Replacing 911 sills and Jacking Points

Barry · Post by **Barry** » Mon Dec 21, 2009 8:22 pm

As a result of a couple of recent threads, I thought it may be of interest to list how I go about changing the sills on these cars, and the various extra jobs that often seem to arise as a result.

On the whole, the pictures come from one car (done a year or so ago), although I may dip into one or two other albums as the guide pans out, depending on what I'd like to show.

So, first of all, do your sills need attention? These are typical early signs that you need to look for:

a) Is the front of the kidney bowl soft or holed when examined from inside the rear wing?
b) Is the base of the B-post where is joins the outer sill 'blown' or bulging?
c) Are there pin holes on either the outer sill, or on the bottom of the middle sill (the panel that takes the base of the outer sill)?
d) Is there movement on the jacking socket (this would be bad)?

In addition, if the car feels very 'soft in the shell', with excessive creaking and general body movement, this could also point to weakness in the sill area.

Typical holing to be found after paint and filler removal:

Further investigation often reveals something like this:

Often you actually reveal something much worse:

At this point, you know that you are in for fairly heavy repairs, and the decision needs to be taken as to whether the use of a jig is appropriate, or whether careful supporting of the car is going to suffice.

Here's something I put on a recent thread regarding jigs, and the supporting of cars:

As for supporting the car, well a jig is always going to be best of course, but franky not everyone has access to one, and we are blessed that 'our' cars ar so adjustable in the wheel-alignment department. My personal feeling is that if it's your own car, and you know that the suspension alignment is good (worth getting it checked before you start work?), the gaps are good, and you are happy with the way that it drives (suspension-wise), then if you do all of the work and end up with it just as it was, then why not?

On the other hand, if you've always found that it's worn tyres out, and the suspension can't be aligned because all of the adjustments have been used, the gaps are all over the place, and it keeps breaking windscreens, then it's time for the jig.

If I'm going to do any structural repairs to any car without using a jig, then this is the way that I support it.

1) With the car on the ground, open and close each door and make a note (or mark) of exactly how it is mating up to the rear wing, and how each door latches. If appropriate, adjust latches to give the best possible door latching (e.g. a nice sound, and no graunching!).

2) Jack the car at the rear, and support it underneath the rear torsion bar end covers using conventional axle stands.

3) Jack the front of the car at the centre, using wood or a jack pad to spread the wieght if required.

4) Then , using either conventional (pinned) axle stands with thin shims (ply, sheet steel, whatever), or better, threaded axle stands (often used for siting mobile homes), set exactly the same gaps left to right. Drop the car down.

5) At the rear of the car (and especially if the engine's still in), put a screw type axle stand, or scissor jack, under the engine and gently take some weight there. Adjust this until the doors open and close exactly as they did before.

I often then use some extra threaded stands around the area that I will be working in as well, just to be sure. I also never use hydraulic jacks for support under the engine, as over a period of weeks (which these things often turn into), you find the jack sinks down a bit. If by then you've removed, say, the rear wings and the sills, you've then lost your reference as to where the rear of the car was jacked to.

These days of course, everything is done on the Celette, but before that came along I was most concerned not to build in the vagaries of by concrete floor into the shell by just dumping the car straight down onto pinned axle stands, cutting all of the strength of the thing out, and then welding it to the shape of my workshop."

I've used this method not just for 911's, but probably thirty or forty or so other big restorations that I've done over the last twenty years ( can't believe it ). I've always been absolutely paranoid about distortion, but the above method has been very reliable for me.

Finally, a jig would be best, but if you can't run to one, and the shell appears fine in tests as above, then simply support the shell very, very well in a way that at least preserves what you have got, without causing new problems. '

More to follow ....

Barry · Post by **Barry** » Mon Dec 21, 2009 8:34 pm

If this area has gone, then the A-post base will usually have joined it:

And the area underneath the A-post base:

This area is usually a reflection of the rear inner wing area that lives beneath the kidney bowl. They are both repaired in a very similar manner, and if you need to do one, you usually need to do the other.

