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MG MGB Technical - Sill, Floor & Rear Valance Panel Restoration

MGB GT Mk1, January 1967



Hi everyone,

After investigation of the floor cross member my suspicions on its weakness has been confirmed, so I've finally bitten the bullet and committed to its replacement. I expected this to be really difficult; as it turns out, this was easy compared to the removal of the sill castle rail sections...

I now intend to replace the outer & middle sill sections, jacking point & support, and floor cross member. The inner sill step, so far, don't seem to need replacement.

From reading the BBS archives recently, I understand the castle rail sections are fixed to the floor pans by a series of spot welds. However, on both side of my car, a previous owner has welded the floor pans to the castle rails along the entire floor length from the underside. In tackling the castle rail replacement, I pondered the grinding out of a 2m long MIG weld seam on each side of the car. Needless to say, I didn't need long to come to the conclusion that this was not a viable option.



I would appreciate if anyone could comment on the two possible solutions I've come up with or suggest any other options.

(A) Remove and replace the floor pans in addition to the sill & castle rail section (Again, I don't think the inner sill steps need replacement).

(B) Remove and replace a 5 to 7cm strip of the floor pan adjacent to the inner sill step. This would effectively remove the heavy MIG welded seam between floor and castle section.

The floor pans are the original factory fitted ones and are in very good condition with just some dents from the underside; some metal repair sections have been welded at the front of the LHS floor pan adjacent to the sill.


My rear valence is quite sound apart from the rear quarters. As the rear valence is a complex panel I've decided to repair only the poor sections. I've designed a paper template that will be used to cut out a 1mm sheet steel repair for both sides of the car. I have designed in cut-out strips in the paper template to allow the metal repair to folded (and closed by welding) in three dimensions.

Again, I'd really appreciate if anyone offered some advice or comment on their experience of rear valence repairs.

Many many thanks,
Brian McIlvenna
Brian McIlvenna

A book that I found to be very helpful is Practical Clsssics: "Colour MGB GT Restoration"

Hard to give you advise without actually seeing what you have. Generally, I would say leave as much good metal as you can.
David Werblow

Brian,
Been there, done that, although I didn't have seam welds to cope with. I didn't change the inner step sill either, but it did need a patch at the front end.

The castle rail and the floor are both spot welded to the inner edge of the step sill. I fitted the castle rail first and put the floor in once the sill was complete. The outer edge of the castle rail and the outer edge of the step sill are the places to weld on the internal diaphragm, so you need to get the vertical gap between them right. Then the outer sill goes on the outside. Use the door to get the outer sill lined up properly. Be patient, the panels are unlikely to be a perfect fit, so time and cunning are required to get it right.

I expect the factory welded all the bits at once, but I didn't. I used a plug welding technique with a MIG welder, fixing the castle rail first, then the diaphragm, then the outer sill, then the floor. In my photo you can see the new castle rail plug welded to the inner step sill.

The floor was the worst - I counted 107 welds on each side of the car to fix the floor panel. Using the MIG down in the footwell was a serious hazard to health!

I think if it was my car I would want to remove all the old floor panel and do the job properly. Only you can decide if you have the stamina to do that. I have several photos of various stages of sill repairs. Let me know what you would like and I'll see what I can do.

Mike



Mike Howlett

You will note in my picture the welded bar across the door opening. This may not be necessary on a GT, but is a must for a roadster shell.
Mike Howlett

Mike,
haven't we all been there ;)

Brian,
there is a repair panel for the outer section of the floor available from (Mike cover your eyes ;) MGOC spares. I'm about to order two for my not so rolling resto on the basis I don't fancy (can't be bothered) unpicking all the spot welds on the full floor for what will be a daily driver. To be fair, there's no need to if the rest of the steel is good and your seam welding is up to standard. I just like to retain as much of the original as possible.

Like all things, if you have time an patience, the rear valance corners are repairable, if a little complex curving two ways. An alternative would be a lower half valance which isn't to difficult to swap or just to cut the bits off you'll need.


