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MG MGB Technical - floor spot welds

Can anyone tell me how many sport welds there are on the floors? Are they all around the perimeter and on both sides of the cross-members?
And a source for a long spot weld drill to cut the welds along the side of the transmission tunnel?
Andy Taylor

I drilled all of them out with 3/8 cobalt drill bits which didn't drill into the underlying metal. Took a long time. Then used a flat chisel to bust them apart if they didn't release easily. Wire brush first to find them all.
I think I counted about 110 spot welds on each side. Someone correct me if I am wrong.
Sam

Andy

If memory serves me right, I counted 230-235 spot welds when I removed the driver floor in my 67 BGT. About one every 1.5 inches.

They are around the perimiter and on each side of the crossmembers. Also, at the rear outside corner, they form a triangle for the corner bracket.

I cleaned off all the sound deadening tar, sprayed a light coat of paint around the edges and lightly sanded. This brought out the welds and made it easier to get the spot removing bit over the weld.

I didn't need an extension for the ones near the tunnel, but imagine it may be easier with one. You can get a drill bit extension at most hardware stores. They come in various lengths.
Bruce Cunha

Sounds about right. When I put new floors in I counted all the new holes I had to make and that was about 120 per side.
Simon Jansen

Andy-
Forgot to suggest - this is a job you would probably want Goober to do for you. Or Gomer, if he's back from the Marine Corpse.

And the spot welds go all the way up and down both sides of all crossmembers.
If they built the levees like these floorboards New Orleans would have never seen any water.
Bob

If he's a corpse, he's not going to be much help! ;-)
Rob Edwards

Eastwood carries special drils for drilling out spot welds, check them out at eastwood.com
John H

You can get a spot weld cutting bit at most automotive stores that carry paint or body working material. One recommendation. Buy at least one extra bit. For the one I have, you get two cutting surfaces, just have to take the bit off and turn it over. I still recommend buying an extra.
Bruce Cunha

Here's my replacement floor after it was drilled for plug welds:

http://mg.stinch.com/images/04091102431.jpg
Rich Stinchcomb

Forget drilling the spot welds out if you have an air hammer with a sharp chisel. If you're careful, all you'll have to do is dress the old welds with a grinder to even up the panels.
B

Drill guide holes from underneath so that you don't cut into cross & side members. Then chop out the floor with an angle grinder from above. Then you can get a chisel in between the floor & the supports or grind the bits of floor off that are left. Barrie E
Barrie Egerton

I found that cutting the old floor remains away with a nibbler and cutting wheel was quicker, then ground off the remaining material around the spot welds with an angle grinder. Left a clean surface to spot weld the new floors to and I belive it was quicker than drilling in the long run.
Bill Young

There is one reason why you may want to drill he spot welds. The old floor makes a nice template for drilling or punching the holes in the new floor.
Bruce Cunha

Thanks for all the information!
MG must have hired their welders from a battleship shipyard. They certainly put enough welds in.
I'm now thinking of checking out our local immigrant body shops; cheap labor for a boring (n.p.i.) job.
I like the idea of pilot holes as a reference.
The air hammer and chisel idea may be my next trick. I have access to a VERY big compressor.
Eastwood is a great source for me, as they are 1 state away. Quick shipping. I'll have to check out their site some more, though.
Rich - great picture. many thanks. Now I know how much work I'm looking at ;-(
Andy Taylor

Andy

Took me longer to weld in all the holes then to drill them out. Also a bit of fun getting the welding helmet under the dash.

As for the number of welds. The floor pan is a part of the body structure as this is a unibody car. The archives talk about some folks using industrial glues to install the floorboards (as they do with some of the new cars). I have not hear anyone give a report back on how that held up.

I like the fact that the floor is very secured by all those welds.
Bruce Cunha

Andy

Here's a link that shows some of the work I did to the floors of my 78 B; http://mg.stinch.com/garage78bbody.html
Rich Stinchcomb

Rich, can you explain those Cleco fasteners to me please? They used them in the MG is born series too. Never ever seen them locally though. How do they work?

When I did my floors I did a similar thing to you with the 4x2s. I used a thinner piece of wood and jambed that up against the firewall down to where I was welding the hold the floor hard against the flanges.

Simon
Simon Jansen

The Clecos are a temporary pop rivet. They are loosened with a special plier and are placed through an 1/8" hole drilled through both panels. They also make another style that is like a mini vice-grip to clamp two panels together or to hold two panels for butt welding. Very handy! You can get them at Eastwoodcompany.com as well as others.
Jeff Schlemmer

Why do I find out about all these useful things only AFTER I finish doing all the major welding on the car :)
Simon Jansen

I've seen the Clecos in the Eastwood catalog, I believe, but have never gotten around to buying them. Drill screws are much cheaper and you can use them ad nauseum. Go slowly driving them or you'll strip them out. Even so, I do strip about one in twenty. In those places or where drill screws won't snug the pieces together, I've used #8 or #10 screws and nuts. Of course, all the holes from the drill screws, etc. need to be welded shut when the plug welds are done. Also, I use 3M "Weld-Thru".