Often the rear inner wing rust reaches rearwards behind the kidney bowl area, and certainly to the base. In the case shown here, the actual reason for replacement was due to heavy indents. Nevertheless, rust repairs would follow the same method. Next picture shows outer sill, kidney bowl, plus inner wing areas all stripped. Please make note of above supporting instructions before getting to this stage, in particular the notes on recording door gaps before starting work:

Barry · Post by **Barry** » Mon Dec 21, 2009 9:10 pm

So, the above posts cover the various areas that are likely to need attention when 'doing the sills'. You will have noticed no doubt, that the base of the B-post (door latch panel), as well as the front of the rear wing has been removed to gain access to the outer sill and kidney bowl, both of which tuck under the outer rear wing.

A few things to note before plunging in:

The front wing will have to be removed, so pop some masking tape up on the scuttle, and on the front wing top, and use a pen / rule to mark across them, to ensure the front wing returns to it's original position.

The door will have to be removed to gain better access to the front end of the assemblies. With this in mind, either punch out the pins to keep the front portion of the hinge in place, or mark around the hinges onto the A-post, so the door can return to it's orginal position during and after repairs. Make a note and photograph, the door to rear wing, and door to sill gaps.

I'd also recommend making a little jig from your jacking point socket to the sill / floor join, so that you know how far in to place the new socket (if required). It's worth popping some masking tape on the doorskin base, and marking exactly where the outer sill and rear outer wing join. This also marks the centreline of the outer jacking socket.

Before cutting the rear wing at all, make a note of its 'in and out' position, perhaps by measuring from the front of the wheel arch into a point marked on the inner wing. As soon as the base is detached from the outer sill, the wing will be free to move in and out, and twist also. Therefore a reference measurement (or stick!) is very useful. In fact, cars often have odd alignment to the rear wings, either by kicking out, or tucking in here, so sill replacement can be a good opportunity to improve things here.

Finally, when the outer sill is removed, make a note of the height of the centre sill web to the inner sill top (often about 3mm or so), plus mark it's fore and aft position as well.

All of the above are very useful double checks, and often prove helpful when putting the thing back together.

911hillclimber · Post by **911hillclimber** » Mon Dec 21, 2009 9:19 pm

This kind of thread is what DDK is all about to me.

From the car in the pics, the panel under the torsion bar looks quite good(?).
I seem to recall someone once made replacement panels for around the torsion bar/inner wing 'outer' and the bottom panel under the tube?

Look forward to the next 'paragraph' Barry.

Barry · Post by **Barry** » Mon Dec 21, 2009 9:28 pm

Once I'm more or less at the above stage, and with the car on the jig, I usually work in the following approximate order:

1) Outer sill, B-post base and outer rear wing base/front removed.
2) Kidney bowl removed after noting it's position.
3) A-post base position carefully noted, particularly height, which I mark further up the inner wing, and A-post base removed if appropriate.
4) Centre sill web removed, after noting fore-aft and height positions as above.
4a) Also jacking point reinforcement removed at same time.

If inspection reveals it has failed, Jacking point socket removed as well, usually involves removing a small section of floor under socket, plus slitting inner sill to release inner lip of socket (inside car, under carpet if still there).

At this point, the only parts that have been removed are the off-the-shelf ones, all of which have been positionally referenced so that you know where new ones are heading.

About now, I'll usually hang the new centre sill in place: it holds the floor edge at the right height, and shows you where you are heading with any fabrication work on both inner wings. Not only that, but it's an easy moral booster that fills in a big hole! Typical front inner wing base repair:

Note original area still in place until last minute as reference. I usually self-tap these pieces in as a starting point. If I'm happy, I then trim the original away, but leaving areas where the self tappers are holding the replacement. I then scribe around the new piece, marking the old. Then I remove the old section, and if required, fettle the new one to fit. Finally it gets welded in ....

Followed by a new A-post section (depending on budget I either make these, or use a genuine one for the better funded work

):

Barry · Post by **Barry** » Mon Dec 21, 2009 9:41 pm

A very quick note on the welding here. Generally, if it's a repair let into an existing panel, I butt weld the joins. You have to ensure that you get perfect penetration with these, but you end up with a factory-looking panel again, and a smooth join that won't attract moisture.

