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MG MGB Technical - Inner Sill Repair

Has anyone repaired only the front 2 feet of the inner sills?

I really took a good look at my existing inner, outer sills, castles and inner rockers (yes I can see the inner rockers through the swiss cheese outer sills). The front (footwell) 2 feet of inner sills are gone while the remainder seem to be solid. I poked and prodded with an awl to check them. I know I will be replacing the full outer sill, castle and inner rockers.

I have some questions:

-Does anyone have experience with replacing
only a portion of the inner sill?
-Does this mean that supporting the car is
not as critical? (gaps are good)
-What type of weld would you use for the
repair sections? (butt?)
-Is it worth it?

TIA, Mike
Mike Zaffarano

Mike. Your best reference for this type of work would be Lindsay Porter's mgb restoration Guide (I think it is currently called, it should be on Amazon.com). I remember something in there about only replacing part of the assembly, but do not remember the specifics. As to the best type of weld, let the welder doing the work make the decision based on his experience. There is some information in the archives on sill replacement. It is expensive because it affects the strength and handling of the car and must be done right. Is it worth it? Only you can answer. One fellow, out in Washington State, had his car re-shelled and felt it was worth it. A very personal decision, not often measured solely in dollars. Les
Les Bengtson

My Porter says "whenever rust shows through the outer sill, or through the bottoms of the front or rear wings adjacent to the sills, you can *guarantee* that the crucial load-bearing inner sills will be corroded". He prefixes that with "it is never enough to replace only the outer part of the sill unless the sill has collision damage and is otherwise sound inside." He doesn't mention partial replacement of any panel at all. With all that you are replacing only doing part of the inner sill seems a pointless economy.

He was probably writing in 1980 and referring to first restoration. I have had to subsequently replace lower front and rear wing panels that were themselves part of a full sill and wing replacement where the sills are sound but the wing panels have corroded through from the inside. This is because, even though the repair had been Waxoyled, the gap between sill and wing panel is so small that the Waxoyl does not run down between them. Since discovering that I inject clean engine oil in those areas and work a length of flat card up and down in the narrow gap in the hope that it gets a reasonable distribution over both surfaces.
Paul Hunt

I have replaced just the ends of the vertical inner sill panel where the centre section was good.

You still need to buy the centre panel - cutting off what you need to replace the rusty outer sections.

The welds should be continuous seam welds - nothing else is acceptable for UK annual test regulations.

While you are in there - fit two jacking point reinforcement braces on each side this adds extra strength and peace of mind when using the jacking point.
chris

"The welds should be continuous seam welds - nothing else is acceptable for UK annual test regulations"

Chris
I have a small spot welding machine that I am using to replace the floor and all of the sills inside and out. I bought it so that it looks original this must be acceptable for the MOT!
Mick
Michael Black

I was refering to patching repairs - see the extract from the MOT testing manual below -

"It is essential that repairs to corroded areas are properly carried out. Only welding is acceptable for repairs to 'prescribed areas'.
Suitable materials of appropriate gauge and thickness should be used for repairs so that
- Any plating or welding extends to a sound part of a load bearing component, and
- The repair must be virtually as strong as the original structure
So only a continuous seam weld is acceptable for patch repairs, although spot welded joints are acceptable where they originally existed."

Most MOT testing stations expect to see seam welds on plates or patches - tack or spot welding is not regarded as strong enough.

Where you are fitting whole panels then spot welding to the original pitch is OK but I personally would seam weld for extra strength on the sills.

The spot weld is a cheap production weld - all rally cars have their bodyshells seam welded.
chris

Thanks all.

I have Porter's book. I find the book to be a good guide but, I'm not getting as good a response when I ask the book a question as I receive here. I want to research this as best as I can before I begin. I guess I was looking to reduce the amount of repair when practical. I really don't want an unsafe vehicle.

I have reservations about "patching" the inner sill. I can't get myself to believe that a "patched" section is as stong as a continuously formed piece. The repair just looks difficult.

Do you really think the US inspectors will check the vehicle structure during inspections? I would hope they do.

I have read Les' (and others) archive threads on this subject but, can anyone explain the method you have used to create the "plug" welds. I will be using a MIG welder. Do you depth drill, drill through,
pre-drill, .... the replacements?

Mike
Mike Zaffarano

Drill right thru the top panel - 1/4 inch holes.

Clamp the two panels tight together and weld into the hole with a circular motion to fill the hole with weld.

You must get good penetration into the bottom panel.

Try it out on some scrap metal first.

Re strength of patched panels. If the weld is good it is stronger than the panels it joins - I would have no qualms at all about a properly welded patch.
chris

Any suggestions on support locations?

Mike
Mike Zaffarano

I presume you mean, "Where do I support the shell to cut out the sils without it all distortig?"

Is it a roadster or a GT?

for a roadster you need to tack weld a bar across the top of the door opening.

Only ever do one side at a time!

I usually support the shell with a stand under the front chassis leg where it first becomes horizontal and with another stand under the front mounting point of the rear spring. Put a jack under the front crossmember and another under the rear axle.

Take just a little weight on the two jacks - they are there just to stop the body flexing.

Tack weld the panels one at a time and refit the door to check the panel gaps are OK at each end - use the jacks to adjust if necessary.

Fully weld each panel in turn

Before tacking up the outer sill, refit the door yet again so that you can ensure the panel gap at the bottom is OK.

Weld the top of the outer sill up first. Use a jack under the bottom edge to lift the panel into line, use clamps to hold it - checking the panel gaps before finally welding it up.

It really is worth taking your time over this as uneven gaps look really bad and you will hate it!!



chris

Thanks all. I will take photos and keep notes so that I can make them available to others to follow or avoid.

Wish me luck.
Mike Zaffarano

Dear Mike:

I am in the middle of replacing floor pans, inner sidemember, inner sill, castle rail and outer rocker. I did the drive side and now doing the pass. side. Floor pan is still out and there is good exposure of the "anatomy". If you want to come and see what I am doing, you are welcome. I live 1-2 miles from Giants Stadium in NJ. PS It is a '76 B. Kirk
Kirk Knutsen

Kirk,

Excellent offer! I will mail you off-board to make arrangments.

Mike
Mike Zaffarano

This thread was discussed between 08/12/2001 and 11/12/2001

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.