"In this Special Series, I document my complete paint & body restoration along with the exterior upgrades to CSL specifications.

In this entry, I document the mythical carbon roof conversion to the Karbonius CSL carbon roof. It's easy as 1, 2, 3 - ouch! Weld it, glue it, bolt it? We settle the debate."
-Matt

I feel you. 

The carbon roof conversion is a costly endeavour in parts alone, when factoring the Karbonius CSL structural roof panel, the new headliner, CSL black roof rails, sound insulation and the new roof bow, it adds up. My intent with this entry is 2 fold, help you save on parts, and help you save on labor. 

Glasses out!

There is no way to circumvent this: the front and rear glass needs to come out. Breaking glass is expensive: the work was subcontracted out to a local, glass guy.

The probabilities you break the front glass are extremely high. I broke mine trying to remove the rear view mirror to ship it off for restoration.  

This is a professional's job only. 

I didn't care to much knowing I wanted to upgraded to a comfort glass. Classify this under E46 things. 

Many online tutorials from shops will tell you to completely pull the front and rear seats. It's a total overkill, at least for my use case. Restoring a car is getting dirty, dirt is easily cleaned away. 

Glasses out, interior in - it's time to pop it. The roof is welded to the chassis with spot welds. Remove the roof rails and they are revealed. They get drilled out and some slight cutting is involved.

The metal skin alone weights 22.5 lbs while the sunroof cassette, rails motors weight roughly 35 lbs for a total of 57.5 lbs. 

The carbon roof panel weights 7 lbs. You can feel it's worth it. 

We test fitted the roof first to validate fitment. The pictures were taken after gluing - life gets in the way at times. It's truly perfect in terms of panel alignment - well done Karbonius. 

The rear fitment is just as good. 

The Karbonius panel comes with the right brackets to fix the CSL roof rails, but it doesn't come drilled for the roof rack threaded bolt holes.

A note on drilling. 

The high tensile strength of pre-preg carbon is real. We had to take the drill out with high temperature, high tensile strength drill bills to manage to get through the pre-preg carbon panel. This picture shows the roof after it was fully glued.

We will come back here to sand away some of the glue before roof rails fitment. 

The roof bow debate.

First, we need to understand what the roof bow is. It's a safety and structural device first by connecting the chassis together at its highest point, right in the middle. It supports either the standard steel slick top or CSL carbon roof to avoid deformation.

The roof bow is right above your head by the B pillars. 

Weld and/or Glue? There are bolt holes!

This is where it starts getting opaque: most shops that advertise this job on YouTube videos will say they tack weld it after grinding away the OEM glue. We couldn't find any other justification than to sell more billable time in covering up your interior as they'd needlessly create metal shavings and glue residue. 

To further highlight our confusion with these shops, BMW had bolt holes already planned into the chassis. This is how steel roof slick tops are from the factory. 

We didn't drill these. Notice the blue marks: measure 3x times..

We applied the same structural adhesive used by BMW on the roof to glue the roof bow to the chassis. 

The adhesive is applied on top of the bow and glues to the carbon panel as well. 

Correcting a production error. 

In the journal entry covering my unboxing impressions of the CSL carbon roof panel, we ran into a critical clear coat failure. The clear coat suffered from outgassing and popping.

No matter if the clear coat had been pristine or not, it was our intention to re-clear the roof panel entirely for the finishing process.

It had dots all over.  

We took a 800 grit sand paper to it.

Up next: we strip her down. PY gets chemically removed from the shell and we're on to primer. 

I'll revert back to the carbon roof later as we reclear the roof and finalize fitment of peripheral hardware upon reassembly.