I'm changing a roof skin and it got a bit complicated!

[stevek]

Hi,

I'm changing the roof skin on my 924 to get rid of the leaky sunroof (and to learn). I haven't done anything like this before, I have got half way through un-stitching the donor skin and got a bit stuck in the windscreen corner. I have done some research and had a thorough look at it myself so I'm going to put a detailed description together, sorry if its a bit lengthy.



I have drilled out most of the spot welds on the 'new' roof section and have cut the weld lines where the skin is welded on over the c-pillar. So the back 1/2 of the panel is loose and ready to come off...



So far, so good but getting involved with the a-pillar corner has got me stuck where to make the cut as there is a brazed joint and the make up of the layers complicates things.

The basic options are:

1) below the brazed joint

2) at the brazed joint

3) above the brazed joint

But none are without some kind of problem.


The main complication is the outside of the a-pillar becomes the inside of the windscreen aperture in one pressing with the roof skin brazed in over the top last. I need to show you the way the structure is put together... 

1st, the roof propped against the wall to help orientate the next pictures. You can see my rough inspection hole down the bottom which is where we're going next...



2nd, The inside of the a-pillar runs into the structure of the the door. You can see I have bent this away slightly to investigate...



3rd, A slightly more head on view to show the layers...



Yellow = Roof skin & outside of windscreen roof aperture.
Green x2 = Inside of windscreen roof aperture & outside of a-pillar.
Blue = Inside of a-pillar
Pink = Joggled fold
Black = Brazed? joint between roof skin and a-pillar.



So my take on the options is:

1) below the brazed joint  

Good = The a-pillar is nice and strong to weld round (not going to warp) and its a short weld line too. 

Bad = No good place to cut in due to that piece continuing over windscreen. Any cut on the car here would really affect the structure wouldn't it because you would need 2 cuts and then wouldn't have access to weld the upper cut? I don't really see how these guys did it...







2) at the brazed joint

Good = Would keep everything original and as intended.

Bad = I gather its not easy to separate a brazed joint and most people seem to recommend avoiding it. (unless you know otherwise?)




3) above the brazed joint

Good = Probably the simplest place to make the cut

Bad = Probably the riskiest as far as warping the roof panel.

This shows the position but has been overlapped with the old skin and joined with spots. Mine would need to be a continuous butt joint as I intend removing the old roof fully at the seams...



Phew that was long, my head is spinning LOL. 

I *think* option 3 is the way to go but I haven't dared go any further because I'm not that sure either. I would love to hear your thoughts.

-Steve-

[guz]

on my mk1 golf i ground away the inner skin and then
the braze to the top skin, at the windscreen i sleeved
it at about 4" down the screen pillar, plug welded everything
and then fully welded the outer skins together.

mine's now a factory sunroof skin though so unlikely to distort,
unlike the aftermarket skin i removed, that was awful

[stevek]

Thanks gus for the info on how you did it, your post in my readers-rides thread helped inspire me to get stuck in. I'm not sure I can do the same as you though and sleeve it down the a pillar due to the construction I tried to describe above.

[stevek]

I tried very carefully to describe the issues I was struggling with but I think it just turned out too complicated. Maybe nobody could understand what was going on from my description.

Anyway one good thing to come from writing it was it helped me think it over and after sleeping on it I had a plan of action for today.

firstly I decided 'option 3' was out. I thought I would go with 'option 1' but that would mean (on the donor roof) I would be cutting off the braized joint. Which meant there was no harm trying to separate the brazed joint to see if I could, so I tried.

I looked up how hot it needed to get to melt the braze...



and looked at a chart for steel temperature by colour...



So aiming for a 'blood red' colour I heated it up with a blow torch. I managed to get it to pop off...



and eventually had the panel off...



Do I dare do it on the car now though? That's the question!

-Steve-

[joe90]

Can you get the car in a garage, could you take most of the roof skin off with a 1mm cutting disk so you can get under the lip with ease when you have drilled the spot welds off, on another note where in Leeds are you Steve, I'm in Bramley LS13.

Bryan

[scimjim]

do you need to replace the whole roof or can you just use it as a repair section for the hole vacated by the sunroof?

[ruffgeezer]

You've done a great job so far, take your time and plan carefully the next step. I like many others here look forward to seeing the results!

[stevek]

joe90 - I'm over near Kilingbeck Asda. Maybe catch you around, I don't know enough car people in Leeds. As for your suggestion, I'm not actually finding it that difficult to split the spot welts. In fact I'm rather getting the hang of it now.

scimjim - Yeah I did think about that. More so when I couldn't find a 924 roof though, I was sizing up other small cars roofs to try welding a fill panel in. I did worry that it might be hard to blend another cars section in though and it seemed quite risky from a warping point of view. By doing it this way it should look 'factory' if I can pull it off.

ruffgeezer - Thanks, I hope its worth seeing in the end an not a horrible mess.

[stevek]

Rear screen and gutter trims removed...



Many spots drilled and split apart, I've done the boot section and one side section today...



Some very careful slicing with the grinder...



There is a reinforcement bar that needs cutting out too...



VERY carefully with the grinder and a sharp hit with a chisel point released that...



And that's one rear corner popped...





No going back now!

-Steve-

[joe90]

Have you been to the Leeds classic and hot rod meet yet mate, good place to meet a few people in one place.

Bryan

[waveman1500]

Your work is very brave and impressively well executed!

Every time I touch bodywork, the best I can get it is what I like to call "motorsport standard."

[guz]

oh, i had access to a decent 3 phase spot welder too,
i'd recommend using one if you can, made the
roof skin and the front panel on my golf real easy,
or paying someone to just spot weld the skin on ?

[stevek]

joe90 - Yeah been to the Leeds one a few times over the years and also occasionally go to the Rotherham Motornutz meet too, I wouldn't say I really know anyone at either though.

waveman1500 - Very kind of you to say but we don't know what the end result will be yet. Plenty of opportunity to mess it up yet! Fingers crossed though.

guz - I have borrowed a brand new Clarke spot welder but just a single phase one. Should do the job nicely I hope.

[stevek]

In more progress (for those who havent seen in my ReadersRides thread) I have got all the spot welds drilled out...



Then cut the welds on the other rear reinforcement pressing...



Out with the slitting disc on the grinder to put that little notch in between the roof skin and the gutter...



and then started making the weld line cut...



...this time it wasn't working out so well as it wasn't cutting the middle bit.

I resorted to wearing the blade out on a rock to reduce the diameter...



That made the blade follow the radius better...



With a little fettling I could split the joint...






And the other rear corner is released ...



Only the 2 brazed a-pillar joints are holding the roof skin on now.

-Steve-