Best of.....
MGmike




M McAndrew

You can buy 1mm thick cutting discs to fit an angle grinder - they make short work of cutting even long lengths of weld or panel.

Buy a pack of ten - they do wear down quite fast!

Chris at Octarine Services

David,

Thanks for the book tip.

Mike,

Thanks for your contribution; I would be interested to see the photos you suggested.

Interestingly, you highlight the need for the door aperture brace. A local mechanic suggested the same to me. I have placed front axle stands under the floor length box sections, just about at the point of the sill ends. The rear axle stands are immediately in front of the rear spring hanger. I've also supported the rear axle and a little of its spring resistance independently at the differential. Another independent support under the front axle cross member is GENTLY resisting fall of the car's front. I feel this multi-point support will insure against floor flexing that may be associated with sill removal.

Regarding the castle rail removals, I will need to at least cut a floor length strip from the outside of each floor plan to realistically have any chance of succeeding in the castle section removal. The MIG weld seams I highlighted have come through much of the floor so I would expect a messy perforated floor if I were to otherwise try and separate it from the castle section using grinder and finish with a sharp flat cold chisel.



The floor pans have captive nuts for the seats, captive bolts for service tunnel straps (on the RHS), weather protected drainage points and grommet holes (approx 30mm dia). Does anyone know if the new floor replacements have these fitted or must they be built in?


Has anyone had any experience in repairing the corner sections of the rear valence?

Thanks for all your contributions,
Brian
Brian McIlvenna

Mike in Lothian - I had to take a heart pill seeing that cursed acronym in your email.

I fitted a new rear valance, which was simple with the rear wings off, although you have to be careful that the heat doesn't melt the solder that fills the body seams above.... How do I know that?

I welded the valance to the chassis ends - you can see the holes ready for plug welding.



Mike Howlett

Guys,

I'll look up that floor panel repair. I have been using the 1mm discs and they are good. Unfortunately, the welding seam is deep above the castle rail lip so I can't see it being practical to remove the weld without causing collateral damage to the floor.

I wonder if the rear valence repair can be fitted tidily as it would need to be joined at the bend of the original valence.

Thanks again,
Brian
Brian McIlvenna

Mike,

Nice work with the Valence:-). I can see the access advantage of removing the rear wings. I had a rear wing replaced in 2003 when I had the car painted and am loath to cut it out to create rear valence access and better access for sill replacement. The other wing is also in good condition. Not sure if I'll just go with the wing dog leg section on each side...

Brian
Brian McIlvenna

I started by cutting out the floor with a cutting disc from under the car (the car was on its side), leaving just a strip welded round the edges. This was removed by drilling and with an air chisel, noisy but effective.


Mike Howlett

The internal diaphragm (membrane) had all but vanished when I got the outer sill off.


Mike Howlett

Brian,

"The floor pans have captive nuts for the seats, captive bolts for service tunnel straps (on the RHS), weather protected drainage points and grommet holes (approx 30mm dia). Does anyone know if the new floor replacements have these fitted or must they be built in?"

If you get proper Heritage floor panels these will be included. "after market" panels don't have any of the nice touches....

Unfortunately 3 sync floor panels are a bit more expensive.

Best of....
MGmike
M McAndrew

Here you can see the patched inner sill and the castle rail fitted. The text I put on the photo was to remind me how to do it when I got to the other side of the car!



Mike Howlett

Here you can see the vital measurement of 5.5 inches from top to bottom.



Mike Howlett

The next thing was to weld on the outrigger repair piece.


Mike Howlett

Then the jacking point reinforcement, then paint. It seems that I had to patch the inner sill at this point - I had forgotten that detail. This is the opposite side of the car.



Mike Howlett

Then the internal diaphragm (membrane). Seeing all those drilled out welds on the side of the footwell reminds me that separating all those layers of metal was really tricky. I've patched the bottom of the A-post too, as you can see.


