched - noticed some heat affected zones. If done correctly you don't usually get this.

None. But I could have used a lower setting on the blowlamp. Or moved it about a bit more.

You shouldn't get any but the picture looked as though you did.

All I have done is wipe some joints and filled small dents, worked out find and a permanent job - no paint reaction either. This was on an older car where there was metal to work with. The whole car was a file finish repair. Just primer surfacer then topcoat and clear.

Nowdays there is no metal to work with, they even laminate (glue) two skins together for strength.I think the Japanese developed this technique with the Suzuki.

It's quite possible. I did the pics in a rush after they were asked for on another forum. So actually undid one of the repairs. But luckily there doesn't seem to be any distortion.

I'm actually interested in knowing how long I can expect this to last. The part on the car at the moment was repaired by a body shop using their normal filler - and that only did a couple of years, or so. My memory of it says it was better (at the time) rust wise than this one. Of course until I remove it I've no idea how well it was painted etc on the underside

Right. ;-) No such 'advances' on this old Rover.

Rust is a complex reaction. Rather than simply being something that happens in one place on the car, it is actually part of a complex electric reaction. The rust just happens to show itself at one end of the circuit. Once cars stopped sporting highly polished chrome bumpers at either end then a major part of the "rust" circuit was eliminated, the shiny metal acting as one of the diodes. One can look to the sacrificial anodes that ships carry to see how this is working. If you can work out what the circuit might be in your car then you can seek to prevent further rusting. No doubt Googling will find some useful tips.

The only problem I have found with old lead wipes is if the lead has not bonded.

Serious rust is usually first obvious at the bottom of a cavity where moisture is trapped. Don't really see what chrome bumpers and diodes have to do with it.

I'm pretty certain this bond is good since it was well melted. When lead loading you tend to keep it at a lower temperture so it retains its shape.

The moisture allows the electricity to flow. That is why things rust only very slowly out in the desert.

See, for instance,

but Googling will find better descriptions. Chrome bumpers were bad because they unwittingly provided one part of the system. The air / metal interface that allow the circuit to run.

When I was studying such things, it was explained to me that minute inclusions of carbon in the steel provided one pole of the battery, and the mildly polluted water provided the electrolyte. Modern cars are less liable to rust because of vastly improved paint technology, which stops the moisture and the air getting to the metal. If you want proof, look at a modern car with accident damage that has damaged the paint film, the damaged bit rusts as quickly as a '70s Leyland rotbox. Modern paint films almost never fail by weathering the way that old ones did.

Chrome on bumpers worked in the same way as paint on steel, but the metal the chrome was on *could* set up a potential difference between the steel of the body and the bumpers when the chrome got damaged. Depending on the metals, though, it was likely that the bumper would act as a sacrificial anode, protecting the steel.

Rob wrote: [snip]

the Suzuki.

Hillman with the Avenger IIRC.

Take any two bits of steel of different sizes, provide an electrolyte, and

*some* current will flow, promoting rust. However, the effect is much over emphasised. Stick one piece of unprotected sheet steel outside and it will soon show signs of rust.

The trick is to prevent that electrolyte making contact with the steel. Cars these days use wax inside cavities to stop this. And many use galvanised steel for the important bits anyway.

However, design has still got a great deal to do with it. Some fairly recent cars were bad for rust penetration - the Ka being one.

? If both plates are the same grade of steel, even in salt water, there won't be any current flow between them unless there's a changing magnetic field inducing a current flow or leakage current from somewhere.

The unprotected single sheet of steel rusts because, if you look closely enough, there are microscopic pieces of carbon embedded in it, and there is an electrochemical reaction between the carbon and the steel. The reason steel corrodes so quickly is that the corrosion products occupy more space than the original metal, so they flake off to leave a new surface to corrode, whereas with most other metals, the corrosion products are the same size as the original metal, so they stay attached, forming a protective layer.

All true, and the major improvement in paint films was when the electrophoretic paints came into use, as the way they are applied ensures that the metal is completely coated with a well bonded, air and moisture proof layer.

I knew there was a reason for disliking them, apart from them being as ugly as sin.

[...]

They are however an absolute hoot to drive, on a par with the original Mini.

Chris