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MG MGB Technical - Anti rust

I have just started a winter project on the roadster, one that I intended to do last winter.
Around the beading on top of the rear wings is showing signs of corrosion under the paintwork. I intend to take it down to the bare metal but do not want to remove the beading. Any suggestions as what to use to kill or slow down further rust from showing after the repair. I have seen a product called Kurust, is it any good.
Trevor Harvey

I've just bought some Fertan, which is supposed to be very good!

http://www.fertan.co.uk/
Dave O'Neill2

I use FE123 which has a very good rep and looks to be the front runner in the Practical Classics long term test. http://www.rust.co.uk/rust-converters.cfm

You do know this will be a short term fix, don't you? The rust starts deep down the bead joint. Most likely from the underside in the boot and cleaning the top will make it look better for a few years. It will return and replacement is the only full cure.

MGmike
M McAndrew

I use phosphoric acid, 2.5% usually but would go 10 or 20% on a job like this known to be difficult to kill. I scratched out as much rust as I could using a scribe point and even a pin before treating. A little bit of liquid soap will reduce surface rension and let it penetrate better. This joint is open in the boot so I painted over it there with the Dinitrol cavity wax.
Stan Best

I find all the Bilt-Hamber stuff excellent - always come out well in Practical Classics test as well.

Do the full range of converters and rustproofing stuff.
Hydrate 80 is their converter.

R.

richard boobier

I used the same method as Stan on both my B's in the 1980's and the rear wing seam continues to be rust free. I used needles - they're harder steel and have a finer point than pins. The cars were only about 5 years old when I did this job, and the rust was only just beginning to show.

At the time I tested a number of the popular rust treatments, most of which are no longer available. I cut off some short lengths of rusty mild steel and applied each of the products, and also used a couple of different primers plus a cellulose top coat. After being left outside for about a year with the occasional sprinkle of salt I could see that some were obviously better than others. I remember Kurust was one of the poor performers - but the current version of Kurust may be an improved formulation. I can't remember the one I selected as best, but I do remember it contained 10% phosphoric acid. I now use phosphoric acid; I buy it as neat 100% (on eBay) and dilute as required. The main thing I learnt from that excercise was that primer does make a difference and the samples which received two coats of Zinc 182 were all better than the one-coat ones, and much better than bog-standard cellulose primer.
Brian Shaw

Thanks for the replies, some useful info.
Brian, I have had a look on ebay,ther is several different types of phospheric acid advertised on there. Is there one in particular that is more suitable.
Mike I realise that to remove the beading is a more permanant job, but I think this would destroy the wing in the process. I have had the roadster for about 5 years now, and the corrosion on the top of the wings has not got much worse in that time, so hopfully a decent repair should last for several years
Trev
Trevor Harvey

Apparently, milkstone remover - available from farm supply shops - is phosphoric acid based.

Also, this product from garden centres...

http://www.greenshorticulture.co.uk/categories/Plant-Nutrition/Nutrient-Management/pH-Down/
Dave O'Neill2

Trevor, the problem is the method of construction. The beading is actually a T-shaped piece of steel which is spot welded between the two sides of the seam. So you have three pieces of steel welded together with no anti-rust protection (because the welding burns it off) and only a skin of paint to keep the water out. The rust starts deep down in the seam, so treating the top will only be a temporary fix.

Paul Hunt has posted sometime ago that he ground the beading out leaving a shallow V-shape on top of the wing. He then fixed a new bead with the leg of the T chopped off into the groove. I can't remember whether he used an adhesive or solder. Short of taking it all apart, that's probably the best cure. I took mine all apart and refitted it without the beading and without welding, so it is rust protected in the seam and filled over to prevent water penetration. I like the rear wings with no beading, but that's just my preference.
Mike Howlett

Trevor, I have a similar problem on the front wing seems with some rust threads occuring on the panel in front of the windscreen. I have treated this temporarily but when I come to paint the car I shall grind off the beading and treat as far down as I can get. I then plan to epoxy in a piece of shallow beading. I don't particularly want to disturb the front wing fixing.
Steve Church

I didn't grind the rear beading out but hacksawed along the length of it i.e. through the leg of the T and the spot welds, then dropped a new length in and mig-welded it from below. This was only a foot or so part of which had corroded away so it was relatively easy to dig in and get a Junior hacksaw blade through the gap to start cutting, the rest was fine. That was over 20 years ago, so far it's not come back, that's longer than the original!
PaulH Solihull

Trevor - the product I bought via eBay was 81% phos acid, not 100% as I stated. It's listed as "PH Down Phosphoric Acid 250ml", probably similar to the one Dave's post links to.
Brian Shaw

phosphoric acid has the advantage of running like water but if you can cut down into the joint, try a dab or two of Zinga - cold galvaniser. Paint over the top and it will be a long time before the rust breaks through again.
FWIW
Roger
R Walker

How would the phos.acid be used. I intend to brush it on the area and try to get it into the joint. Do I need to wash it off after a while as it is an acid. or just let it dry before painting.
Trev
Trevor Harvey

It depends, if its a thin film of ferrous phospate it will be attached to the metal very firmly and you can just paint over it. If theerre was alotof corrosion you may needot brush the loose salt off. Its pretty obvious once it's dried.
Stan Best

This thread was discussed between 25/11/2011 and 29/11/2011

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