Mike Howlett

And finally, the outer sill. Phew, did I really do all that? Hard to believe. By the way, all my panels were from Heritage and the floors did have all the captive nuts. I reinforced the welding around the nuts since I had them break off on another MGB I owned. The floors fitted quite well. The wings weren't so good, but that's another story.
Mike



Mike Howlett

Mike,

Thanks for taking the time to put up the images and descriptions. I take it that maintaining the 5,5" measurement is needed as you weld the castle rail to the inner sill (step)?

To ensure the castle rail outer edge is vertically aligned with the outer edge of the inner sill (step), I take it you had to position and clamp the membrane in place. Would the clamped membrane not give a reference so that the 5,5" distance would not need to be measured?

How did you remove the welds between the old castle rail and inside edge of the inner sill? In the factory, were these spot welded together with the floor pan as one unit or was the floor pan joined to previously welded castle rail and inner sill?

Thanks,
Brian
Brian McIlvenna

Brian, I'll try to answer your questions, but you must realise that this was 7 years ago and my elderly brain gets a bit fuzzy round the edges!

" I take it that maintaining the 5,5" measurement is needed as you weld the castle rail to the inner sill (step)?" - I don't remember being very fussy at the welding stage. Because of the size of the components the measurement is going to be close to 5.5", and I simply tweaked the castle rail once fitted to get the distance right.

"To ensure the castle rail outer edge is vertically aligned with the outer edge of the inner sill (step), I take it you had to position and clamp the membrane in place. Would the clamped membrane not give a reference so that the 5,5" distance would not need to be measured?" - Actually I didn't do that. Seems like a good idea, but not something I thought of! I do recall making sure that the castle rail was dead parallel to the fore-and-aft chassis member that goes forward under the footwells.

"How did you remove the welds between the old castle rail and inside edge of the inner sill? In the factory, were these spot welded together with the floor pan as one unit or was the floor pan joined to previously welded castle rail and inner sill?" - I removed the old welds with special spot welding drill bits. Here is an example http://www.screwfix.com/p/spot-weld-remover-50g/82964. I lost count of how many of these I used. They get blunt fairly quickly. I suspect the factory welded all three panels at one shot, but I reckoned I couldn't achieve that so did the castle rail and sill first. Then drilled holes all round the new floor panel and plug welded it to the lip. See photo.

I don't think I would do it again!

Mike



Mike Howlett

Mike,

Thanks again. It looks from the detail of your recollection that you brain is well sharp. I suspect working on projects such as these help to keep the mind challenged and alert.

From work I did in the past on my first project, I found the cutting and removal much more challenging than the fitting and welding. Fitting involves a lot of mock clamp-ups, measurements and viewing for alignment.

In the last car I made a lot of panels from sheet steel using paper templates. Many such panels included valence and inner wing repairs, which involved bending in two planes. Cutting out slits in strategic locations on the panels resulted in butt welded repairs that worked out very well and the work was very satisfying.

Brian
Brian McIlvenna

Hi Brian,

If your floors and inner step sills really are good why cut them up? Grinding is a pain, but with a good grinder and top quality disk its not so bad. Cut out the castle rail etc. then grind away the welds. Even if you are doing it upside down it should not take too long.

I had a similar task in front of me, took a couple of hours each side.

Have fun!

Oh! Wear thick flameproof overalls (& close the neck), facemask, good goggles, ear defenders and old wooly hat!

Iwan Jones

And give yourself enough room under the car. I was de-rusting using a wire brush when it caught in the sleeve of my overalls and ran up my arm. Still got the scars.

Cutting is pretty easy - easier than grinding - when you use the proper thin discs. I had to cut a pair of rear springs out when the front bolts had seized in the Silentbloc sleeves. I cut through the leaf first just leaving the eye, then both sides of the eye through the bolt. Despite the thickness it only took a few minutes.


Paul Hunt

Thanks for the advice guys. Iwan, you did well to remove each side in a few hours.

I was away for a week and this gave me time to mull on the castle rail to floor pan seam removal. I have decided to cut a lengthwise strip of each floor pan, adjacent to the inner sill step. This will obviate the need for difficult and lengthy above head cutting and grinding of the castle rail seam. Almost all of the cutting should be achievable from the inside of the car.

