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MG MGB Technical - Floor replacement gap

Hi everyone, Im currently replacing a lot of metal on my B and im looking at the floors. A previous owner did an awful job on the sills and as such ive had to cut most of it out. My question is how does the floor weld to the inner sill and castle rail? From a trial fit the floor rests on the inner sill flange which leaves a gap between the floor and the castle rail which surely is a corrosion risk? How do people address this?
A P New

Eh? The castle rail, inner sill flange and floor are all spot welded together. Can you post a photo of your problem area? I can't understand what you mean. Have a look at this page from Paul Hunt
Mike Howlett

As far as I'm aware the floor pan is sandwiched between the castle rail and the sill, then seam-sealed from underneath.

However replacement floor pans seem to have upward flanges which can be used if the surrounding areas have corroded. That was definitely the case on the tunnel side, can't remember for the sill side.
Paul Hunt

sorry what I mean is that the castle rail sticks out further than the inner sill flange and so when you put the floor in you end up with a thin gap between the floor and Castle rail. I'll try to sort out a photo on here. is it meant to be simply seam sealed?
A P New

Ah yes, now I see what you mean. Yes, that's how mine was too, the castle rail is wider on the inner flange than the sill flange. When the floor is welded on top of the sill flange there is a slight gap (the thickness of the sill flange) between the floor and the castle rail. Fill it with seam sealer. That's what I did.
Mike Howlett

"When the floor is welded on top of the sill flange there is a slight gap (the thickness of the sill flange) between the floor and the castle rail."

That's why I think the floor should be sandwiched between the two. It's how my probably original but patched floor was, so I put the replacement back the same. If your inner sill, castle rail and floor pan have been reassembled in a different order in the past, i.e. the castle rail directly up to the sill without a floor, that won't be possible but will still leave that crevice.
Paul Hunt

A P, the outer edge of the floor panel should have a "jolddle" in it to allow the sill to sit on top of the castle rail and the inner sill. After market sills do not have this "raised strip" unlike heritage panels. I can probably get you a photo of a unused panel and of a replaced floor if it helps?
The floor panel welds to both the castle and inner sill. (Mike H yours must be seriously compromised if the floor is not welded to the castle!). Because of the thickness of the inner sill I find it best to weld that to the castle rail then clean up and weld the floor to the castle rail then the inner sill.

Best of.....
M McAndrew

That's interesting because all of my panels are heritage and there is no joggled lip. I have on order an air joggler / hole punch so perhaps I can make a raised lip on the castle rail side of the floor.
A P New

I have had to go back to my photos to find out what I did. After all it's around 10 years ago now. I've also had a quick look under the car with a light and a mirror. My Heritage floors did have the raised edge that Mike McAndrew mentioned. Not knowing any better, I put the floor on top of the sill flange with the castle rail underneath. Having drilled 107 holes in the edges of each floor panel (I counted them), I then puddle welded all three bits together, so I don't think there is any compromising of strength. I also welded the castle rail to the inner sill on the inside of the sill before I put on the inner membrane. It's plenty strong enough and still looks good after six years of all weather use.

Trying to dig up the memories, I can't actually imagine how the floor panel could be fitted between the castle and the sill flange. At the rear there is the triangular heel board extension, where the leaf springs mount. The floor must go above that. I can't see how it could be above that and yet below the sill flange. My floors sat firmly on the cross-brace too - I didn't have to push it down to make contact for welding. Ah well, I'm quite happy with what I did and constant use has not caused any problems with the structure.

Mike Howlett

"At the rear there is the triangular heel board extension, where the leaf springs mount. The floor must go above that."

I did only have to replace the front half of one of mine.
Paul Hunt

Thanks everyone and merry Christmas. Turns out im a 5* plonker, the floor DOES have the flanged edging. But I was able to weld in the castle rail yesterday so things seem to be moving forward.
A P New

Its all a big learning curve, dont stress. Have a great christmas.
Best regards John
john wright

i seem to recall something like this on 'An MG is born' - most parts available on utube. quite a useful series even if you only pick up one tip - and available on DVD for a fiver.
Graham Moore

This thread was discussed between 19/12/2015 and 26/12/2015

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