If you are not sure of your welding (and I'd hope you were pretty confident if you're undertaking this project), do regular test pieces at similar angles to how you are working on the car. Make sure that all welds are penetrating to the rear of the join.

As for the new factory panels that are going on, I use a combination of plug and spot welding. When plug welding, really you want to drill or punch 6mm holes in the new metal. Much smaller, and there is a real danger that you'll MIG the hole up before penetrating welll into the parent metal behind.

At this stage, we should have a neat and strong A-post area, with a smart front inner wing base. Also the centre sill can be pre-drilled ready for all of those plugs welds. I usually go for 20mm centres more or less, or at least as many as the factory. By the way, I don't use the spot welder for the centre sill web, as I've seen a large number of the factory spot welds that have failed along the top edge here, with the top of the sill almost falling way during stripping

. I'm sure this is why some cars feel very soft, where the sill scructure has been compromised by failed factory welds, regardless of rust.

Next image shows a similar repair ready for the rear inner wing, plus the centre sill web drilled for plug welds, and the whole lot dummied up ready for double checking:

Barry · Post by **Barry** » Mon Dec 21, 2009 9:44 pm

And then everything up to this point welded up:

Barry · Post by **Barry** » Mon Dec 21, 2009 9:51 pm

Forgot to say, the centre sill web tucks behind the inner rear wing, overlapping by 120mm or so around the jacking point area. This means that any inner rear wing repairs are completed after the centre sill goes on, not before, and obviously needs completely plug welding throughout the overlap.

Next the jacking point reinforement goes on. Again, I plug-weld this, but with a small seam weld to each corner. There is also a continuous seam right around the front of the reinforcement onto the jacking socket. I also run three vertical welds between the rear fold of the centre sill, and the leading edge of the inner wing (not shown below):

Barry · Post by **Barry** » Mon Dec 21, 2009 9:59 pm

The only genuine sills available now are the later style ones with extra (bonus?) indents. I remove these either by cutting them out, and TIG welding in flats, or latterly I have been beating them out. The first method is a real fiddle, and the second tends to push the sill top upwards even with heavy dollies.

I'm now leaning towards the second method these days, but I've not got pictures, so the first method is shown below:

Gary71 · Post by **Gary71** » Mon Dec 21, 2009 10:06 pm

Great thread Barry, despite my usual repair bravery I know which jig my car will be on when this job gets done

Barry · Post by **Barry** » Mon Dec 21, 2009 10:17 pm

At this point, it's time to re-hang the door, and try the outer sill. The fore-aft position is dictated by the position of the A-post, and by placing the rear wing 'step' a fraction ahead of the centre of the jacking point.

This is also where the mark on the door-skin may be useful (remember that?).

With the outer sill held in place fore and aft, fit the kidney bowl in behind it, so that you get the best position between fitting the new sill well, and getting the kidney bowl as close as possible to it's original position. Bare in mind that you may well have changed the metal underneath the kidney bowl, and that the shape of the new one may be a little different. Nevertheless, self-tap it somewhere near where you are expecting it to be.

The really critical part here is to get the door to sill alignment spot-on. This is both in terms of height (door gap viewed from side), and in width (sill position when viewed from above). The fore and aft is much less critical, as is the position of the kidney bowl, within reason.

You may have to tighten the curve of the sill, or flatten the top a little. Certainly be prepared to be quite firm with the panel, as even genuine ones sometimes need some help to fit. This is time well spent, as there's nothing worse than poor gaps! I often find that it helps at this stage to leave the door on for a while now, and also to fit the kidney bowl (and front wing close if required as well). These to give you something to attach the outer sill to to hold it's height reliably whilst you double and triple check everything.

Again, I plug weld most of the outer sill, although the door seal channel area is much easier with a spot welder if you have one. Another welding note: a lot of commercial welders have a single sided attachment, which look, on the face of it, perfect for the kidney bowl and the outer sill base. From what I've seen, I'd be very reluctant to use these for any car welding, let alone these structural areas. Even the importers of Spanesi welders don't recommend that they are used in this way.