An approximate 100mm wide strip should clear the castle rail welds. Repair sections had been done by a previous owner towards the front of the nearside floor so that should determine the cut width.

Paul, looks like you took an injury there - a good lesson for us all. Hopefully, no serious damage was sustained. I've managed to raise the car by around 250mm; so far, this height has been sufficient to gain good access for the floor cross member removal.



Can anyone comment on the option of rear half-wing versus rear wing dog leg replacement? I favour the latter as both wings are good (one being replaced in 2003). My concern is not achieving the right curvature between the wing dog leg repair panel and existing wing. Butt welding is one option; another one suggested is using a kind of edge crimping tool that allows panels to slightly overlap and mate using a series of puddle welds.

Thanks again,
Brian McIlvenna
Brian McIlvenna

Brian,
If your rear wings are sound around the arch lip and the area below the lights, I would stick with the dog leg. With a half wing it's difficult to get the correct shape below the lights, with a dog leg it's difficult to get the shape in the wing and with both the door shut can be a challenge. Not that I want to put you off doing the work LOL

For me a butt weld is preferable to a "joddled" joint for one reason. A joddled joint leaves a joint that traps moisture and so promotes rust and unless effectively sealed on both sides (difficult inside the wing) it'll last only a few years before a line of rust shows through. Ask me how I know ;)

Best of....
MGmike


M McAndrew

Apart from the lower dog leg area, the near side rear wing is sound with just some surface rust on the arch lip and rear lower arch.

When I buy the panels, I was thinking of using the log leg repair to measure the wing cutting point. Until that time, I plan to remove just enough of the dog leg area to allow removal of the outer wing.

Mike, how did you ensure a good wing fit? Thanks for the advice regarding butt vs joddled joint. I will gently grind the mating edges to create a "v"-shape so as to promote a weld channel. That has just brought to my attention that I'll need to get a welding magnet to ensure butt edges are flush on the outside...

Thanks again,
Brian McIlvenna
Brian McIlvenna

"Apart from the lower dog leg area, the near side rear wing is sound"

"I plan to remove just enough of the dog leg area to allow removal of the outer wing."

These two don't compute. If the wing is sound apart from the lower part over the sill then I wouldn't be removing the wing, or half wing.

I've had to replace both rear sill cover sections on the roadster and didn't find it difficult, despite having done little of this type of work previously. You have several datum points like the B post where it curves down to the sill, the wheel arch flange, the lower sill flange and the curve of the door. As long as any previous repair was done well and the repair panel is dimensionally correct you should be OK. If anything it is getting the correct outer panel curvature as it goes from existing to repair that could be tricky. The secret there is only top remove enough of the existing wing to get into sound metal, which is usually just above the sill top, the repair panel is quite a bit bigger than this, use the minimum amount. The problem with these repair panels is protecting the inner surfaces after welding. Use a weld-through primer *before* welding, then after painting pour clean oil in the narrow gap between sill and repair panel, accessed from inside the cabin by removing the trim panel aft of the door opening. It will run and drip of course. I also used a strip of card poked about in the gap to distribute it. Don't use Waxoyl unless heavily thinned and on a hot day, or it will simply bridge the top of the gap and trap moisture underneath it. The same goes for the front wings over the sills, accessed by removing the splash-panel aft of the wheels.
Paul Hunt

Good comments by Paul.

Oh, I forgot to say I had borrowed a big powerful grinder from a mate. I mean really powerful. It also took a lot of physical effort!

Yep, mark out the panel using the repair section but leave at least half an inch along the curved b-post section; and maybe an inch or more below the top horizontal. Leave plenty of metal if you can, as Paul says. You can cut more out later if needed.

Overlapped joddler is stronger than a butt welded joint. Also, when overlapped you can drill through and pull the two sections/panels together by using self tapping screws or rivets (screws better?). This allows you to get better curvature match; I've seen butt welded joins creating a slight ridging along the join due to movement/stresses. The holes can be plug welded later.

