Air ducts (83)
The air ducts during the final assembly of the car 2018
The air ducts are made out of card board and is often found damaged by wear, tear, moisture, heat, dirt and leaning elbows. Buying new in descent shape is expensive. From MB you can buy new ones made of glass fibre, they are not cheap either. My air ducts had also seen their better days but in my opinion worth saving. What you see below is my version of the restoration instructions found on the Mercedes-Benz Ponton Page.
We take if from the beginning. The first picture shows you one - I think it is the left - with markings from someone's elbow, probably leaning on it trying to remove plugs or adjusting the distributor. Both were carefully sandblasted and repaired with papier mache according to the instructions from the Ponton pages. The papier mache was from a recipe based on boiled, hand-torn strips of newspaper, white glue, chalk and linseed oil. The result was much harder and durable than I could have imagined. It was a pain in the b... to sand it down to the correct shape.
Air ducts for the Ponton being restored at the lake Eklången
The air ducts were thereafter painted inside out (soaked) in a thin mixture of a marine 2k epoxy primer, Hempel Light Primer 45551, hopefully giving it good moisture protection. Then they were puttied and sanded a couple of times before I thought they were ready for the final protection and last - but not least - the semi-gloss black paint (fifth and sixth picture). From the fourth picture you can see that I tried to make this boring work as nice as possible, at our country house at Eklången, close to Eskilstuna. Unfortunately the black paint showed some bad spots so on with some more putty and back to the sandpaper. And then we came to the status shown in the last picture.
Coming so far I turned to the assembly of the flaps. One advice I can give you before you give the air ducts their last, semi-gloss black paint; try the flaps so that you haven't used too much papier mache somewhere... I started the adjustments with a lot of sanding on the inside but it was a scary experience since I didn't want to risk to crack the finished outer surface. Instead I went for another solution which is to smooth the edges of the flap instead. It was certainly easier, gave more control and gave a better result. Then we got some detailing to do. In order to seal the flaps, otherwise they're not tight enough against the sides of the boxes letting air into the coupe, you use felt. In Sweden you can find the exact type and thickness (3mm) at Panduro Hobby.
The same type of felt is also used on the underside of the insect screen. Note here that the second picture of the insect screen points to that it wasn't black but probably white cad. My white cad finishing actually was very bad due to bad preparation from my side. Looking at other cars I decided that semi-gloss black would probably be ok too... Inside the tightening strap for the air duct you use a 1mm felt.