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MG MGB Technical - welding floor pan in

I believe I reviewed all the posts, and have not found an answer to this question. I have experience with drilling out spot welds, and am trying to avoid it (I realy hate this job). I cut out all the pieces of the old floor around the cross and longitudinal supports, on my 1971MGB. Of course the remnants of the old floor pan that are spot welded are still present.

I am thinking of just dressing up the old pan edges to make them flat as possible, and then spot weld the new floor pan onto these old edges. So in essence I get away from drilling out all those spot welds. Do you think this is an acceptable alternative? It certainly would be easier for me.
r schwartz

r,

It will work, and if you clip the old floor between the spots, remove the strip between the spots, and then grind the remnants of the spots off entirely, it may be neater than having the holes.

Also, sharp bits and a good center punch are what take the pain out of drilling spot welds.

Charley
C R Huff

Snap-On tools make an ideal spot weld remover kit. It consists of a variety of sizes of small hole saws and they have a central locating pin.These saws mount on a small mandrel with the spring mounted locator pin.You choose the size of saw needed. Just center-punch the spot weld and place the locator pin in it, The circle cutter surrounds the spot weld and cuts all around it. I have used mine in my shop for over 25 years now and it still cuts well.
Sandy sanders
Sandy Sanders

Whilst the floor pan was originally sandwiched between the inner sill box-section and the castle rail, it's quite OK to drop repair panels (or even original panels) in on top of the sill and tunnel flanges and weld. Repair panels usually come with their own flanges to 'replace' those that might have rotted away from the sill/castle-rail and tunnel. If your flanges are good cut the floor flange off. When welding do one tack on each side first, then gradually fill in halving the distance between them, moving to a new side for each weld. If you try to weld along the join the heat will distort the pan and you will end up with a bulge in the last corner. And before you start *welding*, make sure you have the welded nuts for the seat mountings in place, especially the fronts as they are concealed by the fixed cross-member.
Paul Hunt 2

What the brits would call a "Bodge". It will work, but it is wrong. Your car till you sell it.

When I look at a car either for myself or a friend, this is exactly the kind of thing I look for and that makes me keep looking.

YM2$W

Pete
Pete

Years ago, my brother-in-law and I were rewiring a mutually-owned summer cottage. He was doing incredibly neat work of wiring that would eventually be covered by panelling. As I was admiring it and then trying to imitate it, he said something like: "Isn't it neat that we're doing this just for fun so we can take the time to make it as neat as possible". Wow, what a lesson, and it has never left me.

So, I know it's OK to do the floor pans this way. But I get my pleasure, in working on MGs, out of doing things as well as possible- just for the sake of doing things as well as possible. I feel like it is a better use of my time. Sometimes, that means a LOT more work to make the job more aesthetically pleasing, even though all evidence of it will eventually be covered up. And so it is with my B/GT. As I drive it or just gaze at it, I know the unseen repairs were done really right and it gives me a sense of pride I would not otherwise have.

Your time is the most valuable, irreplaceable, commodity you have. I don't like to waste mine by compromising the quality of my work.

' Guess the ultimate answer really depends on your own temperament, and I shouldn't presume to have the only right answer. The bottom line will be will you enjoy your MG as much as I enjoy mine.

I'll relinquish the soapbox now...

Allen
Allen Bachelder

I don't know anyone who ever enjoyed the job of drilling spot welds and cutting out rusted floor pans. Its a horrible job that's dirty and time consuming. With that said, its your decision on how to make the repairs. Do you plan on repairing the car to sell it, pass it on to your kids, get buried in it? Think about your end goal when you tackle these monotonous jobs.
Jeff Schlemmer

R.

Go to your local auto body supply store (auto paint shop may work). Ask for a spot weld cutter. This is a small bit similar to what Sandy described. These cut around the weld.

It still leaves a raised spot, but short work with a grinder takes these down.