Once again as Paul says plenty of weld through primer, including grinding away paint and priming inside the wing. This should seal most sections ok. I've not had rust along the joints yet 8yrs later after the first one I did. But I also did what Paul says re: protection by oil/waxoyle etc. [On another car, I've had a go at lead loading the gaps of a butt weld along the join too. Lead seems to seep in through the join ok, but very fiddly.]

You can use a joddler along the cut floor edge; the cut edge can then be welded on both sides. Make sure you check the width of the repair section and cut well within that.

Hope this all helps?

Cheers,

Iwan
Iwan Jones

Guys,

Thanks again for the advice. I have just noticed from the comment made by Paul on my statement about the rear dog leg - I mistook an IMPORTANT word that really changes the meaning:-

"I plan to remove just enough of the dog leg area to allow removal of the outer wing."

Should have read:
"I plan to remove just enough of the dog leg area to allow removal of the outer SILL."

I had in mind to only remove enough of the dog leg section as any less than perfect joint lower down the wing would have less visual impact.


The floor pan repair panel looks to be very wide so I'm tending towards fashioning a repair from sheet steel of no more than 50mm in width. That said, I may have to imitate the floor corrugations, which may be challenging. A previous owner has made a strong, albeit effective, seam welded repair. I was studying this area of the car yesterday and concluded this previous repair will complicate my floor repair.

So far, I haven't done any cutting as I would prefer to tread carefully and acquire sufficient understanding first.

I've just purchased the MGB purchase & restoration book by Lindsey Porter on Paul Hunt's advice. I'll study it closely when it arrives.

Thanks again,
Brian McIlvenna
Brian McIlvenna

Well, from my last post I've been under the car on a number of occasions and in that time I've successfully removed the floor cross member, the outer LHS sill, removed weld on the inner membrane as far back as the 'A'-post.

Taking Paul's advice, I only cut the rear wind dog leg as far up as about the height of the outer sill as I really wanted to minimise the visual impact of any possible imperfection of the future repair seam. I've really applied my self to removing the old panels but, because of the restricted access behind the dog leg area, I've struggled with removing the final edges of the outer sill while removal of the membrane in this area is impossible. I now feel that I have only the choice of cutting more of the rear dog area so as to expose the remaining outer sill and membrane metal seams.

What is making panel removal more complicated is that a previous owner has seam welded the outer sill and membrane areas behind the dog leg area. In addition, the castle rails have been seam welded along their entire length on both the floor pan side and within the inner step (sometimes called inner sill). An alternative to the dog leg repair panel replacement is to remove and replace the rear wing half as this will (a) eradicate any dog leg seam imperfections, and (b) remove the need to clean and protect the difficult and vulnerable small areas between the inner wing and rear wing lip. Although my rear wing is good, these inner wing/outer wing lip areas do need attention now before they deteriorate. An earlier contributor advised that fitting a new rear half-wing can be problematic around the light area.

Any thoughts, suggestions and advice will be greatly appreciated.

Brian
Brian McIlvenna

Brian,

I think that might have been me...
It sounds like the PO wasn't going to be the one to change the sill again..

If you do the half wing and the section below the rear light is sound, retain as much of it as possible. I would cut down on the line from the lamp unit (similar
to a Rubber bumper wing) retaining the curve around the base of the lamp. I'll be doing just this after the hols!

Best of...
MGmike
M McAndrew

It was so far back I had forgotten you were going to remove the sill and inner membrane behind the dog-leg cover panel as well. Half-wing replacement does make more sense with that. Not sure about a vertical seam below the light though, I think I'd persevere with fitting it under the light to the seam that is already there.

You can get to the area between the upper arch and the outer wing from inside the boot and by removing the trim panel behind the door as previously mentioned. That's still going to need protecting after fitting of the half-wing.
Paul Hunt

Hi,

If you are going to use a half wing panel. Be aware that there can be fitment problems around the light area on the curved 'half horn' in particular. You might need a lot of fettling. On most panels the curve is not correct, you have to set it yourself, V easy to distort.

