Cant Rail Repairs

Another job I finally got round to on my week off, was repairs to the gutter that the roof sits in. These are the outer part of the cant rail.  

Cross-section of a bolted-on roof

It's only taken me 20 years. I took the roof off the car back in about 2000 or 2001. I recall that I wanted to get it repainted and also to re-seat it to be more confident of a water-tight  seal.

I was fairly pleased with what I found back then: the bolt-on roof still had a continuous crimped edge, with only a few small areas that had rusted away. Not much I can do about that and there was enough of an edge to still bolt the roof down...... 

Crusty roof edge

.....and compared to others you see, the cant rail was very good too. There were however a couple of previous patches that were failing and a few small holes in the outer vertical face that is hidden by the stainless steel roof trim.

Previous repair

More troublesome though, was the hole in the horizontal face that the roof bolts-down on to........

Hole in the base of the gutter

So back in about 2000, the car was in my garage and the roof was off. I couldn't decide what colour to paint the roof - nor how to get it to a sprayers. Without the confidence or knowledge to get the gutter problem fixed, I decided back then to just bolt the roof down again (with generous amounts of mastic), and to leave the niggling problem for another day. I got as far as cleaning the gutter edge and giving it a coat of zinc primer before the roof was loosely put back on the car and it was barn parked for 14 years.....Another 7 years later and I'm finally doing the repair I needed to do. 

These days it's possible to buy complete roof rail repair sections where the profile include the inner cant rail (the part that's inside the car) as well as the gutter that the roof actually sits in. That might not be a bad way to go (as long as the repro parts fit!) as the roof line and cant rail has a subtle sweeping shape  - down and in. While it's that curve that make the shape of the DS attractive, it can make extensive patching of the rail more difficult. The edge is also angle inwards - possibly to counter for the outward forces of the roof spreading when bolted down. Or it might simply be that Bertoni liked the shape that way!

Construction of the side cant rail

I wanted to keep as much original Citroen as possible and, as I only had a few areas that needed repairing, decided to go gown the patching route. By cutting out sections selectively, it left me with a reference point on each side to get the sweep and curve of my patch right.

Using a cut-off tool, I cut back the rotted areas back to good metal. In some cases this only needed to be the vertical face and a little of the gutter bottom.

And so it begins.....

In other cases this needed to be the profile of the whole gutter that the roof sits in.

A bit more work

I also decide to re-do the previous repairs that I had found. I suspect the previous repairs were breaking away because the metal used had been too thin - 0.8mm thickness. I used 1.2mm thick stock to match the original (50% thicker folks!). It proved a lot easier to work with and gave solid-feeling result after the repairs.

An important point to note here is that the cant rail pressing has a rounded profile - not sharp, square corners. This curve needs to be maintained so that the outer stainless steel trim can clip in place as intended. If I had simply welded upright pieces at 90 degrees to the bottom gutter edge then, when I took my grinder to that edge to round it, I would end up removing a lot of the metal I had just put in - leaving it a weak and ineffective patch. 

With this in mind, I started by making up some short lengths of angle - with a curve - and then cutting these down to size to make my patches as needed.

Making up curved patching sections

In this way I was able to introduce an element of the profile curve into the patches so that my butt welding would be between two more parallel (rather than perpendicular) surfaces. Although this did mean I needed to weld either right on the curve of the channel, or from underneath the gutter. In some cases I welded from inside the gutter.

 

You can just see the curve on the weld line of the patch

 To ensure a god fit, I tacked one end, checked patch alignment and then tacked further along  - being careful not to put too much heat in any one area. Use of 1.2mm steel was also more forgiving in terms of blow-through and warping.

 

Multiple patches on the go

I used the same technique to fix the hole across the base of the of the gutter - making up short lengths of profile and then cutting them to shape.

It was more tricky to get the shape right but I was pleased with the result and the patches fitted very well.

Very pleased with this little patch

You'll notice that the vertical faces of my patches are all too tall. That was partly to aid handling of the metal when I shaped it, partly to resist warping while I welde them in and partly so that - once the patch was in, I could work out the correct curve and height for the lip of the patch from the reference points each side.

Patch with high edge

I used a cut-off tool to cut the patches back to shape and to grind off the weld heads. The outer profile of the gutter needs to be smooth and curved to enable the stainless roof trim to clip over it. The inner face of the gutter needs to be smooth so that the rubber roof seal beds down and is water-tight. I found that, having ground the spots back, I would find pin-prick holes remaining between my weld spots, so it took several passes - welding and grinding back to get a good result.

All tidied-up

I think I could have cut out more rotten metal and put in more patches. There are still a few pitted spots that may be prone to rust, and I think one day I will need to re-do this job. If it comes to that, I'd be prepared to do more patching, but next time would also consider replacing the whole cant rail with a repro. If they fit.

I've still not decided what colour I'm going to paint that bloody roof! The car is DEFINITELY going to be AC108 'Gris Palladium'. The leather interior is 'cuir naturel'. Today I'm thinking the roof will be AC200 - 'Noir'........but ask me another day and I'll say AC100 - 'Gris Argent'.