Inspecting my Isetta front floorpan

[AndyL]

Been having a good old scrub on my Isetta floorpan. Corrosion seems to be limited to a few localized areas, and the floor actually looks better from underneath than on top. Quite a lot of pitting around the holed areas, which I think will develop into more holes with additional cleaning. I know from past experience welding flat panels can result in a lot of distortion owing to shrinkage, even with MIG welding techniques, plus the likelihood of blowing through in thin pitted areas so it's making me think it may be easier to replace the complete front pan. I'm loathe to do this, as I'd like to retain as much of the original structure as possible, and the floor is pretty solid.

Another option i was considering was perhaps brazing up the holes.

[Big Al]

Annoying pinholes. I agree, a salvage of the floor would be better. I have had a braised floor, but it failed in places, as the rust had not been removed. Lead loading? Mind you braising, by someone with some dexterity, or skill, can act in the same way.

[marcus]

Tough one: welding is hotter but very rapid, brazing is less hot, but needs heating for much longer and this can cause distortion; it also adds a different type of metal. Not really sure what to advise, but if it were mine I would try to ind a way of clamping/holding/securing stout doughnuts of metal or MDF above and below the pan to cover a group of holes, then weld a sheet of new metal under them, with the Os hopefully reducing distortion.

[Bob Purton]

I think I would cut out the worst and mig patches in. Not under or over the top but in and level with the section removed.
As you say though, if that were to get a bead or sand blast clean I think it would reveal a lot more holes. Maybe you should make the decision once that's done.

[AndyL]

Originally the floor was covered with a bitumen felt pad to dampen noise. The factory put these on with the shells primed and undercoated, then sprayed the top coat afterwards. I think moisture must have got trapped between the two layers. I removed the bitumen pad, and oiled the panel to arrest the corrosion but the damage had already been done through years of being stored in a damp barn/shed.

I can butt weld well, wouldn't lap panels on a car like this, small holes can be plug welded using a length of copper pipe hammered flat and held on the other side.

[Peel replica, Steve Fisk]

If it's a full restoration I would get a replacement panel and cut back all the pitted areas and cut the same out of the new panel and seem weld it , it's got a lot of swage lines to it so it won't distort if your clever with your welding , if it's just to get it on the road treat what's there and have a big 1mm plate cut out and weld it in with a load of tack welds and underseal . Be Easyer and neater than having a patch work quilt

[marcus]

I think Bob is right, you have to find out the full extent of the problem before starting to repair it. brazing needs Oxy-Acetylene and I believe you need a licence and safety cages to use it, MIG is less of a problem.

Joke: She was only the welder's daughter, but she had Acetylene legs!

[Jim Janecek]

that corrosion is over a wide area. That means the metal is much thinner over that entire area with some areas so thin, that holes formed.
simply filling the holes does not replace the rest of the metal missing from corrosion that did not perforate.   

This is a candidate for a new floor pan/patch panels or some other method of adding material to that entire area somehow.  I know there are "spray metal" type services that allow you to literally "paint" with aerosolized steel to fill in things like this but I don't know what is available locally to you or if it would be cost-efficient.

[marcus]

As Isettas have a chassis, does the floor need to be structurally sound? Even if not critical, I think I would rather have a solid new one than a possibly weak, repaired original one.

[AndyL]

You can braze with oxy propane. Gas welding requires acetylene though, and you can also use that for brazing, natch.
I think ultimately it's almost certainly going to need the majority of the front pan replacing, but it will cost nothing but a bit of time to try and patch what is there. Worth a shot I think.

[richard]

Nice one Marcus Acetylene legs  ! 

[marcus]

Well done Richard...a set o' lean legs! Head to the shops and buy a pack of Tunnocks Tea Cakes for your prize!

Shame you don't have an Isetta to eat them in ( < a not very subtle return to topic!)

[steven mandell]

Judging by the preponderance of perforations, and the appearance of a light convex bend alongside, but just slightly oblique to the transverse bead in your photograph- the floor is weak, and has permanently deflected under load already.
It needs to have its sub standard structure replaced.
Count your blessings if you can obtain an accurate replacement panel.  Do the cutting out of your original yourself so that the seam will be least likely to cause warpage, and be least visibly different from stock when done.
No sense trying to save old bad metal, if you have new identically detailed stock to replace it with, for after its painted it will both work and look as if it were original.

Leave it to a good professional welder to properly tack, and then fill in between these tacks in such a manner as to fully seam weld without creating significant distortion.
If you do all the preparatory cutting to the welders specification, you will probably find his charge to be reasonable, and the result to be the best deal overall.
Just make sure that your welder is both experienced and comfortable with the proposition before giving him the job.

[AndyL]

There is no creasing in the panel, that's just shading caused by the change of coating on the panel.

[plas man]

fibre glass matting and resin + hardener , as a permanent/temp fix , you probably get rid of the car anyway most owners do - there's not many true enthusiasts around .
once the floor is fixed and the seat is back in position don't forget the battery cover ...  (I did -hot pants  )