Also, on some panels the depth of the half horn is different to the original ones on the car. I've had 3 where there was a big gap even with placing the horn section inside the cut out area and having to resort to filling the area with weld. Use short sections of curved welding rods to do this.

Furthermore, the half section will need patience in refitting to the inner wing. Use self tapping screws and clamps in profusion. While you can get to the inner wing, cut out any rot, use thin-ish cardboard to copy the cut out sections and to prepare new metal to put back in. Much much cheaper than buying a new inner wing (outer section). Use good bits of metal from the wing you've cut off.

Or: Live with the wing as it is, grind and clean up any problem areas you think you might have, and just do the dogleg. Much less work.

There are obvious benefits to both approaches. Your choice.

By the way, you should find that you have to grind away a vertical cut (next to the inner body) at both the a and b posts in order to fit up the inner membrane and the outer sill. Or cut sections out of the sill bits you have.

Have Fun,

Iwan

Iwan Jones

Paul said " I think I'd persevere with fitting it under the light to the seam that is already there."

Paul have you done this recently?

As Iwan says "On most panels the curve is not correct, you have to set it yourself, V easy to distort."

and IMHO if the original is sound, don't remove it...

Best of...
MGmike
M McAndrew

Guys,

Thanks again for all your help; and happy Christmas.

The half wing repair looks like a lot of work; I'm also not keen on tackling the challenge of establishing a good rear light 'horn' fit. On reflection, it looks like I will opt for a dog leg repair as the wing is definitely very sound, as is the wheel arch. I will try to remove only as much as I need from the dog leg region to allow grinder access to the remnants of the outer sill and membrane.

I need to investigate an effective rust removing & protection solution for the rear arch to inner wing region. Rust is presently only superficial so I want to clear this up. The gap between the arch and inner wing is a real design fault as it is a haven for moisture and its child, i.e. rust. Maybe there is an after sales part that discretely covers and effectively seals the arch rim...


Regarding the rear valence, I've noticed that on one side of the car there is a double metal section at the corner of the panel, between the rear wing and bumper support. Is this normal or is this an improvised reinforcement?

Brian
Brian McIlvenna

Brian,

Not normal at all. It's probably a PO's repair patch over the top of a rusty panel. It'll need to come off for investigation but I suspect a replacement lower valence may be on the cards. Just like mine....

Best of...
MGmike
M McAndrew

Brian and Mike

Unless your rear valence is really really shot, don't try to replace it. It is a biggish job and can be messed up. Lower valence repair section only, bit less of a job.

Much easier is to:

a) find the grot by using a wire twist 'cup brush' on an angle grinder; very aggressive - use very good goggles to protect eyes! [Have previously found bits of the twisted wire embedded in my thigh/arm before]. However, it will clean up the area very well and quickly. If you suspect filler has been applied use a dust mask; I use a v good mask anyway in case of red lead primer having been applied. Also protects face.

Drop petrol tank and do the inner side of the valence area too. Anyway will be welding later??

b) Treat rusty areas. I prefer to use lead loading not filler on pitted areas of rust. If very pitted or just frilly/holy I cut out the whole area, as square/rectangular as possible. Use card to measure outline of shape needed. Take time to form bits of metal that you have cut to the shape needed. To make bottom curve in valence use a steel pipe 1/2 inch clasped in a vice to beat metal over.

c) Use those butterfly clamps to fit the section of repair and hold it. Butt weld by stitch welding first to spread heat. Remove clamps weld any gaps and grind off excess.

Easyish job as you can get to both sides.

Check floor at same time while you have tank off.

Hope it helps!
Iwan Jones

"Paul have you done this recently?"

I've not yet had to fit a wing section round there, but I did have to fabricate one of the 'hulls' as both sides of the vertical seam under the light had rotted. I've also constructed repair sections for the double-curvature area down the outer side and underneath a headlight from flat sheet using just pliers and a couple of hammers in the past. Not saying I'm a genius panel-beater, far from it, but I do have patience.
Paul Hunt

This thread was discussed between 27/11/2013 and 27/12/2013

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