You can also cut the panels, avoiding the rails and then use a air chisel to cut the spots. Will still have some cleanup with a grinder.
Bruce-C

I wouldn't leave the old flanges attached, just another place that will attract rust and start the downfall of your new floors. Rather than drill out all the old spot welds or use the cutter on them, I just started with a 4" grinding disc and started grinding down the sheet metal around each weld. As the metal becomes thinner it will start to glow red in the thin sections and stay darker at the spot welds then you can grind these away and have a nice clean flange to weld your new floors to. It's really pretty fast, much quicker than drilling in my opinion and works great. There will be some welds where the grinder may not reach, drill those. I did cut away all the extra metal and just leave the flanges and area across the crossmember top to grind, made grinding access easier as well.
Bill Young

I wouldn't grind away one of the existing flanges, the three thicknesses are part of the strength of the sill/floor assembly. If you do that you will only have two of them - castle-rail and floor left, unless you are very good at seam welding the floor pan to what remains of the square box-section part of the sill as well as spot or seam welding to the castle-rail.
Paul Hunt 2

Paul, I think I may not have been clear, I didn't mean to grind away anything but the remaining protion of the floor pan after the center areas had been cut away. You're left with the flange from the trans tunnel and sills and the overlapping portion of the floors, just grind the section of the floor away leaving the rest intact. This is working from the top, floor pan side so the top layer would be the old floor pan which is what you want to remove. You will replace that layer when you install the new floor pan and plug weld it in place.
Bill Young

For grinding in tight spots use a die grinder with a carbide burr.
John H

When I did my floors (actually done it twice now on two cars) I used Bill's method. I sanded/ground the existing floors thin enough that I could then get a chisel under the steel and chop off the rest.

The other trick I learned was to cut out most of the floors before you start. I carefully drew on the top surface where it was safe to cut and chopped out three large sections just leaving a thin strip around the spot welds. It made it a lot easier to work on and I was able to do my grinding/chiseling trick and remove the long strips that were left.

As for doing a 'bodge' job well having seen a lot on the car I am building now I find it just makes me wonder what else they didn't do properly. Any subsequent owner will see the job you do and use that as a measure against everything done on the car.

Oh, one other thing I did learn (the hard way) is if you are doing any cutting or grinding in the car make sure you cover up all exposed glass very well. Otherwise you end up with little metal specks melting into your windows!

Simon
Simon Jansen

Jeff,

I didn't say I enjoy drilling spot welds. But I do enjoy the satisfaction of doing things the way they are supposed to be done. I'm glad I'm not trying to do this for a living! The hundreds of extra hours would never pay for themselves. My methodology is pretty much like Bill's. And then I leave the flanges on the new panels because that saves me from a few future moisture traps at the edges of the new floors. Then I punch the new flanges and drill a few hundred holes where I can't reach with the punch, and plug-weld the new floor in. I know there's a running debate about whether to cut the new flanges off or not; that's one place where I differ from the factory technique for reasons already mentioned.

I also agree with Bill about not leaving the old floor edges in place and welding over them. Too much rust in there already between the layers, and what a dandy place for more moisture to accumulate.

FWIW,
Allen
Allen Bachelder

Must remove the flanges for a proper job. It's not too bad a job if you just hook the end of the flange round an old file and then wind the file with a wrench and remove the flange in a similar way to opening a tin of corned beef. Then clean up the remainder with a grinder
Iain MacKintosh

Got you Bill, but I thought the floor pans were sandwiched between the square box-section inner sill and the castle rail from the factory? The sills on my roadster had already been replaced when I got it though. Pete from Canada was rather rude about my 'British Bodge' of dropping the new floor pan on top of the flange (even though when I did mine I cut horizontally through the remains of the old floor pan and its spot-welds, and could slot the new floor into the resulting gap). Although maybe he was referring to the use of the flanges on repair sections that can be used to take the place of rotted sill/tunnel flanges (which I didn't do either).
Paul Hunt 2

When I did mine I painted all around the flange with zinc paint. Then after welding the floors in I seam sealed the bottom of the floor. After that dried I literally poured rust proofing into the seams from the top of the floors. I made sure it was well soaked. Then after leaving it a while I cleaned off the excess from the top and seam sealed that side too. I used a zinc rich sealer we get here called Galvseal. I figure that way the seams are impregnated with rust proofing and the top and bottom are sealed to stop any moisture getting it.

Well, I hope!

Simon
Simon Jansen

This thread was discussed between 13/04/2008 and 16/04/2008

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