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MG Midget and Sprite Technical - Filling holes in sheet steel

What is the best method of filling in some small holes in a piece of sheet steel without causing distortion?

It is the rear deck of my Sprite, which has been drilled with several holes about 7 - 8mm diameter. I think it has had a luggage rack or spare wheel support fitted at some time. I want to fill them - preferably with weld with my MIG, but do not want to cause any heat distortion in the process. Any recommendations on the best technique?

Guy
Guy Weller

Guy,

If I were to do that with MIG I would try putting a piece of copper behind the hole as a chill, then quickly weld around the edge of the hole and in towards the centre. If possible, while the weld is still hot, peen the weld with a backing piece in place to expand it and counter the contraction. Dress the weld slowly afterwards to input as little heat as possible to prevent heat distortion from the dressing.

I would try it first on some scrap to see how it works out.
David Billington

Guy, the Mig will probably be the best tool for the job. Back up the hole with a welder's spoon or a block of copper so that you can use the minimum amount of time on the spot with enough heat to get a good weld. It might help to surround the area with a layer of heat sink material designed for that purpose. Don't know what it would be called over there or where you would get it, but Eastwood calls it "Anti Heat" http://www.eastwood.com/ew-anti-heat-compound-1-qt.html
Bill Young

Thanks, both,
I had a vague idea that the method was to use a block of brass or copper, but wasn't sure if I had dreamt that!.
Guy Weller

How about getting hold of some MIG brazing wire and using that with the MIG set? Heat input will be considerably lower, hence risk of distortion will be less. And it is not structural, so the lower strength is not an issue.

Jonathan
Jonathan Severn

Didn't know you could get MIG brazing wire. Can it be used with any standard MIG - I would have thought the current settings would be too high if it melts at a lower temperature?

Guy
Guy Weller

When I did it I took a piece of sheet metal and punched holes in it with a hand punch. Then I took the slugs, placed them in the hole and tack welded all the way around with the MIG. Make sure the metal is absolutely clean, both around the repair area and the slug itself. If you don't have a punch, rough the slug out with snips, it does not have to fit perfect.

I held the slug in place with tape from the back side. The first tack holds the plug. Remove the tape from the back. Hammer the slug into alignment if needed (use a dolly) and then tack until it is welded all the way around. Keep tacking on opposite sides of the slug. Move from one hole to the next and by the time you get back to the first it will be cool enough to do another tack. Take your time and don't let any area get too hot.

I have also built up from the edges, backing it with a spoon, but it takes more skill and more effort to finish. It is faster than cutting slugs, but I assume speed is not your goal. 5/16" is a good size hole to fill, but of course it can be done. As mentioned above, practice first. If you are doing it in one shot you will put a lot more heat into the panel.

The panels on a midget are pretty stiff, most are curved. I have done a lot of welding on the body of mine replacing rusted areas and I have never had any problem with distortion. It is not like welding on the American autos that have large flat panels stamped from thin sheet.
Paul Noeth

Oh, by the way, an auto darkening welding helmet is the only way to go. You want to put those tack welds in the right place each time. No skating across the boot lid with the arc looking for the hole. Beg, borrow or steal one if you don't have your own.
Paul Noeth

I believe it should be possible to MIG braze using standard MIG equipment, depending on its capabilities and the material you are working with, but I think Paul Noeth's suggestion of using small discs would be worth pursuing. I suggest you talk to a decent welding distributor and explain what equipment you have and what you are trying to achieve. Alternatively, try filling in the form on ESAB's website at http://www.esab.co.uk/gb/en/about/contact.cfm and see how they respond.

Jonathan
Jonathan Severn

Thanks Paul.
I have used that method in the past - for larger holes. I have even welded washers into holes so as to end up with a smaller central hole to infill - both with reasonable success. But I am always keen to learn if there are better techniques than my DIY, self taught methods, and what better place than here to learn from others!

5.16" holes are sort of on the margin between infilling with short blasts with the MIG, and stitching in mini-patch pieces. Given that the rear deck is a fairly large unsupported panel I thought I would check here for improved ideas.

And yes, I do use a self-darkening helmet. One of the absolute essentials for welding as far as I am concerned. The only improvement to it would be to have one with built-in mini "headlights" focussed on the work point as I find that the work does need to be well illuminated to make it properly clear before the moment that the lens darkens.

Guy
Guy Weller

...or one with a tighter fitting cover so that you could get your head inside the rear arch without having the mask banging and catching on the brake drum and wheel bolts. Grrrrrrrrrrrrr!
rob multi-sheds thomas

This thread was discussed between 28/07/2009 and 29/07/2009

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