During a test-fit, I scribe along the edges of the crossmembers from underneath, then pop the floor out and drill all the plugweld holes just inside the scribed lines. The outer perimeter holes I punch with an air punch. Responding to the old argument about leaving/not-leaving the flanges on the floors, I leave them on as (1) I can do a neater, sturdier, job that way, and (2) that leaves the floor in the form of a shallow tray; should some moisture get through to the floors, it won't soak into the seams. I know it's not "correct", and it does involve more hand drilling for plug welds down inside the flanges, but it thus effectively double-welds the perimeter and I don't feel quite so bad if on rare occasion I hear that ominous "tink" as one of my plugwelds cools.

A hand-held welder's mask such as came with my Lincoln 100 is handy in tight under-dash places. I also run a fan while doing these. Otherwise the welding fumes are irritating.

FWIW,
Allen
Allen Bachelder

I am going to be doing some of this myself (soon) I hope. I have my '78 and my buddy's '77 to do floor work on. This is an idea I had while reading everyones suggestions/previous work: Go around the perimiter putting the correct size hole for the plug weld and then alternate with a 1/8 hole for the Cleco fasteners. this way, you can put in several Clecos for an area and each alternating hole is fastened down for the plug weld, once you have gone around the whole thing, redrill the 1/8 Cleco holes and plug weld them as the alternating welds you already did will keep them held down.

btw. what IS the correct size hole for doing the welds on the floor? I saw 3/8 mentioned in the second post, but didnt know if that was standard or not. I assume some of that depends upon how close teh welds are (1.5 inches avg.?) and the amperage of your welder possibly?

Thanks for all the great info guys!

John
John Snider

Yeah, the size of the hole for plug welding is a bit of an issue for me too. I have been trying one of those joddler / hole punch things, but the holes it makes seem too small. When I weld, I don't manage to stick the weld to the metal underneath, just fix a blob over the hole. A bigger hole seems to be the answer, but that means drilling, which is a PITA compared with the punch.

Mike
Mike Howlett

Mike, you could try turning up the power a little on your mig. I have used jodler punch holes and not had any problems. When ever possible I check the other side for evidence of good weld penetration. The spacing I use is no more than 3cm.

David
David Witham

Spot spacing should be one and a half inches and the hole diameter should be 1/4" As David says turn up the heat a bit as you have no penetration. Check on the underside for penetration or try a couple of scraps on the bench to get the right setting
Iain MacKintosh

My joggler tool makes 1/4 inch holes an the seem fine for welding though. I also used about 30mm spacing. When you do weld you could also spray some weld through zinc primer on the flange and underside of the floor. Just to give some extra protection in the seam. When I did mine I seam sealed from the bottom, let that dry then literally poured in rust proofing from the top into the seam. That then crept into the seam. Once I had let that sit a bit (on a hot day is good so it creeps) I wiped off the excess then seam sealed from the top.
Simon Jansen

I have to say that I share Mikes concerns. I just finished welding up one of the two floor panels that I have to install and the problem is not that of not enough heat, but of just getting the weld wire to find the bottom of the hole before hiting the sides and starting the spark prematurely. Being a very amature welder (Just started last year on my own)I had great difficulty with this. Of course starting off all the way forward under the steering wheel didn't help. Half the trick was keeping the welding helmet in front of me. I know I have a number of bad and/or ugly welds up there, so I seam welded the whole thing too. Once I got to the back end of the floor I was doing really well in the holes because I was able to see under the welder nozzel with both eyes and hit the bottom of the hole. Much better welds. But I stil seam welded around there too.

So maybe the right hole size has more to do with where it is.

Mark R.
Mark Rotsky

I find the punch holes to be fine also. I've found it helpful to put the tip of the wire on the base metal right in the center of the hole, keep the voltage high (on the four-step control for the Lincoln 100, either of the top two settings - but I use the top setting when dealing with the heavier gauge metals found in the floor flanges), and don't be afraid to squeeze the triger for a little longer than instinct tells you. Too long and you just burn another hole, but experiment with scrap and see what happens.

Make sure all welding surfaces are VERY clean! I can't emphasize that enough. Sometimes the braided wire brush on my 10,000 rpm 4-1/2" angle grinder is barely equal to the job. Listen carefully to the sound of your weld. The business about "eggs on the skillet" is really true. If you get a sputtering sound, your weld will not be good, and it will usually be because the surfaces were not CLEAN. How about wire speed? Remember to start with 3/8" ESO (electrical stick-out) and err on the fast side. After your weld, do you still have 3/8"? If it's less, speed up the wire feed. Better to end up with perhaps too much. I generally find myself running at faster wire speeds than recommended.

I don't know if you're working with shielded wire or solid wire with bottled C02-Argon, but I HIGHLY recommend the latter. I bought the conversion kit for my Lincoln 100 and it was the best investment I've ever made.

If you tend to worry about wasted wire or gas, GET OVER IT! Don't start a weld with more or less than 3/8" ESO. When your pressure gauge goes to zero, replace the bottle!

I hope this doesn't sound like professional advice, because it isn't. I'm just another self-taught amateur, and every time I squeeze the triger I learn something. I'm still learning, and I'll gladly listen to anybody who knows more than I do because I hope I never stop learning. These are just some of the things that have helped me to improve.

FWIW,
Allen
Allen Bachelder

Won't seam welding make it harder to cut the floors out if they need to be replaced?
Andy Taylor

This thread was discussed between 05/12/2005 and 23/12/2005

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