Anyway, outer sill aligned, checked, checked, checked again (you get the picture

), and ready for welding, along with the kidney bowl ....

Barry · Post by **Barry** » Mon Dec 21, 2009 10:19 pm

Gary71 wrote:Great thread Barry, despite my usual repair bravery I know which jig my car will be on when this job gets done

I thought it was about time I actually posted something that involved cars

.

hot66 · Post by **hot66** » Mon Dec 21, 2009 10:27 pm

Barry wrote:
I thought it was about time I actually posted something that involved cars .

.... you mean just like the rest of us

Great thread as usual Barry

Hope you're wrapping up warm in the workshop

Barry · Post by **Barry** » Mon Dec 21, 2009 10:27 pm

With the sill structure just about finished (with perhaps just the area beneath the door near the A-post to be completed when the door's next off), our attention can turn rearwards, starting with the B-post repairs.

Pattern B-posts are (I believe) the only option as a stand-alone panel (i.e. not attached to a wing), and needless to say, the fit is somewhat crude to start with. Note the fore and aft error here, which is pretty typical:

And width (less of an issue when replacing the whole panel):

I use the door to establish the fore / aft alignment, and if replacing the whole panel, the width as well. In this case, I put the door in it's correct in / out position, and mark the B-post from the front of the door-skin. Then I minus off a suitable amount to allow for the outer wing thickness, and trim the B-post back to suit.

B-post altered in width to match existing:

Barry · Post by **Barry** » Mon Dec 21, 2009 10:54 pm

Before welding in the B-post base we either need to make, or adapt a bought-in, rear wing repair. This one is a little more complex than most, as this particular car (a replica T/R) is to have non-lead loaded seams throughout, so required a factory looking rear wing front.

Usually though, as it is to be welded and leaded, you can get away without this detail, which makes this panel much, much easier to fabricate. I make these by making a card pattern using the door as my leading marker. I then minus off the required door gap (I aim for 3.75mm as my ideal), and scribe this shape onto sheet, a then add on enough for the B-post flange.

The panel is then cut out of sheet, and the flange formed first. Finally I form the main curve that follows the sill line. All being well, this panel can be offered up over the existing rear wing, with a decent overlap. At this point you should be able to refer to the previously mentioned rear wing width measurement (or stick) to ensure that the rear wing is going to follow the correct line through the car.

This is the time to tweak the shape of the panel until it is as near perfect as possible:

Again, the trick for a great fit, is to self-tap into place until it is as perfect as possible, and then scribe around it, onto the panel behind. Here it's also well worth scribing at 90 degress as well, across both the old, and the new panels. This gives a height reference which will be useful when tacking later. Please note that this area is very prone to developing a lot of crown (buldge), whereas it should be near-flat. With this in mind, try to make the repair as flat as possible, knowing that it will tend to default to having too much shape given half a chance. I sometimes have to shrink this area after welding.

If the whole of the outer wing front is to be repaired, it is usually easier to cut much further back, from say a few inches back along the rear quarterlight hole, down rearwards through the upper area of the wheelarch. This gets the repairs out of the flat area, and limits the length of the weld.

For all this though, I believe that the method we have covered is the most DIY friendly, as it disturbs less of the car, and the resulting panel needed is DIY makeable, albeit with some practice.

This panel can now be welded in, but keep in mind that the B-post base also has to be welded. Therefore I find that the order of events is pretty much:

i) Weld up rear wing, ensuring that B-post base can be fiddled in later.
ii) Tidy up wing welding both inside and out, using hammer and dolly after grinding (if using MIG), to level everything out as much as possible.
iii) Tuck new B-post base into place, and ensure that rear outer wing can return to it's correct position. Self-tap into place, and try door for alignment, both on previous wing repair panel (whilst it is fairly easy to panel-beat the gap if required), and on the B-post.
iv) Weld in B-post, using spot or plug welding on outer wing flange, and inner wing (door seal channel). Also plug weld down onto sill top.