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MG MGB Technical - Which comes first, the floors or sills?

After having read everything I can get my hands on concerning sill replacement, I have a question that I can't find a satisfactory answer.

Both the floors and the sills need to be replaced in my '73 rdstr. Should I replace the floors first to add to the structural integrity PRIOR to removing the existing sills? That is, weld them in on three sides leaving the sill side loose?

I know I should be sure the tranny tunnel is well supported, brace the door opening, and maintain level as much as possible, would good serviceable floor panels help in this regard? Or would this simply preserve the existing body sag, making it very difficult to weld up the new sills correctly?

Thanks for any input.
TDHoward

Remove the floor pans first. I found the sill replacement much easier without the floor in the way. However, you could use the line of the floor as a guide for alignment by only removing the first 6 inches. Make sure you brace the door opening well by welding in cross members. Secondly remove one side at a time, this way the tunnel and opposite sill will provide stability for the tunnel crossmember.

-mike
Mike Zaffarano

On our current car I replaced the sills first using the original floorpan as a reference to sill positioning.

There is probably no correct answer to this, you just do whatever feels more comfortable to you, the last B I did (many years ago) I did the floors and sills together, I just hacked eveything out to the tunnel and put the sill and floor back at the same time, I found it made lining everything up easier. At the time I had access to a jig to hold everything in place so there was no worries about alignment, not having use of the jig any more I went the slower but but less nervewracking way of just doing one section at a time.

As the other Mike said, only do one side at a time! One final point, when replacing the sills on a B it is NOT necessary to brace the door gap, carefully placed jack stands are all you need, plus, if you do need to adjust the door gap during the process having a welded brace on there makes it more difficult. A midget does need the bracing. This information came from a Britsh Leyland dealership back in the days they existed and still used to repair our MGs.
MikeB

If you are only replacing the inner membrane and the outer sill with the floors and castle rail then the inner box-section should give enough stability if supported squarely. But I have seen strong recommendations to brace if removing the inner box-section as well - that is rather a big hole to have, how do you ensure that the cut ends stay in the same relative positions as before the cut? Even if the new or old floor is still there it's still going to flex along its outer edge if the ends want to move.
Paul Hunt

TD:
IF the truly structural part of the sill assembly, the heavy gauge inner sill (the part you step over when exiting the car), is not rusted much or at all, it is often left in place with only a clean up and killing of the rust on its inside surface and then sort of coating to prevent further rusting.

Then the castle rail, inner diaphram, and outer cover are replaced and welded in. Since the floor pans weld directly to the lip of the the inner sill, replacing the floors first might well be worthwhile for strength and locating the sill to the rest of body structure IF you know that the inner sill is indeed salvagable. Having a sound floor pan in place would certainly add to the structural rigidity of the unibody while you were working on the sills. JMO
Bob Muenchausen

Unfortunately the inner sill on the left side is not salvageable. I believe it is strong on the right side. That being said, I am probably going to purchase the sill kit from a company in Canada called obsolete auto. Their kit consists of castle rail, inner sill, outer sill inner diaphram and jacking point reinforcers etc. So If I'm buying the works I'd like to go ahead and do it right this time.

To ask a further question if I may. I do not have a rotiserie, where should the body be supported when removing the sill section? Assume I have a nice level workspace, various and sundry jacks and stands.

Thanks again!
TDHoward

Support the front end at the front crossmember. Place the stands on the A-Arm pivot. Use stands under the rear. Place 4"x4"x4" blocks between the rear and the bump stops. Put enough weight in the boot to keep pressure on the blocks. I did this to prevent the body form rising due to the springs rebounding when the inner sills were cut. I also needed to replace the heel boards and I felt the stands placed at the front of the hangers would get in the way.

I like to be cautious and I welded the openings. If the body is that stable without the sills why replace them? IMO if you support the car on both ends and cut out the middle (even one side) the body will twist and bend. This is especially true if the doors are removed. (I took the doors off, they just get in the way.)

Just a note, the braces that I welded in had a bit of stress on them when I tried to remove them. This leads me to the conclusion that something had to have moved during the process. Bracing should limit the movement.

Just my opion.

-mike
Mike Zaffarano

This thread was discussed on 20/11/2002

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